Plant Pathology
The new Illinois Soybean Checkoff Scouting Guide, which provides soybean disease and pest tips from Checkoff-funded researchers, recommends that growers observe the following scouting during the 2006 season:
April/May—After Planting
Phytophthora root rot
Other seedling diseases
Bean leaf beetles
June-September
Asian soybean rust
Early July
Soybean aphids
Frog-eye leaf spot
Mid- to Late July
Brown stem rot
Sudden death syndrome (SDS)
September-Harvest
Charcoal rot
Green stem
Harvest
Tobacco ringspot virus (bud blight)
Anytime During the Season—Post Harvest
Soybean cyst nematode (SCN)
Disease data gathered for the Varietal Information Program for Soybeans (VIPS) has been expanded to include phytophthora root rot ratings, soybean rust, and soybean mosaic virus. Soybean pathologists at the University of Illinois Urbana-Champaign collect the information for the Checkoff-funded VIPS web site to help growers with soybean variety selection.
Soybean Checkoff funds are helping support the first-ever reported research on resistance to the soybean aphid—a new pest and threat to soybean production that came from Asia to the U.S. in 2000. Aphids have the potential to directly limit soybean production—aphid feeding causes severe stunting and leaf distortion. In addition, the aphid is able to transmit certain plant viruses to soybeans, including soybean mosaic virus.
After screening several thousand soybean cultivars and germplasm accessions, University of Illinois Urbana-Champaign researchers have identified 11 ancestral soybean accessions as resistant to the aphid. Information on the inheritance, type, and molecular markers associated with resistance, along with the release of adapted, resistant germplasm, will help facilitate the development of aphid-resistant soybean cultivars. Growers will be able to reap the benefits of this research and buy aphid-resistant varieties in the not-too-distant future.
The total cost attributed to soybean aphids in Illinois in 2003 was $54 million—of which at least $12 million was for treatment and $42 million was in yield loss.
Be on the lookout for Asian soybean rust. Checkoff-funded researchers tell growers that infection can occur at any growth stage, although symptoms are most prevalent in the mid- to late growing season. Symptoms include chlorotic areas that develop into tan or brown or reddish-brown lesions on leaves. Tiny bumps occur within the lesions, and the infection eventually results in premature canopy, pod abortion, and smaller and fewer seeds. For more information, visit the Soybean Rust Pest Alert.
Soybean growers in Illinois lost as many bushels to charcoal rot in 2003 as to SCN—24.5 million bushels. University of Illinois Urbana-Champaign researcher Curt Hill says charcoal rot was a non-significant problem until 2003. Checkoff-funded scientists are evaluating seedling resistance to charcoal rot and hope to develop a multiple-screen method for the disease. In the meantime, Hill says growers concerned about charcoal rot can rotate soybeans with less susceptible hosts, reduce plant stress with lower populations, irrigate and optimize fertility, and evaluate susceptibility of chosen varieties.
Southern root-knot nematode (RKN) activity has been observed in southern Illinois for at least a decade and is most common in White, Gallatin, Saline, Pulaski, and Alexander Counties. RKN was observed as far north as Quincy in 2003. A 2003 field study revealed that yield loss was severe and generally exceeded 70% crop loss. Yield loss was not as dramatic for varieties planted at normal planting dates versus mid-June dates, although at least 30% yield loss still occurred in double-cropped fields. Southern Illinois University Carbondale soybean breeders have identified resistant germplasm used as parents. Five of 15 elite germplasm lines are resistant to RKN, and three that are commercially available to growers also house resistance to SDS and SCN. For details, visit the Southern Illinois University SDS and SCN research page.
Soybean green stem is becoming an increasingly frequent problem in Illinois. Green stem has been attributed to various causes, but Checkoff-funded researchers have reported that bean pod mottle virus (BPMV) is involved. The plant pathology research program team from Southern Illinois University Carbondale and the University of Illinois Urbana-Champaign has found correlations between foliar ratings and green stem, yield, and seed quality, indicating that BPMV causes severe leaf symptoms and green stem in greenhouse settings. Researchers are conducting large-scale commercial variety screening for resistance to BPMV in greenhouse settings as a way to provide a less expensive, faster method to screen varieties and breeding lines.