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| Control of Chrysolina Beetle on St. John’s Wort; Unidentified Beetle on Calendula |
Answered by: Conrad Richter
Question from: Ingrid Gaida
Posted on: January 25, 2004
How can I destroy the St John’s Wort beetle or interrupt their life cycle? My calendula flowers are being eaten by a greyish about 6 mm long beetle.
The products [made from] the flowers of both plants are ingested; what can I possibly use to safely, for us, destroy these beetles?
The St. John’s Wort beetle (Chrysolina hyperici) was introduced to North America to control wild St. John’s Wort in the western states and provinces of North America where the herb had become a serious weed. Many studies document the beetle’s ability to control and reduce wild St. John’s Wort populations, but I am aware of none that address the problem of the beetle inflicting damage to St. John’s Wort crops. There are a few anecdotal reports of serious damage to St. John’s Wort crops, but little on possible preventative or corrective measures.
For small outbreaks picking and destroying the beetles by hand can work. But this is not likely an option in a large production field.
Natural pest controls that are known to work on beetles (but necessarily this beetle) are diatomaceous earth and insecticidal soap formulated with pyrethrum. I would try one or both of these to start with.
At the Third Richters Commercial Herb Growing Conference in 1998, Idaho grower Tim Foley talked about the problem of Chrysolina on his St. John’s Wort crops and the solution he and his colleagues came up with. He didn’t give details, but this is what he said:
"For example, here’s how far we’ve gotten with one problem, the klamath weed beetle (Chrysolina hyperici) used to control wild St. Johnswort: we’re going to start paying the counties to drop the beetle right on top of us. Now what kind of fool sense is that? But we’ve done it. The beetle leaves our St. Johnswort crop alone because we have a foliar program that disguises our plants in the field. It’s completely organic. It was designed by a microbiologist. The beetle walks around in circles and doesn’t know where to go to eat. And yet, he’ll migrate to the woods and eradicate the wild St. Johnswort, which is as it should be since it’s not a native plant."
What Foley’s foliar program was we don’t know.
The pest attacking your calendula could be one of several species of blister-beetle. For a description, photo and other information on blister-beetles, visit:
(For the record, the pests that are known to attack calendula are blister-beetle, cabbage-looper, caterpillar, and leafhopper.)
Chemically, blister-beetles can be controlled with Sevin. But both diatomaceaous earth and insecticidal soap with pyrethrum are worth trying.