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Subhead: Soybean aphid threshold questioned

Fond du Lac — Because of possible effects on pollinator insects, the federal Environmental Protection Agency (EPA) is reviewing the use of the insecticides with neonics as their active ingredient.

That could result in labeling changes and re-registration procedures for those insecticides by 2017 or 2018, University of Wisconsin Extension Service entomologist Bryan Jensen told attendees at the 2016 series of pest management updates. The products are those used as seed treatments on soybeans and corn or as a foliar treatment on soybeans to control aphids, he explained.

Suspension of Transform WG

As an indication of what could be ahead, Jensen pointed to the EPA's vacation a year ago of all the registrations for Transform WG (sulfoxaflor), which had received a registration approval in May of 2013. He described the suspension of the registration as an “unusual action” but noted it came in the wake of a ruling by the federal 9th circuit court of appeals that was based on wanting more information about the impact on pollinators.

Transform WG provided a mode of action for controlling piercing and sucking insects that was different than the mode for neonics, pyrethroids, and organophosphates, Jensen indicated. According to a 2016 update by Dow AgroSciences, Transform WG is no longer labeled for use on soybeans, he reported.

The labeling change limits use of Transform WG to crops which do not attract pollinators. Those crops include small grains, succulents, dry beans, and others which are harvested before they bloom. The labeling changes increase the restrictions on field borders and wind speed at the time of application, Jensen noted.

Lorsban uncertainty

The current labeled practices for Lorsban, for which chlorpyrifos is the active ingredient, are also under EPA review, Jensen continued. He said the 9th circuit court has ordered a decision by the end of 2016 but that the EPA is seeking a time extension.

Uncertainty reigns about what the EPA's decision will be, Jensen remarked. He explained that the concerns with Lorsban, which controls aphids and mites, are about contamination of drinking water in areas of high use and about residues on food.

Soybean aphid thresholds

The Extension Service's threshold on predicting economic losses from soybean aphid populations was questioned this summer by an entity in the private sector, Jensen reported. The challenge was based on an expressed possibility of transmitting fungal and bacterial diseases, the leaking of plant sap, the relatively low cost of insecticides, and a rise in soybean prices since the threshold was set in 2007, he said.

That threshold is a minimum of 250 aphids on at least 80 percent of the soybean plants with a documented rate of increase in the population, Jensen pointed out. The private entity asked to have that threshold lowered to 10 to 20 aphids per plant.

Based on multiple years of observations at many sites around the Midwest, Jensen indicated that there is no evidence that soybean aphids transmit fungal or bacterial diseases, that soybeans do not leak sap as a result of aphid feeding, and that there is no published research data verifying economic losses with infestations below 250 per plant.

While agreeing that insecticide costs are low, Jensen suggested that unnecessary applications would kill beneficial insects, cause wheel traffic losses, create a false sense of security, and possibly have the reverse effect of a soybean aphid resurgence or an outbreak of mite or two-spotted spider infestations because of the elimination of predator species.

Uncovering the slugs

Jensen also reviewed the potential damage caused by slugs, particularly in heavy and wet soils and in no-till or minimal tillage situations. During 2016, he noted that problems were minimal with plant seedlings early in the season but that warm temperatures supported some high populations well into the autumn.

It's not easy to control existing populations of gray field slugs and the less familiar and smaller dark marsh slugs, Jensen observed. Where possible, tillage will make a difference, he said. Early planting will allow plants to outgrow slug feeding, closing seed furrows will deter the offering of an ideal habitat, and using any baits labeled for Wisconsin crops are other options, he advised.

A new concern with slugs has arisen with the surface broadcasting of cereal rye seed into standing corn or soybeans, Jensen pointed out. To avoid the known instances of damage to 25 percent of the seeds with 24 hours or almost all of it within a week, he said the alternatives are to scout for slug populations before seeding and to delay the planting until after the crop is harvested so the seed can drilled into the ground.

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