Wallace's Farmer. IA
08-30-07
Soggy Soybeans May Yield Less
Compiled By Staff
Rainy weather across Iowa this past week may result in lower average yields
than projected by USDA for 2007. And soybean growers will need to be aware of
several diseases to watch for in the next few weeks.
"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
the Iowa Soybean Association. "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 points out that in areas that are most waterlogged, harvest may be
affected because driving in muddy fields causes tracking and compaction.
Too much rain not good for soybeans
"Excessive rain is not good for Iowa soybean production," says David Wright,
ISA's 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 of the pods, 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% yield loss. There have also been an increased
number of reports of sudden death syndrome or SDS throughout the state.
Wright says it is unclear whether the current wet weather is causing these
increases occurrence of SDS, and he encourages growers to be cautious when
identifying the disease. Correct identification is important.
"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—which is a yellowing and browning of the leaves between
the veins. Split the stem of these plants vertically. Plants that are 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 the tissue on the
outer edges will be brown."
Seed decay is another disease to watch
If rainy weather continues during the next few weeks of the growing season,
soybean 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 call him at 515/251-8640.