Blister beetles are voracious feeders of grasshopper eggs and larvae (the good news). And now for the bad news...
If you thought grasshoppers were destructive, hold on tight. Blister beetles can wipe out a plants in a day.
What to know
- The larvae of the common blister beetles are beneficial in that they destroy grasshopper egg pods. Heavy infestations often occur during or just following a grasshopper outbreak. But they are also highly destructive.
- They lay their eggs in masses in soil where grasshoppers normally deposit eggs, and then the newly hatched larva searches for a grasshopper egg pod and gets to work feeding on it.
- The blister beetles recently found in Elbert County and in some area gardens are the ash-gray blister beetles, which feed primarily on the flowers and leaves of "high protein" plants. They are most troublesome to ranchers and farmers, as they contaminate baled hay and when ingested can be fatal to livestock.
- Adult blister beetles are attracted to blooming plants, especially alfalfa and weeds like dandelions. They also eat vegetable crops like tomatoes, corn, beans, cabbage, peas, corns, kale, potatoes, eggplants, and peppers.
- Blister beetles have an oily substance, cantharidin, in their body fluid that causes large blisters to form when a beetle is crushed on a person's skin. It is an extremely unpleasant condition and unless properly cared for, these blisters can become infected.
- The beetles may not affect everything in a garden. They can be quite selective in choosing one or two plants to go after and leave others alone (the good news). Treat the affected plant(s) only (see below), and be vigilant in observing whether they have moved to another, different plant before spraying your entire garden.
What to do if you see blister beetles in your garden/landscape
The good news is that blister beetles, should they show up in our area's fields, gardens, and landscapes, don't stay for long (two to three weeks before they move on or complete their life cycle).
In a garden setting you can knock the beetles off of plants and into a into a bucket of soapy water (be sure to use gloves). Never touch or squash a blister beetle without protection!
Neem oil mixtures (click here for our recipe) have been shown to work, but make sure that if you are you are spraying a plant that is flowering you only apply at night after pollinators are inactive.
If you are using an insecticidal soap spray, you must hit the beetles with it directly.
"Contact" insecticides such as Sevin also work but again, apply only at night when pollinators are inactive. If you are using Sevin, it is important to cut the flowers off the affected plant (includes vegetables) before applying and when bees are not actively visiting (nighttime). Then cover the plant with a fine netting for a few days to exclude any additional beetles from getting to the affected plant.
Important note regarding use of Sevin
Read the label carefully and apply the product according to the instructions on the label. Avoid using product in windy conditions and do not apply to bodies of water and watch for runoff or drift into the same. Do not spray when bees are present or active. Keep children and pets out of sprayed area until product dries.
Before applying, consider the potential effects on non-target insects.
If you have livestock, consult with CSU Extension and your veterinarian about best methods of keeping your animals safe.
Photo credit: Colorado Horse Forum