Wednesday, April 30, 2008

1000' of Nylon Cord and Some Used Plastic

You never know when you're going to need large quantities of used plastic. This afternoon; George (fellow gardener in Conifers and Dogwoods), Joan, and I covered the Fern Valley pond with plastic. I wasn't sure we could do it but darn it, look at the picture! To celebrate May Day (just kidding) gypsy moth caterpillars are being targeted and selected wooded areas at the Arboretum are being sprayed with Dimilin, an insect growth regulator. We covered our pond to protect the aquatic larvae of dragonflies, damselflies, and other good insects. Beech Spring Pond, the largest pond at the Arboretum will not be sprayed, but since the Fern Valley Pond is so small and overhung by trees it will be significantly hit by the chemical.

I am not an unquestioning supporter of the use of chemicals, but the gypsy moth population has obviously been rising steadily for several years. In Fern Valley, we ring some of our most susceptible trees with burlap bands and "harvest" the caterpillars that hide there during the days. We record the numbers per tree per day and this provides an informal method of assessing relative levels from year to year. We knew things were getting bad and when a more systematic analysis suggested that the risk level had been exceeded by an order of magnitude, the decision was made to spray. The chemical of choice, Dimilin interferes with chitin synthesis, preventing insect larvae from growing and so resulting in their death. All studies have shown that there are no negative effects on humans or other higher animals. The frogs and turtles are safe!

Personally I am glad to see this spray happen. In Fern Valley and around the Arboretum, Oaks, trees of choice for gypsy moths, have clearly suffered over the last two years and the number of egg cases last year was frightening. It is likely that a significant side effect of this spray will be that cankerworms, those tiny green or yellow inchworms that drop on you in the woods all summer, will be hit hard too. I have watched the numbers of these increase for at least 10 years. With no scientific or experimental confirmation, it appears that the increase is linear rather than cyclic, and related to decreases in the population of warblers and vireos. Unfortunately these decreases are documented. I remember when cankerworms were not a serious issue but now, every year they seem to be more and more a problem; I hope a significant hit this time of year can bump them back to acceptable levels.

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