How To Combat Late Summer Garden Pests

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Garden pest control is never wholly monotonous. Spraying may be routine but there are always seasonal problems to keep us awake even in lazy August. 

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By then, we have to cope with a few late summer enemies and second broods of some of the spring foes, as well as black spots and other all-season troubles. 

Most Common August Pests

Here are some of the most common August pests.

Japanese Beetles

JAPANESE BEETLES diminish slightly as the season advances, but there is no noticeable decrease in their numbers until after Labor Day. 

Until then, keep African marigolds (the beetles usually ignore French marigolds), zinnias, and roses sprayed each week. 

I prefer lead arsenate to DDT on plants requiring frequent application to ensure continuous coverage of new flowers or foliage. 

DDT may be a better choice for shrubbery that needs only one or two treatments for the season. Either DDT or chlordane is preferable to lead arsenate for grub-proofing lawns.

Blister Beetles

BLISTER BEETLES, which appear about the time Japanese beetles are in full sway, devour both the flowers and foliage of asters, Japanese anemones, and other ornamentals. They are long, slim, and soft-bodied. 

The most common species in the East is solid black; others may be all gray, margined, or striped with gray. 

Although they do not readily succumb to lead arsenate, they can be fairly well controlled with DDT or a combination of rotenone-pyrethrum spray. 

If you resort to handpicking, wear gloves, as the cantharidin in their bodies may cause blisters if the beatles are crushed on the skin.

Diabrotica Beetles

DIABROTICA BEETLES, also late-summer flower visitors, are pale green with twelve black spots. 

These spotted cucumber beetles may sometimes demolish Shasta daisies and chew rose petals long after the last Japanese beetle has departed. 

However, they are not as injurious in the East as in the South and West. Cryolite has been a standard control for them; lindane is more recent.

Unusual Damage

Digger Wasp

Two pests, the digger wasp and the giant hornet cause unusual damage to lawns and lilacs in late summer. 

The DIGGER WASP, also called cicada killer and mule-killer wasp, is large and black, its abdomen conspicuously banded with yellow. 

The female has a long stinger or ovipositor. These wasps are terrifying as they zoom past your head, busy making nests in lawns, gravel walks, or even under cement walks or stone pavements.

They have been known to keep postmen from the swift completion of their rounds and have undermined sidewalks to collapse. Fine lawns have been injured by the mounds of earth beside each burrow. 

When a long tunnel is completed, the female digger wasp goes off in search of a cicada and, having found one, takes off with it glider-fashion from a tree, finally dragging it inside the burrow, laying an egg between its legs and sealing it off in a cell before starting for another victim.

Use Giant Fly Swatter

If you have enough courage, you can kill these wasps with a giant fly swatter made by fastening stout wire mesh onto a long pole. 

My swatter measures 12” by 18” inches, the long sides reinforced with a narrow wood edge. 

I have used it many times without getting stung, although I keep my fingers crossed and a bottle of spirits of ammonia handy. This is finely applied immediately to any bee or yellow-jacket sting.

Use Carbon Disulfide or Cyanogas

The standard control measure for digger wasps is the injection of carbon disulfide from an oil can get into a nest, but some gardeners prefer to spray a whiff of deadly Cyanogas into the burrow. The effectiveness of either one depends upon the wasp being at home. 

I have had some results from dusting DDT around and in the nests. Possibly chlordane is effective, as it is for ants.

Giant Hornet

The GIANT HORNET, or Vespa hornet, is shorter and ‘stouter than the digger wasp and has a fuzz of brown hairs on its dark body. Its abdomen is black with orange markings. 

This hornet can be seen on shrubs, usually lilacs, in late August and September, tearing the bark from twigs, branches, and sometimes from the main trunk to line its nest. 

The stripped branches are often girdled and die hacks to the injured area. Unless you see the hornet at work, you may think a squirrel has done the gnawing. 

Keeping trunks and branches covered with a DDT spray is quite effective, as is frequently applying the special derris-rosin residue spray used for Japanese beetles on grapes and other edible crops. I use this double strength for the hornet.

Leaf Cutter Bee

The LEAF-CUTTER BEE is another insect that injures plants in its search for nesting material. It cuts precise ovals from the margins of rose leaves to line its tunnels in wood, then caps each cell with a circle cut to fit. 

I know of no real control for these bees; in most cases, they do not ruin enough of the rose foliage to seriously interfere with the plants’ manufacture of food.

Fall Webworm

The nests of the FALL WEBWORM are usually first seen in June. However, if the small hairy caterpillars are not controlled, then the webs of a second generation will be conspicuous in late summer. 

The branches are webbed together at the tips rather than at the crotch, as with the tent caterpillar. 

You can cut out infested portions with a pole pruner and burn them. However, do not attempt to burn them out with a torch, as this would be more damaging to the plants than the caterpillars.

Sucking Insects

Mealy Flata

In August and September, I often get numerous telephone calls about “mealy bugs” and “wooly aphids’ all over the stems of hawthorn, viburnum, and other small trees and shrubs. 

The insects which cause such consternation to the uninitiated are MEALY FLATA or lantern flies, sometimes called lightning leafhoppers. 

They are like very large leafhoppers. The adults have pale bluish-green, roof-shaped wings; the nymphs do, which are dusty white and jump like lightning when disturbed. 

They are usually hidden in large white cotton or wooly masses on the stems. These are sucking insects, but I have never seen enough injury caused by mealy flats to worry about control measures.


True LEAFHOPPERS do require attention as they make a fall comeback on Boston ivy, Virginia creeper, and roses. 

If you do not continue spraying roses through October and sometimes into November, the foliage may be marked in a stippled white pattern and sometimes lose nearly all its color. 

This condition is worse when roses are near apples, for the rose leafhopper feeds on both hosts. 

Use DDT Spray

DDT is the approved spray for leafhoppers, but since I do not like to use DDT on roses unless necessary, I am content with the reasonably good control given by pyrethrum and rotenone in my regular combination of rose spray applied each week.


This same spray takes care of APHIDS, which likewise increases in late summer and the cooler weather of early fall. 

Aphids are more readily killed with a spray than dust because of the dislodging action of a forceful stream of water. 

Chrysanthemums nearly always require late treatment for aphids, as do nasturtiums, calendulas, roses, lilies, and sometimes delphinium and New England asters. 

If you do not need a combination spray for other pests, old-fashioned nicotine sulfate, and soap remains the excellent treatment for aphids.

Flies and Hugs

White Flies

WHITEFLIES come into the garden with greenhouse tomatoes, and other plants started under glass. 

Ageratum Heliotrope and -gourds usually abound with the tiny white moth-like adults, which fly out in clouds from underneath the leaves whenever a plant is touched. 

They can be controlled with DDT and sometimes with contact insecticides in combination sprays.

Chinch Bugs

Two true bugs, chinch bugs, and lace bugs, produce late summer broods. If lawns are treated with DDT or chlordane in June, there should be no CHINCH DUG trouble in August. 

But without some previous treatment, the August brood may be severe, continuing to suck the color out of grass blades and making brown patches in lawns all through warm autumn. 

Some commercial preparations combine DDT and chlordane. These can be applied in August at the first sign of injury, which should not be confused with signs of fertilizer burn or scorching.

Lace Bugs

LACE BUGS are no problem after July on rhododendrons, but on azaleas, they continue unabated into early autumn. 

By late summer, the entire foliage of some evergreen azaleas, especially Kurume azalea Hinodegiri (Rhododendron obtusum japonicum), and R. o. amoenum, is the color of the cafe a Tait. 

I have tried DDT to combat azalea lace bugs but have gone back to the old nicotine sulfate and soap, which gives control if repeated about every two weeks. 

I have not yet had experience with lindane, but I expect to use it this season. The hawthorn lace bug damages pyracantha and is increasingly serious on pyracantha south of New York.

Parasite Plant


DODDER shares honor with mistletoe as a seed-bearing plant capable of attacking another plant.

Dodder seed germinates as other seeds do, but when its orange tendril comes in contact with the stein of an annual such as petunia or its favorite perennial, chrysanthemum, or a vine such as English ivy, it twines lovingly around the stem and sends in suckers for food, after which it loses its contact with the ground. 

Dodder, which produces a tangle of orange threads and clusters of beautiful small white flowers, has no green foliage.

Love Vine or Hell Bind

It is sometimes called love vine but is more appropriately known as hell-bind. If you don’t get it out of your garden before it sets seed in August, you will be fighting it the rest of your gardening days. 

It does no good to tear off the tendrils because the merest fraction of an inch left fastened on the plant will start new growth. 

You must ruthlessly cut out all portions of plants to which it is attached, being careful to throw every hit of the host and parasite into the bonfire.

Boxwood Troubles

Both edging and specimen boxwood are subject to a disease commonly called NECTRIA CANKER, more correctly termed VOLUTELLA BLIGHT. When rains come in August, boxwood branches often turn straw-colored. 

If you look closely, you can see salmon-pink spore pustules on the backs of leaves and along the stems. 

Thinning out the hedge so there is room for air to circulate each bush, avoiding too drastic trimming, which results in close, stubby growth, and a yearly house cleaning are ways to avoid Volutella blight.

Preparing Boxwood

Clean boxwood when the foliage is entirely dry; in wet weather, you only spread the fungus spores. Spread newspaper on the ground under the hedge or bush and brush out all accumulated old leaves and other debris. 

Then cut out all dead wood and every twig, which shows a trace of pinkish pustules. Finally, make sure that all this trash is put into the bonfire. 

If you find the Volutella blight is present, follow the cleaning with a spray of liquid lime sulfur, 1 part diluted with 40 parts of water. Spray from the ground up through each bush to thoroughly cover the interior.

Black Spot And Mildew

Sometimes a boxwood hedge will encourage BLACKSPOT of roses by preventing free air circulation and increasing the humidity; more often, the gardener does the encouraging with overhead sprinkling late in the day or overnight. 

The spores of the fungus which cause this disease are spread by splashed water and germinate with 6 hours of continuous moisture. 

Take advantage of the natural dry spells that reduce disease. Water your roses in the morning, or use a soil-soaker hose or water wand.

Directions For Rose Care

Directions for rose care often indicate a moratorium on spraying during dry weather and a lengthening of the intervals between treatments to 2 weeks or more. This, however, allows POWDERY MILDEW to get a fine head start. 

The mildew spores are spread by air currents and do not germinate in an actual drop of water but in the high humidity engendered on leaf surfaces when cool August nights follow warm days.

Sulfur or Copper

Fermate and other carbamate sprays, which are effective against blackspot, do not affect powdery mildew. You must use some form of sulfur or copper. 

Sulfur dust is satisfactory if it contains a high percentage of sulfur, not just 10% to 40% percent, as in some combination dust. 

If the mildew has become established, a spray will reach the tangle of felty threads over the leaf and bud surface more effectively. 

I prefer a combination spray containing copper, which brings nearly complete control of mildew on roses and zinnias, chrysanthemums, dahlias, delphinium, phlox, and other plants which are subject to this late-summer affliction.

44659 by Cynthia Westcott