Amanda de Oliveira Silva, Small Grains Extension Specialist
First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8”, or the diameter of a dime) of hollow stem below the developing grain head (see full explanation). The latest FHS results from OSU forage trials in Stillwater (Table 1) and Chickasha (Table 2) are listed below. For an additional resource, see the Mesonet First Hollow Stem Advisor.
We use an accelerated growth system to report the earliest onset of FHS stage. Trials are seeded early to simulate a grazed system, but the forage is not removed. Varieties reported here with the earliest FHS date should be the first to monitor in commercial fields. In practice, wheat that is grazed will likely reach FHS stage later than reported here, and differences between varieties will likely moderate.
Table 1. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 10/06/22 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.
Table 2. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 10/07/22 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.
Contact your local Extension office and us if you have questions.
Amanda de Oliveira Silva, Small Grains Extension Specialist
With severe dry conditions and high temperatures in our state, it is good to consider the possible effects of high temperature and drought on wheat germination and early growth. As of September 19, soil temperature was in the 80’s F across the state and reached 97 F in some areas (Figure 1). Wheat can germinate in soil temperatures from 40 F to 99 F, but temperatures from 54 F to 77 F are optimal.
Figure 1. Soil temperature across Oklahoma. Figure courtesy Oklahoma Mesonet.
Wheat germination and emergence in HOT soils
Is the variety I am planting high-temperature germination sensitive?
High-temperature germination sensitivity is a more elaborate way of saying that some wheat varieties do not germinate well in hot soil conditions. This is not to say that the seed will not germinate, but it may not germinate until the soil temperature has lowered. Keep in mind too that this sensitivity can vary from year to year. For example, a sensitive variety like Ruby Lee may germinate fine in 90°F soils one year and only produce a 10% stand in the same soil conditions the next. When sowing early, it is best to plant varieties first that do not have high-temperature sensitivity (e.g., Duster, Gallagher). Soil temperatures typically begin to cool by about September 20 due to lower air temperatures and/or rainfall events. However, our summer temperatures seem to be sticking around for longer this year. Waiting until at least mid-September to plant sensitive varieties can help reduce the risk of this issue. A high temperature germination sensitivity rating for wheat varieties can be found in the OSU Fact Sheet (available by clicking here). An updated version of this factsheet will be published soon.
Coleoptile Length
Hot soil conditions at sowing also reduce coleoptile length. The coleoptile is the rigid, sheath-like structure that protects the first true leaf and aids it in navigating and reaching the soil surface. Once the coleoptile breaks the soil surface, the coleoptile will stop growing, and the first true leaf will emerge. If the coleoptile fails to reach the soil surface, the first true leaf will emerge below ground and take on an accordion-like appearance (Figure 2A-B). If this happens, the plant will die.
Figure 2A and 2B. Example of two different wheat seedlings in which the coleoptile failed to break the soil surface. The first true leaf emerged below the soil surface and resulted in this accordion-like appearance.
The coleoptile length for most wheat varieties today can allow for the seed to be safely planted up to 1.5 inches deep. Under hot soil conditions though, the coleoptile length tends to be decreased. Therefore, “dusting in” early-sown wheat at ¾ to 1 inch depth and waiting on a rain event may result in more uniform emergence than trying to plant into soil moisture at a deeper depth, if soil moisture is not available in the top 1 to 1.5 inches of the soil profile. A rating for coleoptile length for wheat varieties can be found in the OSU Fact Sheet PSS-2142 Wheat Variety Comparison. We are also working on updating this.
Wheat germination and emergence in DRY soils
The most important physiological requirement for wheat to germinate and sustain the developing seedling is soil water. Therefore, planting decisions should be based on a combination of available soil moisture and expected rainfall. In addition, other factors such as adequate seeding depth, sowing date, soil fertility, seed treatment, seed quality, etc., should be considered to guarantee good crop establishment. For more information, check the materials on our website.
Wheat seed needs a minimum water content of 35 to 45% of its dry weight to initiate germination, and germination will be more complete as moisture levels increase. Dry soils can still maintain a relative humidity of 99%, which can provide enough moisture for seeds to germinate. It might just take longer than with free-moisture availability. My concern with the current situation in Oklahoma is the severe drought we are in and the lack of rain in the forecast. In some cases, we could have enough moisture to start the germination process in some regions of the state, but seedling emergence and growth could be compromised if we do not see any rain soon.
What happens if the soil completely dries out before wheat emergence?
There are three phases during the germination process: water absorption, activation when the seed coat is ruptured, and visible germination when the radicle emerges, followed by the seminal roots and coleoptile. These processes will start and stop depending on soil moisture availability. Thus, if the soil dries out before the roots and shoots are visible, the seed remains viable, and germination will be paused and continue once water is available. However, if the soil dries out after those structures are emerged (approximately 4-5 days after germination has begun), the seedling may not tolerate the lack of water, resulting in incomplete or loss of stand.
What should I do then? Choose your battle!
The optimal time for planting wheat in central Oklahoma is around mid-September for a dual-purpose system or around mid-October for a grain-only system (Figure 3). With the current forecast, we are planning to wait another 7-10 days to decide on our dual-purpose and forage trials. There are different ways we can go about it, but we must remember that there is always risk involved when planting wheat in dry and hot soil conditions.
Figure 3. Forage and grain yield potential in relation to the day of the year. Every 1,000 kg/ha is equal to approximately 900 lb/acre or 15 bu/acre. Ideal planting dates for dual-purpose wheat in Oklahoma are mid-September (i.e., approximately day 260). Planting for grain-only should occur at least 2-3 weeks after dual-purpose planting (i.e., mid-October or approximately day 285).
If you decide to dust in your wheat and wait for a rainfall event to drive germination, watch your seeding depth. The optimum seeding depth to plant wheat is about 1-1.5” deep. We typically do not have as many issues with winterkill in Oklahoma as in more northern states, so I am comfortable with dusting in at about 0.75 – 1” deep. Planting at 0.5” or less is too shallow in most circumstances. Also, there is always a chance for a pounding rainfall event and subsequent soil crusting, which makes it difficult for the coleoptile to push through the soil surface and may result in poor emergence. Fields with stubble cover may be less affected and reduce the risk of soil crusting. If we receive light rain in the following weeks, that could cause wheat to emerge, but it may not be enough for wheat to continue growing. Most of the fields do not have good subsoil moisture, either.
If subsoil moisture is available and you decide to plant deeper to reach moisture, be careful with the coleoptile length of your variety, and make sure it has a long-enough coleoptile that will allow emergence if conditions are favorable. Consider increasing seeding rate to compensate for reduced emergence, which is prone to occur in this situation.
Should we wait for rain to plant then? This is a farm-by-farm call and it depends on which source of risk you find most comfortable. Personally, I would rather plant my wheat in the optimal planting window and adequate seeding depth than waiting for a rain that may take too long to happen or missing my optimal planting window. If the latter is the case, consider bumping seeding rate to try to compensate for the reduced time for tillering (especially in a grain-only system). Planting wheat at optimal time allows for more time for root growth in seedlings, helping the crop to establish more quickly under dry conditions and possibly help the plant to scavenge for water that is available deeper in the soil profile.
Are there any specific agronomic traits that could help wheat seedling growth under water stress?
Traits that will help with seedling growth in dry conditions are coleoptile length potential, which allows to plant a little deeper in moisture and good emergence (if deep planting is the practice of your choice). There are indications that sowing wheat varieties with larger seed may help to reduce the negative effects of drought during early growth (Mian and Nafziger, 1994). In general, the greater reserves of larger seed result in faster germination and crop establishment by increasing root growth and tiller production. Keep in mind, however, there are varieties with small seed size that germinate more rapidly than larger seeded varieties, owing to their differential response to available moisture.
Amanda de Oliveira Silva, Small Grains Extension Specialist
First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8”, or the diameter of a dime) of hollow stem below the developing grain head (see full explanation). The latest FHS results from OSU forage trials in Stillwater (Table 1) and Chickasha (Table 2) are listed below. For an additional resource, see the Mesonet First Hollow Stem Advisor.
We use an accelerated growth system to report the earliest onset of FHS stage. Trials are seeded early to simulate a grazed system, but the forage is not removed. Varieties reported here with the earliest FHS date should be the first to monitor in commercial fields. In practice, wheat that is grazed will likely reach FHS stage later than reported here, and differences between varieties will likely moderate.
Values can fluctuate from one sampling to another due to environmental variation associated with, among other factors, the winter storm on February 2-4. Additionally, varieties differed widely in their FHS response following this cold period.
Table 1. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/27/21 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red. The overall average represents the mean FHS for the varieties measured within a date.
Table 2. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/28/21 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red. The overall average represents the mean FHS for the varieties measured within a date.
Amanda de Oliveira Silva, Small Grains Extension Specialist
First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8”, or the diameter of a dime) of hollow stem below the developing grain head (see full explanation). The latest FHS results from OSU forage trials in Stillwater (Table 1) and Chickasha (Table 2) are listed below. For an additional resource, see the Mesonet First Hollow Stem Advisor.
We use an accelerated growth system to report the earliest onset of FHS stage. Trials are seeded early to simulate a grazed system, but the forage is not removed. Varieties reported here with the earliest FHS date should be the first to monitor in commercial fields. In practice, wheat that is grazed will likely reach FHS stage later than reported here, and differences between varieties will likely moderate.
Values can fluctuate from one sampling to another due to environmental variation associated with, among other factors, the winter storm on February 2-4. Additionally, varieties differed widely in their FHS response following this cold period.
Table 1. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/27/21 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red. The overall average represents the mean FHS for the varieties measured within a date.
Table 2. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/28/21 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red. The overall average represents the mean FHS for the varieties measured within a date.
Amanda de Oliveira Silva, Small Grains Extension Specialist
First hollow stem (FHS) is the optimal time to remove cattle from wheat pasture. This occurs when there is 1.5 cm (5/8”, or the diameter of a dime) of hollow stem below the developing grain head (see full explanation). The latest FHS results from OSU forage trials in Stillwater (Table 1) and Chickasha (Table 2) are listed below. For an additional resource, see the Mesonet First Hollow Stem Advisor.
We use an accelerated growth system to report the earliest onset of FHS stage. Trials are seeded early to simulate a grazed system, but the forage is not removed. Varieties reported here with the earliest FHS date should be the first to monitor in commercial fields. In practice, wheat that is grazed will likely reach FHS stage later than reported here, and differences between varieties will likely moderate.
Values can fluctuate from one sampling to another due to environmental variation associated with, among other factors, the winter storm on February 2-4. Additionally, varieties differed widely in their FHS response following this cold period.
Table 1. First hollow stem (FHS) results for each variety collected at Stillwater. Plots were planted on 09/27/21 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.
Table 2. First hollow stem (FHS) results for each variety collected at Chickasha. Plots were planted on 09/28/21 but not grazed or clipped. The threshold target for FHS is 1.5 cm (5/8″ or the diameter of a dime). The value of hollow stem for each variety represents the average of ten measurements. Varieties exceeding the threshold are highlighted in red.
Amanda de Oliveira Silva, Small Grains Extension Specialist
Dual-purpose producers were not able to plant wheat in timely fashion (mid-September) due to drought conditions in much of the state. Most of the wheat intended for dual-purpose was “dusted in” and emergence was delayed, but plants established well. Oklahoma received good rainfall in October, which helped the dual-purpose wheat to emerge and grow and enabled grain-only producers to plant in good soil moisture. Although dual-purpose wheat was planted later than desired, the October moisture enabled moderate fall forage production. Oklahoma has not received 0.25” of rainfall for almost two months in some parts of the state and the wheat is showing signs of drought stress. There are also several fields showing symptoms of nitrogen deficiency.
The last several weeks have been warmer than usual. December is on track to be one of the warmest on record. The issue with current temperature fluctuations and abnormally warm temperatures is that the wheat crop is not able to fully acclimate and “cold-harden” before the winter. On December 15, soil temperatures in OK ranged from 47 to 62 F and air temperature in one location changed by 13 degrees (from 67 to 80F) in a matter of hours.
Soil temperature at the crown level will influence wheat vernalization and tolerance to cold temperatures. Wheat needs soil temperatures at the crown level to be below about 50F to initiate the physiological process of cold acclimation. Once below this threshold, cooler temperatures generally mean more rapid acclimation.
If wheat is not well acclimated, severe drops in temperature could cause winterkill or injury, and a reduction in tillering and crop growth in the spring, but we won’t know for certain until later. In addition, dry soils can experience wider oscillation in temperature than moist soils, creating more crop risk if temperatures drop well below freezing before significant rainfall.
In all, the effect of this hot and dry weather on Oklahoma’s wheat crop will depend on several factors, especially how abrupt temperatures decrease and how much rainfall is received soon. Our crop is showing signs of drought stress and could benefit from additional moisture going into the winter.
Wheat field showing signs of drought stress at Caddo County. Photo taken on Dec 7, 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.
Active spore stage of stripe rust
Survival spore stage of stripe rust
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.
Telial/uredinial pustules of the stripe rust fungus. Zack Meyer; Extn Educator; Kingfisher Cnty
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.
Photo credit: Greg Highfill – Extn Educator; Woods Cnty 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.
Stripe rust in northwestern Oklahoma – Photo courtesy Greg Highfill and Darrell McBee
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.
Stripe rust in Pete in Caddo County – photo courtesy David Nowlin
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.
Yellowing in wheat at Kingfisher
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
tan spot
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.”
Temperatures over the weekend were cold enough to cause injury to the Oklahoma wheat crop. As shown in the figure below from the Oklahoma Mesonet many areas of Oklahoma spent several hours below 28F. While temperatures in the wheat canopy might have remained slightly higher than reported air temperatures, they were still probably low enough to result in significant injury to wheat.
Hours spent below 28F March 18 – 20
A few points I would encourage everyone to consider:
Every freeze event is unique – the temperatures and time durations we use regarding freeze injury are rules of thumb and are not exact. I have seen instances where conventional wisdom would indicate complete crop loss and we skate through with minimal damage. It will take a few days to see how bad things are – Symptoms may start to appear later this week and will likely be clearly identifiable by the end of this week. Healthy wheat heads will remain turgid with a green color. Damaged wheat heads will be bleached, yellow, or brown and will easily break when pushed against. I anticipate that we will not have any partial “blanking” of wheat heads and that most wheat heads will either be okay or a complete loss. This post from last year has some pictures showing tell tale signs of freeze injury. The linked post also serves as a reminder that while freeze is the concern of the day, the potential worsening of drought conditions in NW Oklahoma has the potential to do far more damage.
% damaged heads might not = % yield loss – It is still relatively early in the growing season and there is still opportunity for smaller (two nodes or less) wheat to produce additional tillers and/or retain secondary tillers. Whether or not these tillers are able to compensate for larger tillers that were lost due to freeze will depend on moisture and weather. IF (and that is a big if) weather conditions remain favorable, late emerging tillers in central and northern Oklahoma might still have a shot at producing grain. It will be tougher for more advanced wheat in southern Oklahoma to make this type of recovery.
WORLD OF WHEAT 