Early-season soybean pests could be a challenge
Concern about early-season bean leaf beetles, spider mites and soybean aphids might be heightened this year with the weather that has been messing with farmers, but also causing crop consultants and ag retailer agronomists problems.
A large amount of vegetation has grown in most fields, and some of this vegetation is ideal for hosting early-season insects. The busy spring makes it unlikely that all the fields in a company’s service area can be scouted for pests within the short period of time that farmers are pushing to plant.
Therefore, if one field in an area is heavily infested, the common sense recommendation is to spray similar fields. When a field is sprayed with a burndown herbicide mix, it can make a lot of economic sense to put an inexpensive insecticide in the tank, too, to take care of those first emerging insects that are out there feeding.
Extension specialists in the Corn Belt talk Integrated Pest Management, but this approach might need modified as the planting window has everyone pushing to get their beans in the ground as fast as possible. Annually, the adult bean leaf beetle emerges first, but this year there could be more than the adult bean leaf beetle waiting to attack. Late planted soybeans can be susceptible to more insect damage.
In Wisconsin, the Extension service has been informing farmers that “switching to an earlier maturing variety when planting after the first week of June will reduce the chance of damage from an early fall frost.” Mentioning planting that late puts most farmers in a panic, just after they’ve worried about getting their corn in the ground.
Emerson Nafziger at the University of Illinois issued a warning that a 15 percent loss of a soybean yield occurs if soybeans aren’t planted by the end of May in most of the state; that compares to a 25 percent loss in yield for corn not planted by that timeframe.
While growers haven’t been able to get around to planting all their beans and corn, the bean leaf beetle has been emerging. Bean leaf beetles overwinter in leaf litter and appreciate snow cover compared to an open winter.
Erin Hodgson and Adam Sisson, Department of Entomology at Iowa State University, report the past winter was better for bean leaf beetle survival than last year or the 24 year average in Central Iowa. They are predicting the survivorship is greater than 29 percent, which doesn’t sound very large, but it is a problem considering the huge number of bean leaf beetles that populate fields and borders every summer.
As the entomologists note, overwintering adults are strongly attracted to soybeans and will move into fields with newly emerged soybean plants, but they will feed on other hosts waiting for the soybeans.
According to the specialists, scouting for the pest isn’t the easiest. “Bean leaf beetle is easily disturbed and will drop from plants and seek shelter in soil cracks and under debris. Sampling early in the season requires you to be sneaky to estimate actual densities. Although overwintering beetles rarely cause economic damage, their presence may be an indicator of building first and second generations later in the season.”
Those first and second generation bean leaf beetle, soybean aphid, spider mites and Japanese beetles that have had a jump on emerging ahead of the crop could easily build from early-season to late-season levels.
Dave Rummel, MANA insecticide brand leader, said, “Ag retailers and crop consultants need to be recommending something that has knockdown ability for heavy insect pressure but also has residual effect or systemic control to help farmers get through the season. I think it is going to be an interestingly challenging year.”
He added, “Looking down the road, a residual or systemic product that has contact chemistry, too, is going to be very important because the grower needs to spray to knock down what is present and have systemic control in the plant so that as insect pressure rebuilds or new species of insects appear there is systemic control in the leaves.”