Planting wheat after wheat may increase pest risk

The recent run-up in wheat prices has some growers thinking that it may be lucrative to keep their winter wheat acreage up this fall. One way to do this is to seed winter wheat back into recently harvested winter wheat fields; however, this can lead to a number of pest issues. Growers should be aware of these potential problems before deciding to seed wheat back into winter wheat stubble.

Potential disease problems

Various diseases, such as tanspot, survive from one wheat crop to the next on plant residue. Crop rotation with non-host crops allows time for the wheat residue to decompose and the fungus population to decline. Without crop rotation, growers will need to use tillage to destroy or bury the crop residue prior to seeding winter wheat. Although tillage will help reduce disease pressure, it may create conditions conducive to soil loss by erosion and increase soil water loss through increased evaporation.

Other diseases that may become more problematic when wheat immediately follows wheat include common root rot and Fusarium foot rot, take-all, Cephalosporium stripe, and eyespot. Although growers who did not see any disease problems in their 2010 wheat crop may get away with seeding the 2011 wheat crop into the same field, the risk for devastating disease problems grows with each subsequent wheat crop.

Potential insect problems

Insects also may become more problematic in wheat following wheat. The wheat stem sawfly is one example. We have seen a dramatic increase in wheat stem sawfly in the Nebraska Panhandle over the last few years and believe this is at least partially due to the increased use of no-till management. The sawfly larvae overwinter at the base of the wheat stem. Winter survival is greater in no-till systems than in tilled systems. Growing wheat after wheat, especially no-till, allows the wheat stem sawfly to survive the winter in high numbers. It also allows the sawfly, which is not highly mobile and tends to just infest field edges, to move further into a field and cause greater damage.

Other insect pests that may be more problematic in wheat after wheat are wireworms, cutworms, and wheat stem maggot.

Potential weed problems

Weeds also may become problematic in wheat after wheat. The winter annual grasses are particularly troublesome. If downy brome, jointed goatgrass, or feral rye were present in the 2010 wheat crop, even at relatively low levels, they are likely to be major problems in the 2011 crop. Herbicides are available to control these weeds, but they can be expensive and reduce crop rotation options. Also, relying on the same herbicides to control weeds in wheat following wheat leads to increased selection pressure for weeds resistant to the herbicides being used. When crop rotation is used, there is an increased likelihood that alternative herbicide modes-of-action will be incorporated into the system.

Although many growers have reasonable success with a second crop of wheat following wheat, we have seen many disasters when a third crop is attempted. Growers wishing to seed winter wheat after winter wheat may wish to consider using tillage to bury crop residues and weed seeds before seeding the fall crop, although they should be aware of the soil erosion issues that tillage creates.
Economic Considerations

Growers also should realize that we are in a volatile period for grain prices and the relationship between todays grain prices and next summer’s grain prices may be small. Growers should consider whether it is wise to forego a sound crop rotation and take on the additional production risks associated with wheat following wheat for the possibility of strong wheat prices next year.