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How to Identify and Target Insect Pests

This is the second half of a talk by Carol Allen about dealing with insects in an environmentally-friendly way.  To read to first part, about pest controls and beneficial insects, click here.

In general, small soft-bodied insects can be controlled with what Carol calls “power washing.”  This is defined as setting your hose nozzle to a powerful fan/jet spray and blasting the plant, knocking the insects off.

Below is a list of specific pesky insects and how to treat each one.  Click on the photos to enlarge.

Spider Mites
They exist everywhere, but are only destructive in very high numbers. Look for pale stippling on the leaves or, if the plant has a particularly bad infestation, webbing.  To see the mites themselves, you might need a magnifying glass—adults are about the size of a pin prick.  If you think a plant might have them, you can tap a branch over a white sheet of paper, then look for them on the paper.  If they’re black and moving fast, they’re probably good guy predatory mites, but if they’re orange-ish and moving more slowy, they’re spider mites.

Control: Power wash them off or use oil. If a plant is prone to getting them (like dwarf Alberta spruce and indoor palms), you can take preventative measures by power washing every couple of weeks.

Thrips
Tiny, soft-bodied insects with rasping mouths.  They really like chrysanthemums and other daisy-like flowers.  They tend to hide/feed in flowers, flower buds and leaf buds and are hard to get at.

Control: Power wash.  You can do preventative power washing or plant daisies to lure them away from plants you like.

Scale
A sucking insect that latches on to leaves and branches and forms an impenetrable barrier, either a shell or waxy secretion.

Control: Manually scrape off adult scale and then follow with an oil spray.  In June, look for “crawlers” (babies) and power wash, followed by an oil spray.  Getting a good ID on what kind of scale you have helps in spraying when it’s most effective since there are lots of different scale life cycles, some with multiple generations in a year.  As a rule of thumb, though, looking in June is pretty good.

Aphids
Small, soft-bodied sucking insect.  Some are generalists (they’ll eat just about anything) and some are specialists (e.g. the milkweed aphid which will only eat milkweed).

Control: Power wash.  You’ll want to do this every couple of days because aphids are born pregnant and the next generation will be right around the corner.

Flea Beetles
Fast moving and strong fliers.  Adult beetles are chewing insects; these make lots of small holes in the leaves of a variety of plants, like eggplant.   They overwinter as adults and emerge on nice days.

Control: A thick layer of straw mulch will prevent them from emerging.  You can also use barrier fabric if they’re affecting plants that don’t need pollinators.  They really like daikon and radish plants, so you can try planting these to lure them away. If they’re persistent on a specific crop, you may need to break the cycle by not planting that crop for a few years.  Rotating crops will also help.

Squash Vine Borer
A day-flying clear-wing moth.  The larva will bore into the base of a squash vine and kill it by blocking the flow of water to the rest of the plant.  They also carry in a harmful bacterium that causes wilt.

Control: Try setting out a pan painted yellow filled with soapy water; the color attracts them and the water drowns them.  Because there is only one generation per year, you can also try planting a second crop in July to get around their lifecycle.  If you think your squash has a borer, you can cover the vines at an internode (stem in between leaves) with soil/compost beyond the point where the borer is active; the plant will put out new roots and effectively create a new base. You can also just choose to plant squash varieties that are resistant.

Cucumber Beetles
They overwinter as adults and then lay their eggs at the base of cucumbers and melons.  The adults eat the plants and the larvae feed on plant roots.  They also carry the bacterium that causes bacteria wilt which kills infected plants.

Control: Knock beetles into a bowl of soapy water.  If beetle numbers are high, you may want to break the crop cycle.

photo: Destruction flickr photo by Brian shared under a Creative Commons (CC BY 2.0) license

Cabbage Worms
There are several moths and butterflies whose larvae fall under the title “cabbage worm.”  The larvae feed on leafy greens like cabbage, lettuce, broccoli and kale.  There are several broods per year.

Control: Cover crops with fabric as soon as you plant them—cabbage moths and butterflies start laying eggs early when temperatures reach 50°F.

Japanese Beetles
The adults eat leaves and flowers and the grubs eat lawn roots.  They can be destructive in large numbers, however the population in this area has been low for the past few years.

Control: Treat your lawn with Milky Spore.  This is a bacterium that kills grubs and is especially effective against Japanese beetle grubs.  The good news is because it’s a self-perpetuating organism, once you treat your lawn, you never have to do it again.  The bad news is, it can take a few years to take hold.  Also, because Japanese beetles can fly, you may get them coming in from your neighbor’s yard, so talk to your neighbor about treating their yard.  And, while you’re waiting for the milky spore to take effect, knock beetles into bowls of sudsy water.  Whatever you do, don’t use Japanese beetle traps; they’ll just attract more beetles to your yard.

Emerald Ash Borer
Extremely destructive to ash trees.  If you have a tree with a dead top and don’t know what it is, chances are it’s an ash.

Control: Not a lot you can do.  If you have an ash tree, as Carol likes to say: “you have a chainsaw in your future.”  An arborist can inject a pesticide which will help, but it’s probably best just to take the tree out.

Bag Worms
They can completely defoliate an evergreen like a dwarf Alberta spruce.  They like conifers, but can be found on other trees and shrubs as well.  The bags look like little brown tassels made of old pine needles.

Control: Late winter is the best time to remove any bags you find.  The eggs overwinter in the bags, so destroy them now before thousands of new worms hatch in spring.  Cut the bag off (don’t pull because you’ll break the branch it’s attached to) and throw it away.  In early June the worms will be starting new bags; spray them with Bt before they’re totally concealed in the bag.

Eastern Tent Caterpillars
Fuzzy caterpillars with a white stripe down their back that can defoliate trees.  They like plants in the Rosaceae family, especially cherry trees.

Control: In late winter, look for egg masses (look like an inch of black Styrofoam) circling branches and break them off.  After they hatch, while the nest is still small, you can gather it up with your hands (you may want to put on gloves for this), bag it and throw it away.  You can also use Bt when the caterpillars are still babies.  Don’t bother with any controls if the caterpillar tent is on a tree in the woods; tent caterpillars are an important food source for fledgling birds, so should be left alone when possible.

Gypsy Moth
These used to be a huge problem, but animals here have adapted to eating them so numbers have been kept in check.

Brown Marmorated Stink Bugs
Likewise, populations have ebbed so they’re unlikely to do too much damage.  If you do find one feeding, just tap it into a bowl of soapy water.

Spotted Lantern Fly
The next big thing in pest insects.  They haven’t been spotted in the DC area yet, but have been seen in parts of western Maryland and are a huge problem in Pennsylvania.  If you do see one, report it to DontBug.MD@maryland.gov.  For more info about it, click here.

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