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Yearly Archives: 2015
By Tom Royer, Extension Entomologist
Heath Sanders could not have made a more prophetic statement for this Extension Entomologist than when he said: “we learn something new about canola every year”. I have learned something new every year that I have been working with canola, and this year is starting to confirm his “prophesy” once again.
This has been a banner year for fall armyworms. They built up populations early, and migrated into Oklahoma earlier than “normal”, attacking sorghum and pasture grasses. Now, they are ready to attack wheat (once it emerges) and possibly, are marching in to graze on newly emerged canola. Dr. Angela Post, OSU Extension Weeds specialist reported that there were caterpillars that appeared to be either beet armyworm or fall armyworms attacking canola. We are getting confirmation on their identity, but regardless, producers need to be vigilant and protect their fields.
I have already discussed their management in wheat http://entoplp.okstate.edu/pddl/pddl/2015/PA14-41.pdf, but now need to alert canola producers about them attacking seedling canola and eliminating stand.
Look for “window pane” damage in young canola plants and/or cut plants. At this time, with canola so small, armyworm and cutworm caterpillars cannot be allowed the chance to reduce stand. The suggested treatment threshold is 1 or more armyworms per row-foot.
Consult CR-7194 Management of Insect and Mite Pests of Small Grains and CR-7667 Management of Insect and Mite Pests in Canola for specific insecticides that are registered for control. Keep in mind that beet and fall armyworms can sometimes be difficult to control, so vigilance is needed by follow-up scouting following an application to make sure control is achieved.
No, this blog post is not about a get rich quick scheme, but there is a way for the average wheat farmer in the southern Great Plains to add $50,000 to $100,000 to the bottom line in a single day. Many soil tests I have pulled have shown as much as 50 to 90 lb/ac of NO3-N in the top 18 inches of soil. Ninety pounds of N equates to about $45 of N fertilizer, and this knowledge could save a 2,500 acre wheat farmer in excess of $100,000 in fertilizer cost. Soil testing is laborious, but the potential economic returns for spending a day or two soil sampling are outstanding.
There is still time to soil sample. Soil samples only take a few days to process once they are in the OSU lab. It is not unusual for transit time to the lab to the slowest part of the process, so if you need a fast turnaround a trip to drop samples in the Ag Hall basement in Stillwater will help (plus you have probably been wanting cheese fries). If you have already applied pre-plant fertilizer or sown wheat, there is still time to assess soil N availability and uptake via the N-Rich Strip. In its simplest form, the N-rich strip is an area where N is not limiting. Either by visual assessment or with the assistance of an optical sensor, you can use the N-rich strip to determine your top dress N requirement, but you must create the N-rich strip this fall.
The bottom line is that a day of soil testing or putting out N-rich strips is well worth your time investment. On another note, how would you like to make money and improve your health at the same time? I have a multi-level marketing opportunity that I can get you in on the ground floor, but don’t tell anyone else. I can only make this deal for you and only today. There will be a small “buy in” fee that you will need to pay cash up front, though.
Partial funding for the research included in this blog post was provided by USDA Project No.2012-02355 through the National Institute for Food and Agriculture’s Agriculture and Food Research Initiative, Regional Approaches for Adaptation to and Mitigation of Climate Variability and Change
Stories about seed law violations and fines have sprung up occasionally in the farm press over the past few years. These stories have tended to focus on the “penalty” part of the law and the magnitude of the fines rather than how the law protects Oklahoma farmers’ investments in wheat variety development and the provisions in the law that allow farmers to save seed for replanting. The purpose of this article is to answer some of the most frequently asked questions regarding the PVP law.
What is PVP?
The Plant Variety Protection Act (PVP or PVPA) is a federal seed law designed to protect the intellectual property of plant breeders, seed producers, and those who have funded variety development (in our case OSU and Oklahoma Taxpayers). The PVP law that you read about in the news today was enacted in 1994 and was an amendment to a law originally passed in 1970. The law prohibits the sale of farmer-saved seed without the variety owner’s permission. This protection lasts for 20 years for most crops. The ‘Title V’ you sometimes see tacked on to the end of PVP, refers to an amendment to the federal seed act stating that the variety can only be sold as a class of certified seed and by variety name.
Can I save seed from PVP-protected varieties?
Yes. You can save seed from PVP-protected varieties to plant on land you own or rent. You just cannot sell or trade the seed for planting purposes. A comparable example is an audio cd. You can make extra copies of an audio cd for your own use, such as an extra copy for the truck, without creating any problems. However, if you placed copies of the latest Sturgill Simpson cd for sale on Ebay, you would likely be contacted by the owners of the music regarding your unauthorized sale of their intellectual property.
Can I save seed of Clearfield varieties?
No, because Clearfield varieties are protected by a utility patent which protects a specific gene within the cultivar. Other examples of crop seed with genes protected by a utility patent include Roundup Ready, Bollgard, and Liberty Link. Wheat farmers will likely be seeing greater use of utility patents in the future but to my knowledge Clearfield varieties are the only hard wheat cultivars currently protected by a utility patent.
What about selling variety not stated (VNS) seed?
Not allowed. As indicated earlier, Title V of the federal seed act states that PVP-protected varieties can only be sold by variety name as a certified class of seed. This is one of several “ways-around-the-law” type questions that I am frequently asked at meetings and the answer is almost always no, you cannot do that. Other examples of violations would include: selling feed wheat, trading seed, giving seed away, and selling the standing crop of a PVP-protected variety and saving the seed.
The law just applies to the seller, right?
No. If there is a violation, then all parties involved can be included in the lawsuit. This includes the buyer, seller, seed conditioners, and even the entity spreading/planting the seed for the farmer.
How do I know if a variety is protected?
Certified seed of a protected variety will be clearly marked as such on the seed tag or the bulk label. The OSU Wheat Variety Comparison Chart indicates which varieties are PVP-protected and can be found at www.wheat.okstate.edu under Variety Testing, then under Variety Characteristics. Most varieties are now PVP-protected.
OSU is a public institution, why are they PVP-protecting varieties?
First and foremost, OSU acquires PVP-protection for new wheat cultivars to protect our (OSU, farmers, and taxpayers) collective investment in variety development. It takes 10 – 15 years to develop a wheat variety and this is not a cheap process. Without PVP protection others could reproduce an OSU wheat variety and profit from its sale without any benefit returned to farmers or OSU. PVP-protection ensures that when you buy an OSU variety, you are getting exactly the variety you are paying for and OSU has ensured quality-control standards through the certification process. It also ensures that a portion of the purchase price is returned to OSU for re-investment in the wheat breeding program where it is used to develop well-adapted varieties and ensure that the public sector remains competitive in wheat variety development.
Where can I find more information?
I am an agronomist, not a lawyer, so this article was meant to only hit the high points. A complete copy of the law (45 pages) can be found with a Google search of ‘plant variety protection act’. Texas AgriLife Extension also has a good summary of the law that can be found with a Google search for ‘plant variety protection act TAMU’.
Planting date: Much of the winter wheat in Oklahoma is sown with the intent of being used as a dual-purpose crop. In this system wheat is grazed by cattle from late October to early March, 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 such as mite-transmitted viruses, the aphid/barley yellow dwarf complex, and root and foot rots will be more prevalent and more 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 include wheat streak mosaic (WSM), wheat mosaic (formerly called high plains disease), and Triticum mosaic (TrM). All are transmitted by wheat curl mite (WCMs). WCMs and these viruses survive in crops such as wheat and corn, as well as many grassy weeds and volunteer wheat. In the fall, WCMs spread to emerging seedling wheat, feed on that seedling wheat, and transmit virus to the young wheat plants. Wheat infected in the fall is either killed by the next spring or will be severely damaged. Seed treatments are not effective in controlling these virus diseases. However, planting later in the fall (after October 1 in northern OK and after October 15 in southern OK) and controlling volunteer wheat are two practices that provide some control. It is critical that volunteer wheat is completely dead for at least two weeks prior to emergence of seedling wheat because WCMs have a life span of 7-10 days. Thus, destroying volunteer wheat at least two weeks prior to emergence of seedling wheat will greatly reduce mite numbers in the fall. In addition to these cultural controls, two winter wheat varieties (RonL from Kansas and Mace from Nebraska) have resistance to WSM; however, their adaptation to production is limited to northwestern Oklahoma. For more information on mite-transmitted virus diseases, see OSU Fact Sheet 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. 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 (e.g., Duster, Endurance, Gallagher, Iba, Doublestop CL+, Bentley, Everest, Winterhawk, Redhawk) tolerate BYD better than other varieties; however, be aware that no wheat variety has a high level of resistance to the aphid/BYD complex. 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 virus(es) that cause BYD. Systemic seed-treatment insecticides including Gaucho (imidacloprid) and Cruiser (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 infestations occur in the fall and spring. Fall infestations arise from over-summering pupae that emerge when climate conditions become favorable. 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. Some wheat varieties are either resistant (e.g. Duster, Gallagher, SY-Southwind, LCS Wizard, Winterhawk) or partially resistant (e.g. Everest, Iba, Jackpot, PostRock, Ruby Lee, SY-Gold, T-153, Tam 304, WB-Stout) to Hessian fly infestations. 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 fly fall infestations, 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 include several diseases caused by fungi such as dryland (Fusarium) root rot, Rhizoctonia root rot (sharp eyespot), common root rot, take-all, and eyespot (strawbreaker). Controlling root and foot rots is difficult. There are no resistant varieties, and although fungicide seed treatments with activity toward the root and foot rots are available, 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:
- Control of bunts and smuts, including common bunt (also called stinking smut), loose smut, and flag smut (for more information on flag smut, go to end of this report). The similarity of these names can be confusing. All affect the grain of wheat, but whereas common bunt and flag smut spores carryover onseed or in the soil, loose smut carries over in the seed. Seed treatments are highly effective in controlling all three of these bunts/smuts. 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 is strongly recommended. If either common bunt 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 and loose smut is strongly recommended. For more information on common bunt & loose smut, see: http://www.entoplp.okstate.edu/ddd/hosts/wheat.htm and consult the “2015 OSU Extension Agents’ Handbook of Insect, Plant Disease, and Weed Control (OCES publication E-832),” and/or contact your County Extension Educator.
- Enhance seedling emergence, stand establishment and forage production by suppressing root, crown and foot rots. This was discussed above under “Root and Foot Rots.”
- 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.
- 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.
- 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.
A final consideration for fall 2015: In the text above, I made reference to “flag smut,” which is a smut of wheat I have not mentioned previously. Flag smut occurs in the U.S., in particular, the Pacific Northwest. It also has been reported in the Plains States, being first reported in Kansas in the 1920s. However, flag smut has not been observed in the Central Plains for many years until this past spring when it was found in around 20 counties in Kansas from April-June. No flag smut was observed on wheat in Oklahoma in 2015, but much of the wheat in Oklahoma had been harvested when I found out about flag smut occurring in Kansas. Flag smut is similar to common bunt (stinking smut) in terms of its disease cycle, but spores of this fungus erupt through the leaves rather than replace the wheat grain as with common bunt. Additionally, leaves and tillers infected with flag smut often are twisted and deformed.
For more information on flag smut, please go to the following links. The first link is to a press release made in mid-July, 2015 on the finding of flag smut in Kansas. The second link is a KSU fact sheet on flag smut.
By: Dr. Bob Hunger, Extension OSU Wheat Pathologist and Dr. Tom Royer, OSU Extension Entomologist
Heath Sanders, Canola Field Specialist with Great Plains Canola, was scouting some wheat fields for armyworms in southern Oklahoma this past week and sent us some photos of damaged wheat heads that were being fed upon by wheat head armyworm. He stated that he had a hard time finding the worms because they blended in so well with the color of the wheat.
The insect causing the damage was Faronta diffusa, known as the wheat head armyworm. Unlike the armyworm, which was discussed last week, the wheat head armyworm is very capable of damaging wheat kernels. Adult moths lay eggs on plants in the spring, and the larva feed directly on the grain heads, mostly at night. The caterpillars range in color from gray to greenish with distinct yellow, white and brown stripes going lengthwise across the body. They typically have a larger head relative to their body. Because the larvae are so variable in color, the best way to identify them is to send in a sample to the Plant Disease and Insect Diagnostic Lab.
Fields can be scouted with a sweep net to determine numbers of caterpillars. There is no established treatment threshold because it rarely causes economic damage and more often than not the damage is not noticed until the grain is harvested. If wheat is at soft dough, consider treating the field to reduce damage. This insect is often found along the margins of fields so if scouting shows that they are restricted to the field edges, consider spraying the field margins with a border spray. Pay careful attention to pre-harvest intervals when selecting an insecticide.
This insect rarely causes significant damage. The major issue with wheat head armyworm damage has to do with the grain grading which is classified as IDK (Insect Damaged Kernels). Grain elevators will dock wheat when samples contain 6-31 damaged kernels per 100 grams of seed. To coincide with the Food and Drug Administration’s defect action levels, the U.S. Standards for Wheat consider wheat containing 32 or more insect-damaged kernels per 100 grams as U.S. Sample Grade. This grain is unfit for human consumption and can only be sold as animal feed. It is important to note that although the wheat is damaged, it is not an indication of an on-going infestation of grain weevil or some other stored grain insect pest.
The best strategy to manage the problem at harvest is to combine wheat harvested from head rows with wheat harvested from the rest of the field to dilute IDK percentages. Treating a field with insecticide at harvest will be of little help because the damage is already done, most of the caterpillars have already pupated and remaining larvae can’t feed on the mature wheat grain.
If a load is docked or rejected, check on insurance options. Most crop insurance policies have a Quality Loss Adjustment clause that covers the damage up to 25% of the crop’s value, regardless of the yield. Work with your elevator to collect and store samples of the wheat that can be used as evidence of the in-field damage.
This link will access Subpart M for US Standards for Wheat which discusses grades and grade requirements for wheat: http://www.gipsa.usda.gov/fgis/standards/810wheat.pdf
For more information on this topic, contact Tom A. Royer, Extension Entomologist at email@example.com or Edmond Bonjour, Extension Stored Grain Entomologist
We have a late-maturing wheat crop that finally received some needed rain. I received a report of armyworms infesting wheat in the Vernon, Texas area. Armyworm infestations typically occur in late April through the first two weeks of May, but the cooler spring we are experiencing this year may have delayed their development.
Early signs of an infestation include leaves with ragged margins that have been chewed. You may find “frass” i.e. the excrement from armyworm caterpillars, around the base of wheat stems. They also tend to clip heads from developing wheat plants. The head clipping I have noticed over the years us usually restricted to secondary tillers with very small, green heads that would not likely contribute much to yield.
Scout for armyworms, at 5 or more locations looking for “curled up worms”. Armyworm caterpillars tend to feed at night, so a good strategy is to bring a flashlight and look at fields after dusk when they are feeding up on the plant stems. The suggested treatment threshold for armyworms is 4-5 unparasitized caterpillars per linear foot of row.
Armyworms have a number of natural enemies that help keep populations in check, if given a chance. In particular, parasitic wasps and flies attack them. If you find small white cocoons littered on the ground that are about ¾ the size of a cue tip, the natural enemies have already taken care of the problem.
If wheat is past the soft dough stage, control is not warranted unless obvious head clipping can be seen and caterpillars are still present and feeding. Worms feeding on the awns when plants are past soft dough will not cause enough yield loss to justify the expense of an insecticide application that is solely intended for armyworm control. When choosing to spray, keep in mind that some insecticides require a 30 day waiting period for harvest.
Consult CR-7194 Management of Insect and Mite Pests of Small Grains for information on insecticides registered for control of armyworms.
For more information on this topic, contact Tom A. Royer, Extension Entomologist at firstname.lastname@example.org
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.”
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
In addition to looking at wheat around Stillwater this past week, I also was at field meetings near Kingfisher (30 miles northwest of OKC), Kildare (10 miles north of Ponca City), and Lahoma (10 miles west of Enid). Wheat was at full berry to borderline milk.
Stripe rust, leaf rust, and powdery mildew were present at all locations, with stripe rust by far the most prevalent. Where a fungicide had been sprayed (e.g., in Dr. Jeff Edwards variety trial), the effect was striking in terms of green leaf tissue. Difference in variety susceptibility to stripe rust was obvious, with Ruby Lee, Garrision, Pete, and Everest being some of the more common highly susceptible varieties. There also seems to be varieties with high levels of resistance (e.g., Gallagher, Jackpot, etc), and intermediate resistance; however, I’ll wait until I have all ratings in to evaluate this in more detail.
Leaf rust can be found in some varieties at severe levels, but has not increased to a level comparable to stripe rust. Most commonly, I am seeing it on leaves of varieties that are resistant to stripe rust, but susceptible to leaf rust (e.g., Jackpot).
Barley yellow dwarf also was observed at all locations, but little to no stunting was associated with the BYD, so infection most likely occurred in the spring.
Powdery mildew also was observed at every location, but only rarely was on the flag leaf or heads.
I have not seen any Fusarium head blight, but have had a few reports of it from eastern/northeastern OK.
The diagnostic lab continued to receive samples testing positive for Wheat streak mosaic virus, with several also testing positive for High plains virus (Wheat mosaic 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 www.wheat.okstate.edu
Reports/excerpts of reports from other states:
Kansas: Dr. Erick De Wolf (Extension Plant Pathologist); Kansas State Univ, 4-May-2015: “The past week continued to bring more finds and reports of rust diseases in Kansas. Stripe rust is the primary concern many growers and the disease is now established in many areas of the state. The disease has moved onto the upper leaves in many fields in the southeastern and south central regions of the state. The wheat in these areas of the state was at or near the heading and flowering stages of growth this past week. Infections on the upper leaves at these stages of growth places the crop at risk for severe yield losses. Stripe rust was found at low levels in many counties in the central and north central regions. The disease was also reported at low levels in western Kansas. At this point the stripe rust was primarily low to moderate incidence (1-5%) and mostly restricted to the lower leaves of many fields in the central and western regions. However, the weather this past week was very conducive for stripe rust and the disease may soon increase to damaging levels in more areas.
The risk of yield loss in these areas depends heavily on weather over the next 2 weeks. Stripe rust is favored by temperatures in the 40-60’s, frequent rain or heavy dew deposition. The progress of stripe rust often slows when nighttime temperatures exceed 60 degrees F. The weather outlook for the central region indicates that rain is likely this week but also suggests low temperatures may slow further disease development. Temperatures in north central and western Kansas may be more conducive for stripe rust. So far the stripe rust is most severe on varieties known to be susceptible to the disease but there are some early indications of unusual disease reactions on varieties previously thought to be resistant. I will gather more information and come back with reports soon.
Leaf rust has also been detected at trace or low levels at many of the same locations as stripe rust (Crawford, Clay, Ness, Riley, Saline, and Sumner counties). These reports are significant because the presence of leaf rust increases the risk of disease related yield loss in the state. Many of the popular varieties grown in the state are susceptible to leaf rust and finding the disease prior to flowering indicates the leaf rust may also cause problems in some areas. To date the leaf rust appears to be most common on varieties with the Lr39/41 resistance gene (Fuller and WB 4458 for example).
TEXAS: Dr. Clark Neely (Small Grains & Oilseed Extn Specialist; Texas A&M AgriLife; College Station; 7-May-2015: “I spent the past several days attending wheat field days in northeast Texas. Stem rust was found in susceptible soft wheat varieties in Ellis County. After fading away for the most part from warmer temperatues, stripe rust was re-establishing itself on flag leaves of susceptible varieties in due to the cooler, wet weather affecting the region. Most wheat in the region is in the milk-soft dough stage. Leaf rust was moderate to severe on susceptible lines at Howe, TX including TV 8861, however, leaf rust was much lighter at Leonard and Farmersville, TX locations.”
Georgia: Alfredo Martinez, John Youmans, James Buck; University of Georgia; 6-May-2015: “Leaf rust infections have been observed in commercial wheat fields in Southwest Georgia (Seminole Co. Mitchel Co. Taylor Co.). The incidence of leaf rust seems to be localized and the severity was low. Stripe rust was confirmed in northwest GA (Floyd Co.). The incidence and severity was minor. Commercial fields surveyed near UGA College of Agricultural and Environmental Sciences Research Station in Plains, GA and around the UGA CAES Bledsoe Farm near Griffin GA yielded no stripe, leaf rust or stem rust infections. Low rust and powdery mildew on wheat in GA was probably due to the use of resistant varieties and /or timely applied fungicides. However, for a second year in row, Fusarium Head Blight (FHB/Scab) incidences were numerous (albeit not as prevalent as in 2014), in some fields the severity was high. Surveyed fields in Sumter Co. had severity of 50%-60%. Environmental conditions at the time of wheat flowering provided conducive conditions for FHB infections especially in the southernmost part of the state. Stagonospora spot blotch and tan spot were observed throughout the state and seemed more prevalent than previous years.”
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: This past week I spent in fields/nurseries around Stillwater and also attended field days in central OK (Caddo Cnty) and southwestern OK (Jackson Cnty). Most of the wheat I saw was at ¼ to nearly full berry. Foliar diseases have definitely increased.
Around Stillwater, powdery mildew is evident on the lower leaves in my fungicide trial (approx. 25% severity). In the variety demo strips at Stillwater, I can find severities >65% on lower leaves. However, stripe rust is still the most evident foliar disease with mid-canopy leaves of susceptible varieties often completely or nearly completely infected. Flag leaves of susceptible varieties around Stillwater are beginning to show stripe rust pustules, but that is still not uniform in all fields/locations. Also this past week I started to see leaf rust pustules developing on lower leaves; I only occasionally saw pustules on flag leaves with the exception of ‘Jagalene’, which was at 90% or so.
In central OK I saw mostly the same thing. At the variety trial near Kingfisher (Kingfisher Cnty), disease was surprisingly light with stripe rust the most evident. Near Apache OK (southern Caddo Cnty), disease was more prevalent with stripe rust the most severe. Varieties resistant to stripe rust but susceptible to leaf rust (e.g., ‘Jackpot’ were beginning to show more leaf rust pustules). Tan spot also was evident at this variety trial as it is a no-till field.
In southwestern OK (near Altus, OK), stripe rust was severe (90% or so) on the flag leaves of susceptible varieties such as ‘Ruby Lee’, ‘Everest’, and ‘Garrison’. Varieties with resistance to stripe rust such as ‘Gallagher’ and ‘Billings’ showed little sporulation but loss of some green tissue due to the hypersensitive reaction (HR). ‘Greer’ showed no stripe rust and no dead tissue due to the HR. Here again, a variety like Jackpot showed no stripe rust, but leaf rust was at a moderate level. An interesting observation was made by Dillon Butchee (Helena Chemical Rep), who noticed stripe rust sporulating inside the glumes of susceptible varieties, which I have seen only occasionally in Oklahoma.
In more northern OK, Greg Highfill (Extension Educator, Woods Cnty – near Alva, OK) indicated he has seen small amounts of stripe rust in the border of the test plot near Alva. Although temperature is increasing, the forecast for next week is highs only in the low to mid 80s with Tuesday-Thursday being rainy again. These temps will be lower in northern and northwestern OK. Hopefully the rain will continue, but these conditions will favor continued spread and increase of particularly leaf rust. For most of Oklahoma, I believe wheat is past or quickly approaching the point where a fungicide can no longer be applied. For a discussion of this, see “CR-7668 Foliar Fungicides and Wheat Production in Oklahoma – April, 2015,” which is available at www.wheat.okstate.edu.
Finally, the diagnostic lab continues to receive samples testing positive for Wheat streak mosaic 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 www.wheat.okstate.edu
Reports/excerpts of reports from other states:
Nebraska: Dr. Stephen Wegulo (Extension Plant Pathologist); Univ of Nebraska, 28-Apr-2015: “Yesterday I surveyed wheat fields in south central and southeast Nebraska. Stripe rust was widespread (prevalence of >70%) in the southernmost tier of counties. Incidence ranged from about 15% to > 80% in some fields. Severity was mostly trace to low (< 10%), although a few isolated leaves had >50% severity (see attachment). Growth stage was mostly Feekes 6; in a few fields it was Feekes 6 to 8, and in two irrigated fields wheat was in the boot stage. These two irrigated fields apparently had been sprayed and there was no stripe rust in them, but I was able to find some leaves on which stripe rust development was stopped by the fungicide spray. There was severe winter kill in some fields to the extent that the wheat was sprayed with herbicide and another crop will be planted.
Last week (Thursday and Friday) I surveyed wheat fields in the southern and northern Panhandle of Nebraska (the far northwest of the state) and in southwest and west central Nebraska. I found no foliar diseases, but there was root rot in one field that also had some winter kill in the northern Panhandle. In the west central part of the state, there was severe winter kill in some fields (see slide #3 in the attachment). Growth stage ranged from Feekes 5 in the Panhandle to Feekes 5 to 6 in the southwest and west central parts of the state.”
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Oklahoma: Again, a cool and moist week in Oklahoma with rain and cool temperatures in the forecast through the weekend. Wheat is mostly at flowering around Stillwater but by early next week will likely be past flowering. From what I hear across the state, wheat is quickly approaching, at, or will be quickly past flowering (depending on what part of the state, when planted, and how much drought stress was endured).
Around Stillwater there has been an increase in stripe rust and powdery mildew (especially stripe rust). Leaf rust also has increased, but not to the same extent (incidence or severity) as stripe rust. Dr. Brett Carver (OSU Wheat Breeder) indicated he saw significant stripe rust in his nurseries at Lahoma (north-central OK). Gary Strickland (Jackson County Extn Educator) also has observed an increase in stripe rust (and to a lesser extent, leaf rust) in far southwestern Oklahoma. My impression is that stripe rust has activated again with the cool and wet weather, and continues to spread across Oklahoma. This Thursday and Friday there will be field days in central Oklahoma, so look for a more extensive report next week.
To the south of us in Texas (far southern Texas), Dr. Amir Ibrahim (Professor, Small Grains Breeder/Geneticist; Texas A&M AgriLife Research; College Station, TX) has indicated in breeder nurseries near Castroville, TX, that there is a mixture of stripe rust, leaf rust, bacterial leaf streak and some septoria. This has occurred because of back-and-forth switching between cool and warm temperatures mixed in with lots of rain. To some extent, this also has occurred across Oklahoma during April.
Mite-transmitted viruses also are prevalent in Oklahoma this year. Yesterday when in nurseries here at Stillwater I noticed occasional trapped heads scattered throughout the field. In observing these in the lab using a dissecting scope, I found wheat curl mites associated with these trapped heads. Although only sporadic around Stillwater, the Diagnostic Lab has received multiple samples that they confirmed for presence of Wheat streak mosaic virus, Wheat mosaic virus (High plains virus), and/or Barley yellow dwarf virus. This includes samples from Grady, Noble, Grant, Texas and Woods Counties. I would refer you to EPP-7328 (Wheat Streak Mosaic, High Plains Disease, and Triticum Mosaic: Three Virus Diseases of Wheat in Oklahoma) available at http://osufacts.okstate.edu for more information on these mite-transmitted viruses.
Reports/excerpts of reports from other states:
Kansas: Doug Shoup (SE Area Crops/Soil Specialist) & Erick DeWolf (Extn Plant Pathologist), Kansas State University, 22-Apr-2015: “Stripe rust has been found in several fields of wheat in southeast , south central, and north central Kansas. Given the forecast of cool and relatively wet conditions for the next seven days, this is a potentially significant situation for fields anywhere in Kansas planted to varieties susceptible to stripe rust. Intensive scouting of fields should begin now.” [This was the first paragraph of their report, which can be found at: