The wheat crop is off to a good start in many parts of Kansas. The dry conditions common during most of September, which resulted in uneven stands in many fields across the state, have dissipated. Most of Kansas now seems to have enough moisture for good fall wheat development. In some cases, almost too much moisture (Figure 1).
Figure 1. Water logging in a wheat field near McPherson following a nearly 3-inch precipitation event. Photo taken December 3, 2015 by Romulo Lollato, K-State Research and Extension.
With the available moisture in addition to the mild fall temperatures in most of the state, some of the wheat may be showing more fall growth and development than desirable, especially if planted earlier than the optimal planting date (Figure 2). There are reports of wheat in western Kansas in which leaves are as much as a foot long. While the crop may look great, this amount of topgrowth may in fact be more than what we would like to see at this point in the growing season.
It is important that each wheat plant produce sufficient but not excessive tillers. Wheat plants need a minimum of 1-2 tillers and 4-5 leaves to increase the likelihood of surviving the winter. An excessive number of fall tillers and lush fall development may lead to tiller competition for available resources, increased disease incidence, and other detrimental effects.
Figure 2. Wheat crop planted in early- to mid-September near Garden City. Photo by Anserd J. Foster, K-State Research and Extension.
Consequences of excessive fall growth and development
Gradually falling temperatures guide the wheat plant toward developing cold hardiness to protect against cold injury and help survive the winter. Winter wheat is most tolerant to cold temperatures during tillering stages. Excessive fall development with the crop already showing erect leaves may increase the probability of cold temperature damage during the winter and early spring. In this situation, there is good likelihood that winter injury will occur to large primary tillers and they may not survive the winter. If the growing point has emerged from below ground and is not insulated during the winter, chances are that those plants or tillers will not make it through the winter.
Depending on winter and spring weather conditions, the loss of the large primary tillers may not be all bad. The development of secondary tillers may offset the loss of the large tillers as long as the growing point and buds of main stem and tillers survive the winter. Successful development of secondary tillers will depend on moisture, nutrient, and temperature conditions during the winter and spring, and can compensate for the loss of primary tillers to a certain extent. On the other hand, if the larger tillers survive the winter, they will probably be more advanced and thus more susceptible to spring freeze damage to the developing head, which could reduce yield. Spring freezes generally occur late enough that the plants cannot compensate by forming additional tillers.
In some situations, few plants in a field may have jointed or even headed during the fall, the result of partial vernalization. For full article on partial vernalization, please see: https://webapp.agron.ksu.edu/agr_social/eu_article.throck?article_id=92/
Another serious detrimental effect of excessive fall growth is increased soil water depletion due to increased crop biomass. Plant transpiration is directly related to plant biomass. A crop with lush growth requires more maintenance moisture than a thinner canopy. Depleting soil water early during the growing season can induce late-season drought stress if the weather turns dry and the soil profile is not replenished. A wheat crop with good, but not excessive fall development, may result in more soil water being available later in the growing season; while a wheat crop with lush excessive fall growth has a greater probability for yield loss due to drought stress.
One alternative to hold the wheat back and reduce some of the lush growth is to have cattle graze the crop. Grazing will remove some of the aboveground biomass and excessive fall growth. It is important to be aware of soil moisture conditions prior to releasing cattle on the crop, though, especially following last week’s precipitation events. Releasing cattle on the wheat crop when soils are wet can cause compaction and trampling of wheat plants, ultimately decreasing stands.
A mild fall may also result in increased pest incidence, such as greenbugs, wheat curl mite, aphids, and Hessian fly; and consequently an increase in diseases vectored by some of these pests, such as wheat streak mosaic and barley yellow dwarf virus.
While this article addresses the issue of excessive fall growth and development observed in some fields across Kansas, it is important to emphasize that overall, wheat is off to a great start in Kansas. The mild temperatures should have ensured that wheat planted during the optimum planting time, as well as some of the later-planted wheat, have just enough above- and below-ground development to survive the winter. Additionally, the available moisture from the October and November precipitation events can not only promote appropriate fall growth, but also help insulate the crown from low winter temperatures.
Romulo Lollato, Wheat and Forages Extension Specialist
Anserd J. Foster, Southwest Area Agronomist