Before the days of pesticide safety, we youngsters used to ride our bicycles closely behind the city’s mosquito spray truck as it wound its way through the streets belching thick white clouds of heavy fumes.
We pretended we were biking through the fogs of London. Not only were we lacking helmets, we should have been wearing gas masks.
Dealing with insects around the yard and garden is a balance between protecting plants while safeguarding humans and beneficial insects. Before we examine some common individual insects, let’s discuss insecticides.
Some products for insect control are called low-impact sprays because they present a very low risk to people, pets, beneficial insects and the environment. Included in this group are insecticidal soap, neem oil, horticultural oil, pyrethrum, bacillus thuringiensis (BT) and a relatively new product called spinosad. These products are considered the safest materials for insect control.
Products that have longer residual effect, are faster-acting and are considered safe when used judiciously following label directions include Sevin (carbaryl), permethrin and malathion. They have a higher toxicity rating, so observe label waiting periods before harvest. Sevin is very effective when targeting pests, but shouldn’t be used when plants are flowering, because it’s toxic to bees.
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Tree and shrub insects
Tent caterpillars. Mistakenly called armyworms, the 2-inch long, hairy, blue/black caterpillars can defoliate trees. The Eastern tent caterpillar builds web-like nests, while the forest tent caterpillar doesn’t. Trees usually produce new leaves the same season, but consecutive years of defoliation can be harmful. Apply bacillus thuringiensis (BT), insecticidal soap or spinosad. Longer residual sprays include Sevin, malathion, Orthene and permethrin.
Emerald ash borer. Metallic green adult beetles lay eggs that hatch into white wood-boring caterpillars. They’ve caused the death of millions of ash trees in Eastern states, but reportedly the nearest sightings are in Duluth, Minn., and Minneapolis-St. Paul.
Bronze birch borer. Bronze-colored adult beetles produce flattened larvae that tunnel below bark on birch trees, causing visible raised bark ridges and dead upper branches. Check for resistant birch varieties when purchasing. Chemical control is difficult, but systemics can have effect.
Aphids. Small, pear-shaped soft-bodied insects colored green, black, yellow or gray-brown cluster on succulent growth of young leaves, stems and flower buds. As they suck sap from plants they exude honeydew. When aphids feed on trees, cars and objects below are coated with the sticky substance. Eventually, black sooty mold grows on the honeydew. Aphids are a main food source for beneficial insects like ladybird beetles (ladybugs), lacewings, syrphid flies and parasitic wasps. Because these beneficials are quite effective at keeping aphid populations in check, strong, non-discriminant insecticides are not recommended. Instead use insecticidal soap, horticultural oil or pyrethrum. Professional tree services can apply systemic insecticides.
Galls. Mites or insects cause round growths to form on leaves or twigs of maple, oak, hackberry and rose. Because the pests are protected inside the gall, spraying isn’t effective after gall formation. Galls look bad, but don’t harm plants greatly. Apply horticultural oil next spring to tree trunks and branch bark before leaves form.
Fruit insects
Apple maggot. Adult flies begin injecting eggs into apples about July 1. The resulting larvae tunnel through developing fruit. Spray spinosad at weekly intervals beginning in late June. A recent recommendation from the University of Minnesota involves enclosing each apple in a plastic sandwich bag, stapled shut with a lower corner cut for water drainage. If done in late June, it excludes egg-laying flies.
Spotted-wing drosophila. The small fruit fly attacks raspberries and strawberries by inserting eggs into soft fruit, which hatch into small white maggots in each fruit. Apply spinosad to target adult flies before berries ripen and before eggs are laid. Rotate sprays with pyrethrin to avoid insect resistance.
Sap beetle, also called picnic beetle. Small, oval, black beetles with orange spots are a nuisance on raspberry and strawberry fruits. Remove overripe fruits and try spinosad.
Vegetable insects
Flea beetles. Tiny black insects cause numerous tiny holes in leaves of radish, potato and cabbage relatives. Apply spinosad, Sevin, malathion or pyrethrin.
Cabbageworm. White butterflies lay eggs on cabbage, cauliflower and broccoli, resulting in green “loopers” that eat large holes in leaves. Apply BT or spinosad.
Cucumber beetles. Yellow beetle with black stripes or spots feeds on leaves of cucumber, squash, melons and pumpkin. Apply neem oil, pyrethrin or Sevin.
Squash vine borer. Adults lay eggs at the base of vines in late June, resulting in white larvae that tunnel inside stems resulting in vine collapse. Dust base of stems with Sevin in late June and repeat every 10 days until late July.
Roses
Leaf cutter bee. Because they’re pollinators, it’s advised to ignore the neat, circular holes they cut for nesting material.
- Other rose insects will be addressed in a future rose-care column.
