Spongy moths (formerly called gypsy moths) have declined in most parts of Michigan due to the naturally occurring Bt bacterium. That said, there remain pockets where the infestations are still significant. Unfortunately, some of these pockets include the Hofma Park and Preserve and nearby subdivisions.
Moreover, even if the State of Michigan or Ottawa County were still funding the aerial spraying for the spongy moth caterpillars, it is too late for the spraying of Bt to be effective.
Most of the damage will be complete early July and the caterpillars will soon spin their red/brown cocoons which will hatch in late-July to early August. The moths will live only for a few days.
The State of Michigan notes that oaks or other hardwood trees that are defoliated by spongy moth caterpillars may look as if the trees are dead. However, these trees will “re-flush” and produce a second set of leaf buds, usually by late July. This second set of leaves will provide enough energy for the tree to survive winter. Severe defoliation does stress the tree, but trees can tolerate even complete defoliation for a few years.
Further, the infestations typically last no more than two years before the population of the spongy moths collapse due to the naturally occurring Bt bacterium – which is one of the reasons why the State of Michigan and Ottawa County discontinued the spraying the Bt bacterium over a decade prior. The last year that the State of Michigan, Ottawa County and Grand Haven Charter Township collaborated on aerial spraying the Bt bacterium was 2012.
That said, because this is the third year some areas have had to deal with the spongy moth infestation – and because of damage to Hofma Preserve – during the budget process, staff will be looking to include the aerial spraying of the Preserve and surrounding neighborhoods in the Spring of 2024. The cost will be $90k+.
Again, there is not a solution to the current infestation. But the caterpillars should be gone within a couple weeks.