US National Arboretum


Pest Management

Pest Management Tips: April

image of a ladybug     April is a great time to mulch the planting beds around your home. Mulch inhibits weed growth and retains soil moisture. A couple of inches of fresh bark is attractive too. Avoid piling on too much mulch. The practice of mounding up mulch around trees, as seen in some commercial plantings, to a depth of 10 or 12 inches is not a good idea. This much mulch actually acts as a barrier—it repels water and deprives the tree of oxygen.

image of Eastern Tent Caterpillar silken tents image of a ladybug     The silken webs of Eastern tent caterpillar appear in early April. These leaf munchers feed on many fruit trees, including apple, crabapples and cherries and some shade trees. Often found on the native black cherries, their silken tents are located in branch crotches. The caterpillars feed at night on leaves in close proximity to the tent, and return to the tent during the day. Caterpillars grow to 2 inches, with a white stripe and blue markings down the back. A closely related insect, the forest tent caterpillar, feeds on many deciduous trees, including ash, popular and willow. They have prominent blue strips with white spots on its back. Use a brush to mechanically remove the tent, or spray Bacillus thuringiensis on young caterpillars.

image of a ladybug     Check your pines for brown tips or die back. This can be caused by Nantucket pine tip moth larva. The caterpillar burrows into the terminal, causing the growing tip to die. This insect winters in the terminal, so removing the tips will reduce this year’s population. A second generation also occurs in June, so removing dead tips through spring will help control this pest.

image of a ladybug     It’s still not too late to add compost to your vegetable garden pot. Adding organic matter increases drainage and water retention and also makes nutrients available for your summer vegetables.

image of Carpenter bee image of a ladybug     Carpenter bees are active at the Arboretum. These large black bees make their nests in exposed wood, including timbers in the Bonsai Pavilion and various wooden signs on the grounds. These beneficial insects are active pollinators. They seem aggressive as the males try to protect their nests. They can not sting, but they try hard to intimidate you with belligerent buzzing. Try to be patient during the nesting season.

image of a ladybug     Woolly adelgids can be a major pest of hemlocks. These small, aphid-like insects are covered with a white “wool” which is quite visible. Look for little tufts of cotton on the base on individual needles. The adelgid feeds on the sap of the needle, causing it to turn grey or olive green, and then fall off. Heavy infestations over a few years can kill the tree. New juvenile adelgids, called crawlers, hatch in March and April. Tap an infected branch over a sheet of white paper and with the aid of magnifying glass, check for this crawling stage. A 2% horticultural oil spray or insecticidal soap will control crawlers.

image of a ladybug     Don’t let those little weed seedlings grow into big, nasty, hard-to-control weeds. Seedlings can be easily pulled out or removed with a hoe. Don’t procrastinate until the weeds are too large to pull or have set an abundant crop of weed seeds.

image of a ladybug     Spruce spider mites are a major pest of conifers in many parts of the country. They attack spruce, hemlocks, junipers, arborvitae, cryptomeria, and many other species. If you own Dwarf Alberta Spruce, you most likely will have spruce mites at some time. They are most active in the cooler months of spring and again in the fall. A complete generation can occur in about two and a half weeks, so the population can rapidly build. Feeding on the needles, they cause the needles to have a gray or stippled appearance. Young plants with heavy infestations can die; older plants can die after repeated attacks. Place a sheet of while paper under an infected branch and tap lightly. These mites will be visible black specks on the paper. If mites are present, treat with horticultural oil.

Pest Management Tips Home

The best way to manage pests is to use a combination of chemical and non-chemical control. Only take action when the problem is serious enough to damage the plant. If we all use Integrated Pest Management (IPM), we can control pests in an environmentally conscious manner.

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Last Updated   June 11, 2009 3:00 PM

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