URBANDALE, Iowa - Rainy weather across Iowa may result in lower average yields than projected by USDA, and soybean growers will need to be aware of several diseases to watch for in the next few weeks, according to the Iowa Soybean Association (ISA).

“Soybean growers need to watch for potential yield-lowering diseases, but thankfully, since it’s later in the growing season the potential for damage is reduced,” says Ray Gaesser, a soybean grower from Corning and president of ISA. “However, it’s important to be mindful of what diseases are present in fields so producers can take that information into consideration when choosing soybean varieties for next year.”

Gaesser also pointed out that in areas that are most waterlogged, harvest may be affected because driving in muddy fields causes tracking and compaction.

“Excessive rain is not good for Iowa soybean production,” says David Wright, ISA director of contract research.” Saturated soils are low in oxygen. Soil that is saturated for more than 48 hours is more likely to cause soybean plants to abort pods and stop seed fill, which reduces yield. In addition, the wet weather can cause an increase in soybean diseases.”

A number of soybean diseases thrive in wet weather, including white mold, which is known to cause up to 30 percent yield loss. There have also been an increased number of reports of sudden death syndrome (SDS) throughout the state. Wright says it is unclear whether the current wet weather is causing this increases occurrence of SDS, and encourages growers to be cautious when identifying the disease.

“SDS can be confused with brown stem rot, another soybean disease common to Iowa,” says Wright. “To differentiate, growers should pull or dig plants that have intervenal chlorosis and browning of the leaves and split the stem vertically. Plants infected with brown stem rot will have a brown discoloration in the middle of the stem. Plants with SDS will have white tissue in the middle of the stem and tissue on the outer edges will be brown.”

If rain continues, growers should also be on the lookout for phomopsis seed decay, a disease that causes seeds to shrivel and robs producers of profit potential.

All of these diseases can be prevented or reduced by planting resistant varieties, so soybean producers should take note of which diseases appear in their fields this year.

Growers who are unsure of what diseases they’ve found in their fields should send samples to the Plant Diagnostic Clinic at Iowa State University, 351 Bessey Hall, Ames, Iowa 50011, or contact their local certified crop advisor.

For more information about the effect of the wet August weather, contact Wright at dwright@iasoybeans.com or 515/251-8640.