Pests On Gladiolus

Thrips

• Sap-sucking thrips pose the greatest threats to gladiolus plants. In addition to depriving glads of moisture and nutrients, tan or brown western flower thrips transmit potentially fatal impatiens necrotic spot and tomato spotted wilt viruses. Gladiolus thrips take fluid from leaves and developing buds. The tiny yellow, brown or black pests easily escape detection. Symptoms of their presence include speckled, dried leaves and deformed, discolored blooms on sluggishly growing plants. Gladiolus thrip larvae feed on stored corms, producing sticky, cork-textured areas. Keeping corms at a temperature of 35 to 40 degrees Fahrenheit for four months kills the overwintering pests. Thrips on growing plants require weekly applications of insecticide to the runoff point. Insecticides approved for homeowner's use include bifenthrin, imidacloprid and carbaryl. Always apply insecticide according to the manufacturer's specifications.

Aphids

• Aphids also survive on gladiolus fluids. Green peach aphids attack tender leaf and stem tissues. The yellow-green, 1/8-inch insects congregate in groups on the backs of leaves. Small populations do little damage, unless the adults infect glads with cucumber mosaic virus. The virus causes wrinkled, discolored flowers, with yellow-, white- or gray-mottled leaves appearing the following year. Pear-shaped tulip bulb aphids may be gray, green, pink or yellow. They feed beneath the glads’ foliage sheaths and on stored corms. Severely infested corms yield small, sparsely flowered plants. A strong blast of water removes existing green peach aphid colonies from glads. Spraying with malathion or nicotine sulfate insecticide discourages reinfestation. Soaking corms in 114 F water for 90 minutes destroys tulip bulb aphids.

Mites

• Bulb mites decimate growing and stored gladiolus corms. In some areas, these pests have destroyed 70 percent of commercial gladiolus crops, according to the Green Plant Protection Consortium website. The white to tan adults and light brown larvae feed on glad corms and roots, producing stunted plants with wilting, yellowing lower leaves. They also transmit soil-borne root rot fungi and bacterial scab infection. Red spider mites appearing as mobile red specks, suck fluids from gladiolus foliage. Colonized leaves fade to bronze and yellow before dying. Gray, silken threads on leaf undersides indicate spider mites' presence. Immersing glad corms in 110 F water for 30 minutes destroys existing bulb mite populations, but doesn't prevent further attacks. Frequent strong sprays of water are usually sufficient to manage spider mites.

Wireworms

• Wireworms, the larvae of grass-foraging click beetles, favor gladioli in wet soil. The thin, segmented yellow-orange worms burrow into the corms, eating their way up gladiolus stems until the weakened plants collapse. Wireworm control measures include mixing chlordane or diazinon insecticide in the top 6 or 8 inches of soil and dusting it on the corms prior to planting.