Falling leaves, fire danger and box elder bugs

When deciduous plants become dormant, look for box elder bugs to become active

Dormancy in plants

Most broad leaf (deciduous) plants enter a period of dormancy after they drop their leaves. Becoming dormant is a defense mechanism for survival during cold or very dry weather. Dormancy is triggered by the amount of daylight vs. dark (photoperiod), temperatures and lack of rain.

During the summer, trees have well-developed leaves that trap sunlight, converting it to sugars that help the plant grow. Sometime during September, changes occur in the plant that trigger two things -- the formation of an abscission layer in leaves and the movement of sugars from the upper part of the plant down to the roots. These changes cause the fall colors in leaves. Eventually, the leaves drop, the sugars are converted to starch and winter buds develop where leaves once were.

This process reverses itself in the spring when environmental conditions cause the "sap to rise" and leaves to unfurl.

Evergreens never go into true dormancy. They normally have small "needles" or waxy coverings on their leaves that prevent drying out if the soil becomes frozen and the plant can not take up water.

Smokey Bear signs

There are a number of Smokey Bear "fire danger" signs installed around Frederick County -- at major thoroughfares, state parks and volunteer fire companies. The signs are meant to inform the public about the relative forest fire danger by using a catchword and a specific color. The levels of fire danger are low, green; moderate, blue; high, yellow; very high, orange; and extreme, red. Each word corresponds to the chance of starting a significant forest fire.

The Maryland Forest Service collects fire weather data using automated weather stations. Such factors as temperature, relative humidity, wind speed and direction, moisture content in fine fuels (twigs, grass etc.), moisture content in heavy fuels (such as logs), fire spread index and drought index are computed daily and used to determine the prevailing fire danger rating. Hot, dry, windy conditions raise the fire danger level while cool, moist, calm conditions lower the level.

Normally, the fire danger is highest in fall or spring when it is warm and before "green-up." The safest time to burn is during winter, especially if snow is on the ground.

Smokey Bear signs like this are designed to inform the public about the risk of fire danger (Photo by Mike Kay)


Always be careful when burning outdoors. If you notice the fire danger is at a high level or above, consider not burning and wait for the level to drop to moderate or low. In a prolonged period of elevated fire danger, authorities often impose a burning ban so that any kind of outdoor burning is prohibited. Frederick County Health Department institutes a burning ban June 1 through Sept. 1 for a different reason; it is a measure to control air pollution.

The box elder bug (Boisea trivittata) is mostly known as a nuisance because they sometimes invade homes during the fall. These insects can congregate by the thousands on sunny walls; if the home is not well insulated, the insect can make its way inside in large numbers.

Box elder beetles overwinter as adults and lay their eggs on box elder and silver maple trees. The young nymphs hatch in a few weeks and grow over the summer. They are typically attracted to female box elder trees, those that bear the winged samara-like seed. They feed on the leaves, flowers and seed pods of the host tree, doing very little damage to the trees.

The adults begin to seek out warmer locations, such as houses, in fall. The best way to keep them from invading your home is to remove female box elders from landscape settings and to seal up holes around windows or doors. You can spray the bugs if they are congregating on the side of your house. A mixture of dishwashing soap and water is usually adequate to stop these insects.

Nature Notes for 10/26/2008