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Our recent extreme shifts in temperature have resulted in moderate to severe freeze injury in some Oklahoma wheat fields. To be honest, the damage is not as widespread or severe as I thought it would be given that most of our wheat had not had an opportunity to harden off. The dry soil conditions in western and southern Oklahoma did not help the situation, as there was not sufficient soil moisture to buffer the temperature shift in the top few inches of soil.
Freeze injury at this stage of growth (tillering) rarely impacts grain yield, but, as always, there are a few exceptions. Wheat that was very small or late-sown is more susceptible to winter kill. Similarly, wheat that does not have a good root system or that was shallow sown due to crop residue is more susceptible to winter kill. It is best to wait until after a few days of favorable growing conditions to check for freeze injury. Plants with regrowth that is green and healthy should make a full recovery, and this will be the case for most Oklahoma wheat fields.
Over the past week, I have received a few reports of winter grain mite activity in southwest Oklahoma. Winter grain mites are small (about 1 mm long) with black bodies and orange-red legs. Winter grain mites complete two generations per year and the adults can live for up to 40 days. The generation we are dealing with now resulted from oversummering eggs laid last spring. The second generation peaks in March/April and results from eggs laid in January/February.
Winter grain mites are light sensitive and prefer calm air to windy conditions; therefore, scouting early in the morning, late in the evening, or on cloudy days generally works best. Be sure to look under residue in no-till fields and under clumps of soil in conventional-till fields.
Winter grain mites feed by piercing plant cells in the leaf, which results in “stippling”. As injury continues, the leaves take on a characteristic grayish or silverish cast. Winter grain mites are more likely to cause injury in wheat if it is already stressed due to lack of moisture or nutrients. Also be advised that freeze injury can easily be confused for winter grain mite injury.
When to spray
There are no established thresholds for winter grain mite. Healthy, well-fertilized wheat plants can generally outgrow injury, so it takes large numbers to justify control. If there is injury present AND large numbers of mites (~10 per plant) present in grain only wheat this time of year, you might consider control. If the wheat is to be grazed, I would simply monitor the situation in most cases and only spray if injury became severe.
What to spray
There are not a lot of pesticides with winter grain mite listed on the label, and most products have grazing restrictions. Malathion and methyl parathion have been shown to provide effective control in the past. Consult OSU Current Report 7194 Management of insect and mite pests in small grains for a more complete listing of available pesticides.
Back in 2006 it appeared that Hessian fly was going to be the demise of no-till wheat production in Oklahoma. Early planting, lack of crop rotation, and no-till monocrop wheat all create a favorable environment for Hessian fly, and there were several early-sown fields that were completely lost to the Hessian fly in 2006 & 2007. About that same time OSU release a variety named Duster that was an excellent grazing wheat with good yield potential. Duster also happened to be Hessian fly resistant. (If you are not a Star Wars fan, skip the next sentence) This resistance was a clear proton torpedo in the thermal exhaust port of the fully operational Hessian fly Death Star.
Over the past four years, I have received very few calls about Hessian fly. It seemed as thought the adoption of Duster and unfavorable environmental conditions resulted in a dramatic reduction in Hessian fly in Oklahoma, but there are some indications Hessian fly is making a return. I have received a few calls about Hessian fly this fall, most of them from southwest Oklahoma. In most cases producers had either switched to a newer variety that was not Hessian fly resistant or changed to a nonresistant variety because they were displeased with Duster’s performance the past two years.
There are no curative treatments for Hessian fly in wheat. If you currently have a field that is infested with Hessian fly, the first step is to assess the level of infestation. If a plant with four viable tillers has one infected, then the impact on yield might not be that great, as we could have additional tillering in late winter. A field with the majority of tillers infected is likely a good candidate for graze out.
It is never too soon to be thinking of how to limit the impact of Hessian fly on next year’s crop. Planting a resistant variety still remains the most effective technique of combating the Hessian fly menace in Oklahoma for dual-purpose wheat farmers. To determine which varieties are resistant, consult a current OSU Wheat Variety Comparison Chart. Insecticide seed treatments are effective early in the season, but do not typically last long enough to provide season long control in Oklahoma. Cultural practices such as crop rotation and delaying planting until mid October will also help reduce Hessian fly infestations but might not be suitable for all operations.
Wheat disease updates are written by Dr. Bob Hunger, OSU Extension Plant Pathologist
Fall of 2013 has been quiet for wheat diseases with no wheat samples coming into the Diagnostic Lab. Otherwise, the only report of a wheat disease in the state has been a report I received from Brian Vincent who indicated that Keith Castner (BASF) had observed leaf rust in late October on early planted ‘Duster’ near El Reno, OK. This finding is not surprising as leaf rust often is observed in Oklahoma in the fall.
When leaf rust is observed in the fall, the value of spraying to control that rust is asked. Fall-infected leaf rust plants typically have yellowed lower/older leaves with rust pustules, but the youngest 2 or 3 leaves are green and healthy. As temperature drops through November and December, the older rust-infected leaves die and new infections are greatly slowed and inhibited. Grazing also helps to remove these leaves and increase air circulation and drying that are conditions less favorable to spread of the disease. Given these consideration, spraying to control leaf rust in the fall is of limited value. The primary concern with fall infections of leaf rust is that with a mild winter and sufficient moisture, the rust will survive through the winter and inoculum will be present in fields to start the disease early in the spring. Hence, monitoring of these fields through the winter and early next spring is recommended to see if application of a fungicide to control the rust is indicated in the early spring.
I called around to other extension specialists [northwestern OK/panhandle (Rick Kochenower; Area Research & Extension Specialist – Agronomy), south central OK (Mark Gregory Area Extension Agronomy Specialist), and southwestern OK (Gary Strickland; Extension Educator – Jackson County), and all indicated that no foliar or root diseases have been observed to date.
Recent updates from other states:
Kansas (Dr. Erick De Wolf, Extension Plant Pathologist, Kansas State University): Leaf rust was found in research plots near Manhattan KS (Northeast Kansas) on Oct 25. Dr. Bill Bockus reported leaf rust in research plots that were established approximately a month ago (about 2 weeks before the normal planting date), and have ample fall growth. The leaf rust was observed in multiple foci or “hot spots” but was now present at low levels throughout the plots suggesting the disease has been there for more than 3 weeks. The incidence was approximately 2-5% with severity of trace to 10% on any given leaf. The leaf rust was found on the wheat variety 1863. This variety is known to be susceptible to leaf rust. An older variety Newton was also infected.
It is not unusual to find leaf rust near Manhattan this time of year. The winter conditions are often enough to keep the rust population from overwintering in KS, but finding the disease in the fall could be important if we have a mild winter. It has been several years since leaf rust observed in the fall at this location. The absence of rust in these years was likely related to the drought that dominated the central plains in 2011-2012. The drought conditions have lessened in recent months and leaf rust is returning to normal fall activity. We will be monitoring this location and others to check for overwintering leaf rust.
There are a few cattle already on wheat pasture in Oklahoma and more that will be turned out in the coming weeks. An adequate crown root system is required to anchor wheat in place prior to grazing.
Without these roots, wheat can be pulled from the soil during grazing, thinning final stands. Aboveground appearances can be deceiving, so it is important to pull plants from the soil to ensure the crown roots are there even if the plants appear large enough for grazing.
It is also important to make preparations for measuring first hollow stem prior to turning cattle out on wheat pasture. Grazing delays plant development; therefore, first hollow stem has to be checked in a nongrazed area. The nongrazed area does not have to be large and can be achieved through a panel exclosure or by simply moving one of the posts for an electric fence in a few feet. The key is to plan for the nongrazed area now so you can measure first hollow stem in February.
It occurred to me the other day that although I have publicized the forage, grain, and quality results from the OSU Wheat Variety Testing Program, I have never really given much effort to publicizing the day to day activities required to produce these results. So, over the next year I hope to write a few blogs to provide a little more insight into the workings of the system.
Location, location, location
Our program will have replicated trials at 23 sites in 2013/2014. These sites cover the state from Afton to Altus and McLoud to Keyes and some sites (e.g. Apache, Lahoma, Chickasha, Goodwell) have multiple trials. The location of trials are decided upon by throwing darts at a map (just kidding). We pick trial locations according to many factors including: visibility, uniformity, production history, local support, and cooperator involvement. Some locations (e.g. Lamont) have been in the system from the start, and others (e.g. McLoud) are fairly new additions. Given the miles between locations and a finite number of planting and harvest days, 23 locations is about the maximum we can handle and still complete operations in a timely fashion.
In addition to the small, replicated plots we organize and distribute ten-pound demonstration bags for County Educators. We typically have about 40 sets of 15 varieties for these ten pound “demo sets”.
Who pays for all this?
The bulk of the expense of running the program comes in the form of salary, facilities, and miscellaneous overhead expenses and is largely covered by OSU through state appropriations (i.e. Oklahoma taxpayers). The bulk of the day to day operating expenses, such as seed, fuel, and mileage expenses, are covered through grants from the Oklahoma Wheat Commission and Oklahoma Wheat Research Foundation (i.e. Oklahoma wheat farmers). These two organizations also help with large equipment purchases such as tractors and combines. A relatively new area of support for the program is an entry fee system. The $500 per variety fee helps offset increasing expenses and is generally enough to assist with student labor for the project. We typically employ one or two graduate students and one or two undergraduate workers. Yes, we charge licensees for testing released OSU varieties but do not charge for OSU experimental lines.
Little packets of seed
Once we have determined which varieties will go at each location, we will send seed requests to participating companies. If everything goes well, we will receive seed in late August. We request one bag of most varieties and eight bags of varieties that will be included in the county demonstration packets.
Depending on the location, there are 25 to 45 varieties replicated four to eight times at each site. Each one of these plots starts with an envelope with either 60 (grain only) or 120 (dual purpose) grams of seed (120 grams is approximately 1/4 pound). This creates a total of about 4,000 envelopes that are weighed and packaged by hand each year. Envelopes are sorted according to a plot plan which randomly assigns varieties to locations within the field at each site. The plots plans are all created one at a time in Excel.
Planting five feet at a time
We have two planters. Our conventional planter sows eight six-inch rows and our no-till planter sows seven 7.5-inch rows. Seed is dropped into the distribution cone and released in the five foot alley between replications/blocks. A gear box is used to adjust the length of row over which the seed will be distributed. We work the ground with a small field cultivator at some locations and the producer or station manager works the ground for us at others.
Should we plant by seeds per acre or pounds per acre? I will certainly not settle this issue in a single blog post, but I will provide ammunition for those in both camps in the discussion below. Before the discussion begins, I must come clean by acknowledging that when I came to Oklahoma ten years ago, I was solidly in the seeds per acre camp. As a crop consultant I spent most of October every year calibrating clients’ drills each time they changed varieties or field conditions changed. I was certainly not willing to entertain the notion that this could have been wasted time. After reading the published research on the subject, however, I have moved to the pounds per acre camp and will probably remain there unless seed prices increase dramatically OR seed quality improves significantly (I will elaborate below).
Why pounds per acre works
The published research on wheat seed size clearly shows that larger seeds produce more vigorous plants which result in more and larger tillers per plant. Additionally, the research indicates that if you sow the same number of seed of both small and large seeds from the same variety, the large seed will have an approximate 10% better yield potential. While not expressly mentioned in the research, it is reasonable to assume that small seed will produce less fall forage as well. For more reading on this subject consult Kansas Agricultural Experiment Station, Keeping Up With Research numbers 74 (1984) and 101 (1991).
We have established that larger seeds are better on a seed vs. seed basis; however, there are 36% more seeds in a bushel of wheat with 15,000 seeds per pound as compared to a bushel of wheat with 11,000 seeds per pound. So, when sowing by pounds per acre the additional seeds compensate for the smaller seed size and generally results in the same total number of tillers . This compensation effect means that planting by pounds per acre works for a wide range of seed sizes and varieties. This should not be taken as an excuse to plant poor quality seed, as the compensatory effect is not the same if you are sowing shriveled, light, or head-scab damaged seed.
When seeds per acre is a better option
If you are sowing high-quality, large seed, then seeds per acre might be a better option. To get this type of seed usually requires a favorable environment during grain fill, adequate fertility, and a foliar fungicide in-season followed by an aggressive seed cleaning process. I have heard Phil Needham say, and I agree, that 10% seed cleanout is a minimum. Most seed lots require 20 – 40% cleanout to achieve large-seed status. Including a gravity table in the cleaning process will increase seed quality further. The fact of the matter is that most of our wheat seed in the Great Plains simply does not consistently fall into this category. For this reason, if you are sowing “average” quality seed by seeds per acre, then adjust your seeding rate up accordingly to ensure you are not short on tillers.
Seeds per acre may also a better option if you are managing fertility to manipulate final tiller numbers. In this scenario, farmers will sow a set number of seeds per acre and adjust topdress rate and timing to encourage or discourage tillering to reach a desired number of heads at harvest. You can do the same thing when sowing by pounds per acre, but you will need an accurate stand count shortly after emergence. When used in combination with an accurate tiller count in February, a stand count will allow you to accurately estimate potential heads per acre and adjust accordingly.
Finally, if seed costs rise significantly in the future, a switch to seeds per acre might be justified. No one would suggest planting a $300 bag of corn or cotton seed based on pounds per acre. I don’t know what the wheat seed cost threshold is for switching to seeds per acre but would assume that if we ever reach this point seed quality will increase accordingly, making seeds per acre a better option.
As is usually the case in Oklahoma, we currently have a wide range of soil moisture conditions. Soils in central Oklahoma are generally dry on top, but there is ample soil moisture below. Soils in western Oklahoma and the Panhandle are dry all the way down. A few drills have started rolling, but most producers are waiting on a “State Fair” rain to get started (for all you non-Okies, it usually rains sometime during the State Fair in early September). While moisture availability is the primary driver of wheat planting, it is not the only consideration for producers. Hot soil conditions can affect wheat germination too, and there are a few questions producers should ask themselves prior to planting into soil temperatures >90F.
Will you have to plant deep to reach moisture? That first structure protruding from a germinating wheat seed is actually not a leaf. It is the coleoptile. The wheat coleoptile is a rigid structure whose sole purpose is to “punch through” the soil surface so that the first true leaf emerges above the soil surface. If this does not happen, the first true leaf will try to extend below the soil surface, turn yellow, and take on an accordion-like appearance (picture above). Modern semi-dwarf wheat varieties have shorter coleoptiles than older, tall wheat varieties and coleoptile length is shortened even further by hot soil conditions. So it is important to plant a variety with a longer coleoptile length (e.g. Garrison or Doans) if planting deeply into hot soils. A rating of coleoptile lengths for wheat varieties can be found in OSU Fact Sheet 2141 OSU Wheat Variety Comparison Chart available at www.wheat.okstate.edu or at the direct link to the publication here.
Is the variety high temperature germination sensitive? High temperature germination sensitivity is a fancy way of saying that some wheat varieties simply don’t germinate well in hot soil conditions (e.g. 2174, Overley). The extent of the sensitivity varies by year, so Overley might germinate fine in 95F soils one year and produce a 10% stand in the same soil conditions the next. When sowing early, it is best to plant varieties that do not have high temperature germination sensitivity (e.g. Duster, Gallagher, or Armour). Soil conditions generally cool due to lower ambient temperatures or cooling rains by about September 20; however our summer temperatures seem to be arriving late this year, so it is best to know the level of germination sensitivity in the variety you are planting. A rating of high temperature germination sensitivity for wheat varieties can be found in the variety comparison chart linked above. A more detailed explanation of the phenomenon can be found in OSU Fact Sheet PSS 2256 Factors affecting wheat germination and stand establishment in hot soils (available by clicking here).
All Oklahoma wheat variety test sites are now harvested and the results are posted at www.wheat.okstate.edu. I have posted a brief summary of the 2013 crop below. Over the next several weeks, I will be posting additional trial results on this blog along with opinion and analysis of results.
2013 WHEAT CROP OVERVIEW
At the time of writing this report, 2013 Oklahoma wheat production is estimated to be approximately 114 million bushels, which is roughly 26% less than 2012 production (Table 1). The production decrease was due to the combination of lower yields and fewer harvested acres. Given the challenges faced in the 2012-2013 wheat production year, however, most would consider the average yield and total production to be much better than expected.
|Table 1. Oklahoma wheat production for 2012 and 2013 as estimated by OK NASS, June 2013|
We have had several dry starts for wheat planting in Oklahoma, but the fall of 2012 might go down as the driest of the dry. A few timely rains in late August and early September allowed early and mid-September sown wheat to emerge and get a rapid start on forage production. This was the last substantial rain that most of western Oklahoma received until early 2013. As a result, much of our October-sown crop remained partially emerged in dry soil until after the first of the year.
Wheat that had emerged in September had consumed available water by early November and turned brown by December. Many fields were assumed dead, as there was no green tissue remaining above the soil surface (e.g. Marshall Dual-Purpose trial). This left little to no grazing potential for many dual-purpose wheat producers. Our Stillwater forage trial, for example, had less than 500 lb/ac (estimated) of available forage in early December, which is our normal forage measurement timing.
Rain was not plentiful in early 2013, but there was enough to allow the wheat crop to rebound. Wheat seed that had been lying in the soil germinated and early-emerging fields that had turned brown from drought were resuscitated and brought back to life. Wheat in southwestern OK and the Panhandle remained on life support throughout the season, surviving but never really thriving. Given these extreme circumstances, the grain yield at our Chattanooga, Altus, and Hooker sites are nothing short of amazing. Although wheat finally emerged at our Alva, Balko, Buffalo, Cherokee, Gage, Keyes, and Lamont sites, the stands were far too variable for use in comparing the yield potential of wheat varieties.
Drought was not the only weather-related issue Oklahoma wheat producers dealt with in 2013. There were multiple rounds of freeze events in late March and early April. Wheat in southwest Oklahoma and the Panhandle was affected by different freeze events but both sustained 30 to 80% tiller loss and were largely written off in the weeks following the freezes. Outside of far southwestern OK, cooler than normal conditions and some replenishment of soil moisture allowed regeneration of tillers. This, along with extended grainfill duration, allowed many wheat fields to recover and produce greater than expected grain yields (e.g. Apache variety trial). The cooler than normal spring temperatures were beneficial for wheat grainfill, but also delayed harvest by about one month as compared to 2012 and about two weeks as compared to the long term average.
It was a fairly quiet year regarding foliar disease. Pockets of the state suffered from heavy powdery mildew infestation in March and April, and some wheat producers chose to split-apply fungicides to combat this disease. There were also areas affected by glume blotch, tan spot, and septoria, but there was not much leaf or stripe rust present.
Yellow and purple leaves were tell tale signs that a late spring flush of aphids had transmitted barley yellow dwarf virus to several Oklahoma wheat fields. Armyworms were present late in the season, but generally did not reach threshold levels prior to maturity and few fields were sprayed. Winter grain mites took advantage of slow-growing, drought-stressed wheat and were a frequently reported problem in southwest OK, but the wheat curl mite takes top billing among mite pests in 2013. The wheat curl mite transmits wheat streak mosaic and high plains viruses. These two diseases are fairly common in the Panhandle but do not typically affect wheat in central OK. In 2013 fields as far east as Kingfisher tested positive for wheat streak mosaic and several central OK fields were affected. Growers affected by wheat streak mosaic should take care to ensure that any volunteer wheat or corn is dead at least two weeks prior to planting to reduce the risk of this disease in 2013-2014.
Chattanooga, Kingfisher, and Chickasha wheat variety trial results are posted at www.wheat.okstate.edu. Grain yields at Chattanooga ranged from 12 to 36 bushels per acre. It is truly amazing that wheat somehow managed to produce these yields this in the presence of severe drought and three major freezes. Kingfisher wheat grain yields ranged from 32 to 47 bushels per acre and were more or less on par with expectations. This site had less than ideal moisture conditions, but adequate moisture to keep the wheat from turning brown as it did in many locations.
The Chickasha wheat variety trial had some problems. A late March freeze killed up to 58% of viable tillers in some varieties and lodging at harvest was moderate to severe. While leaf rust and stripe rust were not major factors, we did have a variety of leaf spotting diseases (e.g. tan spot, septoria, glum blotch) and severe, widespread bacterial blight/black chaff throughout the plot. In spite of these challenges, average yield at this site was 69 bushels per acre with yields ranging from 50 to 83 bushels per acre. While these yields are outstanding given the challenges of the year, they are not the best at the Chickasha research station. Approximately 200 feet from the variety trial was a growth regulator study planted to Iba that produced 98 to 102 bushels per acre. I have this same trial at two additional locations and will summarize results later in the year.