Resisting Insects

Arm yourself with the latest insect news from Mississippi State University (MSU) so you can be prepared to keep insects out of your soybean fields this year.

Mississippi’s top three soybean insect problems are the stink bug complex, soybean loopers and bollworms. Although severity varies by year, these are typically the top three yield robbers.

Scouting and Thresholds
Don Cook, MSU entomologist, says that farmers should scout their fields at least weekly, and he suggests scouting several areas of the field, not just the edges.

“Farmers should visually inspect the edges, middle and corners of their fields,” he says. “Walking through the field diagonally will give farmers a good idea of any problems they might have.” 

Scouting also helps detect non-insect related problems such as weed and disease issues, and nutrient deficiencies.

Once you’ve scouted the field and noticed a possible problem, the next step is to determine if treatment is necessary. Entomologists develop thresholds to help farmers determine when insect-control treatments will bring an economic benefit.

The two most common insect scouting methods used in soybeans are the sweep net and drop cloth. Both of these methods give objective measures of the insects present in the field.

“After you’ve found some insects in your fields, use the Mississippi Soybean Scouting and Management Guide, Mississippi Insect Management Guide or consult your local extension specialist to determine economic thresholds for that particular insect,” Cook says. 

Resistance Issues
Although Cook says it is too early to tell, resistant soybean loopers have caused problems in the past.

“Soybean loopers have a long history of developing resistance and are resistant to the pyrethroids, carbamates and organophosphates,” he says. 

For soybean looper management in Mississippi, experts recommend a limited number of insecticides.  

• Prevathon® (diamide)
• Besiege® (diamide plus pyrethroid)
• Steward®, Intrepid® (insect growth regulator or IGR)
• Intrepid Edge® (IGR plus spinosyn)
• Radiant® (spinosyn) 
• Blackhawk® (spinosyn) 

Prevathon and Besiege have been used extensively. However, in some cases, 2016 performance of these products was less than in previous years. Plus, in lab studies, more insects survived after exposure to these products and Intrepid when compared to previous years.

Because of this, if poor performance against soybean looper occurs, entomologists suggest that farmers use an alternative product from a different class if a second application is needed.

“Soybean looper does not overwinter here.” Cook says. “They migrate their way up through Mississippi typically in August and September from southern latitudes. Because of that, we don’t create resistance problems with insects like soybean looper, we inherit it.”