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Wednesday, February 5, 2020

Wireworm Update

Wireworms in the larvae stage prefer to feed on cereal crops and other grasses. Each wireworm can eat two or more seedlings a year, depending on the ambient conditions and their stage of development.

Since they can stay in the larvae stage for three to five years, fields can contain wireworms for multiple years in various stages of their life cycle. Since wireworms feed mainly on grasses, they are often found in fields that have been taken out of hay or previously cropped with cereals. They are also commonly found after summer fallow, and prefer medium-to-fine textured soils and knolls in fields. They come to the surface when the soil temperature is above +10°C, so in most cases, we start finding them in May and June. They retreat deeper into the soil when the temperatures get warmer and the soils dry out (usually around +25°C in July).

Infographic of the life cycle of click beetle. Summer eggs are laid, they hatch and become larvae. They stay as larvae for 3-5 years until they transform into adults in the fall. Adults overwinter and then emerge from the soil in the spring.

WIREWORM DAMAGE CAN OFTEN GO UNNOTICED OR BE MISDIAGNOSED, ESPECIALLY WHEN THERE IS A REDUCTION IN PLANT STAND VERSUS NOTICABLE BARE PATCHES.

Cereal field with dead patches where we can see wireworm damage.

When wireworm feeding is heavy and concentrated, you may notice bare patches in your cereal crop in well-drained, light-to-medium textured soils and on knolls (although with heavy populations, you can find them in heavier textured soils). Often you will find wireworms in the soil when you dig around the edges of the bare patches.

Plant stand counts and digging for worms is the best method to monitor wireworm populations. Wireworm-damaged seeds are often hollowed out, and seedlings can have holes/shredded stems that cause wilting and discolouration of the aboveground parts of the plant.

The other option that has been used in the past to tell if wireworms are present in a field is to use bait balls. These can be used to indicate if wireworms exist in a field and at the depth the bait ball was buried, but currently there is no economic threshold based off of bait balls. If used, ensure they are located in the sides of hills where wireworms are expected, bury them 10 to 15 cm down and in temperatures that exceed +10°C.

Click beetle and larvae in the soil.
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