Gardening by Month – August

Monthly Tips and Tasks

OrnamentalsxxxxContinue spraying roses that are susceptible to black spot and other fungus diseases.

xxxxAnnuals may appear leggy and worn now. These can be cut back hard and fertilized to produce a new flush of bloom.

xxxxDeadhead annuals and perennials as needed.

xx Divide oriental poppies now.

xx Feed mums, asters and other fall-blooming perennials for the last time.

xx Roses should receive no further nitrogen fertilizer after August 15th.

xx Powdery mildew on lilacs is unsightly, but causes no harm and rarely warrants control, though common rose fungicides will prove effective.

xx Madonna lilies, bleeding heart (Dicentra) and bloodroot (Sanguinaria) can be divided and replanted.

xx Divide bearded iris now. Discard old center sections and borer damaged parts. Replant so tops of rhizomes are just above ground level.

xx Prune to shape hedges for the last time this season.

xxxOrder bulbs now for fall planting.

xxxEvergreens can be planted or transplanted now to ensure good rooting before winter arrives. Water both the plant and the planting site several days before moving.

xxxIf you want to grow big dahlia flowers, keep side shoots pinched off and plants watered and fertilized regularly.

Lawnsxx Zoysia lawns can receive their final fertilizer application now.

xx Apply insecticides now for grub control on lawns being damaged by their activity.

xxLawns scheduled for renovation this fall should be killed with Roundup now. Have soil tested to determine fertility needs.

xDormant lawns should be soaked now to encourage strong fall growth.

xVerify control of lawn white grubs from earlier insecticide applications.

VegetablesxxxxCompost or till under residues from harvested crops.

xxx Sow seeds of beans, beets, spinach and turnips now for the fall garden. Spinach may germinate better if seeds are refrigerated for one week before planting.

xxx Cure onions in a warm, dry place for 2 weeks before storing.

x Broccoli, cabbage and cauliflower transplants should be set out now for the fall garden.

xxxBegin planting lettuce and radishes for fall now.

xxPinch the growing tips of gourds once adequate fruit set is achieved. This directs energy into ripening fruits, rather than vine production.

FruitsxxxxProp up branches of fruit trees that are threatening to break under the weight of a heavy crop.

xxx Protect ripening fruits from birds by covering plants with a netting.

xxx Continue to spray ripening fruits to prevent brown rot fungus.

x Thornless blackberries are ripening now.

xxxWatch for fall webworm activity now.

xxxCultivate strawberries. Weed preventers can be applied immediately after fertilizing.

xx Spray peach and other stone fruits now to protect against peach tree borers.

xx Fall-bearing red raspberries are ripening now.

xx Sprays will be necessary to protect late peaches from oriental fruit moth damage.

MiscellaneousxxxxSoak shrubs periodically during dry spells with enough water to moisten the soil to a depth of 8-10 inches.

xxxxOnce bagworms reach full size, insecticides are ineffective. Pruning off and burning large bags provides better control.

xx Spray black locust trees now to protect against damage by the locust borer.

xxxHummingbirds are migrating through gardens now.

xx Watch Scotch and Austrian pines now for Zimmerman pine moth damage. Yellowing or browning of branch tips and presence of pitch tubes near leaf whorls are indicative. Prune and destroy infected parts.

xxClean out cold frames to prepare for fall use.

xxMonitor plants for spider mite activity. Hose these pests off with a forceful spray of water.

xx2nd generation pine needle scale crawlers may be present on mugo pine now.

August Pests and Problems

By late summer cool-season fescue lawns are often in tough shape. Dead spots resulting from disease, grubs, and/or summer heat often need to be reseeded. These areas should be reseeded between September 1 and mid-October. If this also involves killing any existing grass, start killing these areas in mid-August with glyphosate. Read the product label information for waiting time required before seed can be planted.

Brown Patch of Cool-season Lawns Dead areas in tall fescue lawn (Festuca) caused by brown patch

Dollar Spot Small, straw-colored dead spots in a lawn killed by dollar spot

Perennial Grassy Weeds in Lawns and Gardens Orchard grass Dactylis glomerata in fescue lawn (Festuca)

In late summer we often see a variety of problems with tomatoes. Blossom-end rot is common, as is septoria leaf spot and fusarium wilt.

Fusarium Wilt of Tomato Tomato plants (Lycopersicon) killed by fusarium wilt

Septoria Leaf Spot of Tomato Spots on tomato leaf (Lycopersicon) caused by septoria leaf spot

Blossom End Rot of Tomato and Pepper Blossom-end rot on tomato fruit (Lycopersicon)

Other tomato problems include late blight, stink bug, and spider mite damage (see general information on spider mites below.)

Late Blight of Tomato Late blight on tomato fruit (Lycopersicon)

Stink Bugs Stink bug (Hemiptera) damage to tomato fruit (Lycopersicon)

Spider Mites – Outdoors A heavy spider mite infestation (Acari) caused the curling, distortion, yellow patches and bronzed patches on the leaves of this tomato plant (Lycopersicon)

Cracking fruit, which is caused by water fluctuations and is more common in some varieties than others, may also be observed. You may also encounter sunscald on fruit of tomatoes and peppers. Watch for the tomato hornworm feeding on tomatoes.

Hornworms Tobacco hornworm (Lepidoptera) on tomato (Lycopersicon); note reddish colored spike or “horn” at tailend that gives the hornworm its name

Sunscald of Tomato and Pepper Sunscald on tomato fruit (Lycopersicon)

Poorly formed fruit on cucumbers and other vine crops can be due to pollination problems.

Pollination Problems of Cucurbits Poor pollination can cause cucumbers (Cucurbita) to be misshapen and stunted.

The yellow jackets is a wasp that makes its home in the ground and is aggressively attracted to sweet items at your picnic. They can deliver a painful sting so use caution. Locate the nest during daylight hours but treat it after dark when the insects are not flying. Apply Sevin dust or an insecticide containing permethrin to the hole entrance and seal the entrance with soil or a flat metal or plastic sheet held down with a heavy weight. Now is the best time to control carpenter bees. Cicada killer wasps are active this time of year. They are beneficial and not dangerous to humans.

Yellow Jackets Yellow jackets (Hymenoptera), often mistaken for bees, are actually wasps

Carpenter Bees Close-up of the exposed tunnels made by carpenter bees (Hymenoptera) for their eggs. The grooves in the wood were made by woodpeckers drilling for the larvae.

Beneficial Insects On the right is a cicada killer wasp (Hymenoptera); on the left is its prey, a cicada (Hemiptera)

July or August is a good time to replant iris and remove any rhizomes that are infested with iris borers. Iris is best dug and divided every 3-4 years.

Iris Borer Larva of iris borer (Lepidoptera) tunneling in iris rhizome (Iris)

In mid- to late summer fall webworms may be seen. Small branches scattered around the yard may be the result of twig girdlers, insects that feed on small branches and result in them breaking off. Damage is usually slight, but collecting the fallen branches and disposing of them through municipal composting may help control the pests by not allowing the insect to complete its lifecycle in your yard.

Fall Webworm Fall webworm (Lepidoptera) on crabapple (Malus)

By the end of July Japanese beetle damage should be all but over for the season as around this time the adults have laid eggs in the ground and died. Japanese beetles have a one-year lifecycle.

Japanese Beetle Japanese beetles (Coleoptera) feed on over 300 species of plants

Monitor and treat for grubs in lawns if required. Treating is only necessary if 10 or more grubs are found in a one square foot area. If this threshold is met, treat with trichlorfon (Dylox) now. Treatment with imidacloprid (Merit) or halofenozide (Mach 2) should have been made in July as they take longer to act.

Grubs in Lawns Grubs (Coleoptera) can be found when the grass killed by their feeding is pulled back.

Damage from spider mites may be observed on many plants. It may be too late to affect much control this year, but note their symptoms so you can use safe and effective controls, such as removal with a strong stream of water, in subsequent years.

Spider Mites – Outdoors Spider mites (Acari) caused the bleaching and stippling of some leaves on this burning bush (Euonymus alatus)

Feed zoysia lawns for the last time in late July or early August.

Don’t apply nitrogen fertilizer to roses after mid-August. Late summer fertilizing can result in tender growth that may be damaged by cold weather. Hold off fertilizing trees and shrubs until mid- to late fall before the ground freezes.

Scorch is a common problem in hot, dry weather. Be sure to keep plants well watered during periods of drought. Stressed plants are more susceptible to attack by insects and disease. Many plants may also exhibit wilting leaves or yellowing foliage due to lack of adequate water. Water during dry spells.

Scorch, Sunburn, and Heat Stress Scorch on dogwood (Cornus) leaves

Environmental Drought stress on magnolia (Magnolia)

Drought and Water Stress Close-up of drought stress on magnolia (Magnolia)

Galls are common on many plants throughout the season. Generally galls on leaves are just cosmetic and do little damage. Horned and gouty oak gall affects twigs and although usually not a serious threat to the health of the tree they can be unsightly. Unfortunately, little can be done to control them. An arborist can remove them, but there is no guarantee that they will not recur again.

Galls on Trees This gall on an oak leaf (Quercus) looks like an oak flake gall caused by a wasp (Hymenoptera) but dissecting the gall is the only sure way to tell what caused the gall

Gouty, Horned and other Twig Galls Gouty oak gall on pin oak (Quercus palustris) caused by a wasp (Hymenoptera)

Apply a preventative insecticide spray to the trunks of peach trees and other stone fruits in the first half of the month to control peachtree borers. Apply again in August.

Peachtree Borer The thick, gummy or jellylike sap mixed with frass at the base or crown of this peach tree (Prunus) is caused by a heavy infestion of peachtree borers (Lepidoptera)

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