Producing wheat can be a challenge some years almost anywhere in Kansas, but the reasons for those challenges are often a little different in southeast Kansas than in other regions of the state. While getting good stand establishment and early crop growth is the first challenge everywhere, ultimately the most significant factor impacting wheat yield in southeast Kansas is often excessive late-spring rainfall (Figure 1). Excessive late-season rains can happen anywhere in the state in any given year, of course, but occur more frequently in southeast Kansas than in other regions.
Figure 1. Wheat yield decreases as total rainfall during the spring increases in southeast Kansas.
That the cause of low yields many years could be related to rainfall may be a bit surprising, as adequate moisture is needed for good grain fill. While a moderate amount of rainfall benefits wheat grain development, however, the excessive late-spring rain so common in southeast Kansas decreases yield. What’s going on here?
The effects of excessive late-season rainfall on wheat
Historical averages show that in southeast Kansas there is more than a 50% chance of rain during the late spring (Figure 2). Most unfortunately, this period of high potential rainfall coincides with wheat maturation.
Late-season rains can have several effects. For one thing, high rainfall amounts in the spring limit when producers can get in the field and harvest the grain. Also, waterlogged soils during grain fill can reduce wheat yields and test weight.
Figure 2. Probability of rainfall in southeast Kansas, and wheat growth stages.
In addition, excessive spring rain contributes to elevated disease pressure, including Fusarium head blight (FHB, often called simply “scab”), stripe rust, leaf rust, tan spot, septoria leaf blotch, glume blotch, and others – all of which have been serious late-season diseases on wheat in recent years in southeast Kansas. This was recently demonstrated by the extreme FHB infestation in 2015 (Figure 3). Rainfall in 2015 was more than 7 inches above normal (Figure 4), and occurred primarily around the time of flowering.
Figure 3. Fusarium head scab in southeast Kansas, 2015. Photo by Doug Shoup, K-State Research and Extension.
Figure 4. Cumulative rainfall during the spring and early summer in southeast Kansas for 5-year average (black line), 2015 (blue line) and 2016 (red line). Arrows indicate dry spell in 2016 that coincided with wheat harvest.
Effect of persistent cloud cover and limited sunlight during grain fill
Previous research has demonstrated that wheat yields may be limited by lack of sufficient solar radiation in growing seasons when total precipitation is more than approximately 20 inches, especially when the bulk of the precipitation occurs during the interval between anthesis (flowering, which begins shortly after heading) and physiological maturity. Figure 2 shows how the average time of flowering in southeast Kansas matches well with an increased probability of rainfall – and therefore cloudy weather. Decreased solar radiation available to the crop during grain fill reduces the amount of photosynthates produced to fulfill the potential grain size originally planned by the plant, reducing grain yield and test weight.
Management considerations
There are some practical wheat management practices that can help producers overcome the problems caused by excessive late-spring rains in southeast Kansas, at least to some extent.
Variety selection. There are three important traits of wheat varieties for withstanding the late-season environmental conditions of southeast Kansas: tolerance to FHB, resistance to stripe rust and other foliar diseases, and excellent straw strength. Early maturity can also help since varieties that can be harvested early can avoid some of these late-season problems. Unfortunately, no one variety offers all of these traits, so producers have to set priorities.
Everest is currently the most widely grown variety in southeast Kansas. Part of the reason is that Everest is an early maturing variety with good straw strength, and has the strongest tolerance to FHB of any variety on the market. Even though the tolerance of Everest to FHB is limited, it’s better than other varieties. FHB is a potentially devastating disease and is difficult to manage with fungicides, so this trait is especially important in southeast Kansas. Everest is susceptible to stripe rust, however, so a foliar fungicide will often be needed. Zenda, a new K-State variety to be released as an Everest replacement, should also be a good candidate for successful performance in southeast Kansas. There are some soft wheat varieties with some level of tolerance to FHB, too.
Varieties with good overall foliar disease resistance can reduce the need for fungicides and can potentially stand better through late-season wet weather. Varieties with good inherent straw strength are also especially useful for the kind of environmental conditions common to southeast Kansas. An updated description of wheat cultivar disease ratings is available online at http://www.bookstore.ksre.ksu.edu/pubs/mf991.pdf/
Seed treatments. Fungicide seed treatments will not help wheat withstand late-season disease pressure, but they can help protect the quality of seed saved from wheat grown in this region. For example, FHB can affect the quality and viability of seed saved for next season’s plantings. Good seed cleaning and a fungicide seed treatment are warranted when saving seed after a growing season with heavy FHB incidence and severity.
Research results
To document the effect some of these management practices can have individually and in combination in protecting wheat yields in southeast Kansas, an experiment was conducted at the Southeast Research and Extension Center at Parsons in 2016. This trial compared the effect of a seed treatment alone, an in-season foliar fungicide treatment alone, and a combination of those two practices on Fusarium-infected (poor) seed and uninfected (good) seed (Figure 5).
The results showed a consistent trend towards better yield with the good quality seed compared to the poor quality seed for all fungicide treatments, including a control that had no fungicide application. These results demonstrate how important it is to test your seed for viability and vigor prior to planting.
Also, yields improved with each additional fungicide treatment.
Figure 5. Impact of fungicide treatment on wheat yield in southeast Kansas, 2016.
In 2016, the early arrival of stripe rust in addition to the cool weather in April and May amplified the foliar fungicide response. Preliminary data (Figure 5) indicates that even in a good year without excessive late-season rainfall, such as 2016, fungicide treatments can also increase yield. The 2016 harvest was blessed with a relatively long period of dry weather (May 31 through June 29 had less than ¾ inches of rain – Figure 4, between arrows), resulting in high wheat yields for the area.
Table 1. Summary of fungicide treatments and impact on yield of Everest in southeast Kansas, 2016.
|
|
|
|
Good quality seed |
Poor quality seed |
|
Treatment |
Product |
Rate |
Yield (bu/acre) |
|
|
Control |
-- |
-- |
70 |
66 |
|
Seed treatment |
Warden Cereal HR |
6 oz/100 lb |
73 |
67 |
|
Foliar fungicide |
Headline, flag leaf + Prosaro, flowering |
9 oz/acre + 6.5 oz/acre |
85 |
79 |
|
Seed treatment + foliar fungicide |
Warden Cereal HR + Headline + Prosaro |
6 oz/100 lb + 9 oz/acre + 6.6 oz/acre |
90 |
83 |
Preliminary conclusions from the 2016 research indicate that applying a foliar fungicide to Everest in a year with heavy stripe rust infections protected yield well above the economic threshold (Table 1). Everest is susceptible to stripe rust. Although this large of a yield increase is not expected every year, fungicide trials on wheat in southeast Kansas have showed similar results in past years (KSRE Report of Progress SRP1105, pages 86 and 88).
Summary
In making planting decisions for wheat in southeast Kansas, the critical components are first to select good quality seed of a variety with good resistance to the most common foliar diseases in your area, and second to consider a fungicide seed treatment. Selecting a variety with the best available tolerance to FHB is also helpful, although this limits you in fall 2016 to Everest or one of the soft wheat varieties with some tolerance to FHB – and means you’ll be more likely to need a foliar fungicide application in the spring to realize the variety’s full yield potential. Another critical step is to test the viability of any saved seed. Following up with scouting for disease presence in the spring, with treatment as needed, can also improve yields.
This research is funded in part by the Kansas Crop Improvement Association. We gratefully acknowledge the farmers who collaborate in our research program.
Gretchen Sassenrath, Agronomist, Southeast Research and Extension Center
Doug Shoup, Southeast Area Crops and Soils Specialist
Xiaomao Lin, State Climatologist, Department of Agronomy
Romulo Lollato, Wheat and Forages Specialist
Erick DeWolf, Extension Plant Pathology
dewolf1@ksu.edu
Tags: