The general target date for planting wheat for optimum grain yields in Kansas is within a week of the best pest management planting date, or BPMP (formerly known as the “Hessian fly-free”) date (Figure 1). If forage production is the primary goal, earlier planting (mid-September) can increase forage yield. However, if grain yield is the primary goal, then waiting until the BPMP date to start planting is the best approach (Figure 2). Planting in mid-September is ideal for dual-purpose wheat systems where forage yields need to be maximized while reducing the effects of early planting on reduced grain yields. Notice that, due to the current dry conditions, coupled with the outlook of continued drought in Kansas, planting wheat for dual-purpose or for forage only does not seem like viable options this year.
Optimum wheat planting dates in Kansas depend on location within the state. Suggested planting dates by zone are as follows:
Zone 1: September 10-30
Zone 2: September 15 – October 20
Zone 3: September 25 – October 20
Zone 4: October 5 – 25
Figure 1. Optimum wheat planting dates by zone in Kansas.
Figure 2. Effect of planting date and seeding rate on wheat fall forage yield in Lahoma, north-central Oklahoma (a) and effect of planting date on wheat grain yield near Hutchinson, south-central Kansas (b). Figure adapted from KSRE numbered publication MF3375.
While the effects of planting date on wheat yield shown in Figure 2 will hold true for most years, they will largely depend on environmental conditions and disease pressure during the growing season. In some years, earlier-planted wheat does best and some years the later-planted wheat does best, and these year-specific performances usually relate to the weather experienced in the fall and spring. For instance, early-planted fields in growing seasons with a warm fall might produce excessive biomass that will use an excessive amount of water during the fall. If the following spring is dry, soil water deficit during grain filling then can reduce grain yield. Conversely, a warm fall would favor tillering of a later-planted wheat crop, helping to compensate for this delay. The opposite is also true: in years with an early onset of cold temperatures during the fall, an earlier planted crop might perform better than a later planted crop due to its ability to produce enough fall tillers to still maximize grain yield. Research conducted by Merle Witt with late-sown wheat in Garden City from 1985 through 1991 is summarized in Figure 3. Averaged across all these years, delaying wheat sowing from October 1 to November 1 delayed heading date by 6 days and decreased wheat yields in 23%. The grain-filling period was progressively shortened by about 1.7 days and occurred under hotter temperatures (about 1.5°F) for every month of delay in sowing date.
Figure 3. Wheat grain yield, test weight, and heading date responses to sowing date between 1985 to 1991. Data adapted from Kansas Agric. Exp. St. SRL 107.
In dry years, seedling emergence and stand establishment can be uneven. These dry conditions can also lead to poor crown root development and fall tillering. If fields become too wet to plant by mid-October and stay that way through the remainder of the fall, then producers end up planting much later than the optimum planting date. Following an unusual year, producers will often start planting earlier than the recommended date if soil conditions are good, because the negative consequences of adverse conditions are fresh on their minds. However, planting early also increases the risk of other production problems including multiple diseases, insect pests, weed infestations and undesirable growth of the crop.
Potential risks of planting wheat early
Increased risk of wheat streak mosaic and related diseases. Wheat curl mites that spread these diseases survive the summer on volunteer wheat and certain other grasses. As those plants die off, the wheat curl mites leave in search of new plants to feed on. Early-planted wheat is likely to become infested, and thus become infected with wheat streak mosaic virus, high plains virus, and Triticum mosaic virus. The wheat curl mites are moved by wind and can be carried a mile or more before dying, so if wheat is planted early, make sure all volunteer wheat within a mile is completely dead at least two weeks before planting. For growers considering planting early, a good management consideration would be to select wheat varieties with resistance to the wheat streak mosaic virus and/or with tolerance to the wheat curl mite, especially in the western portions of the state.
Increased risk of Hessian fly. Over the summer, Hessian fly pupae live in the old crowns of wheat residue. After the first good soaking rain in late summer or early fall, these pupae (or “flaxseed”) will hatch out as adult Hessian flies and start looking for live wheat plants to lay eggs on. They are most likely to find either volunteer wheat or early-planted wheat at that time. After the BPMP date, many of the adult Hessian fly in a given area will have laid their eggs, so there is generally less risk of Hessian fly infestation for wheat planted after that date. Hessian fly adult activity has been noted through November or even early December in Kansas. If planting early, consider varieties with improved tolerance to Hessian fly.
Armyworms and other lepidopteran larvae may also still pose a serious problem to early planted wheat. They may feed on the green wheat plants until the first cold front comes through (temperatures in the mid 20-degree F range for a couple hours). Insecticide seed treatments do not work well against lepidoptera larvae.
Volunteer wheat herbicide applications and insecticides
Because of the relatively large and widespread populations of armyworms/fall armyworms in 2020 and 2021, many wheat producers have been talking about adding an insecticide to their herbicide application this year for volunteer wheat in order to save on application costs. Last year, many fields of volunteer wheat were heavily infested with these caterpillars, which wasn't bad as they helped control some volunteer wheat stands but some were still around when the planted wheat germinated. The addition of an insecticide to a volunteer wheat herbicide application is probably not a good idea for several reasons: 1) If armyworms/fall armyworms are present in volunteer now, killing the volunteer should cause the larvae to starve, or initiate pupation if they are far enough along in their development, or expose them to birds and/or other predators; 2) you should NOT use an insecticide unless the pest is at a vulnerable stage and has reached a treatment threshold; and 3) insecticides applied with a herbicide will not have insecticidal activity by the time the planted wheat germinates anyway. Please resist the urge to mix an insecticide with a volunteer wheat herbicide application but do control the volunteer wheat.
Increased risk of barley yellow dwarf. Many types of aphids can spread barley yellow dwarf. In Kansas, greenbugs and bird cherry-oat aphids are the primary vectors of this viral disease. These insects are more likely to infest wheat during warm weather early in the fall than during cooler weather. Planting wheat after the BPMD reduces the risk of problems with aphids and barley yellow dwarf. If planting early, consider varieties with improved tolerance to Barley Yellow Dwarf virus, especially in central and eastern Kansas or consider the use of seed treatments with imidacloprid (such as Gaucho XT or Rancona Crest).
Increased risk of excessive fall growth and excessive fall tillering. For optimum grain yields and winter survival, the goal is for wheat plants to go into winter with established crown roots and 3-5 tillers. Wheat that is planted early can grow much more than this, especially if moisture, temperature, and nitrogen levels are not limiting. If wheat gets too lush in the fall, it can use up too much soil moisture in unproductive vegetative growth. These fields often experience more drought stress in the spring if soil conditions remain dry, and can show more symptoms of low temperature damage during the winter (Figure 4). The wheat on the left (showing white discoloration of the leaves) was planted mid-September for dual-purpose evaluation, and had an excessive amount of fall growth (near 3,000 pounds of dry matter per acre). The wheat on the right was planted early-to-mid October for grain-only purposes and had much more limited fall biomass. The white discoloration of the high biomass plots occurred after a late-winter, early-spring freeze that was more damaging to the dual-purpose crop. Notice the darker green plots in the upper left corner, amid discolored plots: while these were planted early, their growth was cut back by simulated grazing.
Figure 4. Aerial photo of side-by-side wheat trials near Hutchinson, KS, during the 2021-22 growing season. Photo taken March 2022 by Jorge Romero Soler.
Increased risk of take-all, dryland foot rot, and common root rot. Take-all is usually worse on early-planted wheat than on later-planted wheat. In addition, one of the ways to avoid dryland foot rot (Fusarium graminearum and other Fusarium species) is to avoid early seeding. This practice promotes large plants that more often become water stressed in the fall predisposing them to invasion by the fungi. Early planting of wheat also favors common root rot because this gives the root rot fungi more time to invade and colonize root and crown tissue in the fall. Seed treatments are an option to early season seedling diseases. More information: https://bookstore.ksre.ksu.edu/pubs/MF2955.pdf
Grassy weed infestations become more expensive to control. If cheatgrass, downy brome, Japanese brome, or annual rye come up before the wheat is planted, they can be controlled with glyphosate or tillage. If wheat is planted early and these grassy weeds come up after the wheat has emerged, producers will have to use an appropriate grass herbicide to control them.
Germination problems due to high soil temperatures. Early planted wheat is sown in hotter soils, which may become problematic because some wheat varieties are sensitive to high-temperature during germination. In fact, some varieties will not germinate when soil temperatures are greater than 85°F. Additionally, some varieties can have their coleoptile length reduced in as much as 40% in hot as compared to cool soils. If planting early, it is important to select varieties that do not have high-temperature germination sensitivity or sow sensitive varieties later in the fall, when soil temperatures have cooled down.
Emergence problems due to shortened coleoptile length. Hotter soils tend to decrease the coleoptile length of the germinating wheat. Therefore, deeply planted wheat may not have long-enough coleoptiles to break through the soil surface resulting in decreased emergence and poor stand establishment. When soil temperatures are hot, it is often better plant wheat at a shallower depth (3/4 to 1 inch deep) even if moisture is absent in the top layers of soil. Planting wheat deep (>2 inches) increases the risk of poor emergence and unacceptable stands.
Summary
Early sowing of wheat can lead to several problems, from increased chances of insect- or mite-transmitted viral diseases to decreased emergence due to high temperatures and its consequences on wheat germination of particular varieties and reduced coleoptile length. Ideally, growers would consider planting around the optimum window; but, if planting early due to moisture availability or a dual-purpose system, growers should consider selecting wheat varieties with tolerance to the major yield-reducing factors in their respective region. Growers should strongly consider a seed treatment with both fungicides and insecticides if planting wheat early in Kansas.
Romulo Lollato, Extension Wheat and Forages Specialist
lollato@ksu.edu
John Holman, Cropping Systems Agronomist, Southwest Research-Extension Center
jholman@ksu.edu
Kelsey Andersen Onofre, Extension Wheat Pathologist
andersenk@ksu.edu
Erick DeWolf, Wheat Pathologist
dewolf1@ksu.edu
Jeff Whitworth, Extension Entomologist
jwhitwor@ksu.edu
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