Climate Office - Wheat growth and development this fall in Kansas

Some regions of Kansas had a very good start to the 2016-17 wheat growing season, establishing a good stand at the optimum sowing date. These conditions were experienced in most of central, north central, and northwest Kansas. While northwest Kansas wheat is already experiencing some level of drought stress, most fields in central and north central Kansas are still in very good conditions. In the following article, I’ll discuss some of the major concerns that other regions of the state are currently facing.

Dry fall, poor emergence, and lack of secondary root development

The dry conditions prevailing in a large portion of the Kansas wheat growing region (Figure 1) has impacted secondary root development in many fields across the state. This is particularly prevalent in the southwest portion of the state, where drought has been established for months, current conditions are severe.

Figure 1. U.S. Drought monitor indication that most of the western half of Kansas is experiencing some level of drought stress. Southwest Kansas is the region where drought is more prevalent. Source: http://droughtmonitor.unl.edu/

The severe drought experienced in the southwest has impaired wheat germination and emergence in many fields. As a consequence, stands are erratic, with less than 40-50% of targeted plants per acre in many fields southwest from Finney Co. One example is shown in Figure 2 from a field around Garden City. Producers have a few options in this situation. If the seed has not started to germinate until now, chances are that they are still viable and might germinate and emerge in the spring if moisture conditions allow. Producers can then re-evaluate the conditions and consider whether to maintain the crop. It is important to realize that spring-emerged winter wheat has a much lower yield potential than fall-emerged crops, so producers have the option to consider the economic return of going with an alternative spring-planted crop (depending on any possible residual carryover concerns from herbicides applied to wheat).

Figure 2. Research plots around Garden City showing very scattered emergence. Many fields in southwest Kansas are facing similar conditions. Photo courtesy of A.J. Foster, K-State Research and Extension.

In contrast to the harsh conditions in the far southwest, fields in the west central and northwest portions of the state overall had very good emergence and stand establishment, in many cases better than last year. Still, the lack of precipitation after the crop emerged has led to a different problem: the lack of secondary root development. Figure 3 is a courtesy of Horton Seed Services, wheat producers around Leoti. This photo indicates that although the field looks uniform and with an excellent top growth, the secondary root development is very limited. Some fields in the south central portion of the state are also showing poor secondary root development, which is a concern for the crop’s winterhardiness. The lack of crown root development is due to dry topsoils. A wheat plant should ideally have a well-developed crown root system by now to help prepare it to survive the winter. Crown roots take up most of the water and nutrients from the soil, so they are very important for the plant to survive the winter.

Figure 3. Wheat field with good topgrowth but restricted secondary rooting system. Photo by Rick Horton, Horton Seed Services, Leoti, KS.

Late planted wheat following a summer crop, or delayed by October moisture

In most regions of Kansas, wheat is part of a rotation with other crops. Double-cropped wheat sown after soybeans are sown after the optimum window and will be delayed in development as compared to wheat sown at an optimal date. Many fields in central and north central Kansas fall into this category, especially with the moist 2016 summer prolonging soybean maturity in many parts of the state. In these systems, it was not uncommon for producers to sow wheat after the first of November, which might not have provided the crop enough time to tiller during the fall.

Similar situations occurred in many fields in south central Kansas, but for a different reason. Early October brought several rainfall events to south central Kansas, delaying several producers in getting their crop planted. Many producers who generally aim to have finished sowing by October 10th were still sowing wheat towards the late portion of the month in south central Kansas this year, delaying wheat development and tiller formation. Wheat needs at least 4-5 leaves and 1-2 tillers prior to winter dormancy for maximum cold tolerance. Wheat that has fewer tillers and leaves will be more susceptible to winter kill (Figure 4).

Figure 4. Differences in wheat growth and development as affected by planting date. Wheat planted late October showing no primary tillers, while wheat planted early October has started to tiller. Both crops still need significant fall growth to properly prepare for winter dormancy. Photo taken at the North Agronomy Farm, Manhattan, by Romulo Lollato, K-State Research and Extension.

What to look for?

Producers can assess the status of their wheat crop going into the winter in a few different ways. One important way is looking at the topgrowth and counting leaves and tillers. As mentioned before, wheat needs at least 4-5 leaves and 1-2 tillers prior to winter dormancy for maximum cold tolerance. Wheat that has fewer tillers and leaves will be more susceptible to winter kill (Figure 4).

It is important to look not only at the topgrowth, but at the root system development as well (Figure 5). Roots coming out from the seed are called seminal roots and are used to take up water and nutrients throughout the entire growing season. Still, there aren’t very many of these roots so their contribution to overall wheat water and nutrient uptake is limited. The two white protrusions coming out of the white area about an inch above the seed in the photo of early-October planting in Figure 5 are crown roots. These roots take up most of the water and nutrients the plant will need, and they are very important for the plant to survive the winter. If a cow were grazing on this wheat, though, she would probably pull the plant out of the ground as there aren’t many roots holding the plant in the soil yet. This wheat crop still needs considerable fall growth prior to grazing or winter dormancy.

Figure 5. Wheat seminal and crown roots development as affected by planting date. Both rooting systems are not well enough developed to be grazed, and may be susceptible to nutrient deficiencies or desiccation damage over the winter if the crown roots do not get more developed. Photos taken at the North Agronomy Farm, Manhattan, by Romulo Lollato, K-State Research and Extension.

The photos below illustrate various degrees of what you’d like to see when you examine your wheat this fall.

Figure 6. Wheat fall growth and development as affected by planting date. As expected, there is better canopy coverage with early-planted wheat for dual purpose (mid-September planting) as compared to wheat planted at the optimal planting time for grain only (mid-October planting). This does not necessarily mean the early-planted wheat is in better condition for winter, however. As long as the wheat planted in mid-October has 1-2 tillers and good crown root development (as in Figure 4B below), the plants will have adequate growth going into winter. In addition to having adequate topgrowth and root development, factors such as the extent of the plants’ cold hardening, variety differences in winterhardiness, soil moisture and temperature, and snow or plant residue protection on the soil surface will ultimately have an impact on winter survival. Photos by Romulo Lollato, K-State Research and Extension.

Figure 7. (A) Some of the crown roots are over an inch long. If the weather is mild for a couple more weeks, the roots should grow even more, which would be desirable. (B) Ideal wheat above and below ground development before winter dormancy, with crown roots fully developed and able to provide water and nutrients to the plant. With this amount of crown root development, wheat plants should be well anchored so that if cattle were grazing the wheat they couldn’t pull the plants out of the ground. Photos by Jim Shroyer, professor emeritus, K-State Research and Extension.

Romulo Lollato, Wheat and Forages Specialist
lollato@ksu.edu

Mary Knapp, Weather Data Library
mknapp@ksu.edu