K-State Research and Extension

We have had good growing conditions for the wheat, basically since drilling this fall. The wheat has had the opportunity to put on lush top growth because of the extended period of warm temperatures. Because of the lush wheat, there is concern with the cold temperatures through the end of the week.

Usually, I think through several questions when wondering if the wheat is going to be negatively affected by the cold temperatures. They include these three:

• Has the wheat had the opportunity to harden off to prepare for the cold conditions?
• How well established is the root growth?
• How well protected is the crown area of the plant?

First, I think the hardening off of the wheat is definitely a concern. When we go form T-shirt weather and barely freezing overnight lows to staying below freezing for a predicted 96 hours, the wheat hasn't really had a chance to harden off.

So what is hardening off? Hardening off is the process of plants becoming more acclimated to colder temperatures. It can also mean that individual plant cells accumulate more solutes that can lower their freezing point, much like antifreeze in your pickup's radiator. Cells in the crown area are of the most important part of the plant for getting acclimated to the cold temperatures. The crown is the growing point of the wheat plant and is currently under the soil being insulated from the cold temperatures.

For the root systems, it is important to know that top growth of the wheat plant is not always telling the whole story of the root system. It is a good idea to dig up a couple plants and look at their root systems. Plants that have a good crown root system (roots coming off the crown and not the seed) and two or more tillers will tolerate the cold better. If plants have a few secondary roots and no tillers, they are more susceptible to winterkill and desiccation of leaves, especially if the soil remains dry.

And finally, when looking at your wheat, pay attention to the location of the crown of the wheat plant. If wheat was planted between 1.5 to 2 inches deep and the seed slot was closed well with soil, the crown should be protected from the cold temperatures. Trouble can arise when the crown of the wheat plant is set shallower in the soil. This can be caused by shallower planting, the wheat plant emerging through a thick layer of residue or the seed slot not being completely closed.

It is also important to note the soil temperature at the crown area. Based on information on freezing temperatures for wheat, winterkill is possible if the temperatures in the crown area (approx. 1 inch below the soil surface) fall into the single digits. Any type of insulation will help buffer the cold temperatures - residue, snow, and even just soil moisture in the crown area.

After thinking through the answers to all of these questions for your wheat field, you should realize that we really won't know the full effects (if any) until spring greenup. Hopefully, the wheat is well established this fall and it will be able to just take this cold snap in stride! I have always been told that wheat has nine lives, so we surely haven't been through all of them yet!

- Jeanne Falk Jones, K-State Multi-County Agronomist--- jfalkjones@ksu.edu

I should also note that there is an additional question – has there been insect feeding in your field?

Plants may die during the winter not from winterkill, but from the direct effects of a fall infestation of Hessian fly. Many people are familiar with the lodging that Hessian fly can cause to wheat in the spring, but fewer recognize the damage that can be caused by fall infestations of Hessian fly. Wheat infested in the fall often remains green until the winter when the infested tillers gradually die. Depending on the stage of wheat when the larvae begin their feeding, individual tillers or whole plants can die. If the infestation occurs before multiple tillers are well established then whole plants can die. If the plants have multiple tillers before the plants are infested then often only individual tillers that are infested by the fly larvae will die.

The key to being able to confirm that the Hessian fly is the cause of the dead tillers is to carefully inspect the dead plants or tillers for Hessian fly larvae or pupae. This can be done by carefully removing the plant from the soil and pulling back the leaf material to expose the base of the plant. By late winter all of the larvae should have pupated and thus the pupae should be easily detected as elongated brown structures pressed against the base of the plant. The pupae are fairly resilient and will remain at the base of the plant well into the spring.

Damage from winter grain mites, brown wheat mites, aphids, and crown and root rot diseases can also weaken wheat plants and make them somewhat more susceptible to injury from cold weather stress or desiccation.

Fall armyworms and army cutworms may have fed on emerging wheat in the previous month (prior to the recent frigid weather, we even found live worms as recently as Dec. 3) leaving bare patches. If the worms were fall armyworms they have died by now. If the worms were army cutworms they will overwinter right there in the soil and continue to feed on wheat plants anytime the temperature is 45 degrees or more from now through about April.

So if you have bare patches now, it is a good idea to keep an eye on them and if they slowly expand over the winter, get out and check in the soil around the base of the plants to see if there are small worms curled up about an inch or two below the surface, especially in loose soils. A spot application of a registered insecticide on a warm (above 55 degrees) winter afternoon will do a pretty good job of controlling the worms and allow the plants to come back in the spring as these worms only feed on the above ground leaf tissue, and not on the roots or crown.

If plants are killed outright by cold temperatures, they won't green up next spring. But if they are only damaged, it might take them a while to die. They will green up and then slowly go "backwards" and eventually die. There are enough nutrients in the crown to allow the plants to green up, but the winter injury causes vascular damage so that nutrients that are left cannot move, or root rot diseases move in and kill the plants. This slow death is probably the most common result of winter injury on wheat.

Direct cold injury is not the only source of winter injury. Under dry soil conditions, wheat plants may suffer from desiccation. This can kill or weaken plants, and is actually a more common problem than direct cold injury.

Jim Shroyer, Crop Production Specialist - jshroyer@ksu.edu

Jeff Whitworth, Entomology Specialist - jwhitwor@ksu.edu

Summary

A field study initiated in 2006 was designed to evaluate the effects of three wheat stubble heights on subsequent grain yields of corn and grain sorghum. Grain yields of corn and grain sorghum in 2012 were substantially lower than the long-term average because of lack of precipitation. No effect from the stubble height was observed in 2012 for either corn or grain sorghum. When averaged across 2007-2012, corn grain yields were 11 bu/ac greater when planted into either tall or strip-cut stubble than into low-cut stubble. This increase was primarily due to an increase in the number of kernels per ear. Average grain sorghum yields were not significantly affected by wheat stubble height. Harvesting the previous wheat crop shorter than necessary results in a yield penalty for the subsequent dryland corn crop.

Introduction

Seeding of summer row crops throughout the west-central Great Plains often occurs following wheat in a 3-year rotation (wheat-summer crop-fallow). Wheat residue provides numerous benefits including evaporation suppression, delayed weed growth, improved capture of winter snowfall, and soil erosion reductions. Stubble height affects wind velocity profile, surface radiation interception, and surface temperatures, all of which affect evaporation suppression and winter snow catch. Taller wheat stubble is also beneficial to pheasants in post-harvest and overwinter fallow periods. Use of stripper headers increases harvest capacity and provides taller wheat stubble than previously attainable with conventional small grains platforms. Increasing wheat cutting heights or using a stripper header should further improve the effectiveness of standing wheat stubble. The purpose of this study is to evaluate the effect of wheat stubble height on subsequent summer row crop yields.

Procedures

This study was conducted at the Southwest Research-Extension Center dryland station near Tribune, KS. From 2007 through 2012, corn and grain sorghum were planted into standing wheat stubble of three heights. Optimal (high) cutterbar height is the height necessary to maximize both grain harvested and standing stubble remaining (typically around two-thirds of total plant height), the short cut treatment was half of optimal cutterbar height, and the third treatment was stubble remaining after stripper header harvest. In 2012, these heights were 7, 14, and 21 in.. Average stubble heights from 2007-2012 were 9, 18, and 27 in. In 2012, corn and grain sorghum were seeded at rates of 15,000 seeds/ac and 50,000 seeds/ac, respectively. Nitrogen was applied to all plots at a rate of 100 lb/ac. Starter fertilizer (10-34-0 N-P-K) was applied in-row at a rate of 7 gal/ac. Plots were 40 x 60 ft with treatments arranged in a randomized complete block design with six replications. Two rows from the center of each plot were harvested with a plot combine for yield and yield component analysis. Soil water measurements were obtained with neutron attenuation to a depth of 6 ft in 1-ft increments at seeding and harvest to determine water use and water use efficiency.

Results and Discussion

The 2012 growing season had above-normal temperatures and below-normal precipitation, which negatively affected grain yield. Corn grain yields were about 50 bu/ac lower than the average yields from 2007-2012 (Tables 1 and 2). Stubble height did not affect grain yield or any of the other measured parameters in 2012; however, average corn yields from 2007-2012 were 11 bu/ac greater when planted into high- or strip-cut stubble. This was primarily due to greater number of kernels per ear. Residue production and water use efficiency was also greater with the taller stubble.

Grain sorghum yields were similar to corn yields in 2012 and were not affected by stubble height ( Table 3). When averaged across years from 2007-2012, the highest yields were obtained in the high-cut stubble but were not significantly greater than the other stubble heights. None of the other measured parameters for grain sorghum were affected by stubble height (Table 4).

-Alan Schlegel, Agronomist-in-charge, Tribune

There are now several 2-gene Clearfield wheat varieties on the market in our area: AP503 CL2 from Syngenta/AgriPro and Brawl CL Plus from Colorado State University. More such varieties will no doubt be on the market in the coming years.

What is the difference between these varieties and the original 1-gene Clearfield varieties in terms of how they can be managed, herbicide applications, grass control, and crop injury?

There is no difference in the labeled rates of Beyond that can be applied in a single growing season to 1-gene and 2-gene Clearfield varieties. However, methylated seed oil (MSO) or crop oil concentrate (COC) can be added as an adjuvant to Beyond when it is used on 2-gene Clearfield varieties. On 1-gene Clearfield varieties, only a non-ionic surfactant (NIS) can be used as an adjuvant. In cases, a nitrogen-based fertilizer such as AMS or 28 percent UAN should also be added to the spray solution.

The adjuvant can make a significant difference in the level of feral rye and downy brome control with Beyond, especially with spring treatments. Since cheat, Japanese brome, and jointed goatgrass are usually quite susceptible to Beyond, the adjuvant usually does not make as much difference in the level of control of these grasses. A recent K-State study near Manhattan illustrates the effect.

For spring applications of Beyond, including MSO as an adjuvant measurably improved control of downy brome and feral rye compared to using NIS as the adjuvant. But as mentioned above, Beyond with MSO can only be used on 2-gene Clearfield varieties. MSO has been more effective than COC in these situations.

Beyond is labeled for control of many winter annual grasses (including jointed goatgrass, cheat, downy brome, and Japanese brome), but only suppression of feral rye. Control of feral rye with Beyond in K-State tests has been somewhat erratic and unpredictable. The best control will likely be achieved with fall applications, using the 6 oz rate instead of the 4 oz rate, and using MSO instead of NIS where that is allowed. In general, the best control of feral rye in 1-gene Clearfield varieties has been with fall applications. With 2-gene Clearfield varieties, producers now have more options for better rye control.

The other advantage of 2-gene Clearfield over 1-gene Clearfield wheat varieties is in the higher degree of crop safety from applications of Beyond. Occasionally, Beyond has caused some crop injury to 1-gene Clearfield wheat. This occurs most often where there is spray overlap (2x rates), when stress conditions prevail, or where wheat was not at the recommended treatment stages at the time of application. In K-State tests, 2-gene Clearfield wheat varieties have demonstrated much less potential for crop injury than 1-gene varieties in these situations.

*Note: The maximum single application use rate of Beyond is 6 oz/acre. The 12 oz/acre rate would simulate spray overlaps in the field and is not a labeled broadcast application rate.

In many areas of Kansas, prolonged drought has resulted in short wheat and thin stands. Harvesting wheat in these situations can be a challenge. Special attention needs to be given to cutting height, machine adjustments, and operator control. In short wheat, getting the heads into the combine with less straw will be a challenge. In some cases, the reel may not be able to effectively convey the wheat back from the cutter bar to the auger, nor hold it in place during cutting. Short cutting will also mean more contact potential with the ground and reduced levels of surface residue which can negatively impact cropping systems in water-limited environments.

In the case of material conveyance, stripper heads, air reels, and draper headers may be a great help.

Stripper headers

Stripper headers allow the grain to be harvested efficiently while leaving the maximum amount of standing residue in the field. Research has shown that this preservation of wheat residue can reduce evaporative losses of water after harvest, aid in the moisture retention of snow, and improve the yields of the next year's crop.

To properly use a stripper header, note the following:

Operators need to be aware of the rotor height and the relative position of the hood to the rotor. This position needs to be set correctly so that heads approach the rotor at the proper angle for stripping.

Keep the nose of the hood orientated so that the top of the wheat heads are even with, or slightly below, the forward point of the nose. This may require operating the header with the nose in a slightly lower-than-normal position relative to the rotor. However, it's important to note that running a stripper header lower than necessary will result in increased power consumption and finger wear.

Combine ground speeds should be kept high (above 4 mph) to maintain collection efficiency and minimize header losses.

Several people have reported that adjusting header height with a stripper header is not as critical as it is with a conventional header, and that a stripper header could easily be run by non-experienced people (see step 1).

Continue to adjust stripping rotor speed throughout the day as conditions change. If rotor speeds are too high, that will result in detachment of the entire head and unnecessary increases power requirements. Rotor speeds that are too slow will result in unstripped grain remaining in the head. In general, rotor speeds will be less in thin short wheat than in better stands.

Air reels

Air reels will also aid in the material conveyance from the cutter bar to the auger in reel-type units when crops are light or thin. These units are made in several different types including finger air reels, non-reel, and units that fit over existing reels. Examples of manufacturers are Crary (West Fargo, ND) and AWS (Mitchell, Ontario Canada). Non-reeled units have the advantage of less eye strain from the continuously rotating header reel, but all units have collection efficiencies compared to conventional reels even in sparse or short crops. These units do not control the amount of wheat stubble left in the field and the operator still has to control the cutting height. In short wheat, this may mean little to no field stubble will be left for next season's moisture collection and for these reasons stripper headers may be a better choice for certain areas of Kansas.

Draper headers and flex heads

Draper headers may also help with the conveyance of material since they have a very short distance between the cutter bar and the conveyance belt. The ability to tip the cutter bar completely back will aid in keeping harvested crop material moving across the cutter bar and onto the belt as well as ensuring some stubble remains standing on the soil surface. Cleats on the belt need to be in good to new condition to maximize conveyance of crop material away from the cutter bar. Set gauge wheels properly to maximize cutting height and leave standing residue.

Flex heads will also help deal with the lower cutting heights and potential ground strikes. In thin stands of wheat, it is even more important that sickles and guards are in good condition as there is not as much crop material to push, which would normally help ensure cutting by worn sickles and guards. On headers with finger reels, it is quite likely that the short cut wheat will pass in between the fingers rather than being swept backward. Producers may consider adding material over or behind the fingers to act more as a bat to sweep the cutter bar clean. Plastic/vinyl materials or repurposed round baler belting have been successfully used for this purpose.

If harvesting with a draper or flex header, maintain the cutting height as high as possible to preserve the standing stubble. Typically, cutting wheat at two-thirds of its full height will result in losses of less than 0.05 percent as any missed heads contain grain that will be lost as taillings during the harvesting process.

Conventional headers

Still for many farmers, new equipment may not be an economical choice and you may have to make do with a conventional head on your combine. In this case, adjust the reel to get the best movement of the heads from the cutter bar to the auger. Combining in slighter wetter conditions may help prevent shatter and decrease losses. If wheat heads have flipped out of the header from the top of the auger, an extra "auger stripper bar" may be necessary. A small strip of angle iron can be bolted slightly behind and below the auger to help with material conveyance. In thin stands of wheat, it is even more important that sickles and guards are in good condition as there is not as much crop material to push and ensure cutting by worn sickles and guards.

If harvesting with a conventional header, maintain the cutting height as high as possible to preserve standing stubble. Typically, cutting wheat at two-thirds of its full height will result in losses of less than 0.05 percent as any missed heads contain grain that will be lost as tailings during the harvesting process.

Combine adjustments

In addition to material conveyance and cutting height, lower yields and uneven crop flow may also require performing combine adjustments to the concave/rotor cage clearance, cylinder/rotor speed, and fan speed. Follow the manufacturer's recommendations. The leading cause of grain damage under almost any harvesting condition is overly fast cylinder or rotor speed. This will especially be evident in harvesting short wheat as there will be less material in the concave or rotor cage to thresh against, increasing the likelihood of grain damage if cylinder/rotor speed is too high.

On conventional machines it may be necessary to reduce concave clearance to attain good separation. On rotary combines it may be advantageous to maintain a typical clearance to provide a more normal threshing condition while using less threshing area. The use of blanking plates on the rotor cage may improve separation. You may have to lower the fan speeds slightly to minimize grain losses. Once adjusted properly, try to keep material crop flow as constant as possible as most threshing and cleaning units work best under these constant flow conditions. As the amount of material passing through the combine decreases the response to various settings such as cylinder/rotor speed, concave/rotor cage clearance, and fan speed will be more sensitive than under more normal operating conditions.

Performing kill-stops during harvest will be especially critical in evaluating grain losses and identifying which stage of the harvesting process is the source. After performing a kill-stop the operator should look at shattered grain losses before the header, losses after the header and before the spread pattern of the combine, and losses in the tailings behind the combine. Losses can be quickly checked by looking at the number of seeds in the tailings and elsewhere around the combine.

Typically, 20 seeds per square foot is equal to 1 bushel per acre for a sampling area equal to the cutting width of the combine. For the tailings area, where the material is concentrated, multiple the 20 seeds per square foot by the header-to-tailings width ratio. For example, a combine with a 7-foot spreader width and 28-foot header would have a factor of 4, and 80 seeds per square foot would be the correct number for a bushel-per-acre loss. Also, a normal shoe length is typically one foot, so estimated measurements can be done with your foot. Individual field and header losses are determined by looking at areas before and under the combine. Actual combine threshing losses are determined by subtracting these numbers from the tailing loss.

Summary

Although this maybe a rough year for many farmers, some changes can be made to help maximize harvest efficiencies. If you have ever wanted to try an alternate header (stripper, flex-draper, etc.), this maybe the year for you. For those not wanting to buy, renting may also be an option.

Producers in dryland production systems need to keep in mind that in very low-yielding wheat years anything that can be done to preserve what little crop residue is present will have huge impacts on evaporative losses and productivity of the next crop.

-Lucas Haag, Northwest Area Crops and Soils Specialist

-Ajay Sharda, Extension Biological and Agricultural Engineer

The fairly good topsoil moisture levels and unusually warm temperatures so far this spring have caused wheat to break early dormancy and green up. In fact, it seems like this last week the wheat grew an inch! This is a scenario reminiscent other early spring years, in which freeze injury was a problem. Hopefully we will avoid that this year!

The wheat actually began to grow when we were seeing daytime temperatures for several days above 60 and the nighttime temperatures above freezing. The last week with temperatures in the 80s only further pushed the wheat. It would be much better if temperatures were cooler, especially the nighttime temperatures.

Plants growing at this time of year use valuable soil moisture. Even though topsoil moisture is fairly adequate, we would like to see the moisture used later in the growing season.

In addition, plants will have lost some of their winterhardiness. This won't be a problem if the weather doesn't have an extremely cold snap or if temperatures cool down gradually, so the plants can regain some of their winterhardiness. If the wheat is green and growing, however, and temperatures suddenly go from unusually warm to extremely cold, freeze injury could occur. That being said, if the temperature dips to 24 degrees for 2 hours, wheat can be injured at the jointing stage. As the wheat continues to grow, the wheat can not handle as cold of temperatures. At the boot stage, 28 degrees causes injury. At heading and flowers, 30 degrees causes injury.

Producers should watch their wheat crop for insects and diseases, and make every effort to get on their topdress nitrogen before the crop reaches the first hollow stem. Other than that, there's not much that producers can do to stop the development of the crop. Grazing the wheat can hold back its development, but grazing may not be possible much longer this winter. Cattle should be pulled off before first hollow stem. The longer temperatures remain above normal, the more susceptible the wheat will be to a sudden temperature drop to the single digits or below.

What are we going to do with this weather!?! The temperature swings keep your head spinning, so what do you think it is doing to out wheat?

With the warmer than normal temperatures, there have been many questions regarding the winterhardiness of wheat. As a general rule, night time temperatures need to be above freezing for a week or more for the wheat to lose its winterhardiness. At the Colby weather station, there have been no nights with the temperature greater than freezing. In fact, the average overnight low for January was 17°.

The process of gaining and losing winterhardiness in winter wheat is a gradual one. Temperatures fluctuate most years as winter begins and ends, and the winterhardiness level of wheat tends to ratchet up and down with the temperatures. After a warm spell in winter, wheat will lose some winterhardiness - but wheat will regain its winterhardiness as temperatures get cold again. Every time this happens, however, the wheat will lose some winterhardiness. The peak level of winterhardiness in wheat occurs when temperatures get cold and stay cold all winter. Wheat that greens up and then goes back into dormancy will not have quite the same level of winterhardiness as wheat that remains dormant all winter.

Winterkill has also been on producers' minds. Winterkill most often occurs when the crown area of the wheat plant is not protected. This is often thought to be a problem associated with planting depth. While this is true, it is most associated with the point that the emerging seedling first detects light. If the seedling must first grow through a thickness of residue, the plant will likely set the crown in the residue. This can increase the risk for winterkill because the crown is not protected by soil from temperature changes. The residue gives less protection. Loose, dry soil can also increase the risk for winterkill, due to reduced protection from temperatures.

Producers who want to treat their fields of continuous wheat with a cheatgrass herbicide have to decide when to apply it. Should they spend the money and apply it this fall or wait until spring to see if the wheat is going to yield enough to pay for it? Each of the most commonly used cheatgrass herbicides- PowerFlex, Olympus, Olympus Flex, and Maverick- is most effective on cheatgrass when applied in the fall, especially for control of downy brome. These products should be applied when the cheatgrass is small and actively growing and when the wheat has at least three leaves, but prior to jointing.

Another benefit of fall application compared to spring application is that a fall application helps minimize rotational restrictions because of the extra time between application and planting the next crop. Fall application may even open the door for double-cropping or planting failed acres to soybeans in the spring following PowerFlex or Olympus Flex.

The cheatgrass species present is a very important factor in the level of control to expect. All the listed herbicides can provide very good control of true cheat and Japanese brome (unless the weed population has developed resistance to the ALS class of herbicides), but are less effective on downy brome. ALS-resistant cheat and Japanese brome were first documented in Kansas in 2007. ALS-resistant cheatgrass first appeared in fields with a long history of Olympus and Maverick use. These populations were cross-resistant to all of the cheatgrass herbicides used in wheat. Since that time, other fields of ALS-resistant cheatgrass have also been confirmed.

None of the herbicide previously discussed controls feral rye. To suppress feral rye in wheat, producers would need to have planted a Clearfield wheat variety and use Beyond herbicide. Beyond can also provide control of cheat, Japanese brome, downy brome, and Italian ryegrass. Like the other herbicides, fall applications of Beyond generally are most effective for weed control than spring treatments.

Producers need to realize that rye and ryegrass are not the same plant. Feral rye and Italian ryegrass are two different grassy weeds. PowerFlex and Olympus Flex can give very good ryegrass control, but will not control rye. It is important that producers make that distinction when they hear or read advertisements about ryegrass control with PowerFlex or Olympus Flex.