By Bob Harveson, Extension Plant Pathologist
Wheat crops in western Nebraska have been severely affected by stripe rust for the last decade. It is not necessarily a new disease, but it has become much more prevalent and more problematic than the other wheat rust disease (leaf rust), which previously had been our major rust disease.
In the next few weeks prior to planting wheat, growers can take several steps to manage the threat of stripe rust and help ensure a good stand and a healthy, vigorous crop goes into winter dormancy. Many wheat problems start when stress weaken crops, allowing a greater degree of susceptibility when other biotic stresses such as disease or insects arrive.
When good soil moisture is available, the quicker the stand becomes established in the fall, the healthier it’s apt to be going into dormancy and the better able to respond to additional stresses the following spring. In turn, that allows better responses to additional stresses the following spring.
To achieve a healthier wheat plant this fall consider:
- planting at the appropriate time for the location;
- using recommended cultivars with tolerance to stripe rust or other biotic stresses;
- planting into a firm yet mellow seed bed;
- controlling weeds in summer fallow or volunteers from recently harvested wheat fields; and
- treating seeds with an appropriate fungicide.
1. Planting Date
Research years ago by UNL personnel indicated that planting date recommendations should be made in relation to elevation. For areas of western Nebraska, the “rule of thumb” for planting to minimize stress and early infection of plants is to use a 4,000-foot elevation as a baseline and Sept. 10 as a base date, with each 100-foot difference in elevation being a one-day difference in planting date.
The lower the elevation, the later the best planting date. For example, Banner County (3,800 feet) would have an optimal planting date of Sept. 12. Box Butte or Cheyenne County (4,000 feet) would be Sept. 10, and Kimball County (5,100 feet) a date of Sept. 1.
2. Tolerant Cultivars
Using cultivars with some resistance to a disease (stripe rust) will help avoid or at least delay infection. In general, the later plants are infected, the lower the chance of severe damage. Using these cultivars also may delay infection enough that a fungicide application would not be necessary, depending on environmental conditions.
3. Planting Into a Firm, Mellow Seedbed
The chance of infection by pathogens that cause crown and root rot disease increases when planting into a loose or compacted seedbed. This stresses affected plants, predisposing them to other problems later.
4. Controlling Weeds and Wheat Volunteers in Wheat Fields
Weeds and volunteer wheat remove soil moisture, resulting in greater drought stress to plants, which in turn predisposes plants to later stresses (rot and crown infection, stripe rust, etc.). Volunteer wheat also can serve as a reservoir for curl mites and the wheat streak mosaic virus pathogen they transmit. This “green bridge” allows them to move into newly planted crops in the fall. Early infection by this virus will cause greater damage in spring when plants come out of dormancy and temperatures begin to rise.
5. Treating Seeds with an Appropriate Fungicide
The pathogens causing root rots (Fusarium, Rhizoctonia) are naturally occurring residents in the soil and, once established, never go away. When they infect early after planting in the fall, they do not always kill plants, but can cause a subtle, often unnoticed yield drag that can stress plants and predispose them to other problems the following spring. Fungicide treatments help the plants avoid early infection and establish healthy stands.