Question: My zucchini is being eaten by some kind of worm coming up through the main root, killing the plant and then moves on to the next. What can be done?
Hardiness Zone: 5a
Susan from Leon, Iowa
Answer: Susan,
It sounds like you're dealing with Squash vine borers. Signs include vines that suddenly wilt and die, and you can usually see signs of girdling and yellowish castings from borer holes at the base of stems. Adult moths have narrow, olive-brown forewings, clear hindwings and a red abdomen with black rings. There are also long, reddish fringes on the hind legs. The larvae (borers) look like white grubs with a brown head and are about 1 inch long. They bore into the vines of squash-family plants and eat the inner tissue, filling up the stems with castings and causing the vines to collapse. The larvae or pupae overwinter in the soil, emerging as adults around the time the vines start to lengthen. The adults then lay eggs on the stems or leaf stalks near the base of the plants, and when the eggs hatch the larvae bore into the vines to feed. There is usually only one generation of borers per year (two in the south), which lasts about 4-6 weeks until the larvae return to the soil for winter.
Here are some suggestions for controlling them organically:
- Interplant garlic and onion.
- Destroy crops completely in the fall and plow to destroy pupae.
- Plant tolerant cultivars. Ask your county extension agency for suggestions.
- Plant early or late to avoid peak egg-laying times. Use pheromone traps to monitor adult moths.
- Cover seedlings with floating row covers (make sure to pollinate by hand).
- Fertilize plants for vigorous growth.
- Make small slits in the vines and remove borers by hand. Cover the slits with dirt to encourage rooting.
- Release trichogramma wasps to attack eggs.
- Use parasitic nematodes around plants as mulch, or inject nematodes into bore-holes with a medicine dropper. Pack dirt around the hole when finished.
- Spray Bt (Bacillus thuringiensis) as soon as runners appear on plants.
- For severe infestations and as a last resort, spray the base of plants with rotenone or pyrethrins to kill young larvae before they can enter the vines.
Ellen
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