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Amanda de Oliveira Silva, Small Grains Extension Specialist and Tom Royer, Extension Entomologist
Planting date: Much of the winter wheat sown in Oklahoma is used as a dual-purpose crop. In such a system, wheat is grazed by cattle from late fall through late winter/early spring and then harvested for grain in early summer. In a grain-only system, wheat is generally planted in October, but in a dual-purpose system wheat is planted in early to mid-September to maximize forage production. Planting wheat early significantly increases the likelihood that diseases and insect pests such as mite-transmitted viruses, the aphid/barley yellow dwarf complex, root and foot rots, and Hessian fly will be more prevalent and severe. For more detailed information on planting date and seed treatment considerations on wheat, see CR-7088 (Effect of Planting Date and Seed Treatment on Diseases and Insect Pests of Wheat).
Mite-transmitted virus diseases: These virus diseases are transmitted by wheat curl mites (WCMs) (Figure 1), and include wheat streak mosaic (WSM), high plains disease (HPD), and Triticum mosaic (TrM). Of these, WSM is the most common. WCMs and these viruses survive in crops such as wheat, corn, and sorghum as well as many grassy weeds and volunteer wheat. In the fall and spring, WCMs spread to emerging seedling wheat, feed on that seedling wheat, and transmit virus to the young wheat plants.
Given this disease cycle, it is easy to see several factors that determine the incidence and severity of these diseases. First, controlling volunteer wheat and other grassy weeds that serve as alternative hosts for the mite and the viruses is imperative to help limit these diseases. Often an infected field of commercial wheat is growing immediately adjacent to a field left fallow during the fall and winter (Figure 2). The fallow field contained abundant volunteer wheat and grassy weeds from which WCMs carrying Wheat streak mosaic virus (WSMV) spread into the commercial field. Wheat infected in the fall will be severely damaged the next spring. Wheat infected in the spring also is damaged, but not as severely as wheat infected in the fall. Hence, it is imperative to do yourself and your neighbors a favor by controlling volunteer wheat and grassy weeds in fields left fallow – especially, if they are adjacent to commercial wheat fields.
A second factor linked to the severity of these mite-transmitted virus diseases is planting date. Early planting dates associated with grazing provides for a much longer time period in the fall for mites to spread to and infect seedling wheat. Planting later in the fall (after October 1 in northern OK and after October 15 in southern OK) and controlling volunteer wheat are the two practices that can be employed to help manage these diseases. It is extremely critical that volunteer wheat is completely dead for at least two weeks prior to planting wheat because WCMs have a life span of 7-10 days. Thus, completely killing or destroying volunteer wheat for a period of at least two weeks prior planting will greatly reduce mite numbers in the fall.
The incidence and severity of these mite-transmitted virus diseases as affected by planting date can be illustrated by the number of samples that tested positive for WSMV and HPV during each of the last three years. In 2017, which was the last year mite-transmitted virus diseases were prevalent in Oklahoma, 103 wheat samples were tested by the Plant Disease and Insect Diagnostic Lab at OSU for presence of mite-transmitted viruses. Of these 103 samples, 69 (67%) tested positive for WSMV and 22 (21%) tested positive for HPV. In 2018, only 12 of 126 (10%) samples tested positive for one or both of these viruses. In 2019, only 21 samples were submitted for testing with 7 samples (33%) testing positive for WSMV (no positives for HPV). In 2020, few samples (less than 5) tested positive for any of these viruses. This lower number of positive samples in 2019 and 2020 likely was the result of an overall later planting date of wheat in the fall of 2018 due to wet conditions and in fall 2020 due to extremely dry conditions. I believe this later planting date in conjunction with more awareness and action in limiting the green bridge helped to lower the incidence and severity of the mite-transmitted viruses in Oklahoma in both 2019 and 2020.
Finally, seed treatments and insecticides are NOT effective in controlling the mites or these mite-transmitted virus diseases. Regarding resistant varieties, there are several winter wheat varieties that have resistance to either WSM or the curl mites, but the adaptation of these varieties to Oklahoma is limited, and the resistance is not typically an absolute resistance to the disease. Hence, severe and continuous disease pressure especially at higher temperature (greater than about 75 F) can overcome the resistance. For more information on mite-transmitted virus diseases, see OSU Fact Sheet EPP-7328 (Wheat Streak Mosaic, High Plains Disease and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma).
Aphid/barley yellow dwarf (BYD) complex: Viruses that cause BYD are transmitted by many cereal-feeding aphids (Figure 3). BYD infections that occur in the fall are the most severe because virus has a longer time to damage plants as compared to infections that occur in the spring.
Several steps can be taken to help manage BYD. First, a later planting date (after October 1 in northern Oklahoma and after October 15 in southern Oklahoma) helps reduce the opportunity for fall infection. Second, some wheat varieties tolerate BYD better than other varieties; however, be aware that no wheat variety has a high level of resistance to the aphid/BYD complex. For a listing of reaction of wheat varieties to BYD, other diseases and insect pests, and agronomic traits there are several sources available including variety comparison charts from Oklahoma State University (www.wheat.okstate.edu) and Kansas State University (https://bookstore.ksre.ksu.edu/pubs/MF991.pdf), and the annual wheat variety publication titled, “Wheat Varieties for Kansas and the Great Plains by Layton Ehmke (34 Star Publishing Inc.; firstname.lastname@example.org; https://thewheatfarmer.com; 1-844-643-0170). Third, control aphids that transmit the viruses that cause BYD. This can be done by applying contact insecticides to kill aphids, or by treating seed before planting with a systemic insecticide. Unfortunately, by the time contact insecticides are applied, aphids frequently have already transmitted the viruses that cause BYD. Systemic seed-treatment insecticides containing imidacloprid or thiamethoxam can control aphids during the fall after planting. This may be particularly beneficial if wheat is planted early to obtain forage. Be sure to thoroughly read the label before applying any chemical.
Hessian fly: Hessian fly (Figure 4) infestations can occur in the fall and spring. Fall infestations arise from over-summering pupae that emerge when climate conditions become favorable. In states north of Oklahoma, a “Hessian fly free” planting date often is used to help limit fall infestations by Hessian fly. However, such a planting date does not apply in Oklahoma because Hessian fly can emerge in Oklahoma as late as December (Figure 5).
Delayed planting (after October 1 in northern Oklahoma, and after October 15 in southern Oklahoma) can help reduce the threat of Hessian fly, but a specific “fly free date” does not exist for most of Oklahoma as it does in Kansas and more northern wheat-growing states. This is because smaller, supplementary broods of adult flies emerge throughout the fall and winter. A number of varieties are resistant to Hessian fly; for a listing of reaction of wheat varieties to Hessian fly, other diseases and insect pests, and agronomic traits there are several sources available including variety comparison charts from Oklahoma State University (www.wheat.okstate.edu) and Kansas State University (https://bookstore.ksre.ksu.edu/pubs/MF991.pdf), and the annual wheat variety publication titled, “Wheat Varieties for Kansas and the Great Plains by Layton Ehmke (34 Star Publishing Inc.; email@example.com; https://thewheatfarmer.com; 1-844-643-0170). Hessian fly infestations can be reduced somewhat by destroying volunteer wheat in and around the field at least two weeks prior to emergence of seedling wheat. Seed treatments that contain imidacloprid or thiamethoxam will also help reduce fall infestations of seedling wheat, especially if combined with delayed planting and volunteer destruction. For more information on Hessian fly, see OSU Fact Sheet: EPP-7086 (Hessian fly Management in Oklahoma Winter Wheat).
Root and foot rots: These are caused by fungi and include several diseases such as dryland (Fusarium) root rot, Rhizoctonia root rot (sharp eyespot), common root rot, take-all, and eyespot (strawbreaker). Every year samples are received in the lab that are diagnosed with root rot. Typically wheat affected by seedling/root rots are either submitted in the fall when wheat is in the seedling stage or in later May and early June as plants are maturing. Germinating seeds and seedlings have small root systems that if infected impacts seed germination and seedling emergence (Figure 6). Later in the season (late May/early June), root rots again become apparent as maturing plants are unable to obtain sufficient moisture to finish grain development especially if drought conditions are present. In mature plants, white heads often indicates the presence of root rot (Figure 7).
In 2017-2018, the incidence and severity of root rots across Oklahoma dramatically increased compared to the 2016-2017 season. This increase likely resulted from weather conditions that favored the root rots along with heat and drought in May/June of 2018 that promoted white heads to develop. Dryland (Fusarium) root rot was the most common root rot observed in 2018, and caused significant damage to wheat in southwestern, western, northwestern OK as well as the panhandle. In 2018-2019, dryland (Fusarium) root rot again became prevalent across much of Oklahoma, but was not as damaging as the previous year likely because ample moisture and cool temperatures meant that water stress on plants was much less than in 2017-2018. Root rots were only sparsely observed in 2019-2020 and only at low severity.
Controlling root and foot rots is difficult. There are no resistant varieties, and fungicide seed treatments with activity toward the root and foot rots are effective in protecting germinating seed and emerging seedlings, their activity usually involves early-season control or suppression rather than control at a consistently high level throughout the season. Often, there also are different “levels” of activity related to different treatment rates, so again, CAREFULLY read the label of any seed treatment to be sure activity against the diseases and/or insects of concern are indicated, and be certain that the seed treatment(s) is being used at the rate indicated on the label for activity against those diseases and/or insects. Later planting (after October 1 in northern Oklahoma and after October 15 in southern Oklahoma) also can help reduce the incidence and severity of root rots, but planting later will not entirely eliminate the presence or effects of root rots. If you have a field with a history of severe root rot, consider planting that field as late as possible or plan to use it in a “graze-out” fashion if that is consistent with your overall plan.
For some root rots, there are specific factors that contribute to disease incidence and severity. For example, a high soil pH (>6.5) greatly favors disease development of the root rot called take-all. OSU soil test recommendations factor in this phenomenon by reducing lime recommendations when continuous wheat is the intended crop. Another practice that can help limit take-all and some of the other root rots is the elimination of residue. However, elimination of residue by tillage or burning does not seem to affect the incidence or severity of eyespot (strawbreaker).
Seed treatments: There are several excellent reasons to plant seed wheat treated with an insecticide/fungicide seed treatment. These include:
1. Control of bunts and smuts, including common bunt (also called stinking smut) and loose smut. The similarity of these names can be confusing. All affect the grain of wheat, but whereas common bunt spores carryover on seed or in the soil, loose smut carries over in the seed. Seed treatments labeled to control bunts and smuts are highly effective. If common bunt (stinking smut) was observed in a field and that field is to be planted again with wheat, then planting certified wheat seed treated with a fungicide effective against common bunt (stinking smut) is strongly recommended. If either common bunt (stinking smut) or loose smut was observed in a field, grain harvested from that field should not be used as seed the next year. However, if grain harvested from such a field must be used as seed wheat, treatment of that seed at a high rate of a systemic or a systemic + contact seed treatment effective against common bunt (stinking smut) and loose smut is strongly recommended. In 2020, loose smut in fields and common bunt in harvested grain was observed at higher incidence and severity than for several years, so I strongly recommend planting certified wheat seed that was been treated with a fungicide labeled for control of bunt and smut. For more information on common bunt (stinking smut) & loose smut, see: http://www.entoplp.okstate.edu/ddd/hosts/wheat.htm and consult the “2020 OSU Extension Agents’ Handbook of Insect, Plant Disease, and Weed Control (OCES publication E-832),” and/or contact your County Extension Educator.
2. Enhance seedling emergence, stand establishment, and forage production by suppressing root, crown and foot rots. This was discussed above under “Root and Foot Rots.”
3. Early season control of the aphid/BYDV complex. This can be achieved by using a seed treatment containing an insecticide. Be sure that the treatment includes an insecticide labeled for control of aphids.
4. Control fall foliar diseases including leaf rust and powdery mildew. Seed treatments are effective in controlling foliar diseases (especially leaf rust and powdery mildew) in the fall, which may reduce the inoculum level of these diseases in the spring. However, this control should be viewed as an added benefit and not necessarily as a sole reason to use a seed treatment.
5. Suppression of early emerged Hessian fly. Research suggests that some suppression can be achieved, but an insecticide seed treatment has little residual activity past the seedling stage and Hessian fly often infests wheat after the seedling stage.
Fall Armyworm Potential: We have seen a severe outbreak of fall armyworms infesting bermudagrass and fescues lawns this past month. The strain that is infesting these lawns is known as the “rice” strain, and it overwinters in the Florida Gulf Coast and parts of the Caribbean. We typically see the “corn” strain which typically overwinters in the Texas Gulf Coast and Mexico. The rice strain prefers rice, and grasses, and the corn strain prefers corn and sorghum and as we have seen in the past, winter wheat. This year, Oklahoma is experiencing a “double whammy” of both strains, and unfortunately, they both like wheat. So, our advice is to carefully watch your fields after they emerge and deal with any fall armyworm infestations before they take your stand.
Lanie Hale, from Wheeler Brothers sent a picture of “window paned” wheat from a field that he had scouted in 2017. He counted 3 fall armyworms per row foot from his visual count (which is treatment threshold) but when he looked closely at his photo on his computer, he saw 15 worms in an area the size of his hand (they were very tiny, and probably newly hatched). It is easy to miss some of these little worms in the field because they hide in residue and are very tiny.
Look very closely for “window paned” leaves and count all sizes of larvae. Examine plants along the field margin as well as in the interior, because they sometimes move in from road ditches and weedy areas. The suggested treatment threshold is 2-3 larvae per linear foot of row in wheat with active feeding. Numerous insecticides are registered for control, but they are much more susceptible when caterpillars are small. We won’t get relief from fall armyworms until we get a killing frost, so keep vigilant!
Consult the newly updated OSU Fact Sheets CR-7194 Management of Insect and Mite Pests of Small Grains for control suggestions.
This article was written by Bob Hunger, Extension Wheat Pathologist
Reports of foliar diseases, especially stripe and leaf rust, are starting to increase in southern Texas and around Stillwater. First, here is an update sent out on 24-March by Dr. Amir Ibrahim (Regents Professor & Small Grains Breeder/Geneticist; Texas A&M AgriLife Research). Dr. Ibrahim is finding both stripe rust and leaf rust increasing across southern Texas.
“I visited our small grains trials at McGregor (18 miles southwest of Waco, TX) on March 18, 2021. Stripe rust (caused by P. striiformis Westend. f. sp. tritici Eriks.) continues to be active (Figure 1; photo on the left). Leaf rust (caused by Puccinia triticina Erikss.) is beginning to move to the middle canopy (Figure 1 – photo on the right).”
“We visited the naturally inoculated Rust Evaluation Nursery at Castroville, TX today. The nursery is about 196 miles from Texas A&M University’s main campus in College Station, where we are based. We also visited our trials at Uvalde, TX today. Stripe rust is not very active at both Castroville and Uvalde. Leaf rust is now picking up, especially at the Rust Evaluation Nursery at Castroville. Stripe rust is very actively spreading at the Agronomy Farm near our main campus in College Station as of our last visit on March 23, 2021. Stripe rust is also active in our trials in Greenville (50 miles northeast of Dallas). No reports yet of leaf or stripe rusts in the Texas High Plains. Leaf rust is also developing in our trials at Wharton (60 miles southwest of Houston).”
In Oklahoma, both stripe and leaf rust (Figure 2) have been observed in trials around Stillwater and near Perkins (about 15 miles south of Stillwater). Also recall in my update of 15-March, I indicated seeing powdery mildew, Septoria/Stagonospora (Figure 3) on lower leaves in many trials. These diseases also are present, and with the relatively cool and windy weather in the forecast, I expect the incidence and severity of all these diseases to increase.
This article was written by Dr. Bob Hunger, Extension Wheat Pathologist
Although relatively quiet, some wheat diseases have started to appear across Oklahoma over the last week. For example, around Stillwater I am starting to observe patches of wheat showing symptoms of the wheat soil-borne mosaic (SB)/wheat spindle streak mosaic (SS) complex. So far, I have observed these symptoms only in susceptible varieties in Dr. de Silva’s variety demo and in my SB-SS nursery. These virus diseases are not a problem in Oklahoma or the central plains due to effective and durable genetic resistance in nearly all wheat varieties planted in Oklahoma for the last four decades. However, planting a variety susceptible to either or both of these virus diseases could be an invitation to having an occurrence of these diseases. It seems as though only far northwest Oklahoma and the panhandle have environments that limit the occurrence of these two virus diseases.
In trials around Stillwater towards the end of last week, I found sparse powdery mildew and fairly abundant Septoria/Stagonospora leaf spot on leaves of ‘Ruby Lee’ (Figure 2). This was in Dr. Brett Carver’s dual purpose observation nursery, which is an early planted nursery. In no trials did I find either leaf or stripe rust, although Dr. Amanda de Oliveira Silva had found both leaf rust and powdery mildew in her demonstration trial in later January before the hard freeze and snow occurred in early to mid-February.
Figure 1. Wheat showing reaction to the wheat soil-borne mosaic (WSBM)/wheat spindle streak mosaic (WSSM) complex. Left photo: Wheat breeder line susceptible (left) and resistant (right) to WSBM. Center photo: Symptoms typical of WSBM. Right photo: Symptoms typical of WSSM.
Figure 2. Upper photo are symptoms on a wheat leaf indicative of Septoria or Stagonospora leaf blotch found near Stillwater on 13-Mar-2021. The lower photo is of a wheat leaf with symptoms indicative of tan spot observed in southwest Oklahoma by Gary Strickland, (County Educator; Jackson County), 3-11-2021.
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: I had limited trips outside of Stillwater this past week, and only was able to contact one County Educator before writing this today. Wheat around Stillwater is mostly at various stages of head emergence. I did see a few anthers on scattered heads, but not many. By contrast, Aaron Henson (County Educator; Tillman County in south-central OK) indicated wheat in his area is mostly at flowering.
During this past week, I had several calls about spraying wheat with a fungicide. Although rust (stripe and leaf rust) didn’t appear to increase this past week, conditions reverted to being more favorable for stripe rust development with rainfall, increased dews, and favorable temperature. With more rains and cool temps in the forecast, stripe rust could “reactivate” again, and leaf rust will start to come into the picture. Wheat is now at the point where it will quickly move past the stage (the start of flowering) where it can be sprayed with most fungicides. As far as I know, all wheat foliar fungicides (with the exception of Prosaro) must be applied prior to the start of flowering (Feekes’ growth stage 10.5). Prosaro can be applied through growth stage 10.5.1, which is when flowering is just starting (anthers emerged mostly from the middle of heads). Be sure to read all labels regarding a fungicides use on wheat. There also are varying pre-harvest intervals (PHIs) required for the various fungicides, and often the length of time from heading to harvest can be short in Oklahoma. So, be aware of these PHIs, and spray accordingly.
Active sporulation of stripe rust still can be found around Stillwater and the surrounding area. Stan Fimple (County Educator, Pawnee County just to the northeast of Stillwater) sent me the following photos showing active stripe rust. The photo on the top shows an actively sporulating “stripe” of strip rust (yellowish-orange in color), whereas in the photo on the bottom in the “stripes” you can see dark, blackish specks (teliospores) starting to appear.
Other than this, I have seen scattered leaf rust pustules on lower leaves around Stillwater, and powdery mildew also has become more apparent around Stillwater and at Lahoma as reported by Dr. Brett Carver (OSU Wheat Breeder). However, both of these diseases are at low levels on lower leaves but with coming rain and cool temperatures both (especially leaf rust) could continue to increase on the upper canopy. Around Stillwater, barley yellow dwarf spots continue to be observed but the aphids are now gone or at least in much lower in frequency. If heavy rains come over the next 3 or so days, I would imagine aphid populations will be mostly eliminated.
Finally, I want to raise awareness once again to Fusarium head blight (scab) of wheat. When wheat flowers it is susceptible to infection by the Fusarium fungus that causes scab. That time is quickly approaching. Occasionally Oklahoma has problems with this disease, typically more so in eastern/northeastern Oklahoma than through the central and western parts of the state. However, scab was severe across the state for a couple years around 2010 and there also was some reported last year. For more information on scab, please see PSS-2145 (Fusarium Head Blight (Head Scab) of Wheat: Questions & Answers) and PSS-2136 (Considerations when Rotating Wheat Behind Corn) that can be found at: wheat.okstate.edu. An additional resource is the Fusarium Head Blight Prediction Center at http://www.wheatscab.psu.edu/. At this site you can read commentaries submitted by specialists from each state but more importantly see if weather conditions in your area have been conducive to development of FHB. The site is easy to use and especially may be beneficial in helping make fungicide application decisions.
Reports/excerpts of reports from other states:
Louisiana: Dr. Stephen Harrison, Wheat & Oat Breeder, Louisiana State University, Apr 15, 2016: My research associate (Kelly Arceneaux) is at the Rice Research Station in Crowley (Southwest) Louisiana rating plots today. We plant a double-headrow set of a number of nurseries every year for disease screening at this location in collaboration with Don Growth (rice pathologist). This site is inoculated with scabby corn but is not misted due to the abundance of humidity and free moisture at this site. Nurseries include: Statewide Variety Trial, Uniform Southern Soft Red Winter Wheat Nursery, Uniform Southern Scab Nursery, Sunwheat, GAWN. Kelly reports that stem rust is heavy and widespread at this site. Leaf rust is moderate and scab is at an intermediate level, which is good for distinguishing lines. The earliest plots are starting to mature, probably just past soft dough, while the latest lines are just past heading or not vernalized and not going to head. We only received about 50% of our normal vernalization hours this winter and quite a few lines in the statewide variety trials will not be harvested due to vernalization issues.
Nebraska: Dr. Stephen Wegulo, Extn Plant Pathologist, University of Nebraska, April 14, 2016: “On Friday April 8, Jenny Rees, UNL Extension Educator, found trace amounts of stripe rust in a wheat field in Nuckolls County in south central Nebraska. Earlier this week, samples from several wheat fields in Banner County submitted to the lab of Dr. Bob Harveson (Extension Plant Pathologist) at UNL’s Panhandle Research and Extension Center in Scottsbluff were positive for stripe rust and leaf rust. This week on April 12 and 13 I surveyed wheat fields in the southernmost tier of counties in southeast, south central, and west central Nebraska. Dry weather which has prevailed over the last two weeks or so stopped rust development. I did not find rust in any of the fields I visited in the southernmost tier of counties. Several fields showed symptoms of stress from lack of moisture. Today I looked at research plots at Havelock Farm here in Lincoln (Lancaster County) and at the Agricultural Research and Development Center (ARDC) near Mead (Saunders County, about 35 miles north of Lincoln). I found a few hot spots of stripe rust at Mead (see first attachment), mostly on the lower leaves. I also found trace levels of leaf rust at Mead (second attachment). Powdery mildew was the predominant disease at Lincoln and Mead, but I also saw significant levels of Septoria tritici blotch in one research field at Mead. Wheat growth stage across the state ranges from Feekes 5 and 6 (most fields) to Feekes 7 in some irrigated fields.”
South Dakota: Dr. Emmanuel Byamukama, Extension Plant Pathologist, South Dakota State University; Apr 13, 2016: “Several winter wheat fields in central South Dakota were scouted yesterday for stripe rust. One field originally found with stripe rust last week was the only one we found with stripe rust. Stripe rust was found on old/dying leaves and some of the leaves had teliospores, indicating the source of this rust would have been from overwintered stripe rust in South Dakota.”
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Wheat has advance in maturity across OK this past week flag leaves definitely are emerging around Stillwater. From reports I’ve received I believe across the state wheat ranges from flag leaves emerging to heads starting to emerge (although wheat in far northwest OK and the panhandle may not be quite as far along). I didn’t hear specifics but was told that freeze damage has been observed around Kingfisher in central OK. With frost/freezing temps again last night, additional damage is possible. Drought, although not as bad as last year, also is creeping back into the picture. One producer from southwestern OK indicated to me that “leaves are rolling-up at 2 o’clock in the afternoon.” I didn’t see any wheat that looked stressed, but in several locations had to dig 4” or more to find moist soil.
In my trips this past week to central OK (Watonga) and to more north-central OK (Blackwell), I could find stripe rust, but it doesn’t appear to me that it had advanced (become more severe). In fact, Zack Meyer (Extn Educator; Kingfisher Cnty) sent me the following photo that shows the telial spore stage of the stripe rust fungus forming on wheat leaves. Look closely at the photo and you can see minute yellowish-orange pustules of stripe rust also present on the leaves (especially the greener leaf). The telial stage is considered more of a survival spore stage and indicates that stripe rust is encountering unfavorable conditions and starting to shut down. Although this is good news, stripe rust can quickly “reactivate” if favorable temperature and moisture are resumed.
Unfortunately there also is a lot of active stripe rust still in the state as I have had numerous calls from across OK to discuss spraying options, and Greg Highfill (Extn Educator; Woods Cnty) sent me the following photo showing moderate/severe and active stripe rust on wheat in northern-central OK.
Reports/excerpts of reports from other states: No reports from Texas, but did hear the following from Kansas and Nebraska.
Kansas: Dr. Erick DeWolf; Extn Plant Pathologist; Kansas State University; Manhattan, KS; Apr 1, 2016: “The Kansas wheat crop is progressing rapidly through the jointing stages of development in much of the state. Wheat in the Southeast portion of the state is at or fast approaching flag leaf emergence. The crop is generally considered to be two or three weeks ahead of schedule.
Scouting reports indicate that stripe rust is becoming established in the 2016 wheat crop. This past week, stripe rust was reported in many counties in central and eastern Kansas. The disease is still at low levels in most fields with a few exceptions in Southeast Kansas. This early establishment of stripe rust increases the risk of severe yield loss and growers should continue to monitor the situation carefully. If weather conditions become favorable, the disease could spread rapidly from the lower leaves, where it is now established, to the upper leaves that are critical for grain development. Leaf rust is still active in the western tier of counties bordering CO but remains a low levels in most fields. Powdery mildew is severe in some fields in central and eastern Kansas.”
Nebraska: Dr. Stephen Wegulo; Professor/Extn Plant Pathologist; University of Nebraska-Lincoln; Lincoln, NE, KS; Mar 31, 2016: “Yesterday March 30, 2016: Jennifer Rees, UNL Extension Educator, found trace levels of actively sporulating leaf rust in wheat fields in Nuckolls County in south central Nebraska. Nuckolls County is in the southernmost tier of counties that border Kansas. She did not find actively sporulating stripe rust; however, in one field there was evidence of stripe rust that was active last fall.”
Colorado: Dr. Kirk Broders; Ast Professor; Colorado State University; Ft. Collins, CO; Mar 29, 2016: “As I mentioned last week stripe rust is now present in eastern Colorado with a confirmed report of stripe rust in the Prospect Valley region northeast of Denver. We have received several reports of stripe rust from that same region. This past week was windy with some precipitation in this area of Colorado, so spores were spread but there was limited moisture to promote additional infection. There is rain in the forecast for this coming week and the rain is certainly needed for the wheat, but also will provide a favorable environment for stripe rust to increase because temperature is supposed to be staying in the 50s-70s for the days and 20s-40s at night. If you already have noticeable levels of rust in your field you may want to consider including a fungicide at tillering (GS 4) or when you make your herbicide application. If you do not currently have rust in your fields or in your region, I would recommend waiting until closer to flag leaf and monitor the spread of stripe rust in the state. CSU Extension specialist Wilma Trujillo was able to examine wheat in the southwest part of the state near Lamar, where stripe was present last fall. We examined these leaves and found no evidence stripe rust was able to overwinter in this region of the state. It is still early in the season, but there is certainly the possibility for stripe rust to become a serious problem in the state again this year. There are also the threat of leaf rust we should not forget about. Leaf rust has been present in western Kansas for the last 2 weeks and has likely moved into eastern parts of the state. I have not received in specific reports, but would appreciate you feedback if you have observed either stripe rust of leaf rust in you fields.
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: This past week I looked at wheat around Stillwater as well as in central OK (Blaine County NW of Oklahoma City; Kingfisher just NW of OKC; Apache in Caddo County SW of OKC), and in SW OK around Altus. I saw wheat as far along as approaching flag leaf emergence to at growth stage 6-7. The more advanced wheat typically was planted relatively early and not grazed. Everywhere I was had sufficient moisture, although areas in southwestern and western OK were getting to a point where some rain definitely would be beneficial. In addition to my observations, I’ve received numerous reports that I’ll summarize here.
At nearly all the places I stopped, I observed varying levels of stripe rust, leaf rust, aphids, and powdery mildew, with powdery mildew being by far the least prevalent. Stripe rust typically was scattered across fields, but there were some significant hot spots. In some fields (for example the variety trial at Kingfisher) I saw no stripe rust. Greg Highfill (Extn Educator, Woods County) and Darrell McBee (Extn Educator, Harper County) sent me the photo below showing stripe rust they found this past week. They indicated the stripe rust was scattered and not common, but this does mean that spores are present in the field and will increase with favorable (cool and wet) weather. They also indicated finding a little powdery mildew. I also heard reports of severe stripe rust in susceptible varieties such as Pete, Garrison, and Everest.
More severe hot spots of stripe rust were reported by David Nowlin (Extn Educator; Caddo County), who sent the following photo of stripe rust on ‘Pete’, which is highly susceptible to stripe rust.
Similar reports regarding stripe rust were made by Dr. Brett Carver. He also has reported seeing considerable chlorosis (yellowing) often with the lack of sporulation. I saw the same type of yellowing with no sporulation at Kingfisher yesterday (see photo below). I’m not sure of the cause of this yellowing, but I don’t believe it to be from rust or other foliar diseases because it is widespread in its distribution on lower leaves. Perhaps it is the result of the environment.
In no-till fields near Altus and Apache I saw striking tan spot on lower leaves along with numerous pseudothecia of the tan spot fungus on the wheat residue in the field. Near Altus, this was combined with stripe rust presence such as described above. In such a case, applying a fungicide early to catch both of these diseases should be considered, especially if the field at this point has a good yield potential. For more information to help make this decision, see OSU CR 7668 available at www.wheat.okstate.edu
Reports/excerpts of reports from other states:
Texas : I’ve only received two reports from Texas this past week. One is from a former student that now lives in the Weatherford, TX area. He indicates that stripe rust is in the area. The other report is from David Nowlin (Extn Educator, Caddo County), who indicates a colleague of his located near Denton, TX sent him the following report on 15-March.
“We’re getting hammered with strip and leaf rust as well as powdery mildew on our varieties down here in Denton, TX. We’re just a little further ahead of you. Wheat is not as far along as we normally see.
Kansas: Dr. Erick DeWolf; Extn Plant Pathologist; Kansas State University; Manhattan, KS; Mar 19, 2016: “The wheat crop is growing rapidly throughout Kansas. The crop in the more advanced fields are approaching jointing in the northwest and are about a week away from flag leaf emergence in the south central and southeast portions of the state. The crop is generally considered to be about 3 weeks ahead of schedule with respect to normal growth and development. There are multiple reports of leaf rust and stripe rust in Texas, Oklahoma, and other surrounding states.
The Crops Extension team has been busy scouting for disease in recent weeks. We are finding active leaf rust and stripe rust in the state. Leaf rust was reported in west central and northwest, Kansas with most activity in counties bordering Colorado. Low levels of leaf rust were also observed in research plots in Riley County, which is located in northeast Kansas. The winter has been very mild in Kansas and it is very likely that the leaf rust has overwintered in the state. Stripe rust was reported in multiple counties this past week. Stripe rust is generally at very low levels with most activity reported in the southeast portion of the state. Tan spot and powdery mildew have also been reported in some areas of the state.”
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma – Foliar diseases are becoming active in Oklahoma. Around Stillwater I have found both leaf and stripe rust, powdery mildew, and septoria. Incidence/ severity of all these foliar diseases is relatively light, but I am especially watching what happens to the leaf and stripe rust. The leaf rust pustules are small and on lower/older leaves indicating that leaf rust likely overwintered in Central OK. The stripe rust pustules were on the upper leaves of ‘Pete’ wheat (see photo) indicating the spores causing these initial infections likely blew up from the south. With rain and cool wet weather in the forecast, I definitely expect for there to be an increase in foliar diseases. Around Stillwater, I also have seen quite a few aphids (mostly bird cherry-oat but also a few greenbug) and many lady beetles. However, no symptoms yet of barley yellow dwarf.
Gary Strickland (SWREC Dryland Cropping Systems Spclt – Jackson Cnty) relayed to me that in SW OK he has seen leaf rust in fairly high levels on lower leaves of Endurance and other wheats, and has heard reports of stripe rust but has not seen any himself.
Yesterday I traveled to north-central OK (Alva). On the way there and while there I visited several fields and found a few very small leaf rust pustules. Overall the wheat from I-35 over to Alva (Hwy 11) looked good and was greening-up nicely. Also while in Alva, numerous producers, etc. relayed reports of mostly leaf rust showing up across central OK, such as leaf rust around Geary, OK, etc.
Regarding rust incidence/severity in Texas, I talked to a wheat breeder in Texas last week and he indicated that wheat in southern Texas was showing both leaf and stripe rust but had not yet reached a severe level. Early next week I’ll be at a meeting of wheat pathologists and should be able to find out more about diseases in Texas.
All these reports indicate the potential for significant foliar disease on the current wheat crop. Genetic resistance in some of wheat varieties helps protect against the foliar diseases, but fungicides also provide an excellent management tool to protect not only yield, but also quality (test weight). To help with deciding if and when to apply a fungicide, Dr. Jeff Edwards and I earlier this week updated and revised CR 7668 (Foliar Fungicides and Wheat Production in Oklahoma – March 2016). It can be found at www.wheat.okstate.edu. This Current Report discusses the significant aspects related to using fungicides to manage wheat foliar diseases.
One point I want to be sure to emphasize when using fungicides is the importance to not exceed the maximum amount of a fungicide applied to a crop in a single year. Such a consideration couldespecially be an issue when more than one fungicide application is made. In many states through the southeastern region of the U.S., two fungicide applications on wheat are more common, with the last application typically targeted toward Fusarium head blight (scab). In Oklahoma, where scab usually is not a concern, deciding when to make a single fungicide application typically is the only consideration. However, if you have early disease pressure from stripe rust or have early season powdery mildew, tan spot, or Septoria leaf blotch in no-till fields, more than one application may be needed to adequately manage these diseases. In these situations, care must be taken to insure label compliance. For example, if an early application of a generic form of tebuconazole is applied at 4 oz/ac, a subsequent application of any fungicide containing tebuconazole around heading would put you over the 4 oz limit for the crop season. Thus, be sure to read the label to determine the maximum amount of a chemical that can be applied in a single season and the exact amount of a chemical(s) that is in a fungicide.
South Texas – Amir Ibrahim TAMU Wheat Breeder – The wheat crop in our trials at Castroville and Uvalde, TX is at Feekes stages 5‐10, ranging from the latest winter to the earliest spring types. Growth is very lush and there is no winter kill or frost injury in either winter and spring types. Stripe rust is at 70S, in the medium to upper canopy, on our ‘Patton’ spreader passes across the field. Stripe rust is about 60S on ‘TAM 110’. ‘Coronado’ is hammered with yellow rust at Castroville. Stripe rust is more progressed at Uvalde. We have been getting natural and uniform stripe rust infection at Uvalde every year for the last few years. The Texas A&M AgriLife Center at Uvalde sits at the bottom of a valley with constant morning dew that favors infection. Stripe rust has also been found at low levels in the wheat breeding trials near Chillicothe in the Rolling Plains of Texas.
Texas – Dr. John Fenderson – WestBred. “I saw rampant Stripe in Central TX on Ruby Lee. I also saw it on sensitive lines from I-20 south anywhere it has rained. Some spraying has occurred in the Austin area. I also pulled wheat in the Red River corridor both sides with a lot of stripe on older leaves. It is just waiting on the right conditions to explode. I was all the way down in S. TX this week and I did not see stripe on the spring wheat but there was some on Winter wheat around San Angelo etc.”
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Since my last report, I don’t believe a lot has changed with the disease situation. Similar to what I indicated in mid-December, I have continued to find small pustules of powdery mildew and a few scattered leaf rust pustules in rank wheat around Stillwater. The temperature and weather has been such that these two foliar diseases (powdery mildew and leaf rust) have been able to persist but have not increased in the wheat around Stillwater. This seems to be the case for southwestern and south central OK as well.
Gary Strickland (Extn Educator & SWREC Dry-land Cropping Systems Specialist; Jackson/Greer Cnty in SW OK) indicated wheat in SW OK is quite a ways behind the rest of the state and mostly is just now establishing a solid root system. He had sent us a sample last week in which he expected a root rot to be involved, but we were not able to confirm any root rot pathogens. Gary also indicated that he has confirmed Hessian fly at damaging levels in at least a few fields in Jackson Cnty. He is going out in the next few days to scout additional fields. Aaron Henson (Extn Educator; Tillman Cnty in southern OK) indicated wheat in his area varies from quite small to well-established with the majority of the wheat not yet jointing. He is aware of the earlier reports of scattered stripe rust showing in south-central OK, but has not heard anything to indicate increase in incidence or severity. For additional information regarding early season foliar wheat diseases and possible control with an early fungicide application please see:
- E-Pest Alert (Dec 18, 2015; vol. 14, no. 46) at http://entoplp.okstate.edu/pddl/pdidl
- A fact sheet discussing split application of fungicides at www.wheat.okstate.edu
- A February 9th post on this blog
Also around Stillwater, I am beginning to see symptoms indicative of wheat soil-borne mosaic/wheat spindle streak mosaic in areas such as my WSBM/WSSM screening nursery. At this point, it is somewhat difficult to differentiate between symptoms of WSBM/WSSM and discoloration resulting from cold. The photo below shows the contrast between a variety susceptible to WSBM/WSSM and a resistant variety, but was taken about 2-3 weeks later than today. Thus, over the next month as temperature rises and wheat greens up, symptoms will become more striking. However, nearly 100% of varieties planted across Oklahoma are resistant to both these viruses, so this disease complex has not caused a problem to wheat in Oklahoma (or other states) for many years. For more information on the WSBM/WSSM complex, go to: https://www.youtube.com/user/OSUWheat/videos and watch the video on “Wheat Soilborne Mosaic Virus and Wheat Spindle Streak Mosaic Virus.”
The stripe rust epidemic of 2015 is still fresh on the minds of many wheat farmers. Reports of active stripe rust on wheat in southern Oklahoma has producers now wondering if we are in for a repeat in 2016. While it is too early to tell if environmental conditions will favor a stripe rust outbreak in 2016, having active rust on wheat in the area satisfies at least one of the requirements for an epidemic. Most Oklahoma wheat producers will still be best advised to monitor the situation and make the fungicide decision based on yield potential and likelihood of infection when the flag leaf is emerging. Those with fields already showing heavy infection of foliar disease, however, might also benefit from a two-pass fungicide system. A few talking points and items to consider for those considering a two-pass system are posted below. A fact sheet on the topic of split application of fungicides can be found at www.wheat.okstate.edu
When to apply – The first pass in a two-pass fungicide system should be applied just after jointing. Please note that this is well after topdress nitrogen should be applied. For this and other reasons (see Dr. Arnall’s blog), tank mixing fungicides with nitrogen is generally not a good practice. Remember that the purpose of the early fungicide application is to keep disease in check until you come back with a flag leaf application in April. Going too early can result in too large of a gap between applications and enough time for disease to re-establish. Going too late can reduce the return on investment. Timing is everything with fungicides.
How much to apply – Back in the day, the discussion around split fungicide application centered on half rates for the first application. This recommendation was because of cost savings rather than disease management. The availability of low-cost, generic fungicides, though, has changed our philosophy, and a full rate of a low cost fungicide is the standard for split applications.
Which product to choose – Product choice is at the discretion of the consumer. If you are considering how to best spend your season-long fungicide budget, however, I would strongly recommend saving your “best” and perhaps most expensive product for the flag leaf application.
Watch season-long restrictions – As always, please read labels carefully and make note of season-long application restrictions. You don’t want an early fungicide application to remove the ability to apply your preferred product at flag leaf.
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: Early this week I spent time around Stillwater, Lahoma (10 miles west of Enid), and Cherokee and Alva (north-central OK not far from the Kansas border). Wheat ranged from soft dough around Stillwater to milk at Alva (but quickly approaching dough). There is a big difference between the wheat in these areas; obviously wheat around Alva suffered more drought stress than Cherokee, which is worse than Lahoma or Stillwater. However, lots of moisture and cool temperatures are allowing wheat to fill and mature.
As expected, leaf rust has exploded around Stillwater, with susceptible varieties such as OK Bullet at 80-90S. Leaves are gone on varieties that were highly susceptible to stripe rust, but varieties with stripe rust resistance that are susceptible to leaf rust (e.g., Jackpot, Greer) are now hit hard with leaf rust.
Weather since the middle of April has been reminiscent of the weather in April and May of 2007. As a result, wheat diseases favored by cool and wet weather are starting to occur with increasing frequency and severity. These diseases are causing head discoloration, which can be caused by fungi or bacteria. Around Stillwater and Lahoma, head discoloration due to a bacterium (Xanthomonas) has been observed. l have had reports of similar symptoms on wheat in southwestern OK, where more rain has fallen then around Stillwater. This bacterial disease is called black chaff when on the heads and is called bacterial streak when symptoms are expressed on leaves. The fungi Septoria and Stagonospora also can cause head discoloration, and we have isolated Septoria from several samples during the last week or so. For a full discussion of the various causes of head discoloration along with pictures, clicking on the following link will take you to the e-Pest Alert sent out in June, 2007.
Barley yellow dwarf also was observed this past week, but it was not extensive and little to no stunting was associated with the BYD spots indicating infection most likely occurred in the spring.
I have had reports of Fusarium head blight (scab) from southeastern KS, from Arkansas, and from eastern/northeastern OK, but have had no reports from anywhere else in Oklahoma.
The diagnostic lab continued to receive multiple samples that tested positive for Wheat streak mosaic virus, with several also testing positive for High plains virus (Wheat mosaic virus) and Barley yellow dwarf virus. For information on mite-transmitted diseases, I refer you to EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) also available at http://osufacts.okstate.edu.
Reports/excerpts of reports from other states:
Colorado: Dr. Scott Haley (Wheat Breeder); Colorado State Univ, 13-May-2015: “Stripe rust continues to develop in CO. Cool wet weather will likely favor continued development. Wheat is about at the heading growth stage.”