CHICAGO, Illinois – Infestations of soybean aphids, sucking sap from this year’s already dry crops, threaten to shrink the size of U.S. soybean crop yields, according to agriculture experts.
Populations of the tiny aphids, which latch onto soybean plants and suck sap from the plants’ vascular systems, exploded in the U.S. Midwest after cool weather early this summer allowed the bugs to multiply more quickly than normal.
The dry, searing hot August weather has made the effects of the insects more dramatic.
In Illinois, the second-largest U.S. soybean producing state, crop experts were still tracking aphids’ effect on the state’s crop even as the insects mature and prepare to migrate.
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“The aphid population this year is much denser than we have seen in past years,” said Steve Schwoerer, extension agronomist at University of Illinois. “The question is how much damage they’re doing.”
Extremely high aphid counts in Iowa, the country’s biggest soybean producer, also led to heavy spraying of insecticides this month.
“If there are 250 aphids on every plant in the field a farmer should probably spray. We’re looking at several hundred to several thousand per plant this year,” said Mark Carlton, extension agronomist with Iowa State University.
The infestations in Illinois and Iowa were made worse by the long spell of dry weather that hit the western Midwest in August. The heat and high aphid counts left many soybean fields short and prevented pod development.
“The way they damage the plant is they suck out moisture, so the damage done by aphids is much more severe under drought conditions,” Carlton said.
Yield expectations have fallen sharply in August. On Aug. 25, the U.S. Department of Agriculture cut the percentage of the U.S. soybean crop rated good to excellent to 48 percent, down eight points from last week.
USDA early this month forecast this year’s soybean crop at 2.86 billion bushels, up from 2.73 billion last year. But since then, a major crop tour pegged the crop at 2.735 billion bu.
“Three weeks ago we were looking at yields of 50 to 55 bu., but that’s gone. Now we’re looking at 30 to 35 bu.,” Carlton said of Iowa’s soybean crop.
Yields in Illinois were now expected to average about 45 bu. per acre, a drop from previous expectations for more than 50.
Further east, Indiana and Ohio, the fourth and sixth largest producing states, were also spotting aphids.
But the numbers were smaller than in the more western states and agronomists said most plants were mature enough to prevent much more damage.
“They’re everywhere, but in general I don’t think counts are high enough to justify spraying,” said Ellsworth Christmas, agronomist with Purdue University.
“The further you go into the season, the less damage aphids are going to cause in terms of yield loss.”
Ohio agronomists noted that aphid populations are beginning to thin as the insects develop wings and start mass migration out of the soybean fields.
