Soybean Disease Update – July 2, 2010

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Soybean Cyst Nematode
SCN was diagnosed this week on soybeans. If you see stunting and yellowing, carefully dig up the affected plants with a shovel or trowel and gently shake the soil from the roots. White or yellow females will be seen attached to the infected roots if present. They are small, much smaller than the nitrogen fixing nodules, but can be seen with the naked eye. A 10x hand lens makes the task much easier to see the lemon shaped females. If it is not clear what the problem is or cysts cannot be seen a soil sample of the affected area can be taken and checked for SCN or other nematodes. Test bags and more information are available at the county Extension offices and forms and info at the Plant Diagnostic Lab site at http://ag.udel.edu/extension/pdc/pdf/Nematode_Assay_taking_samples.pdf . We will be having a Soybean Cyst Nematode Workshop on August 3. See the meeting announcements for more information and registration forms.

 

Septoria Brown Spot
Septoria brown spot has not been as prevalent as last year but it has been seen in a few fields so far. It is one of the earliest fungal diseases that we see and can be found on the unifoliate leaves and the lower trifoliate leaves when it is present. Badly infected unifoliate leaves will usually fall from the plant and we will not see this disease again until the soybeans canopy and conditions would be favorable for infection. Most seasons this disease is not yield limiting.

 

Septoria brown spot on unifoliate leaves of soybean

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