Nebraska growers have been severely affected by stripe rust in wheat crops for the last decade, particularly in the western half of the state.
Stripe rust is not necessarily a new disease but it has become much more prevalent and problematic than the other wheat rust disease (leaf rust), which has historically been our major rust disease. It was less damaging in 2017 than in some of the previous seasons, but still emerged late in the season in some isolated areas of the Panhandle. Unfortunately, when it did appear, it was too late to apply any fungicides for management. The extent of the damage in these areas right now is unknown.
Furthermore, 2017 was a horrendous year for growers with the virus disease called wheat streak mosaic. Numerous fields throughout the Panhandle were severely diseased with many being completely abandoned and not harvested. We have not seen this extent of damage from wheat streak mosaic in a number of years.
In the effort to try to reduce a repeat in 2018 from these problems, there are some steps that could be taken (or at least considered) before planting wheat in the next few weeks. These steps will not only help manage stripe rust and wheat streak mosaic, but can also assist in achieving a good stand and a healthy, vigorously growing crop prior to winter and going into dormancy.
Many of the problems on our wheat are due to stresses such as root diseases, resulting in overall weaker crops, allowing a greater degree of susceptibility when other biotic stresses arrive the following spring. The quicker the stands become established in the fall, the healthier they are before going into dormancy. This also allows better responses to additional stresses the following spring.
Five steps to consider for a producing a healthy wheat crop:
1. Planting Date. Research years ago by UNL personnel indicated that planting date recommendation 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 was to use 4,000 feet as a baseline and Sept. 10 as a base date with each 100-foot difference in elevation being one day difference in planting time.
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. 25. 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. Planting cultivars with some resistance to a disease wherever possible (stripe rust and/or wheat streak mosaic) will assist in avoiding or at least delaying infection. In general, plants that become infected later also lower their chance of suffering severe damage. Disease tolerance may also delay infection enough that a fungicide application will not be necessary, depending upon environmental conditions.
3. Planting into a firm, mellow seed bed. Chances of infection by pathogens causing the crown and root rot disease are increased by planting in a loose seedbed or one that is compacted. This puts another stress on affected plants, predisposing them to other problems later.
4. Control weeds and wheat volunteers in wheat fields and summer crops. These plants remove soil moisture resulting in greater drought stress to plants, which in turn predisposes plants to other later stresses (rot and crown infection, stripe rust, etc).
Volunteers also can serve as a reservoir (green bridge) for both curl mites and the wheat streak mosaic virus pathogen, which then 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. This is the primary factor in the high incidence and severity of virus problems in 2017. The majority of the problem fields in 2017 were associated with or near fields damaged by hail storms during 2016, without volunteer wheat control.
5. Treat seeds with an appropriate fungicide. The pathogens causing root rots (Fusarium, Rhizoctonia, Bipolaris) are naturally-occurring residents in the soil, and do not ever go away once established. When they infect early after planting in the fall, they do not always kill the plants, but can cause a subtle, often unnoticed yield drag that provides another stress predisposing plants to other problems the following spring. Fungicide treatments help the plants avoid early infection, and establishing healthy stands.