Features Agronomy Insect Pests
Variable weather and finding solutions to increased European corn borer pressure

European corn borer larvae move in and out of the stalk. That might not seem like too bold a statement, but for a grower caught by an unexpected explosion of ECB pressure, this news can save a crop.

ECB pressure across the Maritimes and through the northeastern United States has been increasing. The mild winter of 2009/2010 did not help. “With the recent milder winters we’ve had more larvae survive the winter than in the past,” says Jim Dwyer, the University of Maine’s area crops specialist based in Presque Isle. “The larvae overwinter in the stalks.”

Several fields in Maine were hit hard with ECB in 2010. “If you have a significant insect population and add drought on top of that, you can get a significant yield impact,” says Dwyer. “Fields that had significant ECB activity saw a lot of crow damage, such as shredded vines, as they went after the larvae. In a couple of fields the bird damage as a result of ECB was more significant than the damage from the ECB themselves.”

Dwyer and other researchers have a theory that the increase in ECB pressure is partly due to the decrease in foliar-applied insecticides. “Historically, as we applied foliar materials for control of Colorado potato beetle, unknowingly we were controlling ECB too,” says Dwyer. “We’re not applying the foliar materials for CPB control in late June and early July like we used to, and ECB has become a significant issue for us.”

That is what Dr. Christine Noronha, an entomologist with Agriculture and Agri-food Canada in Charlottetown, Prince Edward Island, also sees. “In the last 15 years (since about 1995) we started to see an increase, and by 2002, growers were seeing significant damage.”

Changes in weather patterns are not only affecting ECB overwintering; variable summer temperatures are making it harder for consultants when it comes to recommending whether or not to spray a crop. Danny Blanchette is a crop consultant with the Grand Falls Agromart in Grand Falls, New Brunswick. In 2010, he stood in a field of potatoes that was on the verge of being decimated by ECB. Temperatures had gone from consistently cold to hot very quickly. “I’ve never seen anything like it,” says Blanchette. Both he and the processor were scouting. “I’ve never seen it go from so cold to so hot so quickly. We couldn’t even find the eggs or the hatch. It was done in a week and a half. The moths came in and laid eggs before we could monitor.”

“Typically, we try to get material out to control the larvae,” says Dwyer. “That gives us a three-day window, from egg hatch to when they enter the plant. Within that window the larvae are extremely vulnerable. Assail (acetamiprid) has some ovicidal activity to control eggs. Pyrethroids do a good job of controlling the larvae. Coragen (rynaxypyr) does a good job of controlling the larvae and is a translaminar material with a longer residual.”

Dwyer admits that it can be difficult to hit the right timing, especially for growers farming a large number of acres. 

“We usually spray when the eggs hatch,” says Blanchette. But the larvae got into the stalks of the potato plants and everything looked dire.

Blanchette spoke to Dwyer in Maine, who recommended Coragen, an insecticide from Group 28, the Anthranilic diamides. It causes both rapid cessation of feeding but also has excellent residual, multi-stage control of ECB.

Advantages of residuals
ECB has an Achilles heel that growers can use to their advantage. The pest tends to enter and exit the stalk multiple times. When a product has a longer residual, the ECB pick up the material as they exit the stalk. Dwyer has seen a residual insecticide work in the past in fields that appeared too far gone. “We have seen between 60 and 70 percent control of the larvae after they had entered the plant,” says Dwyer. “Historically, once larvae have entered the plant, we’ve had a tough time getting material to them. I was pleased.”

The field in New Brunswick was saved and produced 250 barrels to the acre. Blanchette estimates that the plants would have died and the field would have produced 150 barrels without the spray. “We were shaking ECB carcasses out of the holes in the stems,” he says.

Timing of application is still key but Jim Irish, specialty products manager at DuPont, says it is important to know that ECB moves in and out of the stalk. “With its unique properties, we see why Coragen widens the window of application,” he says. “Along with the extended residual and translaminar activity, Coragen controls hatching insects all the way through to adult stages. These are huge benefits when trying to control ECB, and Coragen often replaces two or three applications.”

It is important to use a product that controls ECB at various stages. Egg hatch can vary tremendously from farm to farm, says Dwyer. When a grower sees dramatic weather change like that, Dwyer says eggs can hatch in as few as three days. It helps to have a product that controls insects at various stages while trying to get fields sprayed at the right time.

A sudden hot spell can cause complications. But during a cold summer, the egg-hatch season can spread over a much longer time period. “During cold summers, the moths keep laying eggs for a longer period of time,” says Noronha. She says sudden temperature spikes can cause a sharp increase in egg laying.

Brian Beaton, potato co-ordinator with the PEI Department of Agriculture, remembers 2009 when people were scouting and not doing cumulative counts. People made the mistake of scouting and counting egg masses one week and then starting from zero the next week. “The summer was cool overall,” says Beaton. “The moths were laying and hatching at different times during a three-week period. People were doing their counts for egg masses but they should have added all the counts together.”

In 2010, Beaton says it was drier and hotter than in 2009 and there was a faster, shorter flush of hatching.

It seems that variable weather is here to stay. Therefore, growers would be advised to consider their insecticides carefully to give themselves some extra breathing room to control ECB.