FUSARIUM AND VERTICILLIUM WILT: Two

FUSARIUM AND VERTICILLIUM WILT: Two major
wilt diseases of tomatoes are Fusarium and Verticillium
wilt. Fusarium wilt, the most prevalent of the two
diseases, in Kansas generally occurs in midsummer
when air and soil temperatures are high. Diseased
plants first develop a yellowing of the oldest leaves
(those nearing the ground). Often the yellowing is restricted
to one side of the plant or even to leaflets on
one side of the petiole. The affected leaves soon wilt
and dry up, but they remain attached to the plant. The
wilting continues on successively younger foliage and
eventually results in the death of the plant (Figure 1).
The stem remains firm and green on the outside, but
exhibits a narrow band of brown discoloration in the
vascular tissue. This discoloration can be viewed easily
by slicing vertically through the stem near the soil
line and looking for a narrow column of browning between
the central pith region and the outer portion of
the stem (Figure 2).
Verticillium wilt tends to develop during the
cooler periods of late spring. Symptoms of the disease
are similar to Fusarium wilt. Older leaves are affected
first; they turn yellow, wilt and eventually drop from
the plant. Unlike Fusarium wilt, Verticillium wilt
causes uniform yellowing and wilting of the lower
leaves. As the disease progresses, younger leaves begin
to wilt and die, until only a few healthy leaves remain
at the top of the plant. Although diseased plants
are not killed, they are stunted and weak and produce
small fruit. Verticillium wilt also causes discoloration
of the vascular system almost identical to that in Fusarium
wilt except that the browning does not extend
quite as far up the stem. Thus, laboratory analysis
may be required to distinguished between the two
diseases