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Supporting beneficial insects

There are measures you can take to protect the beneficial bug population in your field, even if you have to spray

Along with only spraying when necessary, there are several things farmers can do to protect and even encourage beneficial insects.

Making the decision to spray

If you are deciding whether or not to spray, and there is a population of beneficial insects in your field, you may be wondering how they will affect the economic threshold. Will the amount of ladybugs in the field increase the number of insect pests it takes to reach an economic threshold?

There is no fixed method for including beneficials in the count. According to Jeremy Hummel, the Plant and Soil Sciences Instructor at Lethbridge College, counting the amount of beneficial insects is not helpful for determining when to use insecticide.

Though beneficial insects help to keep insect pest populations lower, once pest populations have reached the economic threshold, beneficial insects will not bring the pests under control before the farmer’s bottom line is affected. Hummel explains.

“The natural enemies, for as valuable and important as they are, are not able to change the economic impact of the pest when that pest reaches economic injury level, and they therefore are also not considered to impact the economic threshold for the pest.”

Beneficial insects do not always control the pest population and when pests reach or exceed the economic threshold, it may be necessary to use insecticide to control the pests and prevent economic damage.

Until damaging pests reach the threshold level, it is best to leave the field alone and let the beneficial insects to do their job.

If you have to spray

Once pests have reached the economic threshold and you decide to spray, there are measures you can take to protect beneficials.

1. Consider the season. In some cases, timing spraying correctly can protect beneficials. For example, by the time wheat is flowering, wheat midge have laid their eggs and spraying won’t help. Wasps that parasitize wheat midge peak just after flowering, so spraying at that time harms them and prevents them from parasitizing the wheat midge larvae.

2. Consider the time of day. It is best to spray early in the morning to avoid contact with beneficial insects. Holly Dorchak, previously a research assistant at the Agriculture and Agri-Food Canada Lethbridge Research station. Dorchak says, “The beneficials are less active (in the morning) and less likely to come into contact with insecticide.”

Encouraging beneficials

John Gavloski, entomologist for Manitoba Agriculture, Food and Rural Initiatives, has suggested other methods for controlling pests without harming beneficials.

Plant crops that are insect-resistant to control specific pests without hurting the beneficial insects

When planning crop rotations try to provide a habitat where beneficial insects can survive. For example, including perennial forages such as alfalfa in a rotation boosts the number of beneficial insects.

Trap crops can help to control pests. For example, to control cabbage seedpod weevils, farmers can plant Polish canola along the field’s border. The Polish canola will flower about 10 days earlier than the Argentine canola, attracting pests and allowing farmers to spray a much smaller area. This solution works well in large square fields, of about a half section or larger. †

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