Written by Catherine Wachs
Thursday, Jul 14, 2011 6:59am
When it comes to pest control, often the best thing to do is... nothing.
It’s a common feeling to go into attack mode when your landscape is being chomped on. A client told me, “I buy organic fruit for my family, try not to keep anything in plastic because of the chemicals it leaches, but when I saw my shrubs being devoured by insects, I was ready to get out the DDT!”
There’s a better way.
Don’t Shoot the Messenger
Most infestations are a signal that your plant is not happy. Insects can sense out an unhappy plant. Your plant might need more sunlight, or less sunlight, more– or less– water, or a different soil pH. Whatever the problem, insects will be attracted to a stressed plant. Insect pests are attracted to yellow, which is the color of stressed plant leaves. It’s no coincidence that insect traps are yellow.
If you spray an insecticide, you may do more harm than good. Pesticides don’t discriminate in their insect-destroying mission. Not only have many popular chemicals been linked to lymphoma and hormonal disruptions in humans, innocent bystanders that are killed by these chemicals include earthworms, spiders, ladybugs, ground beetles, centipedes and all the other “good” critters that keep chomping pests in check and your soil‘s ecosystem healthy.
Put Predators to Work
Intervention with chemicals sets into motion a cycle in which you need to keep using chemicals, some quite toxic, in order to control ever-increasing pest populations. Pests are food for other predator insects and birds. So there needs to be a lot of pests. The predators don’t bounce back as fast. You can’t have more predators than food supply. By using chemicals, YOU become the main predator. But I’m sure you already have a life. Let the experts– the good critters– do that job.
I’ve found, over the years, that keeping a diary of plant problems helps me get a jump on pests in the spring, before they create problems. I make a point to inspect the problem plants early and often, and usually find the culprits. One note about bug hunting. The bugs don’t hang out where you can see them. You must look at the undersides of the leaves and at the tips of your shrubs, where new growth occurs.
Right about now, any plant damage you are seeing started in the spring. Brown, withering leaves and flowers or patches of dead grass are the evidence. We had some early, warm days and the pests got a head start on the predators. They were silently sucking on plant juices while you were marveling that we finally were free of winter weather.
Before the Cavalry Arrives
A little nibbling is normal and must be tolerated if you are to have food for predators’ prey. It is rare that an infestation will kill an entire plant. There are times, such as when you are switching to organic pest control from chemical control, that you need a bit of help to control infestations before the “good bug” cavalry comes to the rescue. Listed below are some common pests and their organic control. Most importantly, get to know the good bugs.
The Bad Bugs
Mosquitos: While mosquitoes are not a plant pest they can drive a gardener insane. The best way to protect yourself is to position a large floor fan wherever you are gardening (or dining). These pesky creatures cannot fly in a wind storm. In areas of standing water that don’t drain after 3 days, use bT mosquito dunks, a naturally occurring bacteria that kills mosquito larvae, which live in water.
Soft Bodied Insect Spray.
Make a non-toxic bug spray that will kill most soft-bodied insects (listed below) on contact. In a 16 ounce spray bottle, pour in 1 teaspoon of dishwashing liquid and fill bottle with water. If you have drenched the plant, wash off the soap with a garden hose. Note: inspect all along the stem before spraying. If you see any of the beneficial insects in the Good Bug section of this article, do not spray. You’ll be destroying their lunch.
Aphids: There are over 1,350 species of aphids. 1/16 to 3/8" long, they come in green, pink, black, yellow or gray. They can be winged or wingless. Aphids pierce the leaf and suck the plant sap. Feeding causes distorted leaves and flowers. Aphids secrete “honeydew”, a sugary liquid. Ants often harvest this sweet liquid. If you see ants on your plants, you can bet they are after honeydew.
Mealybugs: Grayish-white, 1/10th of an inch long, covered by white waxy fluff. Mealybugs suck plant juices, particularly new growth. Leaves wither and turn yellow. Fruit drops prematurely. Mealybugs also secrete honeydew, which supports the growth of sooty mold, a leaf disease that looks like soot.
Scale: Scales can be armored or soft. Soft scales are more common in the Northeast. Adult females are oval, legless, winglessfurry white bumps, 1/8" long. They also suck plants and secrete honeydew. Young nymphs move around for a short time and then the females molt into an immobile form. If you have a huge number of scales, prune and destroy infested branches and twigs. I get perverse satisfaction by scraping them off with my fingernails and crushing them.
Spider Mites: These tiny creatures are so small, you usually see their damage before you see the mites. Leaves become stunted. Damage first appears as yellow speckled areas on leaves. Very fine webbing near the end of branches, close to new growth, signals the presence of spider mites. The webbing is seen more easily in the sunlight, where the sun can glint off the very fine strands. Outbreaks can be severe and rapid in hot dry conditions with low humidity.
Whiteflies: Tiny, white-winged flies, 1 mm long, whiteflies also suck plant juices and secrete honeydew. Eggs are tiny gray or yellow cones. The larva are translucent scales on leaf undersides. Large infestations can produce a white cloud of flies when disturbed. You can vacuum the adults off the leaves or use the all-purpose bug spray.
I have had good success controlling grubs (like the larvae listed below) with beneficial nematodes: soil-dwelling, microscopic worms that lay their eggs in grubs, which kills the grub host. Ordered online, they are mailed to you in a sponge. You simply squeeze the sponge into a watering can to release the critters and pour it around the affected plant roots or brown areas on your lawn. After one or two seasons, you will not have any major problems with grubs again. This works on Japanese beetles and June bugs, too, which eat your grass roots. The one exception is if you have remnants of a dead tree stump under your lawn area. The grubs will keep coming back to the decaying wood. If it’s possible, make that area a garden. Tips: Apply nematodes in the evening. These critters like darkness. Water soil well before and after application. Soil must be warmed to around 55 degrees, usually in April. You can water them into the ground in August, too.
Black Vine Weevils: Adult beetles chew telltale notches in the leaves of trees and shrubs, especially rhododendrons. Their larva feed on plant roots. Larva overwinter in the soil, emerging as adult weevils in June.
Japanese Beetles: The bane of rose growers everywhere, these beetles are ravenous eaters. The beneficial nematodes will control them in the grub stage. Since the adult beetles feed during the day in full sun they are easy to spot. Hand-pick them off your plants. Keep a bucket of soapy water handy to drown your catch.
This is just a fancy way of saying hand-pick pests or protect plants by physical means. Use mechanical control for the pests below.
Leafminers: Larvae tunnel through leaves, making curved, winding paths. They are mostly a nuisance rather than a serious problem. As soon as you start to see their tracks, remove the leaves. This is the surefire remedy. Since leafminers are inside the leaf tissue, soap spraying is not very effective. You can spray neem oil if you want to kick it up a notch.
Slugs: The snail’s homeless cousin, slugs love damp places and come out to feed at night. Holes in the middle of the leaves are usually slug damage. Beetles and birds consider them a treat. You can repel slugs and snails In a variety of ways.
The Good Bugs
These bugs will have your back every time. Get to know them, love them, don’t spray them. You can buy beneficial insects but if you stop spraying and provide food and water, they will show up on their own. Plant small and shallow-faced flowers like yarrow, alyssum, dill and daisies to feed them. If you have a bird bath or pool in your garden, place stones or gravel in the water so bugs can drink safely.
Lacewings: 1/2 to 3/4 of an inch long, lace wings have small heads and large eyes. Their wings are transparent and covered with a network of fine veins. Larva resemble tiny alligators. Adult lacewings are usually not predators but their larva feed on aphids, thrips, mealybugs, scales, moth eggs, small caterpillars and mites.
Lady Beetles: Ladybugs are the most well-known beneficial insect. They can consume 300 aphids during their development. Their larva are voracious, yet few people can recognize the alligator-like larva, which dine on aphids, spider mites, mealybugs and soft scales.
Mealybug Destroyer: A type of lady beetle, larva are cream-colored, segmented and covered with long, waxy hair. They resemble their prey: mealybugs.
Parasitic Wasps: Females inject eggs into host insects like aphids, grubs and caterpillars. It’s a horrible, Alien existence for the hosts, but hey, they’re eating your prized plants!
This list is a tiny portion of the insect ecosystem in your backyard. I would happily help you identify any unknown creatures you come across. Just shoot me an e-mail and I will reply. The main thing to remember is that chemicals disrupt the balance of predator and prey. They destroy beneficial insects like honey bees. Without them we would have no fruit and flowers.
So put down the spray and pick up your magnifying glass. You may find some new friends.