The Elm Spanworm (Inchworm)
Is it Raining Worms?
The Elm Spanworm has become quite a nuisance to residents of St John’s in the past few years. Seemingly out of nowhere this pest has appeared in massive numbers, around certain areas of town. There are a number of options available to residents of St John’s when it comes to dealing with the Spanworm problem; some of these options are quite effective, while others are not.
-Image of Elm Spanworm eggs, larvae and an adult moth (Image courtesy of Wikipedia)
What are they!? Why are they EVERYWHERE!?!
Besides being just plain creepy looking, the elm spanworm is also a very hungry resident of our deciduous trees. In St John's we have come to know this pest as the St John’s Spanworm or Inchworm. They are most obvious in their larvae stage of life when they can be observed in tree canopy’s feeding on leaves in mass quantity, in some cases stripping the trees entirely of foliage. This usually takes place between the months of June-July. The larva devastate trees, lower themselves onto property and the pungent odour of their feces can be observed throughout the neighbourhood. The Elm Spanworm population in St John's has been able to explode due to the easy availability of a food source and the absence of the natural parasites that keep spanworm populations in ballance in other regions. After the larval stage has run its course they eventually metamorphisize into moth's. While the Elm Spanworm is a nuisance to deciduous trees and resident’s of St John’s , they are not overly dangerous and infected trees should be able to recover fully.
-Elm Spanworm in Locomotion (Image courtesy of Wikipedia)
Can they be Stopped?
The only insecticide registered in this province for controlling the Elm Spanworms is Btk. Bacillus thuringiensis kurstakiis is a bacteria found naturally in soil. As this bacterium produces spores it also creates microscopic protein crystals that are toxic to the Elm Spanworm. In order for residents to fully take advantage of this, areas of infestation must be sprayed with the Btk as the larva are actually feeding. This should be done while the larva are in their first instar period (when they are the smallest) (Health Canada. 2004). To have a tree treated with Btk its going to cost anywhere from $50-$100 depending on the size of the tree, this can add up to a hefty bill which will have to be paid each year in order to keep the Spanworms under control. There is another insecticide called Ace Cap 97 which is “plugged” into infected tree’s, being drawn into the tree’s sap and causing the leaves to become poisonous to the Elm Spanworm. This insecticide option while often cheaper and more effective is not yet allowed in St John’s as the provincial government has not registered these chemicals as tools for controlling the elm spanworm.
- Btk Being sprayed on
ground shrubs (Image courtesy of
wikipedia)
-Alternative Treatment
- Assortment of chemical pesticides
