Posted 27 September 2010. PMN Crop News.
Late-Planted Soybean Vulnerable to Attack by Soybean Podworm
Source: University of Missouri Press Release. extension.missouri.edu
Blue Springs, Missouri (September 10, 2010)--Those with late-planted soybean or double-crop soybean should scout their fields immediately for soybean podworm, said a University of Missouri Extension regional agronomist.
Many fields in Missouri have elevated levels of soybean podworm, which is the same insect as the corn earworm, said Julie Abendroth. “Within the past two weeks, numerous fields throughout west-central Missouri have seen levels of this insect well above the economic threshold.”
The soybean podworm can damage leaves, stem and flowers, but pods and seeds are especially vulnerable to attack by the third-generation larvae, she said. Podworm will feed on soybean up to the R6 (full seed) growth stage; they normally do not eat R6 soybean, so R1 (flowering) through R5 (beginning seed) are the most critical stages.
If there is more than one podworm per foot of row, or if more than 5 percent of pods are damaged, treatment is recommended.
“When scouting late-planted soybean fields, examine the size of the podworms,” Abendroth said. If the majority of the worms are 1.25-1.5 inches, they will pupate soon and their damage is already done.
Damage varies from field to field, so it is very important to scout. If podworms are small and pod damage is near threshold levels, then an insecticide application is recommended. As with any input cost, producers should consider the yield potential of their fields.
“For those fields in which an insecticide treatment is warranted, both aerial and ground application are options, but it’s important to use a high gallonage of water to achieve good coverage of the soybean canopy,” she said.
For ground applications, use 15 gallons per acre and crop oil with the pyrethroid insecticide. For aerial applications, apply the insecticide with at least five gallons per acre and fly low to the crop. Time of day has shown to influence the level of control achieved. Applications made in the middle of a hot day with low volume (gallonage) were not as effective, she said.
Many pyrethroid and combination insecticide products are labeled for soybean podworm (corn earworm) in soybean; examples include Asana XL, Baythroid, Cobalt, Hero, Mustang Max, Pounce, Steward and Warrior. Comparable products may be available under different trade names. For a full listing of products labeled for this particular insect, contact your local MU Extension Center.
“It is important to treat only if warranted,” Abendroth said. “Unnecessary insecticide applications will do more harm than good, as they reduce beneficial insect populations for approximately 30 days.”
Generally, soybean podworm will feed for at least two weeks; however, if there is quite a range in the size of worms, the feeding time may extend past the two-week point. Once the larva is full grown, it will crawl down the soybean plant and pupate in the soil. The next generation of moths will emerge within 10-25 days.
For more information, see the MU Extension guide “Corn Earworm in Missouri” (G7110), available for free download at extension.missouri.edu/publications.