The 2015 wheat growing season was plagued with severe, widespread epidemics of two diseases: stripe rust (Figure 1) and Fusarium head blight (Figure 2), also known as scab. Whereas stripe rust occurred statewide, Fusarium head blight was most severe in the southeastern, south central, and southwestern parts of Nebraska.
While these two diseases were predominant in 2015, other diseases also can cause wheat losses. They include:
- leaf spot diseases such as tan spot and Septoria tritici blotch;
- diseases affecting the grain such as common bunt (stinking smut) and loose smut;
- bacterial diseases such as bacterial streak and black chaff; and
- virus diseases such as wheat streak mosaic which was severe in localized areas in the southern Panhandle in 2015.
This article summarizes strategies that can be used in the fall to minimize losses during the 2015-16 wheat cropping season.
Figure 2. Fusarium head blight in a grower's field in southeast Nebraska in June 2015.
Use Certified, Fungicide-Treated Seed
Fungicide seed treatments reduce losses caused by seed-transmitted and soilborne fungal diseases of wheat. Some seed treatment products contain a fungicide and an insecticide and offer additional protection against fall season diseases and insect vectors of disease such as aphids. Seedborne diseases controlled by fungicide seed treatments include common bunt (also known as stinking smut) and loose smut which replace the grain on the wheat head. Other seedborne diseases do not affect the wheat head, but cause seedling blights and root and crown rots. They include scab and black point. Soilborne diseases controlled by fungicide seed treatments include Rhizoctonia and Pythium root rots, common root rot, and Fusarium root and crown rots.
This year it is especially important to use certified, fungicide-treated seed because many wheat fields in central and eastern Nebraska were affected by severe Fusarium head blight, resulting in scabby grain that, if untreated and used as seed, can result in severe damping off and seedling blight. Flag smut, which if found can prevent export of wheat grain to certain countries, can be effectively controlled with fungicide seed treatments. This year flag smut was not found in Nebraska, but was found in several counties in Kansas, including some close to the Nebraska border
Control Volunteer Wheat and Grassy Weeds Before Planting
Volunteer wheat, especially that which emerges before harvest as a result of a hailstorm, poses a high risk for wheat streak mosaic and other wheat curl mite-transmitted virus diseases of wheat (Triticum mosaic and High Plains disease). This is because the volunteer wheat serves as a host for wheat curl mites and the viruses during the period between harvest and planting in the fall. If the volunteer wheat is not controlled before planting, the mites move from it to the fall-planted wheat and transmit the viruses, resulting in severe losses the following spring/summer. The mites also can survive on grassy weeds. Volunteer wheat and grassy weeds should be controlled so they are dead at least two weeks before planting.
Plant at the Recommended Date for Your Area
Planting winter wheat too early lengthens the time when environmental conditions (warm temperatures and moisture) are favorable for development of fall season diseases such as wheat streak mosaic, barley yellow dwarf, and leaf rust. Disease-vectoring insects such as aphids and wheat curl mites have more time to transmit diseases if wheat is planted too early. Planting too late gives little time for wheat to establish itself before cold winter temperatures set in. This can result in weak plants that are vulnerable to attack by diseases in the spring. Therefore, it is recommended that winter wheat be planted at the recommended date for the respective wheat growing regions in the state (Figure 3).
Consider Disease Resistance Levels When Selecting Varieties
Some wheat varieties have good levels of resistance to certain diseases. Select varieties that have a good disease resistance package. Disease resistance information can be found in the 2015 Fall Seed Guide. Stripe rust and Fusarium head blight ratings from the 2015 state variety trials in Lancaster, Saunders, and Saline counties in southeast Nebraska are shown in Table 1 and Table 2 (below).
Plant Several Varieties That Differ in Their Genetics
Because of genetic differences, wheat varieties will react differently to diseases and some varieties will mature sooner or later than others. Planting several varieties with different genetic backgrounds, also known as variety complementation, is a strategy that can reduce losses due to diseases. For example, if only one variety is planted and it happens to be susceptible to a predominant disease during the growing season, for example stripe rust in 2015, yield loss can be much greater than if two or three varieties were planted that have different levels of resistance. Fusarium head blight is another disease that was predominant in 2015. Because there is only a short window (flowering) when the Fusarium head blight fungus infects wheat, if two or three varieties differing in flowering dates are planted, the probability that one or two of the varieties will escape heavy infections increases.
Use an Integrated Approach to Manage Wheat Diseases
Integrating all or most of the disease management strategies available to you is the most effective approach to reducing losses in winter wheat. Use as many of the strategies outlined above this fall to minimize losses during the next cropping season.
|Table 1. Stripe rust ratings in state wheat variety trials in southeast Nebraska in 2015.
Rating Scale: 1 = resistant; 9 = susceptible
|Entry||Lancaster Cnty||Saline Cnty||Saunders Cnty||Avg|
|Table 2. Fusarium head blight ratings in state wheat variety trials in southeast Nebraska in 2015.
Rating Scale: 1 = resistant; 9 = susceptible
|Entry||Lancaster Cnty||Saline Cnty||Saunders Cnty||Average|