A local tree expert isn’t convinced that an increase in web worms affecting trees being reported around the area can be completely due to this spring’s warmer weather.
“I believe the main reason they are spreading is that many fruit tree owners do nothing to help manage and control these pests in their trees,” says Charles Claus.
“Fruit trees are high maintenance trees. If a home owner is not prepared to manage their trees they frequently end up with incubator trees that serve to invest similar trees in their neighbourhood.”
Claus says spraying lime sulphur dormant oil during dormancy goes a long way to control web worm. “Now that the bugs are here, control of web worm in apple trees and crab apple trees can be achieved organically with BTK, provided there are still leaves left on the tree,” he says. “The worms eat leaves coated with BTK, it gets into their stomachs and it causes them to die.”
“If the tree has been defoliated, something other than BTK will need to be used. In that case, two organic options would be “Trounce” containing pyrethrum extract and insecticidal soap and “End All’ containing Neem oil and Pyrethrum.”
And Claus adds that the hot dry weather means fruit trees should be given a generous soaking at least once a week.
And if apple, pear and plum trees bear lots of fruit, they should be thinned to reduce stress as that makes them more prone to disease and a biannual production cycle. Excess fruit should be thinned out too.
Bacillus thuringiensis var. kurstaki (BTK for short) is a rod-shaped bacterium that occurs naturally on dead or decaying matter in soil.
Update: An earlier version of this article stated fruit trees should be pruned to reduce stress. That has since been corrected.