Owens delivers recent findings on insect crop pests

Dr. David Owens, Extension entomologist at the University of Delaware, studies control of Dectes stem borer and spider mites in soybeans among numerous other crop pests. (Photo courtesy Delaware Cooperative Extension)

HARRINGTON, Del. — Dr. David Owens, Extension entomologist at the University of Delaware, gave a insect crop pests update during the Agronomy Session of Delaware Ag Week.
A pest survey was taken in Delaware to estimate how pests affect both yield and wallet.
Owens said data from a lot of farmers and consultants was compiled.
“The three most important arthropod pests are corn ear worm, stinkbug and spider mites,” he said.
He also noted that pyrethroid is being added on about 49 percent of the acreage in Delaware when using herbicides or fungicides.
Is it worth it as a prophylactic?
“It’s cheap,” Owens said.
When it comes to seed selection, farmers may save money by reading an article entitled, “Which Bt Traits Do You Need to Purchase?” published in 2017 CropWatch at the University of Nebraska-Lincoln.
Certain proteins are only effective on certain pest species, so why pay for protection against problems you don’t have?
“We have crashed the European corn borer nationwide, Owens said, adding that n the last 10 years, it has been almost nonexistent.
“Corn root worm is not an issue on Delmarva; treatment is not needed for rotated crops.
Corn ear worm is our only major pest, and it’s not an issue in timely planted corn.”
He continued, “So, do we need Bt corn? Yes and no. We need to keep some around to keep ECB from being around. The pest does not affect vegetables much because we use Bt corn.”
White grubs and wire worms are soil pests; they are controlled by neonicotinoids.
Note that some countries require that we show the pest is present before a crop is treated with neonicotinoids.
There are two methods of sampling, done in early April: One is to compact the soil, dig a square 8 inches by 8 inches, 6 inches deep, and count the number of worms.
The other method uses bait. Dig a 4-inch deep hole, add 1 cup wheat and 1 cup corn seed, then cover with plastic.
The sun heats the soil, the seed germinates and the worms come to them.
In either case, one worm per sample is significant enough for application.
Owens said he prefers the compact soil method.
“You don’t have to wait two weeks. Where they are present, you’ll see them when you dig the hole,” he said.
In a test of Poncho Votivo corn seed treatment, half a field was planted with Poncho 250; the other half with Poncho 500.
Where Poncho 250 was used, 1.26 percent of the seedlings were damaged when examined on May 16; 1.62 percent showed damage two weeks later.
With Poncho 500, there was no evidence of damage on May 16 and 1.08 percent of seedlings had damage two weeks later.
With wire worm injury, corn plants will completely wilt and die or show yellow streaking in the center of the leaf or on the leaf edge.
The worm punches a hole in the side of the corn plant so it cannot take up nutrients, Owens said.
Spider mites are a mid-summer soybean pest, which causes yellowing leaves. “We continue to evaluate all labeled spider mite products,” Owens said. Spider mites like pokeweed, and infest the weed in vegetable crops from early to mid-June. Then they move on to field crops in July.
Dectes stem borer is another mid-summer pest. Adult counts never correlate with stem infestation, Owens said. There is no insecticide recommendation.
“It takes a lot of feeding to harm soybeans,” he continued. Sunflower trap plots were tested to see if they would keep Dectes stem borer out of soybeans.
Sunflowers were planted at the edge of fields at test stations. At the end of July, Owens said, the stem borers came out of corn and went to the sunflowers.
Later they moved on to soybeans. In some fields, the percentage of damaged stems in soybeans was minimal.
In a Lewes field, where soybeans have been grown at a dove hunting plot year after year, 100 percent of the soybean stems were infested.
August is “lep (Lepidoptera) season,” Owens said, referencing the order of insects that includes butterflies and moths.
Pheromone traps help track the corn ear worm population. “Late July and August last year saw the most active ear worm populations in years.”
Virginia Tech has been testing ear worms for pyrethroid resistance since 2003, he added.
“In July we were seeing more survivors, which indicates pyrethroids are not providing adequate field control,” Owens said. “In Georgetown, where there was infestation in one field, we tested several chemicals. All the pyrethroids worked equally well in that one field.”
The same was not true a few miles away in a sorghum field, where Warrior had a low rate of 40 to 60 percent control. If pests in a field have resistance, pyrethroids will not be able provide consistent control — and poor control leaves a significant population to eat the crop. Owens also noted that ear worms love hemp. They are very active in September and October and prefer to feed on flowers.
That will be “a huge problem” for hemp growers, he said.
Owens wrapped up his talk with these insecticide updates:
• Transform G4C sulfoxaflor (aphicide)’s supplemental label expansion now includes most field and vegetable crops except for California and New York;
• Magister G21 Fenazaquin (miticide) is now labeled for cucurbits and hops and has powdery mildew activity; and
• Federal regulators approved these pesticide products for hemp: Azadirachtin, Neem oil, and a soybean/garlic/Capsicum extract (an insecticidal soap product by Hawthorne Hydroponics).
He later added a more recent update: The miticide Zeal has been approved for use on sweet corn.