Determining the optimal time to remove cattle from wheat pasture (if you still have pasture to graze…)
The wheat growing season up to this point has been extremely tough to say the least. The forage situation has been a kick-in-the-knees in addition to taking it on the chin with the grain prices. Trying to get wheat pasture established was hard enough between fighting off the fall armyworm and working around the rain. Then on top of all that after getting a stand established, it has not rained since. As a result, many producers have already grazed as much as they could and have removed their cattle, or they have not even had the chance to graze. For the few producers who still have pasture to graze, leaving some leaf material out there after grazing will be important for having any chance of a decent grain crop. Ideally, there should be a minimum of 60% canopy coverage left. It also does not look like we will have cool and wet conditions after cattle removal to allow the plants more time to recover from the grazing injury. This situation is shaping up to be similar to last year, and that puts even more emphasis on removing cattle from wheat pasture at the right time.
The optimal time to remove cattle from wheat pasture is at a growth stage called first hollow stem (FHS, between Feekes 5 and 6). This is the optimal time because the added cattle weight gains associated with grazing past first hollow stem are not enough to offset the value of the reduced grain yield (1-5% every day past FHS). The wheat variety, amount of grazing, time when cattle are removed, and weather conditions after cattle removal determine how much total grain yield potential might be reduced.
One of the moving targets each year is determining when to start scouting for FHS. To help combat this, the First Hollow Stem Advisor was developed by researchers at Oklahoma State University. This is an online tool available on the Mesonet website, https://www.mesonet.org/index.php/agriculture/category/crop/wheat/hollow_stem_advisor. This tool uses soil temperature data to show the current probability of FHS occurrence, as well as 1-week and 2-week projections. With this tool, producers can select their variety from a list of varieties that separates them into three FHS categories: early, middle, and late. Then, maps can be generated to provide the probability of FHS based on current conditions and the 1- and 2-week projections. Charts and tables can also be generated for individual Mesonet sites. Created maps have a color scheme to represent the probability of FHS occurrence. When using this tool, it is recommended to start scouting for FHS from a non-grazed part of the field once the 5% probability is reached (green color). Because stem elongation will begin moving quickly as the temperature warms up, starting your scouting at the 5% level will help give you the time it takes for making the preparations for cattle removal by the time FHS occurs. Methods on how to scout for FHS are listed at the end of this post. For producers who do not scout, it is recommended to remove cattle when the 50% probability level is reached. A 50% probability level indicates that over an evaluated period (e.g., 10 years), FHS would have occurred by that date in 50% of those years (e.g., 5 years). The same interpretation is used for other probability levels.
To give an example of what the tool provides and show some of the FHS conditions around Oklahoma, I have generated some statewide maps below. For producers along the southern Oklahoma border who planted an “early” wheat variety (e.g., Gallagher), now would be the time to go out and start scouting for FHS (Figure 1).
Figure 1. Current FHS probabilities for “early” wheat varieties.
Looking at the 1-week projection for “early” varieties, you can see how the probabilities have increased, and areas further north should begin scouting (Figure 2).
Figure 2. One-week FHS projection (i.e., through February 22) for “early” wheat varieties.
For producers who planted “middle” (e.g., Duster) or “late” (e.g., Doublestop) FHS varieties, the 1-week projections indicate producers across much of the state still have a little bit of time yet before beginning to scout. However, producers along the southern border should begin scouting (Figure 3).
Figure 3. One-week FHS projections (i.e., through February 22) for “middle” (top) and “late” (bottom) wheat varieties.
Remember that this tool should be used as a proxy to begin scouting for FHS. The best estimate of FHS is still to split stems from plants in each field to determine where they are developmentally. Another word of caution I want to mention when using the tool for this year especially is to consider when you were finally able to get stand establishment. If this did not occur until the end of September to the beginning of October, this tool may be a little ahead of where your plants are developmentally. In this case, the tool can still give you the cue to start scouting, but checking for FHS in each field will let you know if you do have some grazing time left.
Methods for scouting for FHS:
- Check for FHS in a non-grazed area of the same variety and planting date. Variety can affect FHS date by as much as three weeks and planting date can affect it even more.
- Dig or pull up a few plants and split the largest tiller longitudinally (lengthways), and measure the amount of hollow stem present below the developing grain head. You must dig plants because the developing grain head may still be below the soil surface at this stage.
- If there is 1.5 cm (~5/8″) of hollow stem present, it is time to remove cattle. 1.5 cm is about the same as the diameter of a dime (see picture below).
- More detailed information on FHS can be found at wheat.okstate.edu under ‘Wheat Management’ then ‘Grazing’ or by clicking here.
The first hollow stem growth stage is reached when there is 1.5 cm of hollow stem (about the diameter of a dime) below the grain head.
Similar to previous years, we will monitor occurrence of FHS in our wheat plots at Stillwater and Chickasha and report the findings on this blog.
When wheat pasture fails due to drought, there are limited opportunities to recover lost forage production. Spring-planted oat is the best option to offset forage losses from wheat pasture and has been a “go to” forage crop in this case for southern Great Plains beef producers for years. The window for spring-planted oat is between February 15 and March 10. Forage production potential is around 1,500 to 2,00 lbs/acre, but you will need about 40 – 60 lbs/acre of nitrogen to make this type of yield. A fact sheet detailing spring oat production for hay and grazing can be found by clicking here or by going to www.wheat.okstate.edu under “Wheat Management” then “Seeding”. Some of the key points from that fact sheet are listed below.
Spring oat can provide an alternative hay or forage source in the spring.
Seed — Plant 80 – 100 lbs/acre of good quality seed that has a germination of no less than 85%. There aren’t many options regarding varieties, so you will likely be limited to whatever seed is available in your area. The key is not to cut back on seeding rate, regardless of variety.
Seedbed — Sow oat seed at approximately 1/2 to 3/4 inches deep. Most producers will be better off with a conventionally-tilled seedbed. You are planting seed at a time of year when the ground is already marginal regarding temperature. Conventionally-tilled seedbeds warm more quickly, which should speed germination. There is one exception to the conventional till recommendation. If you are sowing into a stale seedbed or a failed wheat crop that is very thin, no-till should be okay. Just avoid situations where excessive residue will keep the soil cold.
Grazing — Oat plants should have a minimum of six inches of growth prior to grazing. Unlike fall-seeded cereals, you should not expect a large amount of tillering. A good stand of spring oat can provide a 750 lb animal approximately 60 days of grazing when stocked at 1.5 animals per acre.
Hay — Oat should be cut for hay at early heading to maximize yield and quality.
In response to an elevated number of off-target movement claims in many states in 2017, this training has been mandated by the EPA for application of newly formulated dicamba products. The following formulations of dicamba are approved for use in the Roundup Ready® Xtend Crop System as of November, 2017 and are covered by these trainings:
- XtendiMax® herbicide with VaporGrip® Technology (Monsanto)
- DuPont® FeXapan® herbicide Plus VaporGrip® Technology
- Engenia® Herbicide (BASF)
The application requirements in these trainings apply to all labeled uses of these products in Oklahoma. These trainings are designed to satisfy the federal requirement for mandatory dicamba applicator training and to satisfy the Oklahoma Department of Agriculture, Food & Forestry requirement for dicamba specific training. This training is not a substitute for the state-specific Certified Applicator training which is required to purchase and use Restricted Use Pesticides.
For more information contact the Oklahoma Department of Agriculture, Food & Forestry (Debbie Mandrell – 405.522.5949 – Debbie.Mandrell@ag.ok.gov) or your local Oklahoma Cooperative Extension Service county office.
Normally the alarm for beginning wheat N topdressing gets sounded right away in early January. However, it might be understatement to say this year has been dry so far – “drier than a popcorn fart” may be a better description. At the time of writing this blog, a significant portion of the Oklahoma wheat belt has now gone 90+ days with less than 0.25” of rain. The great folks at Mesonet reminded us on January 18 that the long term forecast is not providing us much hope either (Fig. 1).
Figure 1. The Oklahoma Mesonet tweet from January 18.
Because it has been dry and no significant rain is in the current forecast, the question is what do we do now about topdressing? This is a tough question to answer as there is not a really “good” option at the moment to be honest. Here are some thoughts to consider:
- In the parts of the state where it is dry and dry deeper than the majority of the rooting zone (> 6”), we should not worry about filling up the nitrogen tank as long as the water tank is empty. As it stands currently, the best option is to hold off for now and wait to apply topdress N right in front of a real chance of rain. The good news is we still have some time yet to get N applied and not limit yield potential if we do get that rain. Ideally, we need the N down in the rooting zone just prior to jointing. Several things, including the number of potential grain sites, are determined just prior to jointing, and it is imperative that the plant has the fuel it needs to complete these tasks. Jointing occurs around the end of February in southern OK and around the second week of March in northern OK. Jointing also marks the beginning of rapid nitrogen uptake by the plant which is used to build new leaves, stem, and the developing grain head. The nitrogen stored in these plant parts will be used to fill the grain later in the season, and the plant is dependent on this stored nitrogen to complete grain fill. And while it does seem like it right now, we still have the potential to make a decent crop if we can get rain before we break winter dormancy. If we do not get the rain though soon as it is appearing, we will not have spent as much money on this crop by holding off on topdress N, and the likelihood of getting the return on our N investment goes down as our yield potential goes down.
- What we can and should do right now is apply N-rich strips. An N-rich strip can help put your mind more at ease by taking the guesswork out of knowing if nitrogen needs to be applied and how much should be applied. The N-rich strip can be as simple as using a small lawn fertilizer spreader with a bag of urea. You local county extension educator can also provide more information on N-rich strips and even has access to lending small fertilizer spreaders!
For those producers who have too much ground and cannot cover all of it just prior to a rain or for those who want to apply now as they are worried about nitrogen being limited after it does start raining, here are few more considerations:
- For conventional-tilled fields that have limited to no residue, applying UAN through streamer nozzles is an okay option. Why? With UAN, there is a very high percentage of soil-fertilizer contact. This immediately improves the efficiency compared to urea. In fields with crop residue, flat fan nozzles are not recommended right now as the likelihood up of N tie-up is too high.
- For no-till fields, the two big concerns are ammonia (NH3) volatilization with dry urea and tie-up on the residue with liquid UAN. Picking the best option in this scenario is a much tougher decision with not a real good conclusion. So, here it goes. If there is tall standing stubble with dry soil below, the dry urea gets the edge. Why? If the stubble is not in a mat, the urea prill can work its way down towards the soil surface. If it can get there, it is out of the high winds, and it will remain there until we get a rain, heavy dew, or increase in humidity. Is there still a chance for loss due to volatilization? Absolutely. Again, it goes back to whether there is any chance that you can wait to apply?
- There have been some questions about using urease inhibitors with broadcasting urea. That is a good question, but it is hard to make an argument for their use until we get a good chance of rain in the 10-day forecast. Typically, these products do not have the life span to hold off urease (i.e., the enzyme that breaks urea into NH3) for more than 10-12 days.
The latter points also apply to those who use the local co-op or ag retailer for application. Some of these groups require 30 days or more to cover all of the acres they service.
Since it is dry and we still have some time yet to apply N, this may turn out to be the perfect year to topdress urea with a grain drill (Fig. 2). For those interested in this method, you can find research results from last year on this topic, as well as a calibration guide, by clicking here. More information about nitrogen applications that are “thinking outside the box” can be found by clicking here.
Figure 2. Using a 3 pt conventional double-disk type drill to apply urea in-season.
For more information, contact Brian Arnall or David Marburger.
Some producers throughout Oklahoma have been delayed in getting their wheat crop established due to fall armyworm and/or the rainfall we have had throughout October. While we are now outside of the optimum planting window for grain-only wheat production, the good news is that late-planted wheat can still yield well if environmental conditions cooperate and if producers make a couple management adjustments.
Seeding rates: The main problem with late-planted wheat is reduced tillering and slowed canopy closure when compared to earlier-planted wheat. On average, wheat plants sown in early- to mid-October will produce 2-3 tillers/plant. At a seeding rate of 60 lbs/acre (20-25 seeds/ft2 depending on seed size), the 2-3 tillers/plant can help us achieve the 60-70 heads/ft2 needed to maximize grain yield. Wheat planted in early- to mid-November may only produce 1-2 tillers/plant. Therefore, seeding rates right now should be increased by as much as 50% and increased by as much as 100% if planting gets delayed past mid-November. So, if a producer uses a 60 lbs/acre seeding rate during the optimum planting time, the seeding rate should be increased to around 90 lbs/acre for right now and then increased to 120 lbs/acre past mid-November.
There may be questions too on replanting decisions during this time of year. This can be a challenging decision, but the first step is to count the number of plants in different parts of the field to assess the stand. A thin but uniform stand will have more yield potential than one that is thick in some areas but nonexistent in others. During the optimum planting time, a thin but uniform stand (50% of the target stand for example) would likely be enough to keep, given adequate fertility and favorable weather conditions that would allow for tillering to help compensate. However, a similar scenario for a wheat field emerging at this time will need help. After assessing the stand, areas with thin or nonexistent stands should be filled in to reach your desired stand target. If replanting into an existing stand, it should be done at an angle (up to 45 degrees) to minimize damage to the existing stand.
Fertility: Late-planted wheat will need all the help it can get when it comes to fertility. The root system for late-planted wheat will likely not be extensive enough to intercept a significant amount of soil phosphorus until the spring. An in-furrow application a P fertilizer (50 lbs/acre of DAP for example) can be of great benefit. With this, the fertilizer is closer to the young seeding, and the plant can get to it sooner. Nitrogen fertilizer can also be used to encourage tillering. However, rather than increasing fall N rates, late-planted fields should be put at the top of the list for topdressing in January or February. There is most likely enough N available between residual soil N and any starter fertilizer N for growth this fall since wheat in grain-only production does not need much N (up to 20-25 lbs/acre) in the fall to get good establishment. Using N-rich strips can aid in determining when to apply topdress N, and a more accurate amount to apply can be determined using sensor-based methods.
Variety selection: It is most likely too late to make any switches in variety selection. If there is an opportunity to change varieties though, using a variety with good tillering ability and earlier maturity may be of benefit. A good tillering variety can help compensate for the less available time this fall for tiller development; whereas, a low-tillering variety may not be able to produce any tillers this fall. Late-planted wheat may also result in delayed development in the spring and force the grain fill period to be shorter by occurring later when environmental conditions are likely warmer and drier. An earlier maturing variety could be used to offset this chance that grain fill occurs during suboptimal conditions.
Pests: Finally, it is important not to short-change a late-planted wheat crop in terms of pest management. Remember that a late-planted crop has less competitive ability than an early-planted crop. Control insect pests as soon as thresholds are reached, and make herbicide applications while weeds are still small and have not yet removed large amounts of nutrients and soil moisture.
This article was written by Dr. Tom Royer, Extension Entomologist
Lanie Hale, from Wheeler Brothers sent a picture of “window paned” wheat from a field that he had scouted. 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.
Soil temperatures in Oklahoma can be hot when planting in late August to early September for forage-only or dual-purpose wheat (Figure 1). Seed that was planted into soils with temperatures above 85° F may result in delayed germination or prevent wheat seedling emergence. In addition to the soil moisture status since planting, listed below are two factors that may cause poor early stand establishment when wheat is sown into hot soils.
Figure 1. Maximum soil temperature at a 4 inch depth under bare soil over the past three weeks near Altus. We can assume that the maximum soil temperature at shallower depths was likely higher. Data is from Oklahoma Mesonet.
High temperature germination sensitivity: This 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 at all, 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 germination sensitivity (e.g., Duster, Gallagher). Soil temperatures typically begin to cool by about September 20 due to lower air temperatures and/or rainfall events. Waiting until at least mid September to plant sensitive varieties can help reduce the risk of this issue. A rating of high temperature germination sensitivity for wheat varieties can be found in the OSU Fact Sheet PSS-2256 Factors Affecting Wheat Germination and Stand Establishment in Hot Soils.
Coleoptile length: The coleoptile is the rigid, sheath-like structure which protects the first true leaf and aids it in navigating and reaching the soil surface. Once the coleoptile breaks the soil surface, it 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 usually takes 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 (P.S. we are working on updating this).
Fall armyworm was a significant pest for producers in Oklahoma last year, and this year is setting up to be the same scenario. It is out in full force already in some areas, and you may have seen or heard Dr. Tom Royer recently discuss how this insect has been active over this summer, especially on bermudagrass and fescue pastures. Wheat planting is already underway in some areas of the state. As wheat planting progresses here in September, producers need to check their wheat fields very regularly after seedling emergence. Fall armyworm can decimate large fields within a few days. Scout for fall armyworms by examining plants in several (5 or more) locations in the field. A good place to start is along the field margin as they sometimes move in from the road ditches and weedy areas, but make sure to examine the interior of the field as well. Fall armyworms are most active in the morning or late afternoon.
Fall armyworms are small (3/8-1 1/2″) and can be easily overlooked (top photo). Feeding on leaves gives a transparent (“window paned”) appearance (bottom photo). Photos courtesy of Dr. Tom Royer.
Be on the lookout for “window paned” leaves, and count all sizes of larvae. 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 will not get relief from fall armyworms until we get a killing frost. So make sure to keep scouting regularly, especially with this early-planted wheat!
Fall armyworm can cause significant damage like this across large areas very quickly, so scout early and scout often. Photo courtesy of B. Boeckman.
Control suggestions for fall armyworm are available in the OSU Fact Sheets CR-7194 Management of Insect and Mite Pests of Small Grains.
The 2017-2018 wheat growing season is setting up similar to last year with many producers wanting to target more of the forage side of wheat production given the low commodity prices. That, coupled with the available soil moisture from the rainfall throughout August, has prompted some producers to get the drills rolling already over the past week in some parts of the state. As planting gets going, here are a couple considerations when it comes to planting dates and seeding rates for winter wheat in Oklahoma.
The optimal window for dual-purpose wheat for most of Oklahoma is between September 10-20 (approximately day 260 in Figure 1). This window represents a trade-off between maximizing forage production while minimizing potential grain yield loss. Earlier planting dates, last week into this week for example, will provide more fall forage potential, but this is usually not recommended unless the wheat is intended to be produced for grazing, or “grazeout.” Planting dates for grain-only producers will be at least 2-3 weeks later than what is the ideal dual-purpose planting date for your area. For many areas in Oklahoma, this will be around mid-October (approximately day 285 in Figure 1).
Figure 1. 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).
Producers in forage-only or dual-purpose management should plant 1.5-2x the amount of seed that is recommended for grain-only production. For example, data collected in north-central Oklahoma has showed that increasing the seeding rate from 60 to 120 lb/acre can increase fall forage potential by as much as 500 lb/acre for a mid-September planting date (September 11 in Figure 2). The increase in forage potential by using this higher seeding rate can justify the cost of the extra seed. OSU recommends 120 lb seed/acre for most areas of Oklahoma, including irrigated fields in the Panhandle. Seeding rates for dryland fields in the Panhandle for this type of management can be lowered to 90 lb/acre. OSU recommends a 60 lb/acre seeding rate for grain-only production when planted during that optimal mid-October time. Dryland fields in the Panhandle can have their seeding rate lowered to 45 lb/acre. If planting happens to get delayed in November this year, seeding rates will need to increase to provide enough available tillers to still maintain maximum grain yield potential.
Figure 2. Fall forage yield collected in north-central Oklahoma as affected by seeding rate and planting date. Source: PSS-2178.
More information about dual-purpose wheat management can be found in the fact sheet PSS-2178 Dual-purpose Wheat: Management for Forage and Grain Production.
This article was written by: Dr. Bob Hunger, Extension Wheat Pathologist, & Dr. Tom Royer, Extension Entomologist, Department of Entomology & Plant Pathology Oklahoma State University
Planting date: Much of the winter wheat in Oklahoma is sown with the intent of being 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 at http://wheat.okstate.edu/wheat-management/seeding/CR-7088web2012.pdf.
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 (also called wheat mosaic), and Triticum mosaic (TrM). 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, WCMs spread to emerging seedling wheat, feed on that seedling wheat, and transmit virus to the young wheat plants. During 2016 and 2017, these mite transmitted virus diseases (especially WSM) were severe across much of the wheat growing areas of Oklahoma as well as in many of the other Great Plains states. Weather is a determining factor in the increased incidence and severity of these virus diseases, but another major contributor is the lack of control of volunteer wheat and other grassy weeds that serve as alternative hosts for the mite and the viruses. 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. 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.
Seed treatments and insecticides are not effective in controlling the mites or these mite-transmitted 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 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 emergence of seedling 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 to emergence of seedling wheat will greatly reduce mite numbers in the fall. 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. Additionally, the resistance is not an absolute resistance to the disease. Hence, severe and continuous disease pressure can overcome the resistance although disease effects typically is less as compared to a susceptible variety. 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) at: http://wheat.okstate.edu/wheat-management/diseasesinsects/EPP-7328%20three%20virus%20diseases%20of%20wheat.pdf.
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 (e.g., Duster, Billings, Gallagher, Iba, Bentley, Tatanka, and Winterhawk) 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 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. Some wheat varieties are either resistant (e.g., Duster, Gallagher, SY Flint, and LCS Wizard) or partially resistant [e.g., LCS Chrome, Everest, Ruby Lee (at cooler temperatures)] 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 at: http://wheat.okstate.edu/wheat-management/diseasesinsects/EPP7086hessianflyinoklahoma.pdf.
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) (Figure 6). During the late spring of 2016 and 2017, several samples of wheat were received that were diagnosed as being affected by take all and other root rots. This could indicate a greater incidence of wheat root rots in 2017-18, but the incidence and severity of root rots is highly dependent on weather conditions so it is impossible to predict their incidence and severity this early.
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) and loose smut. The similarity of these names can be confusing. All affect the grain of wheat, but whereas common bunt and flag smut spores carryover on seed or in the soil, loose smut carries over in the seed. Seed treatments are highly effective in controlling all the 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 “2017 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.