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2002 Annual Report

Insects in Dryland Cropping Systems at Briggsdale

D.J. Poss

PROBLEM: The Russian wheat aphid (RWA) has become a major pest in small grains in Colorado. Cultural, mechanical, chemical, and biological control methods are all possible. Chemical control has been the most effective. However, it is costly and is not a long term solution. Combining cultural and biological controls may be the best choice. A diverse cropping system may promote an environment in which the predators can survive.

APPROACH: In 1999 an experiment was set up near Briggsdale, Akron, and Lamar, CO to study the impact more diverse cropping systems have on RWA and its predators. This report focuses on the Briggsdale site which is located 3 miles south of Briggsdale. The plots are 0.85 acres in size. Russian wheat aphid and its predators are the primary insects we are studying. Common pests in the other crops are also monitored. The hypothesis is that with a more diverse system predatory insects (specifically those that prey on RWA) will move to prey on other crops. In a Wheat/Fallow system there is approximately a 12 week period between dry down of a wheat crop to emergence of the following crop. Most predators life cycle is much shorter than this, making it difficult for them to survive. By introducing more crops to a system there is a green bridge. In other words there is a green crop growing when there is no green wheat present that the predator insects can move into and prey on the insects in that crop. The rotations at Briggsdale include a Wheat/Fallow rotation which has been the traditional rotation in the area for decades; a Wheat/Millet/Fallow rotation which is becoming a more common rotation for the area; and a Wheat/Wheat/Corn/Corn/Sunflower/Fallow rotation. The six year rotation allows us to examine how nontraditional crops will do in this area. The two primary crops in this area are wheat and millet. It would be beneficial to the producers if we could find other crops that will grow in this area.

RESULTS: 2002 was a record dry year at Briggsdale, similar to most of Colorado. Precipitation was less than half of average during the wheat growing season and slightly over half during the corn growing season (Table 1). However, 3.65 inches of the 6.43 inches of precipitation was received in September after the corn was nearly dead. The Briggsdale area has a dry climate with the average precipitation equal to 13 inches per year. When the total is less than half the average, producing viable crops becomes very difficult.

Wheat yields were low due to the drought, ranging from zero to nearly 20 bu/ac. A nearly full soil profile of soil water allowed the wheat crop to produce the yield it did, even though the amount of precipitation received during the growing season was well below average. This is evident when looking at the stored soil water at wheat planting. Total soil water in the WF and WMF rotations was approximately 10% (Table 2). The first year wheat in the W’WCCSfF rotation also had fallow, however the crop in 2000 was sunflowers which has the ability to deplete the soil of water and nutrients to lower levels than most crops. Also, the soil in this treatment had very little cover compared to the second year wheat (wheat following wheat) which may have allowed this rotation to have approximately the same soil water at planting.

Yields for all other crops were also very low. No spring planted crops were harvested for grain. Total biomass yields were taken for all crops. Foxtail millet did well considering the drought with a yield of 1,570 lb/ac. Corn was planted into two treatments, following wheat and following corn. The corn biomass yield following corn was much better than following wheat (2,600 lb/ac vs. 930 lb/ac). If you look at the soil water at planting (Table 2) those yields correlate with biomass yield. Also, the corn in the wheat stubble was obviously better where the combine drove during wheat harvest the previous year. In this area the combine left more chaff which resulted in more cover and less evaporation in this area. Grain sorghum biomass yeilded 820 lb/ac. This was our first attempt at grain sorghum at Briggsdale. Three of the four plots had a severe witchgrass and stinkgrass infestation. The plot that had good weed control looked good enough that we may consider trying grain sorghum again in the future. Sunflowers died shortly after emergence, so no yield was taken.

Only a few insects were found in wheat in 2002. Those that were found were brown wheat mite, army cutworm, and pale western cutworm. No insects were found in the other crops. Beneficial insects are scouted for and monitored several times for each crop. No beneficial insects were found during the timed scouting periods.

For more information email: David.Poss@ColoState.edu Or call: 970-345-0513