After-harvest Wheat Disease Management Strategies for Reducing Losses in 2024
Every growing season is different when it comes to the diseases that occur in Nebraska wheat fields and the levels to which the diseases develop. This year we had drought-like conditions in the eastern part of the state, resulting in little disease development. In western Nebraska, however, frequent rainfall led to the development of fungal leaf spots, mainly tan spot (Figure 1) and Septoria leaf blotch, and Fusarium head blight (Figure 2). Wheat streak mosaic (Figure 3) was also observed at high levels in one field in the southern Panhandle. Stripe rust (Figure 4) and leaf rust (Figure 5) arrived late in the growing season and did not develop to damaging levels.
Although not observed at economically significant levels this year, seed transmitted diseases affecting the grain such as common bunt (stinking smut, Figure 6) and loose smut (Figure 7) can occur and cause significant losses during any growing season.
This article summarizes strategies that can be used between now and planting winter wheat this fall to minimize losses due to diseases during next year’s growing season.
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 with fungal spores on the wheat head. Flag smut (Figure 8) — which, if found, can prevent export of wheat grain to certain countries — can be effectively controlled with fungicide seed treatments. Other seedborne diseases do not affect the wheat head but cause seedling blights and root and crown rots. They include Fusarium head blight 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 some wheat fields in western Nebraska were affected by Fusarium head blight, resulting in scabby grain that, if untreated and used as seed, can result in severe damping off and seedling blight.
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 wheat mosaic). 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 growing season. The mites can also survive on grassy weeds. Volunteer wheat and grassy weeds should be controlled so that they are completely 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, stripe rust, leaf rust, and root and crown rots. Wheat curl mites and insect vectors of diseases — for example, aphids — 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 winter kill and 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 9).
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 Fall Seed Guide and brochures provided by private companies.
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 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, yield loss can be much greater than if two or three varieties were planted that have different levels of resistance. Because there is only a short window (flowering) during which 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 between now and planting in the fall to minimize losses during next year’s wheat growing season.