Controlling Common Asparagus Beetle During Harvest Season

By Andi Anderson

The common asparagus beetle can cause significant damage during the asparagus harvest season. These pests, whose larvae hatch in late summer and overwinter in surrounding areas, emerge in spring ready to feed, mate, and lay eggs on young asparagus spears.

Effective control is crucial to reduce crop loss and maintain healthy asparagus production.

Sources of Asparagus Beetles During Harvest

In late summer, larvae, or “grubs,” hatch and feed on asparagus ferns. After they pupate in the soil, they seek overwintering sites such as loose bark or hollow asparagus stems. As temperatures warm in spring, these beetles emerge to infest fresh asparagus spears during harvest season.

Asparagus Beetle Control Strategies

Michigan State University Extension recommends several strategies for controlling asparagus beetles during the harvest season:

Apply Insecticides on Warm, Sunny Days

Asparagus beetles are generally inactive during colder weather, making it difficult to apply insecticides effectively. Apply insecticides on warm, sunny days to ensure better contact with beetles, as they become more active and more likely to come into contact with insecticide residues.

Control Beetles in the Fern Season

Effective beetle control begins in the previous year’s fern season. Beetles from the current season’s infestation emerge from the previous year’s ferns, so reducing populations during this time can help mitigate problems during harvest. Some growers apply insecticides in late summer to early fall to reduce overwintering beetle populations.

Banded Insecticide Applications

Banded applications, where insecticide is applied to a specific strip over the row, can help reduce costs. This method ensures that beetles, which move to the tips of spears, come into contact with the insecticide while reducing the overall quantity applied.

Timing Flexibility

Insecticide applications can be timed to coincide with spears at various lengths. Even if only the tip of the spear is treated, this is enough since beetles naturally move to the spear tips to feed and lay eggs. Full coverage is not necessary for effective control.

Labeled Products and Notes on Use

Several insecticides are labeled for use during the asparagus harvest season with a one-day preharvest interval. These include:

• Carbamates (1A): Carbaryl, a long-standing standard, is highly effective against both adults and egg-laying beetles. It’s recommended to use the cheapest formulation available, as spears are frequently harvested.
• Pyrethroids (3A): Permethrin can control beetles, but its effectiveness against adult beetles is limited. It’s more suitable for use during the fern season to control other pests like Japanese beetles.
• Neonicotinoids (4A): Acetamiprid is effective against both adults and egg-laying beetles, making it comparable to carbaryl in effectiveness.
• Chlorantraniliprole (28): Coragen is a newer insecticide that prevents beetles from laying eggs but does not kill them. It offers a one-day preharvest interval.
• Organic Products: Pyganic and Entrust are organic options. Pyganic has shown limited efficacy in reducing beetles but can reduce eggs. Entrust has not been effective in controlling beetles or eggs compared to untreated fields.

Additional Considerations

Excessive nutrient levels, especially nitrogen, magnesium, and potassium, can exacerbate soil compaction and attract beetles. Maintaining balanced nutrient levels and managing soil health is critical to preventing further pest issues.

By applying the right insecticides at the appropriate times and implementing effective control measures during the fern season, farmers can reduce common asparagus beetle populations and protect their harvests.

Regular monitoring and strategic application will ensure a successful, productive asparagus season.

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