US National Arboretum


Pest Management

Pest Management Tips: September

image of a ladybugimage of a tree affected by drought   Many areas in the United States have experienced a hot and dry summer, which continues into fall. Record heat and lack of significant rainfall makes for drought conditions. Many trees are showing symptoms of this stressed condition. Leaves wilt, then desiccate. Dry, crispy areas, usually starting at the tip of the leaf, which spread throughout the leaf blade, are a good indication that your plants are suffering.

Trees also respond to this lack of moisture by showing fall color early and dropping their leaves prematurely. It is an excellent idea to water your trees during times of drought stress. Stressed trees are very susceptible to attack by borers, which can eventually kill a tree. Run a soaker hose underneath the leaf canopy and water deeply, or place a soaker bag, available at garden centers, around the trunk and fill with water. These bags are designed to slowly release water into the soil over an extended period of time. A small investment of irrigation supplies can prevent the need to replace expensive trees lost to drought.

(Above, right: a photo of a tree affected by drought)

image of a ladybug    September is a good time to check your iris rhizomes for borers. The larvae of miller moths feed on bearded and Louisiana iris. These 2-inch brown and yellow moths are seldom seen in the garden because they fly at night. Eggs are laid in the fall on leaves and flower stalks, hatching in late spring. Tiny caterpillars tunnel into the leaves, then make their way down to the rhizome, where the pink caterpillars feed in summer and early fall, eventually becoming 1- 2 inches long. These infected rhizomes are susceptible to bacterial soft rot (Erwinia carotovora), which turns healthy rhizomes into smelly, rotting mush. There is no cure for this soft rot, so borer control is essential. Poke a piece of wire into borer holes to kill the caterpillars. Beneficial nematodes will also attack these caterpillars. Later in the season, remove dead leaves from the rhizome. This will prevent any eggs from surviving over the winter months.

image of a ladybug    Holly leafminer causes discolored trails on the surface of holly leaves. When an infected leaf is torn open, a tiny maggot is found inside. A heavily infected plant may drop many or most of its leaves. A tiny fly deposits eggs inside a leaf in early spring. The hatching maggots feed inside of the leaf, resulting in the visible trails. Most of the damage is done in late autumn, so September is a good time to assess the damage. A light infestation can be controlled by picking off the damaged leaves and destroying them, before the insect can complete its lifecycle. A heavy infestation may require a systemic pesticide application. A pesticide containing imidacloprid, available at garden centers and home improvement centers, can be applied as a drench around the base of the plant. 

image of a ladybugimage of a saddleback caterpillar   We found this saddleback caterpillar (photo below, left) feeding on one of the bonsai azaleas. It did not do any damage, but it could “sting” if the hairs were touched. With a sting as painful as that of a bee, it should be avoided, particularly by those individuals who are sensitive. An ice pack will reduce the pain and swelling.

(Above: a photo of a saddleback caterpillar)

image of a ladybug    In September, boxelder bugs may swarm around the house and patio areas and become a nuisance. These blackish bugs are about ½ inch in length, with orangey red strips on their wings. They have an unpleasant odor when crushed. In the spring, the females lay eggs in the bark of boxelder, Acer negundo, and other trees. The young feed on leaves, causing distortion, and on twigs and seeds throughout the summer. They tend to do little damage overall to the host tree. In the fall, they move to dry areas, including homes and other buildings, looking for a protected spot to spend the winter. In the spring, they move back outside, to boxelder trees. To control them, try vacuuming them up with a shop vacuum or spraying them away from your house or patio with a jet of water from a hose. Be sure to keep doors and windows closed or well screened if you have problems with this pest.

image of a ladybug    As the temperature cools, watch for Southern red mites on azaleas and hollies. Infected leaves become lighter in color. Upon closer inspection, the leaves are stippled yellow or grey, as the leaf tissue breaks down as these mites feed. Silken webbing may also be evident with severe infestations. Hold a white sheet of paper underneath a branch and tap. Tiny specks, the size of pepper grains that move around, confirm the presence of mites. Hose down the leaves frequently with water to knock off the mites. A 2-percent horticultural oil spray will control these mites.

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 2:58 PM