Studies on cover crops and sudden death syndrome of soybean
Soybean sudden death syndrome (SDS), caused by Fusarium virguliforme, is a major soybean disease affecting soybean production in the United States. In search for more diversified cropping systems, the adoption of cover crops in the corn-soybean rotation is being encouraged. However, there is lack of information regarding the impact that cover cropping can have on SDS. On the one hand, it is possible that the improvements in soil health caused by cover crop can create an environment that is not favorable to the disease. On the other hand, F. virguliforme is able to colonize many plant species and, if a host plant is chosen as a cover crop, it is possible that inoculum will increase in the soil, therefore increasing the disease.
In order to investigate this theme, two studies were conducted to determine: 1) the susceptibility of cover crop species to F. virguliforme and 2) the effects of rye cover crop on soybean SDS in field conditions.
In the first study, several species of cover crops were inoculated with F. virguliforme in the greenhouse. All legumes species tested developed root rot symptoms and showed pathogen DNA levels associated with roots similar to soybean; thus they are considered as hosts of F. virguliforme. In general, the Brassica and grass species tested did not develop typical SDS symptoms and showed minimal or no pathogen DNA associated with roots; thus they are not considered as hosts of F. virguliforme. The second study was conducted in a long-term field trial with two treatments: winter rye cover crop and no winter rye cover crop. The plots were artificially infested with F. virguliforme. In the two years of the field trial, SDS levels were low and the rye cover crop did not affect SDS development, plant growth or yield.
The findings obtained in this study are important to help us understand the relationship between SDS and cover crop. This is the first study to report crimson clover and hairy vetch as hosts of F. virguliforme. In the field experiment, there was no effect of rye cover crop on SDS in subsequent soybean. Further studies are needed to investigate the effect of cover crops on SDS in field conditions.