Despite headlines of the past year detailing misuse of pesticides, most gardeners realize that some chemical control of plant pests is still necessary for plant health.
If the headlines scare us into:
- Really reading labels before opening packages
- Following exact directions as to dosage, timing, and safety precautions
- Safely disposing of leftover sprays and empty containers
- An integrated program of using chemicals only as needed to supplement the proper cultural and biological control methods
… that is all to the good.
But suppose the headlines scare us into giving up all garden use of chemicals and cause us to work against their large-scale use in producing all the food, fiber, and wood needed to keep our expanding population fed, clothed, and housed. In that case, we will sink back into the Dark Ages and endure the famines and pestilences described in the Bible.
Most Common Types Of Insects And Diseases
The following is a very brief summary of some of the more common types of insects and diseases that may be expected on ornamentals this summer and some of the chemicals that may be used with reasonable precautions but without protective clothing, respirator, goggles, and rubber gloves.
Whenever these are indicated on a label, it means hands-off for the casual amateur. Many of these pests require a single chemical applied once or twice a year. Directions on the label give the proper dosage for the specific pests and plants mentioned.
Please do not increase the dosage or use it for purposes not indicated on the label. For roses that require weekly spraying, use an all-purpose mixture containing one or two insecticides, a miticide, and a fungicide.
Many rosarians use malathion combined with a fungicide for blackspot and mildew. Please do not add any sticker spreader; it may harm roses somewhat.
A great many combination sprays and dust are available. Finding one best suited to your own plants, pests, and climate is a matter of trial and error.
Aphids
Soft-bodied, sticking plant lice of many colors (black, red, green, yellow, brown, lavender, or covered with white wool) deform buds, curl leaves, transmit plant diseases, and secrete honeydew that attracts ants and forms a substratum for a black, sooty mold.
Spray, as noticed, with malathion, neem oil, or insecticidal soap. For house plants and spot treatment, out-of-doors.
Bagworms
Caterpillars inside spindle-shaped bags feed voraciously on evergreens, sometimes deciduous shrubs and trees.
Spray after hatching (late May or early June) with malathion, or Sevin. Prune out bags whenever seen.
Beetles
The Japanese beetle has become a major importance in the last country. Foliage may be protected by often spraying enough to keep new growth protected with Sevin, and Neem Oil.
Lawns may be grub proofed with Sevin, Malathion and Neem drenches (which will also control grubs of several other beetles) or, for biological control, treated with milky disease spore dust.
Borers
Larvae of moths or beetles tunnel inside stems, causing (tieback and loss of vigor. Prevent egg-laying by spraying or painting lilac, rhododendron, and trunks of dogwoods with Sevin.
Dust iris foliage with Sevin starting early; dust dahlias for stalk and corn borers in midsummer. Cut and burn infested stalks or branches. Spinisad spray is also an option.
Botrytis Blights
Fungus diseases characterized by gray mold may rot peonies as they emerge from soil or turn flower buds black, spot tulip flowers, and produce tan oval leaf spots on lilies.
Spray peonies and tulips with zineb; lilies with copper. Cut peony stalks at ground level in October.
Chinch Bugs
Minute black and white sucking insects turn grass brown in patches as soon as the soil warms up in June. Treat with diazinon.
Crown Rot
Southern Blight is when plants rot at the crown with white fungus threads and small, reddish-tan sclerotia (resting bodies resembling mustard seed) on the soil and up the stem. In late June, Ajuga, delphinium, and many other ornamentals are subject to crown rot.
Remove the plant and all surrounding soil immediately. The best way to save a plant with crown rot is to REDUCE the SOIL MOISTURE. DO NOT use chemical fungicides unless you know exactly the pathogen attacking the plant. Read the label and Use it with care.
Lace Bugs
Small, flat lace-winged adults and dark spiny nymphs suck from the underside of leaves of andromeda, aster, azalea, chrysanthemum, hawthorn, pyracantha, rhododendron, and other flowers and shrubs.
Leaves are yellowed or silvered with color lost in a stippled pattern. The underside of the leaves appears rusty.
Spray with Malathion or Neem Oil as nymphs hatch (early June for some species); repeat as necessary for late broods.
Leafhoppers
Small, wedge-shaped insects suck from the underside of foliage, producing myriads of white dots on the upper surface. The rose leafhopper is prevalent on that host in early fall.
The potato leafhopper curls and browns the margins of dahlia leaves and causes a stunt. The six-spotted leafhopper transmits the virus of aster yellows.
For control, malathion may be used. For natural control, use Neem oil or Diatomaceous earth.
Leaf Miners
Maggots of flies, or larvae of sawflies, work between two leaf surfaces, causing blighting (birch), blisters (boxwood), or blotch or serpentine mines (holly).
Use malathion on birches, boxwood and holly, mid-May or earlier, depending on location.
Leaf Spots
Many leaf spots are so unimportant they may be safely ignored, but rose black spot is usually the most serious ornamental disease in a home garden.
Unless a protective fungicide (maneb, captan, or copper) is kept on developing foliage, there will be repeated defoliation through the summer with consequent weakening and winter loss.
The leaf spots are black with a fringed margin. The cane lesions are small, dark, and inconspicuous.
Start spraying when the rose comes into full leaf and repeat every seven to ten days until hard frost. Do not work with roses when wet; do not water so late in the day plants cannot dry off rapidly.
Mealybugs
Oval, soft scales with a crenelated margin and covered with white wax are common on house plants and sometimes heavily infest yew outdoors. Spray with malathion.
Mites
Minute creatures of the spider family are of two types. The web-spinning mites (red spiders) suck from the underside of leaves, turning them yellow, gray, or brown, often completely defoliating a rose bush, webbing spruce needles together, and giving shrubs a very dingy appearance.
Spray with insecticidal soaps, horticultural oils, and neem oil. Syringing with a strong stream of water is also helpful. The cyclamen mite, too small to see with the naked eye, spins no webs but seriously stunts and deforms African violets in the house, delphiniums, and other plants outdoors.
The best control is immediately removing infested plants before mites can be spread by handling.
Moths
Pine shoot moths are often important on small ornamental pines. Break out the crooked, straw-colored tips before moths emerge in June. If necessary, spray with malathion in late June or early July.
Powdery Mildew
A white felt or powdery coating covers succulent new rose foliage and deforms buds. Leaves of phlox, chrysanthemum, zinnia, lilac, and other plants are often white by late summer.
Keep plants well-spaced; provide air circulation. Use copper in the regular weekly combination rose spray.
Rusts
Orange spots on crab apple leave result from infection by spores produced in orange horns on red-cedar galls in spring.
Remove the least important host plant, or spray crabs with verbal and sulfur. Spray snapdragons and hollyhocks with zineb to control rust.
Sawflies
Caterpillar-like larvae feed in groups on small ornamental pines, eating off all needles on one branch before moving to the next. Rose slugs are sawfly larvae that skeletonize rose foliage.
Spray with Malathion or Neem Oil.
Scale Insects
The minute yellow crawling stage of lilac, euonymus, juniper, pine needle, and other scales appears in late spring or early slimmer and sometimes again in late summer.
Spray crawlers with malathion before they get their protective shells.
Slugs
Large holes are eaten in leaves near the ground, and there is a slimy trail between plants.
Use a metaldehyde bait (under boards or jar covers to protect birds and pets) or apply diatomaceous Earth.
Thrips
Very slight, slender, bristle-winged insects rasp and suck foliage, causing silvering and spot and deform flowers.
The gladiolus thrips can be controlled with Malathion, Neem oil or a Pyrethroid applied to foliage weekly until flowering, and by shaking corms with Sevin dust after harvest.
The flower thrips that ball and brown peony and rose blooms in early June come from flowers of trees and grasses in the vicinity and are very difficult to control. The period of serious infestation is quite brief.
Virus Diseases
Plants are yellowed, stunted, streaked, or mottled. Remove infected plants immediately before insects can spread the virus. Spray to control leafhoppers and aphids.
Wasps
Two large wasps are prevalent in gardens in late summer. The digger wasp (cicada-killer) tunnels into lawns, leaving unsightly mounds of earth. Drench with Neem oil into the openings.
The giant hornet tears bark, girdling twigs and branches of lilacs and other shrubs, causing dieback. Spray bark in late summer with Sevin.
Webworms
Caterpillars of the fall webworm start in June to web together ends of branches of many trees and shrubs. Usually, the infested portions can be cut off and burned.
The mimosa webworm is a serious pest of mimosa (Albizzia) and honeylocust, producing conspicuous webbing and defoliation. Spray with Sevin or Malathion.
Weevils
Adults feed on foliage, often notching leaves from margins; grubs eat off roots. The black vine weevil, a common pest of yew, hemlock, rhododendron, and other shrubs, feeds at night in June.
Spray ground and lower portion of bushes with Neem oil.
Wilts
Fungi living in the soil invade the plant via the roots and interfere with the vascular system. There is no control by external spraying.
Remove diseased plants; replant with resistant varieties where possible.
44659 by C Westcott