Getting Rid of Cut Worms

(Question)

Dear Sir or Madam,

I have an allotment garden here in Toronto which I have been tending for over 10 years. I specialize in growing heirloom tomatoes. In the last two years I have noticed some cut worms in my soil. Approx. 1 to 1 1/2 inches long, pale yellow/green colour. They are back again this year. Killed three of them this morning. They did some damage to my heirloom tomato seedlings last year. Eating into one of my plants at ground level until it toppled over and died. I want to get rid of them before I plant at the end of May. A gentleman at Sheridan Nurseries told me to use Nematodes. I had no idea what they were but he explained to me that they feed on cut worms and would do the trick. I am totally unfamiliar with Nematodes. Some of the things I have read about them are a bit scary. So I am not sure what to do. Do Nematodes really get rid of cutr worms? Would Nematodes be ok to introduce into my soil? Will they harm my expensive heirloom tomato seedlings or other plants in my garden? Any advice you have on Nematodes and their suitability for my problem would be much appreciated.

Thank You
Brian Smuck
Toronto

 

(Answer)

Thank for contacting the Toronto Master Gardeners.

Cutworms are caterpillars, but they are often mistaken for grubs. In fact cutworms are the larvae of several types of moths. Eggs that hatch in the fall produce larvae capable of overwintering in the soil. These pests do the most damage early in the gardening season (early-mid spring), when they emerge from hibernation. The moth larvae hide under leaf litter or soil during the day, coming out in the dark to feed on your plants.They typically attack the first part of the plant it encounters, namely the stem of a seedling, and consequently cuts it down.

There are a number of things that you can do to block this pest from gaining easy access to your plants. Placing circles of abrasive material such as crushed egg shells or diatomaceous earth around the stems of the plants will deter crawling pests. Diatomaceous earth is made from the fossilized remains of tiny aquatic creatures called “diatoms”. This powder scratches the the bodies of the insects as they crawl over it, causing them to dehydrate and die.

Creating a physical barrier around your seedlings will prevent the cutworms from crawling close and feeding. This can be as simple as a cardboard collar, styrofoam cups/plastic containers with the bottoms cut out or collars of aluminum foil. Whatever you use, just make sure that the barrier completely surrounds the stem and are set 2.5cm deep in the soil.

Lastly “beneficial nematodes” can be used for the biological control of soil insect pests.  While lethal to several different types of soil-dwelling insects, beneficial nematodes are completely harmless to plants, animals and humans, and are an effective and safe alternative to chemical pesticides. Nematodes are microscopic worms that parasitize many types of soil-dwelling insects including cutworms and Japanese beetle grubs.

Nematodes can be applied anytime but should typically be timed with the lifecycle of the target pest and soil temperatures.  Optimal soil temperatures vary for each species of beneficial nematode, but generally fall within about 20C to 28C (70F to 83F), so application is typically done in the spring and autumn.

Nematodes have a limited “shelf life” in their transportation containers.  Most suppliers recommend that the nematodes be applied within two weeks of receipt.  Before application, nematodes should be stored in a fridge.   Most suppliers recommend two applications about 7 to 10 days apart. Check with your suppliers’ specific recommendations for storage, viability and application.

Be sure to follow the instructions on the package, in particular to water before and after the application as the nematodes need moisture to make their way into the soil.  It is also best to apply them on an overcast day or in the early evening to help keep the nematodes from drying out.

This link gives additional information on nematodes as a biological control for cutworms.

Armed with all the above strategies you should see a decrease in your cutworm population and be able to enjoy a bountiful harvest.