This disease is caused by a pathogen so small
that hundreds can be found in bacterial exudate the size
of a drop of water. The pathogen can quickly
multiply and plug the vascular tissues so that water
transport does not occur. This tiny bacterium is
transported from plant to plant by both striped and
spotted cucumber beetles.
Bacterial wilt is most devastating on
cucumbers and muskmelons (cantaloupes). The disease can
also occur on pumpkins and squash, although not often
as severely. It rarely infects watermelon. In all
cases, wilt symptoms appear first on individual leaves
and quickly spread to lateral shoots, causing the
entire plant to wilt. Symptoms develop more quickly
on younger, smaller plants.
To confirm the presence of bacterial wilt, cut a
live, wilted runner off the plant. (Take the five or
six inches of stem nearest the crown.) Cut the
stem section in two, then hold the cut ends back
together and squeeze them until the plant sap flows out
and intermingles from each cut edge. Slowly pull the
cut ends apart. If there is a strand of sticky sap
between the cut ends, then a bacterium is likely present
and bacterial wilt is a strong possibility.
Unfortunately, once you confirm this disease, nothing can
in the infected plant. However, steps can be taken
to prevent the wilt in next year's plants.
The primary method for controlling bacterial wilt
is to control the beetle vector. The beetles overwinter
as adults that are present when the vine crops
emerge. The application of both preplant systemic
and postemergence protectant insecticides might be necessary
to prevent a problem with bacterial wilt
in commercial plantings. Because the beetles are
most attracted to plants in the cotyledon stage,
insecticides should be initiated immediately after planting.
Entomologists warn that when blossoming begins,
insecticides should be applied late in the day so as not
to interfere with pollination by bees. Consult Report
on Plant Diseases No. 905 for details about