Managing garden herbivores, Part 3: cutworms and aphids

By Reeser Manley,
Posted Jan. 06, 2012, at 7:14 p.m.

Cutworms, the larval (caterpillar) stage of several species of night-flying moths, are a major herbivore in Marjorie’s Garden each spring, cutting down unprotected young transplants at or below the soil surface and devouring seedlings before they break through the soil. As with all garden herbivores, understanding the life cycle of the cutworm gives clues to effective controls.

Cutworms overwinter in the late-larval or pupal stage. The adults, brownish-gray moths, appear with the warm weather in spring, flying at night. They are attracted to weedy fields, particularly to mustard and quack grass, and also lay eggs in weedy gardens during early spring.

Once gardens are planted, the young larvae feed on small roots until half-grown (about three-quarters of an inch long), at which point they become more likely to cut off plants at or just below the ground, often dragging parts of the plant into the soil where they hide during the day. Their favorite garden plants include tomatoes, peppers, beans and corn.

Maine gardeners are fortunate in that most cutworm species have only one generation per year, although a few have two. And because there are several different cutworm species, the larvae will vary in color from gray to brown or black, striped or spotted. A mature cutworm larvae can be up to two inches long and will curl up into a tight ball if disturbed.

Management begins with keeping the garden as weed-free as possible. Unfortunately, egg-laying moths are also attracted to green manures and cover crops in spring, so getting these crops incorporated into the soil as soon as possible in spring should be a priority. Using aged composted manure in lieu of green manures may be necessary if cutworms get out of hand.

Cutworm collars, properly installed, will deter damage to transplanted seedlings. We use newspaper collars because they are biodegradable, rolling a two-inch-wide strip several times

around the seedling stem, positioned so that half of the collar will be buried beneath the soil after planting. We put these collars on every seedling transplanted to the garden.

Minimizing cutworm damage to direct-sown crops is trickier. Direct-sown beans, for example, may never make it above ground if cutworms sever the embryonic stem as it emerges from the seed. Eliminating all weeds from potential seed beds is a start, since the moth is unlikely to lay eggs in bare soil. Shallow raking and sifting of the soil before sowing is another precautionary measure, destroying any cutworms found by crushing or drowning in soapy water.

Once seedlings of crops with succulent stems, such as squash, cucumbers and beans, have successfully emerged from the ground, I surround each seedling with a two-inch tall collar cut from a plastic water bottle, pushing each collar an inch into the ground around the seedling.

These crops, the ones with juicy stems, seem to be the cutworm favorites, but only for the first week or so after emergence. The stems soon harden and the collars can be removed.

Finally, get proactive. If you have cutworm damage, usually evidenced at the crack of dawn by a severed seedling or two lying on the ground, dig two or three inches into the soil around the damaged plant and you will likely find the culprit. And visit the garden at night with a flashlight, looking for cutworms on top of the soil.

Aphids

Also known as plant lice, aphids form colonies on the tender new growth of garden plants, eventually drawing the gardener’s attention with their sheer numbers, a herd of sap-sucking insects crowding the stem tips of your favorite rose or herbaceous perennial or shrub.

There are numerous species, each a different color, and each species typically feeds on one plant species or a group of related plant species. Colonies grow as females give birth to live young, all female; males enter the picture only when it is time to produce eggs for overwintering. In a typical colony, some aphids will be winged, others wingless.

I have known otherwise rational gardeners that would bring out the big guns from the tool shed shelf when they spotted a single aphid on their roses. Some of the most toxic insecticides, including nicotine sulfate, malathion, diazinon and dimethoate, have been used in the past to kill aphids along with beneficial insects and other forms of garden life.

I would plead the case that a few aphids are evidence of a healthy garden ecosystem.

Aphids have many predators, including ladybugs, lacewings, parasitic wasps and syrphid flies.

Of course, to maintain populations of these beneficial insects, there needs to be a steady supply of aphids. If I see a few aphids in the garden along with numerous ladybugs, or lots of aphid exoskeletons punctured with the emergence holes of adult wasps, I feel that all is right in the garden world.

Entomologists who study aphids would agree with me: Aphids rarely do enough damage to warrant intervention by the gardener. And in exceptional situations, when predators cannot keep up with a heavy infestation on young plants or your prize roses, mechanical controls will work. The gardener can dislodge them with a strong stream of water or trap them with sticky yellow cards, thin plastic cards painted with Rustoleum Safety Yellow paint and Tanglefoot (an organic paste) applied for stickiness.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.

 

http://bangordailynews.com/2012/01/06/living/blogs-and-columns-living/managing-garden-herbivores-part-3-cutworms-and-aphids/ printed on July 26, 2014