August 8, 2008

Many crops benefit from early planting. Winter wheat is not one of those crops. Nebraska research has shown that wheat planted before the recommended planting dates may not provide optimum yields, especially in areas where soil moisture is limited. In addition, planting wheat too early can lead to increased disease and insect problems.

Figure 1. Recommended planting dates for Nebraska winter wheat.

In much of Nebraska's wheat growing area, water is the most important yield limiting factor. Wheat seeded too early in the fall uses more soil water in the fall and can contribute to more freeze injury in the spring since drier soils cool down faster.

The recommended seeding dates for Nebraska's winter wheat vary substantially from one end of the state to the other - from September 1 in the extreme northwest area to October 1 in the southeast tip — and have been proven and verified through years of research and farmer experience. Some years an earlier seeding may have an advantage and some years a later date may have an advantage, but in the long term, the suggested seeding dates will give the highest average yield.

Research at UNL's West Central Research and Extension Center at North Platte found early seeded winter wheat to yield less than later planted wheat (Table 1).

The recommended seeding date represents a goal for seeding completion (Figure 1). As farm size and the number of acres increases for individual farmers, so does the length of time needed to complete seeding. The goal should be to have all the wheat planted by the ideal date. Plan your field order for planting accordingly. For example, plant higher elevation fields and those containing sandy soil first and leave lower fields and those with higher clay content until last.

Delayed Seeding

Figure 2. Effect of seeding date on performance of seed and dual placement methods of phosphorus application at three locations.

If weather conditions interfere and the seeding date is delayed by 10-14 days after the recommended planting date, apply starter fertilizer with the seed. Research has indicated that with fertilizer, later planting dates can outyield earlier dates if soil water is limited (Figure 2). Also, remember to check compliance dates for crop insurance and certification for required seeding dates.

Disease Implications

The virus diseases, wheat streak mosaic, Triticum mosaic, soilborne wheat mosaic, High Plains virus and barley yellow dwarf, thrive on early planted wheat. By planting wheat early, you provide a longer window for infection in the fall as well as a longer time for the disease to develop before winter. Both of these factors increase the incidence and severity of the disease. Also, the risk of multiple infections by more than one virus is greater.

Dual infection by two viruses such as wheat streak mosaic and High Plains, wheat streak mosaic and Triticum mosaic, or wheat streak mosaic and barley yellow dwarf can significantly reduce yields. During the 2008 growing season, some wheat samples submitted to the Plant and Pest Diagnostic Clinic tested positive for three viruses.  For information on limiting the risk of wheat streak mosaic by breaking the “green bridge” between last year’s crop and next year’s crop, see the Aug. 8 CropWatch article, Control of Pre-harvest Volunteer Wheat Critical to Virus Management.

Planting early also increases the risk of developing fall foliar diseases such as powdery mildew, leaf spots, and leaf rust. These diseases can cause significant damage especially if the winter turns out to be mild.

Insect Implications

Early planting increases the risk for several insect problems, including the wheat curl mite (vector for wheat streak mosaic), grasshoppers and Hessian flies.  Planting wheat before the recommended dates increases the time that wheat curl mites have to infest the new crop wheat and also lengthens the time that the virus is active in the plants in the fall. Both of these factors will increase the damage potential from this virus complex. (For more information, see Control of Pre-harvest Volunteer Wheat Critical to Virus Management.)

Grasshoppers, which have been prevalent around crop fields in high numbers this summer, could move to and significantly damage nearby emerging wheat fields as they clip back the small emerging wheat plants. Grasshopper populations tend to decrease through the fall, so later planting will reduce this risk from damage.

Hessian flies also can be a problem in early planted wheat. The Hessian fly spends the summer in the flaxseed stage on wheat stubble and emerges as an adult in the fall to deposit eggs for its fall generation on early seeded or volunteer wheat.  Planting after the fly-safe date allows seedlings to emerge after most adult flies have died, thus reducing the risk of significant damage.

Robert Klein
Extension Cropping Systems Specialist
West Central REC, North Platte
Stephen Wegulo
Extension Plant Pathologist, Lincoln
Gary Hein
Extension Entomologist, Panhandle REC