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 pest controls, and a careful adherence to important rules.
A very helpful source of information on Natural Yard Care and Integrated Pest Management is found online at GrowSmartGrowSafe.org which includes natural controls and chemical controls for insects, diseases, slugs & snails and weeds. Pesticides are rated Lowest Hazard, Low Hazard, Moderate Hazard and Highest Hazard. The website can also search for pest controls by pest or by crop or application area.
Additional information with pictures of pests and recommended controls can be found on these websites: Washington State University Hortsense, Pacific Northwest Handbooks, UC IPM Online, Oregon State University Extension Service.
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 shothole disease.
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, information is available on the internet, especially the websites listed above.
Decide if the pest is serious enough to justify controlling it. Plants can lose ten percent of their leaves without it having any significant 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 thirty European 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.Apply appropriate control measures at the proper time. Different controls are very effective for some pests and no help at all for others. That is why it is so important to correctly identify the problem. It is also just as important to be familiar with different control measures to know which are effective against that particular pest.
Also, some pests are much easier to control 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 most 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 places and 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.
It is illegal to use any pesticide in a manner that is inconsistent with the label. The Oregon Department of Agriculture regularly collects stiff fines from pesticide applicators who violate the label.
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 do not 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 is not 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, many 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.
Hundreds, perhaps thousands, of different kinds of insects are likely to be found in gardens every year. The presence of insects does not mean that there is a problem. Only about one tenth of all kinds of insects cause damage. Some insects just rest on plants then fly off without causing any damage. Some insects are beneficial because they eat insects that cause damage. A guide to beneficial insects with pictures and be found at GrowSmartGrowSafe.org by clicking on Good Bugs.
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. Larvae of moths and butterflies are caterpillars. Larvae of flies are maggots. Larvae of these insects often damage plants but the adults do no damage other than laying eggs. Beetle larvae are grubs. Both the grubs and the adult beetles may damage plants.
Other insects have young nymphs that look the same as the adult except that adults have wings and can mate. Grasshoppers have chewing mouths while true bugs and aphids have sucking mouths. Some true bugs 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 are closely related to spiders, and have sucking mouths. Damage is done by both nymphs and adults.
Slugs also make holes in leaves, but the edges of the holes are ragged because their teeth are on their tongues.
Controlling Insects with Integrated Pest Management (IPM)
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 fabrics 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 many insects. Smearing Tanglefoot, a sticky cream, on a red ball and hanging it in an apple 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 insects they can catch. Green lacewings eat lacebugs and other insects. 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 a 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. 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. Kelthane is an effective miticide that can also be used on edibles or ornamentals.
Pyrethrum, rotenone, neem oil and horticultural oil are broad spectrum organic insecticides which can be used on edibles or ornamentals, while spinosad is more selective. Horticultural oil is also a miticide. For certified organic products, look for the Organic Materials Review Institute insignia: OMRI. There are also several synthetic pyrethrins, such as permethrin and others all ending in -thrin, which are broad spectrum insecticides. Check the label to see if they can be used on edibles.
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.
Imidacloprid is a systemic which is labeled for use on ornamentals and edibles. When applied to the trunk or roots, it will eventually move to the tops of even the tallest tree, although it may take thirty to sixty days. Imidacloprid continues to protect against insects for a long time, even years.
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. Choose pesticides with different Group numbers.
Sprays for insect control are effective for anywhere from three days for some organics to three weeks for some systemics. Sprays will kill insects within minutes or hours. For these reasons, insect sprays, except for imidacloprid, should not be applied until insects are present for maximum control and minimal side effects.
An excellent resource for identifying and controlling insects is the PNW Insect Management Handbook published by the Extension Services of Oregon, Washington and Idaho. A copy can by purchased at local extension offices or the information be found on the internet at http://pnwhandbooks.org/insect
Slug control begins with removing places where slugs hide from the sun and reproduce. Low decks and litter are favorite places for slugs. Also, beds of round river rock are a perfect breeding ground for slugs. Metaldehyde and iron phosphate are both good for slug control. Metaldehyde is a little more effective but iron phosphate is much safer for pets. Both should be scattered and never put in piles where pets might eat them.
I have found the slug bait is most effective when it is applied in early spring when hosta buds are one to two inches tall. This indicates that the soil is warm enough slugs are active, but there is not much for them to eat. Applying slug bait at the maximum rate at that time will usually prevent slug damage for most of the spring and summer.
Always check labels for approved uses. It is illegal to use a pesticide in a manner inconsistent with its label. Active ingredient Brandname Natural/ Use on Comments INSECTICIDES Organic Edibles Acetamiprid Rose and Flower Insect N N Azadirachtin Bio-Neem Y Y Also controls some diseases Bacillus thuringiensis B.T. Y Y Bacteria that kills caterpillars Bifenthrin Ortho Bug B Gon N Y Canola Oil Y Y Carbaryl Sevin N Y Most effective spray for caterpillars Cyfluthrin Bayer Veg. and Garden N Y Broad spectrum, last for months Imidacloprid Bayer Complete Insect N N Systemic, lasts three years Malathion Ortho Malathion N Y Neem Oil Y N Also a Fungicide Petroleum Oil Volck Oil Spray Y Y Also a Miticide Potassium Salts of Safer Insect Killing Soap Y Y Fatty Acids Pyrethrins Y Y Quick acting organic Silicon Dioxide Diatomaceous Earth Y Y Spinosad Captain Jack's Dead Y Y Produced by a bacteria Bug Brew MITICIDES Cottonseed, Clove, Mite X Y Y & Garlic Oil Petroleum Oil Volck Oil Spray Y Y FUNGICIDES Basic Copper Sulfate Y Y Also controls Bacteria Beta-Pinene Wilt Pruf Y Y Protectorant, not a fungicide Chlorothanonil Daconil N Y Might cure a recent infection Copper Octanoate Liquid Copper Fungicide Y Y Also controls Bacteria Myclobutanil Immunox N Y Can cure a recent infection Propriconozole Bayer Fungus Control N N Can cure a recent infection Sulfur Y Y Protectorant Tebuconozole Rose & Flower Disease N N Can cure a recent infection BIOFUNGICIDES Bacillus subtilis Serenade Disease Control Y Y Beneficial bacteria Streptomyces lydicus Actinovate, Cease, Regalia Y Y Beneficial bacteria COMBINATION INSECTICIDE, MITICIDE AND FUNGICIDE DORMANT SPRAY Calcium Polysulfides Lime Sulfur Y Y Used on fruit trees, roses and + Petroleum Oil Volck Oil Spray Y Y deciduous shrubs SLUG & SNAIL Iron Phosphate Sluggo Y Y Safer for pets Metaldehyde Deadline N N Sodium Ferric EDTA N Y PREDATORS TRAPS AND LURES ANIMAL REPELLANTS Beneficial Nematodes Pheremone Lures Bird Netting and Flash Tape Green Lacewing Yellow Jacket Traps Deer Repellent Ladybird Beetle Yellow Sticky Traps Scarecrows
Diseases may be caused by bacteria, fungi or viruses. Bacteria are one-celled animals that multiply by dividing. Bacterial diseases include leaf spots, blights and wilts. Diseased areas are usually black. Bacterial leaf spots have irregular margins because bacteria diseases usually do not cross leaf veins.
Fungal diseases resemble plants in the way they grow. They are spread by spores which, like seeds, germinate and grow into the plant when a film of water is on the leaf. 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 will infect many kinds of 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. Sometimes, careful fertilizing and watering can hide the symptoms, but the only cure is to remove and destroy virus infected plants, although some plants tolerate certain viruses.
Spots on the leaves may be caused by bacteria, fungi or viruses. Wilting and blackened leaves and twigs are usually caused by bacteria. When an entire plant wilts while the soil is moist, it is either root rot or crown rot, which may be caused by bacteria or fungi. Crown rot causes the wood at ground level to turn brown while the wood in the branches is still green. Often there are dark streaks in the wood. Always check soil moisture before watering a wilted plant, because watering only makes crown rot worse.
The websites listed at the beginning of this article have excellent colored pictures and descriptions to help identify diseases.
Avoid plants which are disease prone. Look for varieties which are disease resistant. For example, tomato varieties with VFN after the name are resistant to verticillium wilt, fusarium wilt and nematodes.
Place plants where growing conditions are favorable to reduce stress. Avoid combining plants which prefer dry soil with plants which need moist soil. The plant lists include preferences for sun or shade, moist or dry.
Crown rot and root rot are common plant killers, but can easily be controlled by proper planting and watering. Susceptible plants, such as heather, daphne, tulips and Japanese maples should be planted on a mound or slope. Always position the crown of a plant an inch above surrounding soil so water does not collect at the trunk. Never cover the branches or more than an inch of the trunk with mulch. Let the soil dry out between waterings. Always check soil moisture before watering a wilted plant, because watering only makes crown rot and root rot worse.
As with controlling insects, good sanitation and crop rotation helps control diseases. One difference from controlling insects is that very few sprays will control a disease once it gets into a leaf. Usually, there is no treatment to get rid of diseases 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.
Copper based products are effective for controlling bacteria as well as many fungal diseases. Some bacterial diseases can be prevented by a beneficial bacteria, Bacillus subtilis.
Captan and Clorothalonil are broad spectrum fungicides. Triforine, Myclobutanil, Propiconazole and Tebuconazole are especially good for powdery mildews, rusts and leaf spots. They will penetrate into the leaf and cure an infection if it is recent.
Lime sulfur is most effective when applied at full strength as a dormant spray when no leaves are present. It can be used on some plants with leaves if it is greatly diluted. It controls powdery mildew, scab, brown rot, peach leaf curl, rusts and mites.
Phosphite fungicides are very effective on many diseases and can be used on ornamentals and edibles.
Sulfur, neem oil and jojoba oil are natural fungicides. Coating leaves with Wiltpruf, which looks and acts like Elmer's Glue, can prevent disease spores from reaching the leaves.
Bacillus subtilis and Streptomyces lydicus are beneficial bacteria that produce natural fungicides which are effective in preventing a number of diseases on fruits, vegetables and ornamentals.
When spraying for diseases, it is not as necessary to cover the underside of the leaves because bacteria and fungus spores normally drift down and land on the topside of leaves. However, some diseases which over winter in the soil can be splashed up by raindrops on the the bottoms of the lower leaves.
An excellent resource for identifying and controlling diseases is the PNW Plant Disease Management Handbook published by the Extension Services of Oregon, Washington and Idaho. A copy can by purchased at local extension offices or the information be found on the internet at http://pnwhandbooks.org/plantdisease.
The online version also contains disease susceptibility tables for varieties of apples, beans, blackberries, blueberries, cherries, crabapples, hazelnuts, junipers, pears, raspberries, roses, strawberries and tomatoes.
A weed is any plant in a place where it is not wanted. Weeds, like other plants are divided into grassy weeds and broadleaf weeds.
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. Besides bark dust and compost, grass clippings and oak leaves also make excellent mulches for weed control.
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 down through them.
There are some natural, organic weed controls. Corn gluten has been widely recommended, but it has not proven to be effective in the Willamette Valley. It works by absorbing water, and drying out the soil, but there is usually no shortage of water for weed seeds in this area. Another organic weed killer is a very strong form of vinegar which burns leaves and stems but does not kill roots. Other natural controls are boiling water and burning with an electric heat gun or a propane torch. Some people use salt to burn weeds, but salt produces salt burn on surrounding plants and can destroy soil structure.
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. Halts and Team control grassy weeds in lawns, but have to be applied at the right time. Apply them in the spring when the first dandelion flowers appear to control crabgrass. Apply them about Labor Day to prevent annual bluegrass.
Preen and Surflan are effective against both grassy and broadleaf weeds. Both can be used around established plants including annuals after they are established. Ronstar can be used even on newly planted annuals.
Casoron will kill grass and young broadleaf weeds, and will prevent more weeds from growing for about a year. It can be applied around trees and shrubs but it will kill annuals, perennials and bulbs. Do not apply Casoron within a foot of a lawn, or within three feet if the ground slopes toward a lawn. If weeds have already started to grow, apply Casoron first, then apply a post emergent weed killer a week or two later to any remaining weeds.
Post-emergent weed controls have to be applied directly to the growing weeds. Roundup is effective against both grassy and broadleaf weeds. Be careful that Roundup is not tracked onto the lawn, or shoe shaped dead spots will appear in the lawn.
Fluazifop selectively controls grassy weeds. It can be sprayed on most broadleafed plants without hurting them. 2,4-D and Dicamba selectively control broadleaf weeds in lawns. Sulfentrazone and Quinclorac kill crabgrass and some broadleaf weeds, and can be used on most lawn grasses, but not on bentgrass.
Equisetum, or horse tails, is difficult to control, but I did find an effective method. First, I dragged a hose over the horse tails to bruise them so they would absorb more herbicide. Then I sprayed them with Ortho Brush B Gon. The entire patch died down and only a few sprouts appeared the following spring.
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.
An excellent resource for identifying and controlling weeds is the PNW Weed Management Handbook published by the Extension Services of Oregon, Washington and Idaho. A copy can by purchased at local extension offices or the information be found on the internet at PNW Weed Management Handbook
Spray precautions Every pesticide label has a special word to indicate the relative danger of the pesticide: Caution, Warning, Danger or Poison. Poisons will also have the Skull and Crossbones symbol, but they are normally not available to homeowners without a pesticide applicator license.
With any spray, it is important to read the label carefully and follow the directions. The label is the law. It is illegal to use any pesticide in a manner which is inconsistent with the label. The Oregon Department of Agriculture regularly collects stiff fines from pesticide applicators who violate the label.
The label includes information on places it can or cannot be used, pests controlled, plants it can or cannot be used on, warnings about hazards, personal protective equipment required, symptoms of over exposure and how to treat them.
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 sprayer. Puncture the empty container so it cannot be reused, then throw it away. Old or unused pesticides should be disposed of properly as hazardous waste.
Personal protective equipment is required for all pesticides. Long sleeves, long pants, shoes and socks are a bare minimum. Waterproof gloves and boots, and a filter mask are recommended. Complete rain gear including a rain hat is recommended for spraying overhead. Some pesticides require goggles and a filter mask. The label will indicate what Personal Protective Equipment is required. Many pesticides have a Restricted Entry Interval following application.
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.
If more pesticide is mixed with water than needed, it is better to spray out where the label allows instead of storing it. Never pour pesticides down the drain because most of them are hazardous to fish and aquatic animals. 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, drinking or using the bathroom. 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. Then, take a shower.
Resistance to a pesticide will eventually appear if the same product is used repeatedly. It is important to rotate between pesticides with different modes of action (groups) to prevent resistance.
Additional information on pest control with pictures of pests and recommended controls can be found on these websites:
Washington State University Hortsense
Pacific Northwest Handbooks
UC IPM Online
Oregon State University Extension Service
Annuals, Biennials, Perennials and Bulbs
Fruit Tree Tips