It’s a simple concept: Well-maintained, healthy plants are less susceptible to pests and diseases than stressed, sick or injured ones.
Inspect your garden plants often to detect any pest and disease problems early. This way you can promptly treat infestations and infections using the least-toxic remedies possible.
Photo Credit: ©2002 Dolezal Publishing/John M. Rickard
Beetles of various types can damage tender shoots and flower buds. Handpicking and applying insecticidal soap directly to the pest are effective means of control.
Photo Credit: ©2002 Dolezal Publishing/John M. Rickard
It’s crucial that you purchase the correct control product for your exact problem. Carefully identify all pests and diseases before treatment, and make sure the plant you need to treat is listed on the chemical label, along with the insect or disease you’re fighting.
Photo Credit: ©2002 Dolezal Publishing/John M. Rickard
Well-maintained, healthy plants are less susceptible to pests and diseases than stressed, sick or injured ones.
Photo Credit: ©2002 Dolezal Publishing/John M. Rickard
Don’t forget to protect your tender young plants from animal pests. Fences are a good method – just be sure they extend below the ground, too.
Photo Credit: ©2002 Dolezal Publishing/John M. Rickard
You can help keep your plants healthy with regular TLC and a little common sense: Water each plant properly according to its needs. Make sure there’s good air circulation between and within plants. Keep your garden tidy by removing weeds and debris. Adjust soil pH to suit the plant species growing in your planting beds, and fertilize based on the results of a soil test.
Frequently walk through your garden and keep an eye out for pests and diseases, too. Look carefully at each plant, noting any discolored or tattered foliage or anything else that may seem amiss. Should you notice any signs of diseases or pests, try to identify what’s wrong. If you can’t positively identify the offender, take a sample (in a sealed bag) to your local Cooperative Extension office for diagnosis.
The following list includes some common pests and diseases that you may find on your trees and shrubs, along with suggested remedies for each problem.
Anthracnose
Symptoms: Black, tan or red spots on leaves; premature leaf drop; black cankers on stems, with a general wilt of branch tips.
Offender: This fungal disease is sometimes called black spot or twig blight. It occurs in late spring and summer, typically after humid conditions.
Remedies: Remove infected leaves and branch tips. Collect and destroy infected fallen leaves – do not put them in the compost pile. Thin excessive growth to promote air circulation. Spray with a fungicide only as a last resort, carefully reading and following all instructions and warnings on the product label.
Aphids
Symptoms: Leaves curled and twisted, often with a black sooty appearance; stunted or deformed blooms on new growth.
Offender: Quarter-inch-long, soft-bodied aphids that can vary in color from green to yellow to black. (They’re common on a wide range of plants.)
Remedies: Wash off light infestations with a strong stream of water. If that’s ineffective, spray with horticultural oil. Only spray with botanical neem or pyrethrin as a last resort, carefully reading and following all instructions and warnings on the product label.
Bagworms
Symptoms: Weakened and defoliated trees and shrubs; small, silken bags about 1-2 inches long hanging from branches.
Offender: Bagworm caterpillars are hidden by their silky bags. They’re found east of the Rocky Mountains in North America on deciduous plants and conifers. The worst damage is found on arborvitae and cedars.
Remedies: For small infestations, handpick and destroy bags. For large infestations, spray with Bacillus thuringiensis (Bt) as soon as young bagworms are noticed, following all instructions on the product label.
Beetles
Symptoms: Green foliage eaten away, with only veins remaining; leaves later become dry and skeletonized.
Offenders: Hard-shelled beetles, including Japanese beetles, elm leaf beetles and willow leaf beetles. (They’re most active in the heat of the day.)
Remedies: Handpick beetles on small shrubs in early morning while they’re inactive. Apply milky spore (Bacillus popilliae) to lawns to give long-term control for Japanese beetle grubs.
Botrytis Rot (Gray Mold)
Symptoms: Collapsed flowers under heavy fuzz of gray or brown fungal spores.
Offender: Fungus.
Remedies: Remove affected blossoms, foliage or entire plant (if necessary). Space plants for more air circulation and reduce nitrogen fertilizer.
Fall Webworm
Symptoms: Chewed leaves; in summer and fall, silky webs appear at the tip end of branches, with larvae visible inside.
Offenders: Adult webworms, about 1 inch long with a dark stripe down their backs. They’re common on deciduous trees and shrubs.
Remedies: Prune and destroy branches infested with webs. If necessary, spray with Bt after breaking open the web with a stick.
Fireblight
Symptoms: Young twigs and branches that die back, starting at tip ends; leaves shrivel and turn brown; twig tips curl, resembling a hook.
Offender: This bacterial disease is common on ornamental pears, crabapples and quinces. The infection occurs in early spring and is favored by wet conditions.
Remedies: Prune out branches 6 inches below signs of damage. Dip pruning tool in isopropyl alcohol after each cut to sterilize and prevent spreading infection. Avoid heavy nitrogen fertilization.
Lace Bugs
Symptoms: Silvery spots on upper surfaces of leaves; black spots on undersides of leaves.
Offender: Lace bugs are 1/8-1/4 inches long and common on rhododendrons, laurels, hawthorns and elms during the growing season.
Remedies: Wash off light infestations with a strong stream of water. If necessary, spray with horticultural oil. Only use botanical neem or pyrethrin as a last resort.
Leaf Gall
Symptoms: Leaves turn light green and are puffy, swollen and distorted.
Offender: Leaf gall is a fungal disease is found on azaleas, camellias and rhododendrons.
Remedies: Pick off and destroy affected leaves as soon as galls are noticed.
Powdery Mildew
Symptoms: White to grayish powdery patches on leaves, as though they’ve been dusted with flour.
Offender: Powdery mildew is a fungal disease that becomes prevalent when days are hot and nights are cool. It mostly attacks new leaves.
Remedies: Thin branches to improve air circulation. Spray with a 0.5 percent solution of baking soda (1 teaspoon baking soda per 1 quart of water).
Spider Mites and Other Mites
Symptoms: Bronzed or yellowed, curled and dried leaves; foliage may fall off; stunted plants; webs may be present.
Offenders: Mites are microscopic in size and difficult to spot. They’re prevalent in hot, dry areas on both conifers and deciduous plants.
Remedies: Wash off light infestations with a strong stream of water. If necessary, spray with insecticidal soap. Only spray with a miticide as a last resort, following all label instructions and warnings.
Tent Caterpillars
Symptoms: In spring and summer, silky webs (or tents) appear in the forks of small limbs; leaves are eaten. In winter, masses of eggs encircle stems.
Offender: Adult tent caterpillars are 1-2 inches long with short, fuzzy bodies. They’re common only on deciduous trees and shrubs.
Remedies: In winter, remove egg masses from bare branches. In spring, prune branches with small tents and destroy clippings. If necessary, spray with insecticidal soap or Bt.
Remember, if you find pests in your garden, consider all your options before taking action. About 90-95 percent of all insects found are either beneficial or relatively harmless, and most plants can tolerate quite a bit of foliage loss or other damage without serious consequence. The environmentally safe practices of handpicking any visible pests, knocking pests off a plant with a strong stream of water from a garden hose or pruning out any diseased portions of the affected plant may very well be the only steps you’ll need to take. (To avoid spreading disease, sterilize your shears between cuts by dipping them in dilute bleach solution or wiping them with rubbing alcohol.)
For large infestations that don’t respond to handpicking or other non-chemical means, you may have to use spot applications of stronger controls such as horticultural oil or insecticidal soap. Note that any control you use in your garden should list the specific disease or pest you’re treating on the label, as well as the plants it’s safe to use on.
If you keep regular watch over your garden, you should be able to spot any problems before they become fully established – meaning a healthier, beautiful plants to enjoy throughout the growing season.
