Suppression of Soybean Diseases Through the Use of Cover Crops
Evaluations of the impact of fall cover crops (included rye, rape, canola, mustard, and fallow treatments) on diseases in spring planted soybean crops were conducted at 6 locations in Illinois in 2011. Soybean stand establishment was significantly reduced in sub-plots inoculated with the fungal pathogen Rhizoctonia in the fallow and mustard treatments, while establishment in the rye plots were similar to those in the non-inoculated plots. Other measurements of root and foliar disease severity did not show a significant impact of cover crop treatments. Pathogen and non-pathogen microbial population evaluations are being conducted.
Cover crop plots were established in the fall of 2011 in on-farm and on-station trials in three regions of Illinois (six locations in all). On-farm trial treatments included cereal rye, rape, and fallow. On-station trials included cereal rye, rape, canola, mustard, and fallow. The mustard crop winter-killed in most locations. The rye crop established well, and the rape and canola crops established well in some locations, but poorly in others, based on fall rainfall amounts. Cover crop biomass was incorporated into the soil in the on-station trials, but left standing in the on-farm trials, as this fit with the standard practices used by the farmer-cooperators. Cover crops were again established in the six locations (different fields) in the fall of 2011 to prepare for the 2012 soybean cropping season.
Soil samples were collected in the fall or early spring to establish baseline levels of soil disease suppression and microbial populations. Soybeans were planted into the plots in the spring of 2011. Preliminary bioassays of disease suppressiveness were conducted in the winter/spirng of 2011 to standardize protocols. Bioassays of samples from all six locations are now being conducted on the soil samples collected before and after incorporation of the cover crop biomass. Subsamples were collected from each soil sample (from each treatment plot) and immediately frozen at -80 C for later use in DNA analysis. DNA is being extracted from these samples and used to quantify populations of selected soybean pathogens including Fusarium virguliforme, Phytophthora sojae, Heterodera glycines, Phialophora gregata, Macrophomina phaseolina, and Colletotrichum truncatum. We are also quantifying levels of “fluorescent Psuodomonads”, bacteria that are used as indicators of biocontrol activity. So far, we have only tested the pre-cover crop soil samples in both the bioassay and DNA analysis tests, and as we expected, there were no treatment effects on either suppressiveness or the population levels. We are now starting to test the post cover crop soil samples to determine if there are any treatment differences. ARISA analysis also will be done on selected samples to determine if there are general changes in the microbial community structure as a result of cover cropping. The ARISA tests are expensive, so only a few treatments/locations will be tested.
Soybeans were planted into all treatment plots in the spring of 2011. At the University of Illinois (UIUC) on-station location, subplots were inoculated with either Rhizoctonia solani or Fusarium virguliforme by planting inoculum along with the soybean seed. Stand counts were recorded approximately two weeks after planting. In most locations there were no effects of cover crop treatment on soybean stand establishment. In the UIUC location, soybean stand counts in the Rhizoctonia solani inoculated plots were very low (<5 plants per meter) in the fallow and mustard treatment plots, while counts in the rye treatment plots were similar to those in the non-inoculated plots (>25 plants per meter). Counts in the canola and rape plots were intermediate. (10-18 plants per meter).
Plants were evaluated for foliar and root diseases in the late vegetative stages and early reproductive soybean growth stages and for vascular diseases (sudden death syndrome [SDS]and brown stem rot) in the late reproductive stages (R6). At the UIUC location there was a slight reduction in early season foliar diseases in the rye and canola plots as compared to the rape plots. No differences in late season diseases were observed a the UIUC location. At the Hunt farm, there were no differences in late season disease levels associated with cover crop treatments. At the Western Illinois University on-station location SDS severity ratings were slightly higher in the rye and mustard plots, and lowest in the canola plots. We are still waiting to receive data from Southern Illinois trials.
Impacts and Contributions/Outcomes
We have just completed one year of the field trials, and we are still analyzing the soil samples and the data collected during the growing season. We are seeing mixed results, with some impact of cover cropping, especially the rye treatments, on lowering disease levels, but not at all locations. The project has received attention from several media outlets. A press package on the project was released by the University of Illinois, College of ACES, and the story was run in several print publications, including “Prairie Farmer”. We also submitted an article on the project to the New Ag Network. Members of the research team summarized results collected thus far at winter extension meetings.
University of Wisconsin River Falls
312 Ag Science Bldg
410 S. 3rd Street
River Falls, WI 54022
Office Phone: 7154253989
Southern Illinois University Carbondale
Department of Plant, Soil Science and Agricultural Systems
Mail Code 4415
Carbondale, IL 62901
Office Phone: 6184534309