Asiatic Beetles: Mysterious Midnight Munchers UnMasked!
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Question. Mike: My pepper and basil plants are taking a real beating from nocturnal munching Asiatic beetles. I've been going out every night to pick them off and smoosh them. At first I was picking over 200 beetles every night, but now that it's gotten hotter and dryer, I'm only getting 10 to 30 a night. (I heard that drought prevents their eggs from maturing.) Is there anything else that I can do? I've heard that nematodes or milky spore can help for next year, but I'm loosing sleep this year. I use homemade leaf mulch on all my plants and recently discovered that the beetles burrow into the mulch in the morning to spend the day. I've found as many as 35 in the mulch under just one plant. Oh well; at least I spotted two toads in the garden last night; maybe they'll be of some help....
- ---Kevin in Great Falls, VA
Answer. Well first I have to congratulate you on successfully identifying your problem, Kev. Damage caused overnight is generally attributed to slugs and snails; and I'm very impressed that you took the time to catch the real villain in the act (and in doing so you've reminded me that not all nighttime damage IS done by slugs).
Now, people who don't already know exactly which nocturnal pest is eating their garden in the middle of the night should start with beer traps. Fill small saucers—like the half-pint-size plastic ones used for deli counter takeout —with fresh beer at sunset and place them around the plants. If there be slugs, the traps will be filled with dead ones in the morning. Then either keep filling the traps fresh every evening (slugs are not attracted to old, stale beer any more than I am) or use one of the iron phosphate products sold for slug and snail control; they're completely non-toxic to anything other than malicious mollusks and they are highly effective.
Then test for Asiatic beetles (which look like Japanese beetles, but chestnut brown in color and kind of velvety). The adults are highly attracted to artificial light, and are often found on window screens and buzzing around porch lights, so make a light trap. It doesn't have to be complex; just get a light out to the garden area and surround it with sticky stuff. You can hang flypaper around it, wrap the area around the light with double-sided tape, or hang sections of cardboard coated with a 'stickum' type material like Tangle trap under the light.
Or, as Kevin did so well, just go out into the garden a couple hours after dark and go snooping around.
He is correct that dry conditions will destroy the eggs and crescent-shaped ugly little grubs that are the immature life cycles of the scarab beetles; so don't over water. (This is especially important if you need to control any kind of beetle grubs in lawns.)
I love that Kev noticed them hiding down in the mulch during the day; slugs do this as well. Remove the mulch temporarily and lay down wooden boards or old flat pieces of scrap wood on the soil around the plants being eaten. In the morning, go out with a five gallon bucket with a few inches of soapy water in the bottom and use a piece of flat metal to scrape the beetles (and any slugs cohabitating with them) into the soapy water. Never use gasoline, kerosene or other dangerous material for this chore; soapy water works perfectly well and you won't risk destroying your garden (and groundwater) if you stumble and spill the bucket.
And rig some long-term light traps outside the garden. Not too far away, but not in the center of your plantings either; no sense leading the pests to dinner. If you have a lamppost, wrap the area underneath the mantle in sticky paper and leave the light on at night for awhile.
Milky spore powder—a naturally occurring disease organism that only affects the grubs of scarab beetles—should help. Apply it to your garden as directed, and any grubs that ingest the spores will both die and breed more of the spores when they die. The more grubs in your soil, the more quickly milky spore will control them.
Beneficial nematodes are highly effective against underground soft-bodied pests like grubs. And nematodes begin to work immediately (in a matter of weeks), not years like milky spore. Purchase the nematodes mail order and apply them to the soil as directed. Don't release them during a dry heat wave; they need moisture to survive. And don't release them in the morning or during the day; only water them into the soil after the sun goes down, so they have lots of time to get safely underground. These microscopic garden helpers will tunnel into the bodies of your grubs and destroy them; but they won't harm you, your pets, beneficial creatures or anything else in the environment.
And finally, yes—make local toads happy with a damp shady spot to hide during the day and a birdbath saucer filled with water placed flush to the ground in your garden. And use no toxic pesticides; they would harm your toads and other garden helpers. (If you wish, you can safely spray the adults with an insecticidal soap or light horticultural oil.)
Oh, and consider