Gypsy moths are not native to America. That is one of the reasons that they are such a pest. They have no long-term relationship with predator species as do our native insects. There are several predator wasps which do attack the egg masses and these have been on the increase lately. However, as with most predator/prey interactions, the predator populations lag behind that of the prey. You have to have a lot of gypsy moth caterpillars for them to feed on before you get enough wasps to help control the pest.

The real control of gypsy moth caterpillars seems to come from a naturally occurring virus that the insect carries with it. Unfortunately, this virus does not do its dirty work until the caterpillars are stressed from having eaten all their food supply. Generally, after two or three years of heavy infestation, there are so many caterpillars that they start to get hungry. This is when the virus kicks in and begins to kill off large numbers of the pest. Then, populations crash and the problem goes away for a few years until the caterpillars build up again.

Another factor that may influence the level of the problem this year is the impact of the cold temperatures from last January and February. It is known that temperatures below minus twenty degrees Fahrenheit will kill large numbers of eggs. A temperature of minus ten will kill some of the eggs. Although we did not reach the minus twenty level, there were several nights with temperatures in the minus ten to fifteen range. Only time will tell if this had any significant impact.

Gypsy moth caterpillars begin to hatch in early to mid-May and start eating on the leaves at the top of the trees. Oaks, poplars, crabapples, willows, birches and red leaf cultivars of Norway maple are their favorites. If populations get high, they may also munch on other trees too.

The caterpillars continue to feed and grow larger until late June or early July. Then, they stop feeding, pupate and become adult moths. The female moth is whitish in color and cannot fly. She lays eggs for next year's brood somewhere near where she emerges from her pupal case.

Remember, gypsy moth caterpillars DO NOT form web nests like the Eastern tent caterpillar or the fall webworm. They are extremely hairy caterpillars with five pairs of blue dots and six pairs of red dots along the back. This pest is only actively eating in the trees for about 6 weeks between May to early July. Most of the damage occurs in mid to late June when the caterpillars are at their largest size.

In heavily wooded areas, aerial spraying with the biological agent Bt (Bacillus thuringiensis) are used to minimize the damage. However, this is not practical in more urban areas or to protect a few trees in a back yard. Fortunately, there are some options available to protect individual trees in the backyard.

Winter is a good time to inspect trees, buildings and lawn furniture for gypsy moth egg masses. The eggs are laid in a "velvety" mass about the size of a half dollar. Scrape them off into a container of soapy water or otherwise destroy them. Do not just drop them to the ground.

Small caterpillars feed on trees during the daytime. As they get bigger, they begin to move down the tree to hide during the day and go back up to feed in the evening. Homeowners can take advantage of this daily migration to eliminate some of the caterpillars.

Several techniques may be employed. Using burlap and string or twine, construct a "hiding" place for the caterpillars. Burlap should be 12 to 18 inches wide and long enough to wrap completely around the tree about chest height. Tie it to the tree with the twine and fold the upper portion down to form a flap or "skirt" around the trunk.

During the morning hours, caterpillars will collect under the flap. In the afternoon, lift the flap and sweep the critters into a bucket of soapy water. Use a small brush, broom or rubber gloves to move the caterpillars. Some people experience an allergic reaction from touching the "hairs" of the caterpillars.

Another alternative is to place a piece of slippery tape around the tree. This allows the caterpillars to go down the tree but, when they try to go back up, they cannot cross the slippery area. Sticky bands may also be used to snag the caterpillars as they move down the trunk. Buy a commercially prepared tree wrap or put a several inch wide band of a non-porous tape around the tree. Place tanglefoot on the tape in order to catch the insects as they crawl down the tree.

NEVER, NEVER, NEVER put the tanglefoot or grease, tar or creosote DIRECTLY onto the bark. This will leave a permanent stain and may severely damage younger trees.

Small trees may be protected with sprays using a low volume sprayer. Bt sold as Dipel, Thuricide or Bactur is a biologically safe spray. This bacteria only affects the caterpillars and will not kill other insects, birds or mammals. Spray it on the leaves and allow the insects to eat them. They will quickly stop eating, develop a gut infection and die.

Unfortunately, Bt must be used when the caterpillars are small (less than 1 inch) to be effective. It will not work on large caterpillars.

Chemical insecticides labeled for gypsy moth control may also be used. These insecticides are non-selective and will also kill honeybees and beneficial insects such as parasitic wasps that feed on the gypsy moth. So, take care when using them and be sure to follow the label directions, avoid windy days and use these sprays sparingly.

For small numbers of trees, a systemic implant called Ace Caps may also work. Holes must be drilled into the base of the tree and the capsules are implanted to release their chemicals directly into the trees vascular system. If not done properly, this may cause damage to the tree and may also result in uneven distribution of the chemical throughout the canopy of the tree. Generally, these caps are applied by a professional applicator.

In larger wooded areas, neighbors may need to group together and hire an aerial sprayer to cover the area. Check with the spray company for details but they usually need an area of at least 10 to 15 acres in size to make this option viable.

Experience in parts of the country which have had severe infestations for years indicates that an otherwise healthy tree can survive total defoliation for 2 or 3 years in a row. Trees that are already under stress from old age, disease or poor site conditions will be further stressed. In some cases, this could push them over the edge.

In the end, the best defense will be to keep the trees otherwise healthy by proper watering, fertilizing and pruning. Banding techniques can help to minimize damage in severe infestations. Insecticide applications may help but, due to the size of many infested trees, it is expensive and difficult.
 

Gypsy Moth Facts

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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