FREEHOLD – The Monmouth County Shade Tree Commission began spraying for gypsy moth caterpillars on Monday and will be in Howell today.

About 6,891 acres of parks and woodlands are targeted in Millstone, Freehold, Freehold Township, Howell, Colts Neck, Marlboro, Farmingdale, Tinton Falls and Wall. There is only a narrow window in which to spray the larvae as they hatch and before the caterpillars can damage the trees.

“Since 2005 we have been battling the gypsy moth caterpillars that have been damaging our parks and open spaces,” Freeholder Barbara J. McMorrow said. “We had a minor setback with all the rain last week, but the weather looks good this week and we are spraying every day.”

Spraying will last 21 days, and target the larvae as the caterpillars hatch. The Shade Tree Commission is spraying a naturally occurring, soil-dwelling bacterium called Bacillus thuringiensis, or “Bt” for short. Neither Bt bacteria nor the protein toxins it produces have any effect on people or pets.

“On Monday we sprayed in Millstone and yesterday we finished up in Freehold Township,” said John W. Tobia, director of Public Works & Engineering who also oversees the Shade Tree Commission. “We have mapped out 6,891 acres for spraying. Because of the volume of acreage and the narrow window in which to spray, we will once again be using both county helicopters.”

The gypsy moth caterpillar population is cyclical. The county began making preparations to combat the gypsy moth caterpillars in 2005, when they were spotted in concentrated pockets in Wall, Howell and Freehold Township. Spraying for this population cycle began in spring 2006.

“Even though we spray, we cannot expect to control all of the larvae,” Tobia said. “However, we do interrupt their cycle and slow them down. The food source, the environment and the weather are all factors that affect the numbers of gypsy moth caterpillars in a given year.”

The caterpillar first began defoliating New Jersey forests in 1966, and three major population cycles have occurred: one in 1972 when 256,000 acres were defoliated, another in 1981 when 798,000 acres were defoliated, and another in 1990 when 431,000 acres were defoliated.  In 2007, it is expected that over 125,000 acres will be affected.

Caterpillars hatch in April and early May and climb into tree canopies to begin feeding. If their first tree is not to their liking, they will produce a silken thread that carries them on wind currents to other trees. The caterpillars continue feeding throughout the spring, undergoing five to six molts.

The first three caterpillar instars have black heads and generally black bodies. By mid June, the caterpillars are about one-inch long, have brown heads, bodies covered with black and brown hairs, and a series of five pairs of blue spots followed by five pairs of red spots on the tops of the bodies.

In wooded suburban areas, during infestation when trees are visibly defoliated, gypsy moth larvae can be seen crawling up and down walls, across roads, over outdoor furniture, and even inside homes. During periods of feeding they leave behind a mixture of small pieces of leaves and excrement.

The greatest damage is done by older caterpillars during the last two weeks of June, sometimes making it appear as if trees are stripped of leaves overnight. After they have completed feeding in early July, caterpillars enter the pupal stage from which adult moths emerge after 10 to 14 days. 
 
The Monmouth County Shade Tree Commission had visited areas where the caterpillars have been reported by residents, and mobilizes each September to conduct egg mass counts. The egg masses are described as a velvet mass attached to the trunks of trees, rocks, benches or wood piles. These counts help the county focus its aerial spray program the following spring.
 
Gypsy moth larvae prefer hardwoods, but may feed on several hundred different species of trees and shrubs. In the East, the gypsy moth prefers oaks, apple, sweetgum, speckled alder, basswood, gray and white birch, poplar, willow and hawthorn, although other species are also affected.
 
When gypsy moth populations are dense the caterpillar feeds on almost all vegetation, but has avoided ash, yellow poplar, sycamore, butternut, black walnut, catalpa, flowering dogwood, balsam fir, red cedar, American holly, and shrubs such as mountain laurel, rhododendron, and arborvitae.
 
Homeowners who find egg masses are urged to contact the Monmouth County Shade Tree Commission at (732) 431-7903 to report their location and obtain information on how to destroy them.

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