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The most unpleasant part of gardening is pest control. Pests are a nuisance and the process of controlling them can be even worse. On top of all that, some methods of pest control can be dangerous to the gardener and to the garden if used carelessly. Gardeners who grab a can of bug killer every time they see an insect do the worst damage.

Safe and effective pest control requires an extensive knowledge of garden pests and controls and a careful adherence to important rules.

Four steps of pest control

Identify the pest. The most important step of pest control is to recognize the problem. Sometimes it is obvious, such as a caterpillar chewing a hole in a tomato. Sometimes it is not obvious, such as one plant that is off color and not growing as fast as others in the yard.

The key to identifying pests is to be very observant. If one side of a plant is a different color than the rest, then observe whether it is the sunny or shady side or the wetter or dryer side or if the soil has been disturbed on that side. It may be that a shade loving plant is getting sunburned or a sun loving plant is starving for sun. It may be that the soil is too wet or too dry. It may be that the roots have been damaged by gophers or by digging. Occasionally the problem will be that the soil has been poisoned by a gas leak or that there were fumes from a weed killer applied on a hot day. Since branches are mainly fed by the roots directly beneath them, one side of a plant may be affected while the rest is normal.

Holes in the leaf are usually caused by insects but shothole disease will also cause holes because the infected spots stop growing and tear out as the rest of the leaf continues to expand. It is necessary to observe the early stages of the damage to identify it.

Scouting through the yard regularly for insects or diseases and carefully observing changes in plant appearance is essential for effective pest control.

Once a problem is noticed, the Ortho Problem Solver is a great a great tool for identifying pests since it has color pictures of hundreds of pests. The Ortho Problem Solver can be found at most garden centers. Or the abridged version, The Ortho Home Gardener’s Problem Solver, can be purchased at a reasonable price.

Decide if the pest is serious enough to justify controlling it. Plants can lose ten percent of their leaves without it having any appreciable effect on plant growth. Blemishes on fruits and vegetables may not even affect their flavor or appearance, especially if they will be peeled before being used.

How the plants are being used affects how much damage is tolerable. Flowers providing color in the flowerbed do not have to be as nice as cut flowers for the table.

Lawns can have up to thirteen crane fly larvae per square foot without any visible effect on the lawn. I never bothered to treat my lawn for crane fly larvae because I knew that before it turned brown a flock of starlings would show up and have a feast.

Also, it is much easier to control some pests at certain stages of their growth. For example, several insecticides will control scale insects at the crawler stage when they hatch out and are looking for a place to attach themselves to the plant. But, once they are attached, they cover themselves with a waxy coating so those insecticides have no effect. Many weed controls have to be applied before weeds appear. Timing is very important.

Preference should be given to methods that selectively control pests while not harming plants or beneficial insects. My first choice in insect control is to pick and smash the insects. It is 100% effective with no damage to the environment or to beneficial insects. But it is impractical for large plants or large numbers of insects. My first choice in disease control is to keep the leaves dry by applying water to the soil instead of the leaves and by avoiding watering in the evening since plants will often stay wet until morning. This prevents diseases since diseases need a film of water on the leaf in order to infect the plant.

For large numbers of plants or insects, sprays may be the only practical control. It is very important to read and follow the instructions. The label will list which pests it controls, which plants it is approved for and how to mix and apply it. Millions of dollars are spent in testing each product for each pest on each plant on the label to determine safety and effectiveness. Several times I have heard of someone who has severely damaged his plants by using the wrong product so read the label carefully.

Many people have the idea that organic pesticides are safer than synthetic pesticides. This is not true. Toxicology testing shows that they are comparably poisonous. Organic pesticides usually break down quicker so they don’t build up in the environment but they also have to be applied more often.

Some people think that home remedies are safer than commercial pesticides. Apparently they are lulled into complacency because the products are familiar. But some of the home remedies I have seen are many times more toxic than commercial products and there isn’t the extensive testing to back up the claims.

Follow up to see if the pest control was effective or more treatment is needed. It may be that the pest was misidentified. Sometimes two pests will be present at one time so additional treatment is needed.

Some products require two applications to be effective. For example, most miticides will kill spider mites but not the eggs. At summer temperatures, it takes only seven days for an egg to turn into an egg laying adult. A second spray is required to kill the mites that hatch after the first spray but before they start laying eggs. Since the first spray also kills the natural predators on mites, they will come back worse than before if the second spray is not applied. Gardeners who spray once a month have more trouble with spider mites than gardeners who never spray.

This last step is very much like the first step. Careful observation and regular scouting for pests is necessary for effective pest control.

These same steps should be followed whether the pest is insect, disease or weed.

Insects

Hundreds, perhaps thousands, of different kinds of insects are likely to be found in gardens every year. The presence of insects doesn’t mean that there is a problem. Some insects just rest on plants then fly off without causing any damage. Some insects are beneficial because they eat insects that cause damage. Only about one tenth of all insects cause damage.

Holes in leaves are not always caused by insects. Holes may be caused by shothole disease or by slugs.

Identify the pest While there are so many different kinds of insects, they are divided into a few groups based on their characteristics. Some go through complete metamorphosis, that is, a great change from the larva stage through the pupa state to the adult. Others have young nymphs that look the same as the adult except that adults have wings and can mate. Some have chewing mouths while others have sucking mouths. Some do damage as larvae while others do damage as adults and some do damage at both stages.

Some chewing insects leave holes in leaves or eat the entire leaf. Examples are caterpillars and beetles. Leaf miners chew tunnels in leaves while borers and bark beetles chew tunnels through wood.

Sucking insects pierce leaves and stems and suck out the sap or cell contents. This may leave discolored spots of local damage or it may weaken the entire plant.

Mites are not insects but closely related to spiders. Damage is done by both nymphs and adults which have sucking mouths.

Slugs are a common pest. They do not have teeth but they have a rough tongue that they use to make ragged holes in leaves.

Controlling Insects There are many ways to control insects other than spraying poisons. Physical barriers can be effective controls. A copper strip forms a barrier that slugs will not cross. A cardboard cylinder around a young transplant will keep cutworms away. Garden blankets are finely woven but lightweight plastic sheets that are put over a garden. It prevents flying insects from reaching the plants. An agriculture development worker in Thailand said that they put a foam plastic bag around every young fruit which kept away insects and was then used for protective packing at harvest time.

Practicing good sanitation that removes fallen fruit and leaves will remove many overwintering insects. Removing weeds can remove places that insects hide. Tilling the garden in the fall to bury crop residues suffocates many garden insects while exposing others to freezing and to predators. Rotating crops to different parts of the garden each year also helps to starve insects.

Traps can be very selective and effective for controlling small numbers of insects. Commercially made traps are available that use sexual attractants so they are very selective. A yellow sticky paddle is an excellent trap for whiteflies. Smearing Tanglefoot, a sticky cream, on a red ball and hanging it in the tree can make an excellent trap for apple pests. A trap for fruit flies can be made from a milk jug by putting in it a quart of water, a cup of sugar, a tablespoon of vinegar and a banana peel. While traps may not control large numbers of insects, they will indicate how many of which kind of insects are present and when it is time to spray.

Biological controls can be very selective and effective control. B.T., which stands for Bacillus thuringiensis, is a bacteria that infects caterpillars and quickly kills them but has no effect on other animals. Milky spore disease targets Japanese Beetles. Beneficial nematodes are microscopic worms that kill insects in the soil but have no effect on other animals. Parasitic wasps lay eggs in caterpillars which are soon immobilized and killed. Ladybugs, or more properly Ladybird beetles, have a voracious appetite for aphids, scale insects and mealybugs. Praying Mantises will eat aphids as well as any other insect it can catch. These biological controls are available for purchase to be released in the yard. Other biological controls are spiders and birds. Birds will be attracted to the yard if there is a birdbath next to a large shrub.

Companion plants are another biological control. Planting marigolds or tomatoes in the garden reduces the number of aphids because they both contain natural aphid killers. Nasturtiums attract aphids away from other plants. Then the nasturtiums can be sprayed instead of spraying everything.

New varieties of plants have been bred to be resistant to certain insects. Plants can also be made somewhat more resistant to insects by keeping them in good health. Borers and Bark Beetles are especially attracted to plants that are under stress. Proper soil preparation, fertilizing and watering will help plants ward off insects.

Sometimes all of the above do not keep insects in control so chemical controls are necessary. Many chemical controls are broad spectrum so they kill a wide variety of insects, both destructive and beneficial. Some are more selective. Some can be used on edibles as well as ornamentals but some are limited only to ornamentals.

Malathion and Sevin are broad spectrum insecticides that can be used on edibles as well as ornamentals. Kelthane is an effective miticide that can also be used on edibles or ornamentals.

Malathion is one of the safest for humans of any of the chemical insecticides, synthetic or organic. However, it can cause damage to ferns and maples. Sevin is especially effective on caterpillars and beetles.

Pyrethrum, rotenone and neem oil are broad spectrum organic insecticides which can be used on edibles or ornamentals.

Orthene, Cygon and Di-Syston are systemic which means that they will absorb into the plant and move to areas that were not sprayed directly. This makes them more effective but it also means that they cannot be used around edible plants. Vendex is an effective miticide that is mixed with Orthene to make Isotox, which controls both insects and mites.

Insects can become resistant to insecticides, especially if the same one is used every time. Rotating between three or four pesticides is a good way to prevent resistance.

Sprays for insect control are effective for anywhere from three days to two weeks. Sprays will kill insects within minutes or hours. For these reasons, insect sprays should not be applied until insects are present for maximum control and minimal side effects.

The Extension Offices of Oregon, Washington and Idaho maintain a website which describes insect control methods for most agricultural and ornamental plants. The index is found at Pacific Northwest Insect Management Handbook

Diseases

Fungal diseases resemble plants in the way they grow. They are spread by spores which, like seeds, germinate and grow into the plant when water is present. Fungal diseases include leaf spots, mildew, mold, crown rot and rust. Fungal leaf spots are usually round, sometimes with a dark edge like a bullseye. Most fungi are very specific in infecting only a few plants but a few such as anthracnose will infect a large number of different plants.

Yellow streaking and speckles on leaves are sometimes caused by plant viruses, which are like animal or human viruses. They are usually spread by insects or by taking cuttings from infected plants. The only treatment is to remove and destroy infected plants.

Identifying Diseases Symptoms that indicate diseases are leaf spots, leaves and twigs wilting and turning black or entire plants suddenly wilting. Often there are dark streaks in the wood. Crown rot causes the wood at ground level to turn brown while the wood in the branches is still green.

The Ortho Problem Solver or The Ortho Home Gardener’s Problem Solver have excellent colored pictures and descriptions to help identify the disease.

Controlling Diseases As with controlling insects, good sanitation and crop rotation helps control diseases. One difference from controlling insects is that once the disease gets into a leaf, there is no treatment to get rid of it other than to remove and destroy infected leaves, branches or plants.

Infected twigs should be removed three to six inches below where symptoms are showing.

Keeping the leaves dry helps prevent disease spores from growing. Unfortunately in the Pacific Northwest, rain comes frequently in the spring when there is soft new growth that is easily invaded by disease.

For these reasons, sprays for disease control are usually applied when the weather conditions are right for diseases rather than waiting for disease symptoms to appear.

Tribasic copper sulfate is effective for controlling bacteria as well as many fungus disease.

Daconil is a broad spectrum fungicide. Other good fungicides are Funginex and benomyl. Sulfur and neem oil are two natural fungicides.

The Oregon State University Extension Office maintains a website which describes plant disease control methods for most agricultural and ornamental plants. The index is found at PNW Plant Disease Management Handbook

Weeds

A weed is any plant in a place where it isn’t wanted. Weeds, like other plants are divided into grassy weeds and broadleaf weeds.

Weed control

Pulling individual weeds is still the most selective and effective weed control. Hoes can make it easier and quicker for large areas. I prefer the Ames Action Hoe because it can be pushed or pulled and it slices off the weeds below ground level without disturbing mulch or chemical weed controls. A two to four inch layer of mulch controls weeds because the mulch dries out quickly and kills small weeds.

A thick, healthy lawn effectively controls weeds by smothering them. Lawn weeds are a sign that the lawn is stressed, usually because of watering, fertilizing, mowing too short or from compacted soil.

Various weed control fabrics have not proven to be effective. They may stop weeds from growing up from below but weeds still grow on top of them and roots can grow through them.

Chemical weed controls fall into three groups: pre-emergent, post-emergent and soil sterilant.

Pre-emergent weed controls have to be applied before weeds germinate. Treflan and Surflan are effective against both grassy and broadleaf weeds.

Casoron will kill grass and young weeds but needs to be applied before broadleaf weeds are established.

Post-emergent weed controls have to be applied directly to the growing weeds. Roundup is effective against both grassy and broadleaf weeds. Fluazifop selectively controls grassy weeds. 2,4-D and Trimec selectively control broadleaf weeds.

Soil sterilants are effective against both grassy and broad leaf weeds and can be applied either pre-emergent or post emergent. Monobor chlorate and Triox are effective but they cannot be used within twenty feet of trees or shrubs.

The Oregon State University Extension Office maintains a website which describes weed control methods for most agricultural and landscape uses. The index is found at PNW Weed Management Handbook

Spray precautions

Pesticides should be stored in the original containers where they are inaccessible to children and pets. Separate measuring spoons and cups should be used. Empty containers should be triple rinsed into the spray tank then thrown away. Old or unused pesticides should be disposed of properly as hazardous waste.

Long sleeves, long pants and waterproof shoes are a bare minimum. Complete rain gear including a rain hat is recommended. Some pesticides require goggles and a filter mask.

Make sure all kids and pets are out of the area. Check neighbor’s yards also. Avoid spraying on windy days although a light breeze may be beneficial. Start spraying on the downwind side of the yard and work into the wind to avoid spray fumes. Never spray directly into the wind.

Pesticides mixed with water should be sprayed out instead of stored. A better solution is to use a sprayer such as Ortho Dial’N’Spray that only mixes in the water as it is sprayed. The pesticide still in the jar can be poured back into the original container with no waste.

Wash face and hands before eating or drinking. When finished spraying, put all clothes directly into the washing machine or into a bag to keep it separate from the rest of the laundry and take a shower.

Additional information on pest control can be found on these websites:
Washington State University Hortsense
Oregon State University Extension Service

More gardening information can be found on my webpages:
Landscape Design | Improving Soil | Plant Nutrients | Planting in Clay Soil | Roses
Edible Landscaping | Fruit Tree Tips | Planting a Vegetable Garden | Lawn Care | Pest Control
Pruning for Shade, Flowers and Fruit | Seasonal Pruning Guide | Remove Trees Roots and All
Fall Planting | Water Wise Gardening | Winter Plant Protection
House Plants | Plant Propagation

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