After decades of improving the soil in my garden, I have an Asian hopper worm infestation. They can eat all the organic matter in the soil, depleting it terribly. These alien invaders multiply faster than our common worms, surpassing them. Everything I’ve read about them says it’s bad news for gardeners.
Scientists are working on organic solutions to the Asian jumping worm problem. I was able to phone Brad Herrick, a researcher at the University of Wisconsin who has been studying them for years. He explained that although they arrived in the United States almost a hundred years ago, the worms are spreading rapidly and now infest 37 states. Their worst impact may be in the forest: they eat dead leaves and forest dust, potentially creating soil devoid of the organic matter that nourishes native wildflowers and trees. The soil can become sterile.
To see if you have any, start with a shaded, mulched bed – this is where they like it best. Remove the leaves or mulch your soil. The worms feed on the surface, live in the top few inches of the soil, and are easily seen on the soil surface. Touch one, and it moves fast – quite a contrast to our relatively slow regular worms. Infested areas often give the impression that coffee grounds are strewn on the ground – which is their droppings or droppings.
The clitellum that produces the egg sacs or cocoons is a whitish band near the head of the worm. This contrasts with our common worms, which have a reddish-brown clitellum that is usually a bit raised.
Herrick explained that unlike the earthworms we know and love, these types can reproduce asexually, so even a worm can trigger an infestation. But they are also spread when the cocoons, which rest on the surface of the soil, are washed away by the rains. This allows them to expand their territory quickly, especially on the hillsides.
I don’t know how I got them. They may have arrived when I bought plants for a new flower bed. I know my source of compost and I know it was heated enough to kill all the weed seeds which would have killed all the cocoons as well. And I don’t see any of the worms in my purchased compost pile. But I had work done on my septic system and soil was brought in.
According to Herrick, freezing temperatures kill all adult worms every winter. Unfortunately, this doesn’t kill the eggs, which overwinter and start the cycle again. The eggs hatch once the soil temperature reaches 50 degrees, perhaps in April or May. He said it takes 70-90 days to reach maturity, after which they start producing eggs. They continue to produce eggs from late June until frost.
If you have a new infestation, you can try to remove it by hand. Scientists often use a solution of yellow mustard powder in water to bring worms to the surface, one-third of a cup per gallon of water. But if you have a large area, it might not be practical. The best time to do this is in early summer before the new worms have reached maturity.
Herrick said you can heat the soil to kill the worms by solarizing it with clear plastic. The worms – and casts – will self-destruct at 104 degrees for three days, maybe less. Unfortunately this won’t work in forests or shady beds, that’s where I got them.
Worms can live in sunny beds if they are mulched. In fact, Herrick told me, worms have an enzyme that allows them to eat wood mulch. I’m wondering if mulching with peastone or small gravel instead of bark or leaf mulch might help reduce the problem? If they run out of food, they risk dying. This theory has not been tested and you may not like the look of stone mulch. If you do this let me know if it helps.
My worm problem, so far, only exists in a large shaded area. Here is my plan: After the frost I will rake the leaves and mulch (and collect and destroy any worms I see). The worms are usually within an inch or two of the surface. I will treat these leaves as toxic waste, as they will likely contain cocoons, which I don’t want to put in my compost pile.
I hope I can burn my rakes in the aisle to destroy the leaves and cocoons. Then I will cut all my perennials and go over the area with a flame weed killer. This is a torch attached to an eight gallon propane tank that sends out a large flame. This should burn the cocoons to the surface of the soil. Flame weeders are available from Johnny’s Selected Seeds or Fedco Seeds.
Herrick told me about a product, BotaniGard, which contains a fungus listed to kill worms. However, in a University of Vermont study that I read, it is only about 70% effective in the lab. That’s not enough for me, especially since even a tapeworm can produce viable eggs. And it sells for $ 90 a pound online.
When purchasing nursery stock look for the appearance of coffee grounds on the surface of the pot and when removing the root ball look for worms. If you see either one, don’t crash it and report the problem to the seller. Also check the purchased compost for worms. Clean your tools and shoes if you work in beds with worms – egg cocoons are tiny and not visible to the naked eye.
We will do it. Remember when we were told that impatiens plants all carry a terrible fungus and we could never grow them again? Does not occur. It’s more serious, but I think we’ll be able to deal with it.
Henry Homeyer’s blog appears twice a week on gardening-guy.com. Write to him at PO Box 364, Cornish Flat, NH 03746. Please include a stamped envelope with your address if you would like a reply by mail. Or send an email to [email protected]