Beetles and Loopers and Slugs, Oh My….

For you vegetable gardeners who are early planters- peas, potatoes, brassicas (cabbage, cauliflower, etc), lettuce, spinach and a few other crops should be up and growing.  Now let’s talk about three of the most common garden insect pests. These are the Colorado Potato Beetle, the White Cabbage Moth, sometimes called a Cabbage Looper because of its erratic flight pattern, and the common Garden Slug.

The Colorado Potato Beetle over winters as an adult in the soil. Adults become active in May and will start to lay eggs as soon as they can find host plants. Adult beetles are yellow with ten black longitudinal stripes on their rounded wing covers. They are about 3/8 inch long and lay clumps of 20 to 40 yellow-orange eggs on the undersides of  leaves. These eggs hatch in 4 to 15 days depending upon temperature. The ugly red-brown larvae have six legs and have two rows of black spots on each side. They are about 1/8 to 1/2 inch long.

Both larvae and adults feed on the foliage and can cause extensive damage. The beetles prefer potato plants but will also attack eggplant, husk tomatoes, and tomatoes.

Hand-picking the adults or larvae is possible on small plantings. Get a piece of white cloth or paper about 18 inches square with a cut from one edge to the center.  Slip the cut around the potato plant stem and give the plant a light shake,  Adult beetles will drop onto the cloth where they can be picked by hand.  You can do this without the cloth by attempting to grab the beetles from the leaves but as soon as an adult beetle is allowed to drop into the soil or mulch, it is  almost impossible to find. Larvae can be squashed against the leaves between your fingers if you’re not squeamish.

Two strains of Bacillus thuringiensis, or B.t. for short, are effective against potato beetle larvae. They are sold under the names M-One and Trident. Bacillus thuringiensis is safe for mammals, birds, fish, and beneficial insects. Make a thorough application every 5 to 7 days until all the eggs have hatched.  B.t. is a gut bacterium and the young larvae must eat some of it before it can work.  Ladybird beetles and green lacewings feed on both eggs and larvae.  See – there is something good about that multitude of little yellow/orange house invaders that you’ve fought since September.

Colorado potato beetles have become resistant to many chemical insecticides. If you wish to use them, alternate between different classes of insecticides for your applications. The major classes are: pyrethrums, rotenone, organo-phosphates such as diazanon, organo-chlorines such as methoxychlor, and carbamates such as carbaryl (Sevin). Sevin may no longer be effective.

The White Cabbage Moth is a white to tan medium-sized moth characterized by four distinct black spots on its upper wings and an erratic looping flight path. Unlike the potato beetle, the adult cabbage moth does not cause damage but its larvae, a small green caterpillar, can do extensive damage to your brassicas.  Control of these pests consists of companion plantings, floating row covers, hand picking the larvae, Bacillus thuringiensis, or insecticides.

 Companion planting is planting certain other varieties of plants in and around your main crop.  Using aromatic herbs such as mints, parsley, chives, marjoram, basil, caraway, chamomile, sage, thyme, and rosemary confuses pests that are guided to their food by scent. Nasturtiums are also great companion plants by also deterring wooly aphids, squash bugs, and whiteflies.

Floating row covers prevent the Cabbage Moth from laying its eggs on your plants.  It is a gauzy fabric that allows light and water through, but not insects, usually available at garden supply stores and through gardening catalogs.  It is either held up by the crop itself or by metal wire hoops, and is anchored at the sides by soil or small rocks.  It is inconvenient when you have to weed.

Finally, the same bacterial and insecticide controls that work on the Colorado potato beetle will work on the cabbage moth caterpillar.  If you are considering using B.t., read the label and make sure that the variety of B.t. that you are buying will control cabbage moth caterpillars.  Not all varieties of B.t. will work on all pests.

The common garden slug is evident by its slime trails and by the damage it can do.  Slugs are only active at night and seek refuge under garden litter, mulch, and flat rocks during the heat of the day.  They feed on vegetation and can consume a tender young seedling completely or take a large gouge out of an almost-ripe tomato. The standard slug control methods are traps, baits, and barriers.

The best trap is stale beer. Put out shallow dishes or tuna cans containing beer. Slugs love it and will crawl in and drown. A rolled up newspaper will work also. Slugs will use the newspaper as a daytime hiding spot. Just make a habit of stomping on the newspaper trap each day. When it gets too slimy, compost it!  Commercial poison baits are available.

The best barrier is an edging containing copper. The slime on the slug reacts with the copper, creating an electric charge which stings the slug. Diatomaceous earth will work until it gets wet. Wood ashes also work, but using a lot of wood ash in the garden can cause a build up of harmful salts in your garden soil.

Other good gardening practices will also discourage slugs who need spaces to move through the soil. Creating a good fine tilth will discourage them. Moving the soil surface with a rake in late fall will expose many slugs and their eggs to frost damage. Remove fallen and damaged leaves as they are a slug food source.