As we progressed with our field scouting this past week, it has become evident that Soybean Vein Necrosis Virus (SVNV) is making a noticeable presence in our soybean crops across various regions. SVNV, a viral disease primarily spread by thrips, manifests typically as yellowing and necrosis along the veins of the soybean leaves. Initial symptoms include chlorotic lesions that evolve, resulting in a necrotic, vein-associated appearance. The impact of SVNV on overall yield is still under investigation, but early infection is generally more detrimental. Growers should be vigilant about thrip populations and adopt integrated pest management strategies, including the use of resistant varieties if available, to mitigate the spread of this virus.
In tandem with the rise in SVNV cases, we have also observed an uptick in Downy Mildew infections. Downy Mildew (Fig. 1), caused by the oomycete Peronospora manshurica, presents on the top of the leaves as pale green to yellow spots which can become more extensive and ultimately lead to leaves curling and becoming necrotic. On the underside, the pathogen produces a greyish, fluffy growth. This pathogen thrives in cool, moist conditions, making our recent weather patterns prime for its propagation. The disease rarely causes severe damage to a crop, but there are some reports that it has reduced seed size and quality if present early in the season and at high levels. Effective management includes crop rotation, planting clean seeds, and resistant varieties. Fungicides commonly used on soybeans are not recommended for downy mildew.
Figure 1. Leaf tops showing pale green to yellow spots (A); underside with greyish, fluffy pathogen growth (B). [Photo courtesy: Frank Becker – OSU Extension – Wayne County, Ohio]
Scouting is crucial in catching an outbreak early to implement timely control measures. By maintaining vigilant crop monitoring and adopting proactive management practices, we can efficiently tackle these diseases and safeguard our soybean yields. Walk your fields, scout for soybean diseases, and submit your samples to the Soybean Pathology and Nematology Lab at Ohio State University.
For more information on how to submit a sample to our lab, click HERE.
Mail your samples to:
OSU Soybean Pathology and Nematology Lab
Attn: Horacio Lopez-Nicora, Ph.D.
110 Kottman Hall
2021 Coffey Rd.
Columbus, Ohio 43210
lopez-nicora.1@osu.edu