Farm Progress

In the warm and humid South, an effective fungicide program usually pays dividends beyond the cost of the fungicide. 

July 5, 2016

3 Min Read
<p>Grower in mid-season soybean field, checking pods</p>

Stop the Worm Complex

Insect damage can take a bite out of yields and profits, especially when infestations outlast insecticide control or populations develop resistance to well-used active ingredients.

Some of the most damaging pests include lepidopteran worms such as corn earworm, armyworm, European corn borer, green cloverworm, cabbage looper, soybean looper, western bean cutworm and velvetbean caterpillar. Crops may face waves of different insect species or a complex of multiple insect species, including potentially resistant populations.

Cool spring weather can delay planting while fields harbored heavy overwintering egg loads. Then, as weather warms, growers are at risk for an overwhelming number of insects hatching, developing and feeding more quickly than crops can grow. Intense heat and drought puts crops at a disadvantage as plants stop growing, but insects keep feeding.

Gus Lorenz, a University of Arkansas extension entomologist, says late-planted soybeans can be hit especially hard. “Worm pests defoliating plants can cause yield loss, but the real loss occurs when corn earworm feeds on the blooms and pods. Growers who planted soybeans late or planted double-crop soybeans this year should scout closely and be prepared to spray.”

Better Residual Control

With conventional insect-control products, keeping up with heavy insect pressure may require applications every three days, which may accelerate the rate of populations developing resistance.

“Over the past four years, worms have gotten harder to control with commonly used products,” says Brian Hayes, an independent crop consultant in Mississippi. “We’re applying every four days and still seeing huge worms.”

Hayes and other crop consultants are reporting good results with DuPont Prevathon® insect control powered by Rynaxypyr®. Registered for use on soybeans, corn, cotton, sorghum and many other crops, Prevathon® controls the key worm complex with residual control of 14 to 21 days.

Put a Stop to Resistance

“We’ve noticed an increasing number of fields with worms that appear to be resistant to pyrethroid insecticides,” says Lorenz. “Most growers now understand that resistance occurs if they use the same insecticide on the same field more than once in season. Now we are starting to see that northward migration of adult moths on weather fronts may mean that worm pests in Arkansas could represent populations that were treated with pyrethroids on fields from as far away as Texas and Mexico. If insects have been exposed to pyrethroids earlier, that may be why we are seeing some loss of control on later-season insects.”

Triple Threat

The objective for growers is to stop yield-robbing pests immediately, prevent resistance issues for the long term and avoid harm to beneficial predators and pollinators. Prevathon® with its alternative mode of action and residual control not only preserve yield, but also help address insect pest resistance challenges by reducing the need for additional applications. And Prevathon® has a favorable environmental profile, including minimal impact on beneficial insects and natural insect predators.

Yield Advantage and ROI

Compared to the untreated check plots, acres treated with Prevathon® produced 6 bushels more per acre for soybeans and 150 to 300 more pounds per acre of cotton. In combined Midwest and Mid-South large-plot field strip trials, applications of Prevathon® across corn hybrids delivered 5 to 30 more bushels per acre than grower standard insecticide programs.

The treatment threshold, or number of insects at which the cost of control will pay for itself in saved yield, is based on several factors including pest size, species, crop stage and row spacing. The University of Arkansas recently updated its advice for corn earworm treatment on soybeans in Arkansas and the Mid-South. When using a standard 15-inch diameter sweep net, the new treatment threshold for corn earworm is nine larvae per 25 sweeps. Treatment of defoliating insects is also advised at 35 to 40 percent defoliation prior to bloom and 25 percent defoliation after bloom.

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Always read and follow all label directions and precautions for use.

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