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August 2016Roof-Top Critters
Just when you think it can’t happen here, it does. Interestingly, there are no deer here, being in the middle of the city, but there are squirrels, caterpillars, dogs, cats and birds.
According to a NY Times article by Elisabeth Rosenthal, the American Bird Conservancy determined nearly 500 million birds are killed by cats each year – half by pets and half by feral cats!
Cats aren’t the only critters that pester plants on roof-tops, as we learned one morning when I pulled a half-buried candy bar wrapper from out of the pot of dill. Was it a dog on this second floor balcony? A cat? Both were highly unlikely. It had to be a squirrel, of which there are plenty.
We soon noticed holes in cabbage, kale and kohlrabi leaves and, after a little research, hand-picked them off and drowned them in soapy water, thinking they were cabbage loopers (Trichoplusia ni), a.k.a. cabbageworms, also a.k.a. inchworms. But the questions were: how did they get up on a roof garden to eat our veggies and where did they come from?
(An inch worm memory: When I was 8 or 9, I found the biggest rock I could hold and threw it at an inchworm dangling from a low branch. In my childhood euphoria, I neglected to see the Studebaker behind the caterpillar as the rock whizzed through the air, missed the worm, and broke the car window of the “baddest man in the whole dang town.” As the other old tune went: “I ran all the way home.”)
Enter Peter Nitzsche, County Extension Dept. Head, Agricultural Agent, Rutgers NJ Agricultural Experiment Station, Morristown, NJ, who quickly enlightened me. They were “Imported cabbageworms” (Pieris rapae) – not loopers or “cabbage worms” – and he offered the best Integrated Pest Management methods to control them.
Cabbage loopers do not survive the harsh winters of NY, NJ, CT and Eastern PA, but the adult moths usually migrate here by late July/early August and immediately deposit their eggs, he says. The night-flying, dark, grey/brown moths with a silver V-shaped spot on each wing rest between the plant’s leaves during the day. The caterpillars have white stripes on sides and back and feed on the undersides and tops of leaves and bore into the cabbage heads sometimes making them unfit to eat.
Imported cabbage worms have visible legs and faint yellow stripes across the back but often appear just green. They too, bore into cabbage heads, leaving dark green lumps behind. The adult is the small, white, day-flitting moth that loves nepeta and other mint family plants, Russian sage, salvia, caryopteris. These plants may be pretty and are quite useful but don’t use them near the veggie garden!
Peter Nitzsche’s Recommendations
Put row covers on early. It’s too late now but netting can be used to keep the white cabbage moths at bay.
Inspect the plants daily and hand-pick the caterpillars and throw them in soapy water. As steward of the veggies, Julian inspects the plants every morning and evening.
Douse the plants with BT (Bacillus thuringiensis) a bacterium that comes as powder or liquid. It kills caterpillars of all types because they have alkaline stomachs, but it doesn’t harm birds, bees and humans because we don’t have alkaline stomachs. BUT, do not use BT on plants that you want for butterflies, such as milkweeds. Some labels say it may be applied up to harvest day, but then, why bother. You can just wash the leaves in the sink.
Another option: Spinosad, a new, organic pesticide discovered as a fermentation product at a rum distillery.
It is good to use companion plants that attract carnivorous insects and birds that are natural predators, but be careful not to use mints or other plants that attract those cute little white moths whose larvae will soon destroy your food. Try parsley, dill, fennel and coriander. Insectivorous wasps love them!
Harvest cabbage as soon as possible because Imported cabbagewoms are active all season. Bury damaged leaves of all cole crops. Treatment is the same for loopers and imports.
University of Florida articles:
Rutgers NJ Agricultural Experiment Station, Morris County
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