Garden pest control is never entirely repetitious. Spraying may be a regular routine, but seasonal problems keep us busy even in lazy August. We always need to deal with a few late summer enemies along with the second hatch of some of the spring foes, as well as blackspot and other all-season troubles. Here are some of the most common garden pests arriving in late summer.
Japanese Beetles diminish slightly as the season advances, but it is not until after Labor day we will see a noticeable decrease in their numbers. Until that time, keep African marigolds (the beetles usually ignore French marigolds), zinnias and roses sprayed each week with Neem oil or an insecticidal soap.
Blister Beetles, which appear about the time Japanese beetles are in full attack mode, devouring 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.
If you resort to handpicking, wear gloves, as the cantharidin in their bodies may cause blisters if the beetles are crushed on the skin. [Wikipedia]
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. They are not as injurious in the East, however, as in the South and West. To control try Kaolin clay, Pyrethrum or Spinosad. WSU
Unusual Damage: Digger Wasp and Giant Hornet
Two pests, the digger wasp, and the giant hornet cause unusual damage in late summer to lawns and lilacs. The Digger Wasp, also called cicada killer and mule-killer wasp, is large and black, its abdomen noticeably 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.Good looking 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 off for another victim.Keep a bottle of ammonia handy as it’s as little old-fashion remedy to apply immediately to any bee or yellow-jacket sting.The standard control measure for digger wasps is a dust of SEVIN or using pyrethrins.
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. You can find this hornet on lilac shrubs 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 hack 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 SEVIN spray is quite effective.The Leaf-Cutter Bee is another insect which 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. In most cases, they do not ruin enough of the rose foliage to seriously interfere with the plants’ manufacturing of food.The nests of the Fall Webworm first show up in June. If not controlled you may find the webs of the small hairy caterpillars second generation 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.
In August and September you’ll find “mealybugs” and “woolly aphids” all over stems of hawthorn, viburnum and other small trees and shrubs. The insects to the uninitiated are lanternflies (Lycorma delicatula) , sometimes called lightning leafhoppers. They are like very large leafhoppers. The adults have pale bluish-green, roof-shaped wings; the nymphs, which are a dusty white, jump like lightning when disturbed. They are usually hidden in large white cottony or woolly masses on the stems. These are sucking insects and control measures are being evaluated. [penn.gov]
True Leafhoppers do require attention, as they make a fall comeback on Boston ivy, Virginia creeper, and roses. If you do not continue to spray roses through October and sometimes into November, the foliage may be marked in a stippled white pattern and sometimes may lose nearly all its color. This condition is worse when roses are near apples, for the rose leafhopper feeds on both hosts. Aphids increase in late summer and in the cooler weather of early fall. Aphids are more readily killed with a spray like Neem oil or a DIY insecticidal soap instead of a 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 asters.
Flies and Bugs
Whiteflies come into the garden, 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 sometimes be controlled with contact insecticides in combination sprays.Two true bugs, chinch bugs, and lace bugs produce late summer broods. If lawns are treated in June, there should be no chinch bug trouble in August, but without some previous treatment, the August family may be severe, continuing to suck the color out of grass blades and making brown patches in lawns all through a warm autumn.
Lace Bugs are no problem after July on rhododendrons, but on azaleas, they continue unabated into early autumn. The hawthorn lace bug damages pyracantha and is increasingly pressing on pyracantha south of New York.
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 around each bush. Avoiding the too drastic trimming which results in close, stubby growth and a yearly housecleaning are ways to avoid Volutella blight.Clean boxwood when the foliage is entirely dry; in wet weather, you only spread the fungus spores. Spread newspaper or plastic sheets 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. If possible, make sure all this trash is burned. 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.
Blackspot and Mildew
Sometimes a boxwood hedge will encourage Blackspot of roses by preventing the free circulation of air and increasing the humidity; more often the gardener does the encouraging with overhead sprinkling late in the day or overnight. Splashed water spreads the spores of the fungus which causes this disease 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 waterwand.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 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.
Sulphur or Copper
You must use some form of sulfur or copper. Sulphur dust is satisfactory if it contains a high percentage of sulfur and not just 10 to 40 percent as in some combination dusts. If the mildew becomes established, a spray will reach the tangle of felty threads over the leaf and bud surface more effectively. Use a combination spray containing copper, which brings better control of mildew on roses, and also on zinnias, Chrysanthemums, dahlias, delphinium, phlox and other plants subject to this late-summer affliction.