FLOWER THRIPS (Frankliniella tritici,
and related species in various sections). This is present on nearly every type of flower but most
disastrous to roses, peonies, daylilies, and iris. Buds ball, not opening
at all or opening part way with brown edges to petals. Light-colored
roses and peonies are most affected; on roses June bloom is affected more
often than the autumn display. Daylilies are streaked and distorted. Young
nymphs, very slender, lemon-colored, can be seen only by pulling open
the flowers and looking at base of petals. Adults are brownish yellow,
1/25 inch long. This species breeds in various grasses and weeds, migrating to flowers in late May and June. In warm weather the life cycle is
repeated every 2 weeks.
Control. Lindane is somewhat preferable to DDT because it does not
increase mites. Chlordane is used to some extent. Older recommendations
called for spraying roses every few days with tartar emetic and brown
sugar. To protect a few roses try Antrol Rose Spray Flower Bomb, which
contains lindane in aerosol form.
GLADIOLUS THRIPS (Taeniothrips simplex).
This species is a limiting factor in growing gladiolus over the country and infests also amaryllis,
freesia, iris, and lilies. The adults are relatively large for thrips, 1/16 inch
long, brownish black with basal part of wings white. Kidney-shaped
eggs are laid in growing leaves or corms with nymphs appearing in about
a week. These are white in the first instar, then yellow and orange before changing to the dark adult. A generation is completed in 2 to 4
Gladiolus foliage has silvery streaks, then browns and dies; flowers are
streaked or flecked, much deformed, with many spikes failing to open;
corms are russeted, corky, sticky, often failing to sprout.
Control. Before DDT, many gardeners had become completely discouraged about gladiolus; now they are easy to grow. Spray or dust with
DDT every 10 days from the time foliage is 6 inches high to flowering.
After corms ripen, shake them in a paper bag with 5% DDT dust. Thrips
seldom live over winter in the soil in northern gardens, but they can in
the South. There it is wise to rotate planting areas. Chlordane and toxaphene may be used through the growing season in place of DDT.
GREENHOUSE THRIPS (Heliothrips haemorrhoidalis and other species).
Many flowering plants are seriously damaged in greenhouses and
outdoors in warm climates, but the feeding is confined to foliage and
fruit. Surface of leaves is whitened or flecked, the underside covered with
black specks of excrement. Tips wither and curl, buds fail to open.
Roses, carnations, chrysanthemums, crotons, cinerarias, and fuchsias seem
to suffer most in greenhouses. The adult is dark brown with light appendages and a network of lines over the body.