Beware of pollinators in soybeans

As we get close to soybeans flowering across the state (growth stages R1-R2), we need to bring up an important issue related not specifically to honey bees, but to pollinators in general (albeit honey bees in soybeans is still a concern).

Although soybeans are a self-pollinated crop, generalist pollinators such as bumblebees and other solitary bees do visit soybean fields regularly during the crop’s flowering stage. These pollinators will also visit other nearby sites, offering pollinating services to other plants including flowers and if present, vegetable crops. Research out of Iowa State University indicates that many generalist pollinators make regular visits to soybeans and are at danger from insecticide sprays; researchers at the OARDC have recently joined these studies.

Luckily, there are few insect pests that reach economic levels during flowering in Ohio; almost all occur during pod development or seed fill stages (R3-R5). Thus, when following an IPM strategy, little insecticide should be sprayed at flowering because a treatment application, as we all know, should only be applied when needed, when a threshold is reached, and not applied as a preventive application.

However, we are aware that many growers are adding insecticides to spray tanks when applying fungicides for plant health purposes and even late applications of herbicides because: “Well, I’m going over the field anyway so I thought I’d add an insecticide for insurance purposes! The insecticide is relatively cheap and soybeans are worth so much!”

As we have always stated, we do not recommend this practice, and feel an IPM approach is much better for everyone and everything, including the environment and in this case, pollinators. We never recommend an insecticide application unless there is a need. And with the recent information and concern about generalist pollinators, this caution is even more important.

To illustrate this potential problem, there recently was a significant bumblebee kill in Oregon, when over 50,000 bumblebees were killed by an insecticide sprayed (in this case a material called Safari) on linden trees in a parking lot during a time period when the trees were in flower and being visited by bumblebees.

This was with an insecticide that had the warning about being highly toxic to bees on its label and the need to not spray flowering plants or trees.
Growers and applicators should remember, having read the label, that most insecticides have a statement about spraying around bees and on blooming crops. The typical statement is: “This product is highly toxic to bees exposed to direct treatment or residues on blooming crops or weeds. Do not apply this product or allow it to drift to blooming crops or weeds if bees are actively visiting the treatment area.”

We continue to advise that growers and applicators maintain good communications with bee keepers near their fields to prevent and limit unintended problems. A listing of registered apiaries can be obtained from the Ohio Department of Agriculture. The list can be requested via e-mail to the address

Applicators should avoid spraying when bees are active in the field with flowering crops or weeds. Other times to avoid spraying are from 10 a.m. to 7 p.m. or when temperatures are above 65 degrees F. On extremely hot days, bees may be active later into the evening.

Follow label precautions that relate to drift and be aware of the potential risk to neighboring crops or areas. Filter strips or other conservation areas that border fields may have flowering plants with foraging bees. Bees have a long range and can forage up to two and one-half miles from the apiary.

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