Wheat update – Planting and fall armyworm

Posted on October 11, 2024 by Amanda De Oliveira Silva

Amanda de Oliveira Silva, Small Grains Extension Specialist and Ashleigh Faris, Cropping Systems Extension Entomologist

Wheat planting in Oklahoma is off to a slow start due to extremely dry conditions, with only 32% of wheat planted as of October 7 (according to the USDA Crop Progress Report).

For most of Oklahoma, the optimal time to plant dual-purpose wheat is between September 10-20 (approximately day 260 in Figure 1). This period represents a balance between achieving good forage production and minimizing the risk of grain yield loss. Planting earlier can provide more fall forage potential but is usually only recommended if wheat is intended for grazing or “grazeout.” If you are planting wheat just for grain, you could wait at least 2-3 weeks after the dual-purpose planting window, which puts the best time for planting around mid-October (approximately day 285 in Figure 1) in many parts of the state. We have been evaluating how delayed wheat planting affects wheat yields, and it appears there might be more flexibility in the planting window than previously thought. I will be sharing more details about this research in an upcoming post!

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).

Rainfall on September 22 helped some fields in north-central, northwest, and Panhandle areas, and wheat that was planted before then has now emerged and looks good, though more rain would certainly help (Figure 2). In the fields we planted in Panhandle and northwest, we found moisture at about 1.5 inches deep, but the drought is holding us back in other parts of the state.

*Figure 2. Wheat field planted before the September 22 rain event. Photo taken on October 8, 2024, near Goltry, OK by Josh Bushong.*

For fields where wheat was planted before the September rain, we are receiving reports of fall armyworms. They have been especially active in north-central Oklahoma over the past week. We recommend checking your fields daily after wheat emerges. The worms are small and hard to spot, but you may notice symptoms like “window pane” feeding on the leaves (Figure 3). Also, check under crop residue where they might be hiding from the heat (Figure 4).

*Figure 3. Symptom of “window paned” leaves shows severe feeding from the fall armyworm. Photo taken on October 2, 2019, at Canadian County by Amanda Silva.*

*Figure 4. Fall armyworms may be found under crop residue during the day. Photo taken on October 2, 2019 at Canadian County by Amanda Silva.*

Below is some information regarding monitoring and management of fall armyworms. Typically, fall armyworm population spikes are due to increases in precipitation in summer months. Fall armyworms are identifiable due to the light colored, inverted “Y” on their head (Figure 5). They are generally light tan to light green caterpillars that have a brownish-black head (may appear orangish). For more on the biology of the insect and its identification, check out the EPP-23-21 e-Pest Alert from this past summer.

*Figure 5. Image of fall armyworm with two common features used to differentiate it from other caterpillar pests. Image: Corteva Agriscience.*

Fall armyworm larvae will begin to consume vegetation in the early instars (1-3) but often this damage goes unnoticed because of the small amount consumed. As fall armyworms enter the later instars (4-6) the rate of consumption increases, and damage is more noticeable. The reason for rapid crop loss at this stage is caterpillars do most of their feeding (80-90%) in the final two instars. Fall armyworms cause damage by defoliating leaves and cutting seedlings at the surface level. Small larvae, unable to completely chew through the leaf, will often feed on vegetation by scraping it, lending to a windowpane appearance (as mentioned above, Figure 3).

Recommendations

Begin scouting for fall armyworms as soon as wheat emerges, particularly in the morning hours at the edges of wheat fields that share borders with pasture or road ditches. Look closely for signs of windowpaned leaves and the fall armyworms themselves. Treat if three to four larvae are found per foot of row AND feeding damage is evident. The early instars are more susceptible to insecticides so early detection is important for providing effective chemical control. While pyrethroid-based insecticides are low-cost, they are often ineffective when populations of fall armyworms are high. Instead, consider mixing a pyrethroid with another product that has chlorantraniliprole or diflubenzuron as an active ingredient which have a longer residual. Chlorantraniliprole products offer the advantage of being rainfast as well as protection against bigger fall armyworms. Products with diflubenzuron have a long residual but do not work well on larger worms. The good news is first frost will help knockback fall armyworm populations, until then producers are encouraged to have fall armyworm scouting as part of their daily routine and to be on the ready to spray when threshold is met.

We will not get relief from fall armyworms until we get a killing frost, so keep vigilant!

Reach out to us and contact your county Extension office for more information.

Amanda Silva – silvaa@okstate.edu

Ashleigh Faris – ashleigh.faris@okstate.edu

Planting wheat in hot and dry soils

Posted on September 20, 2022 by Amanda De Oliveira Silva

Amanda de Oliveira Silva, Small Grains Extension Specialist

With severe dry conditions and high temperatures in our state, it is good to consider the possible effects of high temperature and drought on wheat germination and early growth. As of September 19, soil temperature was in the 80’s F across the state and reached 97 F in some areas (Figure 1). Wheat can germinate in soil temperatures from 40 F to 99 F, but temperatures from 54 F to 77 F are optimal.

*Figure 1. Soil temperature across Oklahoma. Figure courtesy Oklahoma Mesonet.*

Wheat germination and emergence in HOT soils

Is the variety I am planting high-temperature germination sensitive?

High-temperature germination sensitivity is a more elaborate way of saying that some wheat varieties do not germinate well in hot soil conditions. This is not to say that the seed will not germinate, but it may not germinate until the soil temperature has lowered. Keep in mind too that this sensitivity can vary from year to year. For example, a sensitive variety like Ruby Lee may germinate fine in 90°F soils one year and only produce a 10% stand in the same soil conditions the next. When sowing early, it is best to plant varieties first that do not have high-temperature sensitivity (e.g., Duster, Gallagher). Soil temperatures typically begin to cool by about September 20 due to lower air temperatures and/or rainfall events. However, our summer temperatures seem to be sticking around for longer this year. Waiting until at least mid-September to plant sensitive varieties can help reduce the risk of this issue. A high temperature germination sensitivity rating for wheat varieties can be found in the OSU Fact Sheet (available by clicking here). An updated version of this factsheet will be published soon.

Coleoptile Length

Hot soil conditions at sowing also reduce coleoptile length. The coleoptile is the rigid, sheath-like structure that protects the first true leaf and aids it in navigating and reaching the soil surface. Once the coleoptile breaks the soil surface, the coleoptile will stop growing, and the first true leaf will emerge. If the coleoptile fails to reach the soil surface, the first true leaf will emerge below ground and take on an accordion-like appearance (Figure 2A-B). If this happens, the plant will die.

Figure 2A and 2B. Example of two different wheat seedlings in which the coleoptile failed to break the soil surface. The first true leaf emerged below the soil surface and resulted in this accordion-like appearance.

The coleoptile length for most wheat varieties today can allow for the seed to be safely planted up to 1.5 inches deep. Under hot soil conditions though, the coleoptile length tends to be decreased. Therefore, “dusting in” early-sown wheat at ¾ to 1 inch depth and waiting on a rain event may result in more uniform emergence than trying to plant into soil moisture at a deeper depth, if soil moisture is not available in the top 1 to 1.5 inches of the soil profile. A rating for coleoptile length for wheat varieties can be found in the OSU Fact Sheet PSS-2142 Wheat Variety Comparison. We are also working on updating this.

Wheat germination and emergence in DRY soils

The most important physiological requirement for wheat to germinate and sustain the developing seedling is soil water. Therefore, planting decisions should be based on a combination of available soil moisture and expected rainfall. In addition, other factors such as adequate seeding depth, sowing date, soil fertility, seed treatment, seed quality, etc., should be considered to guarantee good crop establishment. For more information, check the materials on our website.

Wheat seed needs a minimum water content of 35 to 45% of its dry weight to initiate germination, and germination will be more complete as moisture levels increase. Dry soils can still maintain a relative humidity of 99%, which can provide enough moisture for seeds to germinate. It might just take longer than with free-moisture availability. My concern with the current situation in Oklahoma is the severe drought we are in and the lack of rain in the forecast. In some cases, we could have enough moisture to start the germination process in some regions of the state, but seedling emergence and growth could be compromised if we do not see any rain soon.

What happens if the soil completely dries out before wheat emergence?

There are three phases during the germination process: water absorption, activation when the seed coat is ruptured, and visible germination when the radicle emerges, followed by the seminal roots and coleoptile. These processes will start and stop depending on soil moisture availability. Thus, if the soil dries out before the roots and shoots are visible, the seed remains viable, and germination will be paused and continue once water is available. However, if the soil dries out after those structures are emerged (approximately 4-5 days after germination has begun), the seedling may not tolerate the lack of water, resulting in incomplete or loss of stand.

What should I do then? Choose your battle!

The optimal time for planting wheat in central Oklahoma is around mid-September for a dual-purpose system or around mid-October for a grain-only system (Figure 3). With the current forecast, we are planning to wait another 7-10 days to decide on our dual-purpose and forage trials. There are different ways we can go about it, but we must remember that there is always risk involved when planting wheat in dry and hot soil conditions.

Figure 3. Forage and grain yield potential in relation to the day of the year. Every 1,000 kg/ha is equal to approximately 900 lb/acre or 15 bu/acre. Ideal planting dates for dual-purpose wheat in Oklahoma are mid-September (i.e., approximately day 260). Planting for grain-only should occur at least 2-3 weeks after dual-purpose planting (i.e., mid-October or approximately day 285).

If you decide to dust in your wheat and wait for a rainfall event to drive germination, watch your seeding depth. The optimum seeding depth to plant wheat is about 1-1.5” deep. We typically do not have as many issues with winterkill in Oklahoma as in more northern states, so I am comfortable with dusting in at about 0.75 – 1” deep. Planting at 0.5” or less is too shallow in most circumstances. Also, there is always a chance for a pounding rainfall event and subsequent soil crusting, which makes it difficult for the coleoptile to push through the soil surface and may result in poor emergence. Fields with stubble cover may be less affected and reduce the risk of soil crusting. If we receive light rain in the following weeks, that could cause wheat to emerge, but it may not be enough for wheat to continue growing. Most of the fields do not have good subsoil moisture, either.

If subsoil moisture is available and you decide to plant deeper to reach moisture, be careful with the coleoptile length of your variety, and make sure it has a long-enough coleoptile that will allow emergence if conditions are favorable. Consider increasing seeding rate to compensate for reduced emergence, which is prone to occur in this situation.

Should we wait for rain to plant then? This is a farm-by-farm call and it depends on which source of risk you find most comfortable. Personally, I would rather plant my wheat in the optimal planting window and adequate seeding depth than waiting for a rain that may take too long to happen or missing my optimal planting window. If the latter is the case, consider bumping seeding rate to try to compensate for the reduced time for tillering (especially in a grain-only system). Planting wheat at optimal time allows for more time for root growth in seedlings, helping the crop to establish more quickly under dry conditions and possibly help the plant to scavenge for water that is available deeper in the soil profile.

Are there any specific agronomic traits that could help wheat seedling growth under water stress?

Traits that will help with seedling growth in dry conditions are coleoptile length potential, which allows to plant a little deeper in moisture and good emergence (if deep planting is the practice of your choice). There are indications that sowing wheat varieties with larger seed may help to reduce the negative effects of drought during early growth (Mian and Nafziger, 1994). In general, the greater reserves of larger seed result in faster germination and crop establishment by increasing root growth and tiller production. Keep in mind, however, there are varieties with small seed size that germinate more rapidly than larger seeded varieties, owing to their differential response to available moisture.

Uneven wheat emergence and stand establishment – is my wheat going to make it?

Posted on November 20, 2020 by Amanda De Oliveira Silva

Amanda de Oliveira Silva, Small Grains Extension Specialist

I have been watching some wheat fields consistently after that ice storm came in late October. I am currently seeing anything from good looking wheat fields to areas with incomplete, thin, and uneven stands. We might not see complete stands for a while as the wheat emergence seems to be very uneven, and the wheat is still slowly coming up (Figure 1).

Figure 1. Uneven wheat emergence in a field planted on October 16. Picture was taken on November 9, 2020.

The thin and uneven stand establishment of the current wheat crop is likely due to the severe drought from the end of September to most of October. Then, most of Oklahoma was hit by the ice storm during the last week of October, with some areas receiving up to 5 inches of rain. Although that rain came in a much-needed time, it could have created a crust in the soil preventing the coleoptile from breaking through the soil surface.

If the wheat fails to emerge as expected in your field, dig up the soil and look for an “accordion” like plant. If you see that wheat has emerged its first true leaf under the soil surface, and it has been sitting there for a week or more, it will probably not going make it (Figure 2).

Figure 2. Wheat that has emerged its first true leaf under the soil surface will lose viability after one week or so. Field planted on October 21. Picture taken on November 9, 2020.

However, I am seeing crinkled coleoptiles in fields around Stillwater that are coming up slowly and will be fine. The crinkles probably occurred when the heavy rain occurred during the ice storm, but it was not enough to prevent the coleoptile from continuing to grow and pushing through the soil surface for the most part (Figure 3).

Figure 3. Part of the coleoptile got crinkled due to heavy rain and light soil crusting during the emergence period. Still, most of the plants seem to continue growing and breaking through the soil surface. Field planted on October 21. Picture was taken on November 9, 2020.

Overall, our variety trials that were planted sometime in October are coming up nicely, but we might not have a complete stand for a little while in some locations. Robert Calhoun, the Senior Agriculturalist of OSU Small Grains Program.

Some fields that were planted in early-mid October is also just now starting to emerge near Kay County. Shannon Mallory, Kay County Extension Educator.

About 95% of the wheat in our variety trial at Altus has emerged and shows adequate stands (planted on September 29). Gary Strickland, the Jackson County Extension Agriculture Educator and Southwest Research and Extension Center Regional Agronomist.

Josh Bushong, the OSU Area Extension Agronomy Specialist, reported in his Ag Insights November report that most of the fields in the North Central region are showing thin and uneven stands. He also mentioned this would likely have a small effect for grain only-producers.

As a summary, most of the fields that I am seeing or hearing about that were planted in October are still coming up. Wheat growth is a function of temperature. The cooler temperatures and lower cumulative growing degree days in the coming months will slow down growth until March or so. Plants may compensate to a certain extent for that reduced stand, and wheat producers aiming for grain-only production should not be concerned yet.