May 7, 2008  

In witnessing our very early spring, I report that April 8th thru April 12th temperatures averaged almost 10 degrees F above normal, daily; April 16tth thru April 26th averaged more than 18 degrees F above normal, daily. Finally, by April 27th we've returned to seasonal temperatures with a blessing of some much needed rain the last couple of days.  

The Eastern Tent Caterpillar eggs laid last summer have hatched out and the caterpillars are now forming and expanding their conspicuous silken tents in the branch crotches and forks of wild cherry, apple and flowering crabapple trees as well as hawthorn, other prunus species and occasionally on deciduous forest and ornamental trees.  

They are ahead of schedule by a few weeks, so when you read this, there should already be noticeable silk houses evident in trees along roadways and landscapes. (When I say '... ahead of schedule' I'm only thinking of the usual calendar date. Their arrival is coincident with the blooming of Amelanchier or Shadblow, and the Growing Degree Day base 50 = 100.) There may be as many as a few hundred juvenile caterpillars in a single nest. Mother Nature's timing is always exquisite, and the early warmth signaled the moth larvae to hatch just as their food source (young, tender cherry, peach, or plum leaves) was becoming available.  

Malacosoma americanum is a native tree defoliator reported on as early as 1646 in Massachusetts. As I write this, the caterpillar larvae are very tiny, no bigger than the small black ants one sees at this time of year. The communal nest is for protection from birds, other predators, rain and unexpected cold weather, during which they will huddle together to conserve heat.  

Bringing along their silken trail, they venture out at night to feed on newly forming leaves. As they feed and grow, so, too, does their webby shelter. The larvae have six stages of growth (instars) before they finally reach maturity after four to six weeks of feeding. By then they are 2 to 2 1/2 inches long. Fully grown now, they are hairy, nearly black with a white stripe along the back and a row of oval pale blue spots on each side. There are many short irregular goldish brown markings on the side of each body segment.  

In some years when populations are very high, entire trees can be observed encased in the silken webbing. Total defoliation is the result. Their feeding about over, they abandon the nest in search of safe places to spin their white cocoons and pupate. These locations might include stonewalls, fences, trees trunks or man made objects. Anywhere safe from predators will do.  

Within their cocoons for about three weeks, they then transform into reddish-yellowish brown moths with two white stripes across each forewing. Adult moths have a wingspan of 1 to 2 inches, are medium-sized, hairy, and heavy bodied. They are active at night.  

The adult moths emerge to mate and lay eggs. This is usually in late June or early July, but the timing is more temperature driven than calendar correct. There is a single generation each year. Again, Mother Nature's impeccable guidance leads the ETC moth to lay its eggs on its favorite host tree for the following year. The egg mass appears as a brownish cylindrical formation around a twig; it appears shiny as if it's varnished; it has the consistency of Styrofoam and is easy to remove with a thumbnail. It will be there by July, but usually concealed by the trees foliage in summer.  

If you see a tent on your favorite ornamental cherry, crabapple or other treasured landscape plant, simply remove it by hand or with pruning shears and destroy it. Don't just leave it on the ground, because the caterpillars will just ascend the tree again, begin to feed once more, and construct a new tent.  

It's probably too late for any spray to be effective. The pesticide of choice for control very early in the season is Bt (Bacillus thuringiensis), a naturally occurring microbe that controls many kinds of young caterpillars and is harmless to humans, pets and beneficial insects. Tie a ribbon around a branch of the tree to remind yourself to check it in fall or winter for egg masses.  

Going after mature caterpillars with stronger chemical sprays is a bit of a futile effort since all of the defoliation has come to an end as the caterpillars are now seeking pupation sites. Yes, you might reduce the number of fewer adult moths to lay eggs, but I wonder how many beneficial insects and other critters might be harmed by the chemical approach. It's never been a favorite of mine.  

Bear in mind that the trees that were partially or even totally defoliated, experienced this early in the growing season, and will likely re-leaf and recover. Only repeated defoliations, year after year, will seriously harm trees that are victims of the ETC. An attentive ally is all the trees need to return to their original vigor.  

Make sure affected trees are supplied with adequate water if conditions are dry during summer. Remember to check ribboned trees after leaves fall to scrape off egg masses into a small container of soapy water. They will return to their former glorious splendor come spring next year.  

In nature, nothing is perfect and everything is perfect.    - Alice Walker

From The Garden of Ed. Submitted for publication in The Towne Crier on May 07, 2008

© 2008 Ed Mues. All Rights Reserved.

eMail:  eGarden@MountainAir.us