There were poor weather conditions earlier this year, particularly in the central Midwest, and that means that a lot of soybean planting was delayed until late into the season. This is a good time to check for fungal diseases among soybeans, particularly on fields that have been continuously planted with soybeans over multiple seasons – the fungi that cause a lot of these diseases can really build up on acreage that doesn’t have a crop turnover now and again.

There are a number of diseases in particular that soybean farmers should watch out for – white mold, brown stem rot, and sudden death syndrome in particular. If your crop shows signs of any of these, take remedial action as soon as you can, usually by spraying fungicide.

White mold is scientifically named “Sclerotina stem rot”, and comes from a fungus that lives in the soil. The fungus bodies in the ground are actually black, and form hard nodules called sclerotia. They can survive in soil for years, are highly resistant to heat (no heat level on your farm is going to kill them, unless you’re burning off fields), and don’t mind freezing and thawing one bit – you can see how they might make a home out of your soybean field. The infection of growing plants occurs at the time of flowering, and infection potential is made worse with high levels of moisture in the ground and in the air, cool temperatures, and lots of rain. White mold shows a white, fluffy growth that appears on the stems, along with wilted leaves and bleached stems.

Brown stem rot comes from a fungus that lives in crop residues (usually the stem) and in the soil as well. The fungus strikes when the plants are in the reproductive portion of their cycle, during cool weather, causing interveinal chlorosis (a yellowing of the leaves between the veins). This symptom of brown stem rot is worse when there is heavy rainfall keeping the plants wet all the time. Under dryer conditions, interveinal chlorosis is reduced or eliminated, and instead the leaves turn brown and dry up, but remain attached to the plant. The vascular tissues and pith of a plant with BSR are infected and have a dark brown discoloration all the way from the roots up.

Sudden death syndrome occurs a lot when the weather is cool before flowering and pod set. The fungus lives in the soil, and flourishes when the soil is wet. SDS is often found in plants growing on low spots and where the soil is compacted. Small yellow spots develop on the upper leaves, and eventually get larger and have a rotting appearance. However, the pith stays clean and white and you can definitively distinguish SDS from BSR by checking the pith.

None of these diseases are fun or easy to deal with, but early detection is the best way to keep on top of them.