Roses are the most beloved plant, not just by countless humans throughout recorded history but also by numerous pathogens and insects.
As a horticulturist my specialty is roses, and I’ve developed an intimate knowledge of a number of species that perpetuate their numbers by attacking the plants that have been my responsibility at Wyck in Germantown, the oldest rose garden in the country.
Although there are an increasing number of rose growers who are using organic controls, the conventional wisdom among old-school rosarians is still to scramble for the nearest chemical at the first sign of insect presence.
This week I noticed rose sawfly larva on my few bushes I brought from my old house when I recently moved. These juicy worms chew holes in the leaves at night, and curl up during the day.
I think that the main damage that bugs like this sawfly larva cause is to the gardener’s ego. My roses look pretty ragged so full of holes, but this type of insect damage doesn’t really hurt the plant. A rose could have most of its leaves chewed off and still be okay the following year.
And a new generation of research shows that the sap suckers and leaf chewers which attack ornamental plants actually are a very important constituency of a garden. Insects provide a bridge between lower and higher life forms. Plants contain a lot of energy, but it isn’t usable by most animals. Insects are the little processing systems that convert plant energy into something accessible by higher trophic levels.
If we want wildlife like birds and toads in our gardens, it’s counterproductive to try to eradicate creatures like this delicious worm. Eighty to ninety percent of birds eat insects for at least some part of their life, particularly when they are young.
A healthy landscape has to have pests, probably lots of them. Being low down on the food chain, they attract beneficial natural enemies, and these are the species that we love to have in the garden, and are often the animals whose populations are declining.
When I want to avoid getting into tense situations with my conventional gardening friends, it usually works to say that I’m using biological controls to manage pests. It sounds good, but the truth is it’s just doublespeak for leaving the bugs alone.