St John's Wort Beetle - Ask Extension
I have volunteer St John's Wort growing in my front yard, this is the second year I've noticed it growing. However, this year there are dark bronze co...
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St John's Wort Beetle #878052
Asked July 20, 2024, 4:12 PM EDT
I have volunteer St John's Wort growing in my front yard, this is the second year I've noticed it growing. However, this year there are dark bronze colored beetles colonizing over the plants and eating the leaves. They appear to be only on the St. John's Wort, so I am assuming it is the Agrilus hyperici. How do I effectively eliminate these beetles and keep them from returning? I'd like to keep a small section of St. John's Wort growing in my garden.
Clark County Washington
Expert Response
Good morning and thanks for using Ask Extension, Agrilus hyperici is actually a different insect (a stem borer for St. John's wort), the leaf beetle shown is either Chrysolina hyperici or Chrysolina quadrigemina. These are biological weed control agents - often intentionally released to help manage invasive weeds.
As you have noticed, they can be quite prolific once established. Row covers can be effective, but it looks like your desired plants are in a highly vegetated area. Removing the beetles by hand may be your best bet. Simply mix a very small amount of dish soap with water and pluck the beetles off into the solution and dispose.
If the population is very large, you might consider contacting Oregon Dept. of Agriculture's biocontrol program to see if they might be interested in collecting and redistributing. WSU also has a great program.
General information about the beetles
ODA Weed biocontrol program - Joel Price's contact info is at the bottom of the page
As you have noticed, they can be quite prolific once established. Row covers can be effective, but it looks like your desired plants are in a highly vegetated area. Removing the beetles by hand may be your best bet. Simply mix a very small amount of dish soap with water and pluck the beetles off into the solution and dispose.
If the population is very large, you might consider contacting Oregon Dept. of Agriculture's biocontrol program to see if they might be interested in collecting and redistributing. WSU also has a great program.
General information about the beetles
ODA Weed biocontrol program - Joel Price's contact info is at the bottom of the page
