Research: Silverleaf Whitefly
Silverleaf whitefly (SLWF) Bemisia tabaci biotype B, is a small sucking insect
(Homoptera) so named for the silvering effect on foliage of squash and pumpkin caused
by feeding of the immature “nymph” stage. Another physiological disorder caused
by nymphal feeding of SLWF is tomato irregular ripening that caused major losses
during the 1988 and 1989 seasons. Biotype B is an invader from the Old World first
detected in Florida in 1986 following a whitefly explosion in greenhouse poinsettias
that quickly spread to vegetable fields and eventually to a large number of agronomic
and horticultural crops. A native biotype or race of B. tabaci had been known
in Florida since the late 1800’s but had a limited host range and caused few problems.
By 1989 the previously unknown tomato mottle virus (ToMoV) vectored by the whitefly
had appeared and spread through tomato fields in south Florida, soon to be followed
in 1995 by the more severe tomato yellow leafcurl virus (TYLCV) first seen in the
Middle East. More recently, three new whitefly-borne viruses have appeared in cucurbit
crops in Florida, the most severe, squash vein yellowing virus (SqVYV) also previously
unknown and causing watermelon vine decline that devastated that crop in the early
years of the present century.
All these problems have earned SLWF the dubious honor of key pest in fruiting vegetables
throughout the southern tier of the state, often spreading north to Georgia and
beyond. An early breakthrough in SLWF management was the realization that a host
free period, especially in summer was key to successful management of the pest and
associated viral diseases in South Florida. Prompt crop destruction and field sanitation
to eliminate hosts of whiteflies and viruses for at least 3 generations serves to
reduce inoculums sources and provide a clean start the following season. Insecticidal
control, especially with the systemic “neonicontinoid” insecticides has also been
a powerful tool with which to manage whiteflies, but is under constant pressure
from selection for insecticide resistance that continues to increase. We are constantly
testing new products as they appear as well as urging growers to conserve those
they have by rotating modes of action and refraining from unnecessary use. We are
also conducting an active program of research in biological control and have had
good success controlling whiteflies as well as thrips and broadmites in eggplant
and to a lesser extent pepper using the commercially available predaceous mite Amblysieus
swirskii. We believe that biological control offers a safe and effective
alternative in these and other crops such as cucumber that can serve to reduce pressure
on key insecticides that are needed in more difficult to manage crops such as tomato.
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