Comparison of Pest Management Interactions in Spring Wheat-Cover Crop and Spring Wheat-Fallow Cropping Systems
1. Determine and compare geographically referenced distributions of wheat stem sawfly, wild oats, and root rot complex in two cropping systems, spring wheat-fallow and spring wheat-legume.
2. Quantify and compare interactions among pests on spring wheat yield and quality in the two cropping systems.
3. Identify the spatial locations of pest populations in the two cropping systems and identify pest and edaphic factor interactions that can cause variation in spring wheat yield.
4. Disseminate information and economic implications of impact of green manure cropping system on pest management using innovative methods of program delivery.
We are assessing the importance of crop diversification and pest interactions in spring wheat production systems by determining spatial associations of pest populations and crop response. Utilizing global positioning systems/geographic information systems (GPS/GIS), in eight fields we mapped insect, disease, and weed populations, nitrate and water in soil, and wheat grain yield and protein. Fields of wheat following pulses had lower levels of wheat stem sawfly infestation, soil water, soil nitrate, tiller densities, and wheat grain yield. Weed infestation and Fusarium crown rot infection were higher in wheat in rotation with alternate crops than wheat in cereal-only rotations. The 1999 crop year was characterized by low precipitation at most of our research sites, resulting in severe drought stress in grain fields following pulses.
Eight fields on three farms were surveyed on a three-quarter-acre grid system for arthropod, weed, and diseases of spring wheat grown in rotations with and without pulses or other non-cereal crops. Additionally, pre-plant soil water and nitrate, and crop stand and tiller numbers were determined at the same sampling points. Field areas mapped ranged from 40 to 56 acres. Crop yields were determined with continuous grain yield sensors mounted on the cooperators' combines. Grain samples were taken every one minute during harvest for protein analysis.
Across fields, there was reduced soil water, soil nitrate, wheat stem sawfly infestation, wheat tiller density and decreased wheat yield in wheat fields following a pulse crop compared to summer fallow. These differences likely were due to the dry growing season. As occurred in 1998, the 1999 crop year was characterized by low precipitation and extremely high temperatures in July, resulting in severe drought stress in grain fields following pulses. Densities of wheat and weed stands and Fusarium crown root were greater in wheat crops following pulses than standard cereal-only rotations. Differences were not found between cropping systems for common root rot or foliar diseases. Grain yields were similar between cropping systems at the organic production site, but yields at one conventional site were about one-third as much following a 1998 chickpea crop compared to summer fallow in 1998. This yield difference was due largely to the large decreases in available soil water and soil nitrate, along with increased weed competition. Grain protein analyses have not been completed and generalizations about the influence of cropping system on grain protein cannot be made.
Within fields, common root rot and Fusarium crown rot were positively correlated in three fields. Single fields had significant and positive correlations of foliar disease vs. Fusarium crown rot, weed density, and common root rot, Fusarium crown rot vs. wheat stem sawfly, and common root rot vs. weed density, indicating that relationships among crop pests are complex. For the six fields where determination of wheat stem sawfly infestation has been completed, WSS was not correlated with common root rot, foliar diseases, or total weed density.
Common root rot and Fusarium crown rot were negatively correlated with available soil water, but only in wheat grown in cereal rotations. Foliar disease ratings were positively and significantly correlated with available soil water, but only in wheat grown in the diverse rotations. Most correlations of pest densities or intensities with soil nitrate concentrations were nonsignificant, perhaps because water was generally the most limiting factor in 1999. Numerous other correlations were significant for pest X soil factor interactions in one case over the eight fields sampled.
As seen in1998, 1999 was another very dry year at most sites. It was notable that in recropped fields, preplant soil water only extended down to 16-20" at planting, below which a dry zone extended to about 24" in depth. Below 24", soils still held useable water but plant roots in the recropped fields were unable to penetrate through the dry zone and utilize the deeper water.
Spatial autocorrelations were significant for numerous factors, including grain yield and protein, soil water and nitrate, and several pest ratings, but not all factors were significantly correlated spatially in all fields.
Dissemination of Findings
The overall purpose and plan of the study were presented by Andy Lenssen and Bruce Maxwell to about 90 producers, consultants, and Extension personnel at a Field Day at Robert and Ann Boettcher's farm on 2 July 1999. Lenssen and Blodgett presented results from this trial at several Extension meetings in 1999, and Blodgett, Grey, and Lenssen will be presenting findings at other Cooperative Extension meetings across Montana during the upcoming winter. We likely will be one of the tour sites on the 2000 Hill County Seed Growers Association annual field tour and program. Robert Boettcher has utilized results from this trial in several presentations he gave during the past year.
Farmer Adoption and Direct Impact
Grain producers in Montana and the northern Great Plains are replacing summer fallow with pulse and oilseed crops because crop options, profitability and sustainability of the traditional wheat-summer fallow system have changed with the most recent federal farm bill.
The producer-cooperators have been crucial to conducting and developing this study. The Peterson and Grass farms are growing pulse and oilseed crops for cash sales instead of as green manures. We have changed our experimental protocols accordingly.
This summary was prepared by the project coordinator for the 2000 reporting cycle.