Using Fungicide-Only Treated Seed and Following IPM

Ontario has experienced significant honey bee kill incidences during corn and soybean planting during the past two years. Based on the analysis conducted by PMRA the neonicotinoid (i.e. Poncho, Cruiser) seed treatments are the likely cause. To try to mitigate the risk of these incidences, best management practices (BMPs) have been implemented. As we learn more about the issue, the BMPs will be strengthened with further steps to help reduce the risk. Information on the current BMPs can be found on the OMAFRA website.

There are many components of the BMPs for reducing the risk to bees at planting. One important component is to go back to following Integrated Pest Management (IPM) and make a choice to use non-insecticide treated seed in fields that don't have a history of pest issues. Fewer fields planted with neonicotinoid seed treatments helps reduce the chance of bees coming into contact with contaminated planter dust. We have seen the use of neonicotinoid seed treatment evolve from being used on those acres that needed it for specific pest problems, to being used on nearly 100% of corn acres and 65% of soybean acres in Ontario. Not all of those acres have pest problems. Because of the risk to pollinators, some growers are considering ordering non-insecticide treated (fungicide-only) seed. Others are uncertain because they are not sure what their pest risks really are. Based on my experience, only 10 to 20% of the corn and soybean acres are actually at risk of most of the soil pests on the product labels. But where are those acres and who are most at risk?

The key soil / early-season pests that the neonicotinoid seed treatments protect corn and soybeans from include seed corn maggot, wireworms, grubs (chafer, June beetle), black cutworm, corn flea beetle, corn rootworm, bean leaf beetle and soybean aphids. Some fields are more at risk than others. So what are these risk factors?

High Risk Factors

1. Soil Type

Heavy clay soils are prone to corn rootworm infestations, but crop rotation and using rootworm Bt corn hybrids are more effective control options that should be considered. Fields with sandy soil are most likely to have grub or wireworm issues. If you look at a soil map of Ontario, the sandy soil areas very closely match our grub and wireworm hot spot areas. Wireworm and grubs can be scouted for in the early fall, since they are the same larvae that overwinter and feed on the crop in the spring. Digging in sandy knolls or in problem areas where crop emergence has been a concern can help determine their presence. Bait traps can also be used to monitor for activity. For information on how to scout for grubs and wireworms, refer to the OMAFRA website.

2. Crop Rotation

Fields following alfalfa, sod or other grassy crops (corn, wheat, etc) are prone to wireworms and grub infestations. Corn following corn is prone to corn rootworm infestations.

3. Field / Pest History

Some growers know they have a pest issue. Most growers who have grubs, know they do because even the neonicotinoid seed treatments can't protect the crop as well in heavy infestation years. Gaps in the stand are still noticeable in these situations. Growers with wireworms tend to experience this too. Early season bean leaf beetle infestations tend to be more prevalent in the 5 most southern counties of Ontario, especially those planted early and those neighbouring alfalfa fields.

Time of Planting Relative to Neighbouring Fields - The earliest fields to emerge in any given area are most attractive to bean leaf beetles (soys), black cutworm (corn) and corn flea beetles (seed corn). The latest planted corn fields from the previous year are likely to have higher corn rootworm infestations in corn the next year.

4. Mild Winters

The milder the winter, the easier it is for the beetle pests in particular to overwinter. They overwinter at the soil surface under crop debris and leaf litter. Springs following mild winters are at high risk of bean leaf beetle and corn flea beetles infestations.

5. Cool, Wet Springs/No Till Fields

Cool, wet soil conditions in the spring leads to poor crop emergence, which gives the soil insect pests in particular the upper hand. Wireworm and grub feeding can be prolonged, keeping the crop from growing ahead of the root feeding injury. Fields are more prone to seed corn maggot in cool, wet springs when the seed sits in the soil longer than usual. The risk is greater in no-till fields, deep planting situations, fields with recently applied manure or incorporated green manure. Seed corn maggot is really only a pest of soybeans, and is rarely a pest in corn in Ontario.

6. Weed Management/Cover Crops

Fields with annual weeds present in late winter / early spring (ie. chickweed) or cover crops are most attractive to black cutworm moths that will lay their eggs on this green vegetation. Fields with poor grass control harbour wireworm and grub infestations.

Soybean Aphids

Most of the soybean acreage is at risk of soybean aphids, but the majority are at risk every other year. Fields next to buckthorn and early planted fields are most at risk of early infestations, but any field can be infested later in the season. Soybean aphids are not actually controlled by the seed treatments when it counts the most, during the R1 to R5 stages of soybeans when yield is at risk. At best, the seed treatments are keeping early season infestations from starting up early. Experience has shown that Ontario's soybean aphid infestations really don't start to get out of control until around R3 or later, and it doesn't matter then if the field was treated with Cruiser or not. The 2013 season is a great example of that. The exception might be Eastern Ontario, where they do see early season infestations and threshold tends to be reached very close to early flowering (R1). In this scenario, fields treated with Cruiser tend not to need control until a few weeks later. But the Cruiser doesn't necessarily stop a spray from happening. Regardless, a foliar insecticide spray at threshold is still the only method of controlling soybean aphids during the growth stages R1 to R5.

Alternate Control Methods

There are other insecticide options for some of these pests. For corn, granular units can be installed on corn planters, and Force 3G (tefluthrin) can be used in-furrow for wireworm, rootworm and seed corn maggot. There is a cost to adding the units to the newer planters, but over a 10 year life span of a planter, it works out to about $2 per acre cost. Force 3G is currently not registered for use on grubs, though research has shown to work on European chafer. Unfortunately, there currently are no soil applied insecticide options for soybeans.

Black cutworm, bean leaf beetle, soybean aphids and corn flea beetles can be controlled by foliar insecticides, if timed correctly. Scouting for these early and spraying at threshold is very important.

Food Grade Soybeans & Seed Corn

Where I am particularly concerned is for our higher value corn and soybean crops, such as food grade soybeans and seed corn production. These crops cannot afford to be infected with viruses. Foliar insecticides tend not to adequately reduce the transmission of these viruses like the neonicotinoid seed treatments have. Bean leaf beetles can vector bean pod mottle virus to soybeans, impacting yield, quality and export opportunities. Corn flea beetles vector Stewart's wilt, which some parent lines of seed corn are susceptible to. This disease is quarantined in over 100 countries, so it can have a serious risk to seed exportation. In these crops, I still see significant value in the neonicotinoid seed treatments.

Bottom Line

I recognize the ease that insecticide seed treatments have provided, but they are insecticides and should be used for that purpose. Growers not fitting into the high risk factors may not need insecticide seed treatment, and should consider trying fungicide-only seed next year. If in doubt, plant test strips on your field to learn which fields do need protection and which do not.