Blister Beetles

Symptoms by part

Causes

• The presence of nearby grasshopper egg masses, as the larvae of many blister beetle species feed on them.
• Warm, dry weather conditions that favor the rapid movement and feeding activity of adult swarms.
• Gardens located near uncultivated fields or pastures where the beetles naturally congregate.

Could be confused with

• Japanese Beetles · Japanese beetles have a metallic green and copper appearance, whereas blister beetles are typically longer, narrower, and have a distinct neck.
• Flea Beetles · Flea beetles are much smaller and create tiny, pinprick holes in leaves rather than the large, ragged patches caused by blister beetles.

Treatment

1. Wear thick gloves to protect your skin from the chemical the beetles release, which can cause blisters.
2. Place a bucket of soapy water beneath the infested branches to catch the beetles as you knock them off.
3. Gently shake the plant or use a small brush to dislodge the beetles directly into the soapy water.
4. Hand pick any remaining beetles using long tweezers or tongs if you prefer not to touch them.

Without chemicals

• Use row covers on young or vulnerable plants to physically block the beetles from landing.
• Remove weeds and tall grasses from the perimeter of your garden to reduce the habitat for their larvae.

Chemical options

• Spinosad, spray directly onto the foliage where beetles are feeding, follow the label.
• Pyrethrins, apply as a contact spray to the insects, follow the label.

Preventing it

• Keep your garden beds well weeded to make the area less attractive to the beetles.
• Encourage natural predators like birds and ground beetles that may feed on the larvae.
• Check your plants frequently during the peak of the warm season so you can catch a swarm before it grows.

When to act

Act immediately upon seeing a swarm to prevent rapid defoliation. If a plant has lost more than half of its foliage, it may struggle to recover, but you rarely need to remove the plant entirely.

Questions people ask

Why are they called blister beetles?

They contain a chemical called cantharidin that can cause painful blisters if the crushed insect comes into contact with your skin.

Will these beetles kill my plants?

While they can defoliate a plant quickly, most healthy plants will recover once the beetles are removed and the growing season continues.

Do I need to worry about them in my vegetable garden?

Yes, they can be quite destructive to vegetable crops, so it is best to remove them as soon as you spot them.

Plants it affects

• Siberian Pea Shrub