by Deborah Jeanne Sergeant
Is insurance pest management worth it? That depends. Partnership for Ag Resources Management hosted “The Pros and Cons of Insurance Pest Management: The New IPM” as a recent webinar presented by Dr. Christian Krupke, a professor of entomology at Purdue University. The partnership is a project of the IPM Institute of North America Inc.
Krupke called insurance pest management “the new IPM.”
He focused his presentation on America’s top two field crops, corn (90 million acres) and soybeans (77 million acres), which most farmers rotate annually. “What we do in corn and soybeans affect one another,” Krupke said.
The majority – 85% – is Bt corn. Few U.S. corn varieties are single trait varieties; more favor several “stacked” traits. Krupke said that since all Bt corn is sold with neonicotinoid seed treatment (NST) applied, it’s important to see how that affects the environment.
“NST is effective against a broad range of insects, especially xylem (sap) feeders,” Krupke said. “Virtually all corn and most soybeans are treated with NST, usually clothianidin or thiamethoxam.” He added that the coating on a single corn kernel treated at the high rate of 1.25 mg/seed has the potential to kill 312,500 honeybees.
The USDA’s report on insecticide use in corn production from 1996 – 2010 indicates that its use is decreasing for farmers growing corn. “We’re generally using less insecticide,” Krupke said.
Ironically, the spray’s toxicity to honeybees has increased over the years, despite lower levels of use. Krupke said part of the reason chemicals affects bees is when honeybees are collecting resources. That peaks in spring, when farmers are planting, and declines by late summer and autumn.
“Bees build up friction as they fly through the air,” Krupke explained. “When they land on plants, they’re charged, and that attracts pollen to their pollen baskets.” Though that’s helpful in getting valuable pollen on bees, it also makes chemicals in the air stick to them.
“Most corn planters use air to singulate seeds on seed disks and are reliable,” Krupke said. “When using that much air, you have to exhaust that air. We’re also exhausting fragments of seeds. Corn seed is usually green, yellow or pink. The exhaust is that same color.” And the chemicals in this exhaust stick to bees.
“We knew we were carrying the materials on the seed; we just didn’t know how far it was going,” Krupke said.
Evaluating the risk includes looking at hive locations, crop type data, land cover and wind velocity. Since foraging bees move across the landscape, that makes a difference in how the residue affects them.
“All of our corn and the majority of our soybeans are treated with insecticides,” Krupke said. “What is the hazard there? Is this something we should worry about for bees, even if they’re not beside corn?”
Besides honeybees, insecticides can negatively affect other pollinators and other beneficial insects. Krupke recommended beekeepers close off their hives’ entrances on planting days and use a sprinkler on bee boxes to convince them it’s raining so they instinctively stay in for the day.
“They’ll be crabby, but it’s better than having them fly around and encountering these residues,” Krupke said.
While that may mitigate some of the damage for apiaries, it doesn’t address the welfare of non-managed hives and other insects. Krupke said strategies such as talc or graphite for seed lubrication cause little reduction in non-target exposure.
“We want it in the corn plant to protect it,” Krupke said of NST.
He said that 1% – 2% of the NST is taken up by the plant and 2% – 3% is lost as dust at planting. “Once the plant is saturated, no more will go in,” Krupke said. “If it’s raining, the material is leaching off the plant and leaving.”
Krupke also said NST can leach into water, causing more issues. He said the vast majority of neonicotinoid applied never enters target plants.
Because of that, they’re present in honey. Krupke mentioned a study of honey from six continents that showed that 75% of samples had one neonicotinoid present, 45% had two present and 10% contained four or five.
“Even in plants that honeybees are visiting, which are generally non-crop plants and are plants that are incidentally there, they’re coming in contact with these materials,” Krupke said. “It’s showing up quite prevalent in plants all over the world. Just because we find it doesn’t mean it’s important as far as a lethal dose.”
In addition to planter dust, he said that other major routes of pesticide exposure for foraging honeybees include spray application, drift of spray or dust and contaminated runoff water consumed by bees.
Neonicotinoids offer seed treatments labeled for corn rootworm, seedcorn maggot, wireworm, black cutworm and white grub, among others, but Krupke said research from 2012 shows no statistical difference between untreated and treated seeds for yield per acre. Additional studies indicate that “management practices had a greater influence than seed treatments” on yields.
“Fine-tuning your seeding rate and getting things like that right are more important than seed treatments,” Krupke added.
By minimizing pest management, farmers can “reduce the status of pests to tolerable levels while maintaining a quality environment,” Krupke said.
Krupke listed challenges for IPM, including the difficulty of monitoring and tracking target pests; gaps in knowledge on the abundances and field histories; and fear of having to use other insecticides instead of NSTs.
“Almost all insect pest management in corn and soybeans is done preventatively,” Krupke said. “Pest pressures are undocumented. Yield benefits are rarely seen. Neonicotinoid seed treatments offer a short window of pest protection, but target pests are uncommon. These two factors combine to explain infrequent observations of yield response. Universal adoption, high toxicity and high water solubility mean that environmental stewardship will remain a challenge.”
He offered as a possible solution reducing the proportion of seeds treated with insecticides, along with offering elite hybrids and varieties that with and without NST to allow in-field comparisons.