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Pest and Disease Control: What's Wrong, What Helps 

By Adrian Higgins
Washington Post Staff Writer
Thursday, May 10, 2001

Return to "Growing Green in the Garden"

Lawn Symptoms Likely Causes Organic Control

Turf thin and peels away

White grubs of Japanese beetle or other species Milky spore, beneficial nematodes

Small patches of dead grass; blades severed at ground level

Cutworms Bt
Boradleaf weeds fill spaces left by declining turfgrass Mowing too short, fertilizing too much or too little Corn gluten or lemon/vinegar herbicides. Reseeding in the fall will diminish weed problems.
Circular patches of brown, dead grass occurring in humid weather Fungus named brown patch Leave alone; grass will regrow. Proper lawn care will diminish occurrences.

Ornamental Symptoms

Likely Causes

Organic Control

Leaves and flower buds distorted Aphids Insecticidal soap, neem oil
Leaves lose green color, plant weakened, webs apparent Mites Hose down plants; use horticultural oil or predatory mites
Insects covered in white wax on hemlock needles Hemlock wooly adelgid Horticultural oil, most effective  between July and October
Chewed and disfigured leaves and flower buds in early to midsummer Japanese beetles Sweep beetles into soapy water or spray with neem oil or pyrethrin
Azalea leaves washed out, stippled; black dots on underside of leaf Azalea lacebug Insecticdal soap or horticultural oil
Holes in bark of peach trees, ornamental cherries, purple leaf plums and cherry-laurels Peach tree borer Kill grubs by prodding holes with wire or use predatory nematodes
Stems of euonymous, hollies and other shrubs covered in clinging insects preotected by waxy shells of gray, brown or white Scale insects Spray with horticultural oil. Cut out heavily infested branches
Summer defoliation of woody ornamentals, especially evergreens Bagworms - feeding caterpillars enclosed in camoflauged cocoons up to three inches Handpick or spray with Bt between June 15 and July 15
Chalky white mold covering leaves. Especially affects lilacs, dogwoods, crape myrtles, asters, zinias and phlox Powdery mildew Select resistant plants, and place them in areas of goof air circulation. Use horticultural oil or sulfur sprays.
Branch dieback and sunken areas on stems. Different fungi affect vinca, pachysandra, junipers, boxwood, rhododendrons, azaleas, redbuds and cherry trees. Might look like drought damage. Stem blight and cankers Cut out infected branches, and spray with copper fungicides.
Rose leaves turn yellow, develop black spots and drop Black spot fungus Clean debris at base of roses; remove and bag yellow leaves at first sign. Spray preventively with horticultural oil or sulfur, lime-sulfur or copper fungicides.

Herbs and Vegetables  Symptoms

Likely Causes

Organic Control

Leaves of edibles mottled and yellowed. Plants stunted or distorted. Small insects fly around when the plant is disturbed. Aphids, whiteflies, leafhoppers and other soft-bodied pests Insecticidal soap, hot pepper wax, sticky cards
Young plant stems severed at ground level. Chewed leaves. Caterpillars, including cutworms and cabbage worms Bt or predatory wasps
Holes in leaves of greens and cucumbers, zucchini, melons or squash Striped or spotted cucumber beetles or flea beetles Pyrethrin or handpick
Tomato leaves develop, from the bottom up, brown spots with yellow rings Fungus named brown patch Lay mulch, irrigate roots only and remove infected leaves. Spray with a copper fungicide.

2001 The Washington Post Company