TREE WORMS WILL WAKE UP HUNGRY

April 26, 2007

 

BY JANE STEPHENS - VICTORIA COUNTY MASTER GARDENER

EDITED BY CHARLA BORCHERS LEON

 

It's finally springtime. The robins have returned and our beautiful bluebonnets grace our highways, byways and fields. And the tree worms have hatched in Texas. The unwelcome little critters were last spring's eggs and are this spring's worms.

 

MOST COMMON SPECIES

 

The oak leaf roller, the tussock moth larva, the forest tent caterpillar, the sawfly larva and the fall webworm are the most common species of worms. All of these worms (except the fall webworm) start out as small moths that lay their eggs in late spring of the previous year and hatch early the next spring.

 

Now a description of each:

 

The worms that we are seeing now are the green worms with black heads known as the oak leaf roller.

 

The fuzzy ones with white fuzzy growth on their backs and antennae-looking heads and tails are the tussock moth larvae.

 

A less fuzzy, maybe greenish-gray one with blue spots along the body is the forest tent caterpillar, and a translucent, colorless small worm with a black head is the sawfly larva.

 

And, finally, the fall webworm is pale green to yellowish with tufts of white and black hairs. It is the only one that overwinters in the pupae or cocoon stage versus coming from eggs laid in the previous year. It is also the only one that may have up to four generations per year while the others have only one generation.

 

Once hatched from eggs, the worms are hungry and can be destructive to our trees' foliage. The tender new buds and leaves are the gourmet menu that the critters crave. Trees that are heavily infested can be completely defoliated by late April. At that time, the fully grown caterpillar (the stage when most people realize they have tree worms and want to spray them) is basically through eating and will form a cocoon.

 

While pesticides will control them at this late stage, their damage has been done.

 

From the cocoons, moths will emerge around the first of May to begin laying their eggs for next year.

 

When any tree is defoliated during the growing season, damage can occur. The defoliated tree is unable to manufacture the sugar that is later converted into carbohydrates that allow the tree to grow. The tree will re-foliate and try to maintain life for a short period of time as it uses its reserve food supply. When this happens, the trees are more susceptible to disease and insect attacks. Complete defoliation year after year could result in weakening the tree and, possibly, death. While control may be warranted for the homeowner's sake of not having to contend with worms, it has been said that a healthy tree possibly can loose up to five sets of leaves before the tree dies.

 

Controlling Worms

 

There are several types of wasps that will attack and kill the worms, but many times they do not occur in sufficient numbers to curtail these pesky pests.

 

Some birds will feed on the caterpillars, but again, not in sufficient numbers.

 

Insecticidal control may be necessary for your valuable landscape trees. Use this method only if significant leaf feeding and damage is occurring. Insecticidal sprays containing biological controls, including the use of "Bt" or Bacillus thuringiensis, is recommended. There are many pesticides sold with "Bt" as the active ingredient.

 

Spinosad, a chemical in the insecticide Conserve, is virtually nontoxic to humans and pets. It is recommended for caterpillars trying to homestead your ornamental shade trees. The active ingredient in Spinosad is derived from a naturally occurring soil-dwelling bacterium called Saccharopolyspora spinosa. This bacterium was discovered in the soil of an abandoned rum distillery on a Caribbean Island in 1982. The discovery was made by a scientist who was there on vacation. I have included this tidbit, as I know how many people have wondered what a scientist does on vacation.

 

There are other insecticides available for control including acephate (brand name Urethane), bifenthrin, cyfluthrin, cypermethrin, carbaryl (Sevin), deltamethjrin, esfenvalerate, imidacloprid (Merit or Imicide) and malathion. Whether you use natural or synthetic pesticides, please remember to always read all of the directions, always wear the appropriate clothing and use the proper recommended equipment.

 

Restoring Trees

 

If your trees suffer severe damage, they will need to be fertilized and watered regularly to restore the vigor. To do this, select a balanced fertilizer and apply it at the rate of one pound per diameter inch of the trunk. The fertilizer should be applied in a circular pattern around the drip line of the tree.

 

If your trees have not suffered significant damage, the nuisance is exactly that - a nuisance. The majority of us - and our trees - will live through this cycle of pests. While we are living through it, wear old shoes and stomp the little critters whenever you can.

 

The Gardeners' Dirt is written by members of the Victoria County Master Gardener Association, an educational outreach of Texas Cooperative Extension-Victoria County. Mail your questions in care of the Advocate, P.O. Box 1518, Victoria, Texas 77901; or vcmga@vicad.com, or comment on this column at www.VictoriaAdvocate.com.

 

COMMON TREE WORMS

Spring tree worm photo credits: 

Dr. Bart Drees, Entomologist, Texas Cooperative Extension, Texas A&M University

 

The top five tree worm pests are shown here. All of these worms (except the fall webworm) start out as small moths that lay their eggs in late spring of the previous year and hatch early the next spring. The fall webworm overwinters in the cocoon stage versus coming from eggs laid in the previous year.

 

OAK LEAF ROLLER - bright green body with black head

 

TUSSOCK MOTH LARVA - Cream to gray body with four brush-like tufts or bunches of light tan hairs on the back, sometimes have antennae-looking heads and tails.

 

FOREST TENT CATERPILLAR - white hair on a greenish-gray body with blue spots along the body.

 

SAWFLY LARVA - colorless small worm with a black head.

 

FALL WEBWORM - pale green to yellowish body with many white and black hairs that has multiple generations per year.

 

Spring tree worm photo credits: 

Dr. Bart Drees, Entomologist, Texas Cooperative Extension, Texas A&M University

http://insects.tamu.edu/fieldguide/