There are two soil born diseases that are a problem in the
southwest. Verticillium wilt and
Fusarium wilt both can decimate tomato plants seemingly overnight. These
diseases also affect peppers, eggplants and potatoes.
With Verticillium wilt, you will see leaves turn yellow and
die without wilting, or drop prematurely with shoot tips wilting slightly
during the day. As the disease progresses, the leaves may curl up at the margin
but remain alive for a short time. There is no cure, so you must choose
resistant varieties. I’ve had decent luck with a preventive soil treatment
called “Root Guardian” available from Gardens Alive! It doesn’t always work, as
I still may lose a few plants, but it must be doing something because the rest
of the plants are doing fine.
Fusarium wilt starts out with leaf yellowing at the bottom
of the plant working its way up. The
yellow leaves wilt before they die, followed by the entire plant. Again there is no cure, but “Root Guardian”, as
mentioned above, helps. Fusarium wilt is more common in the southwest than
Verticillium.
Keep in mind that these diseases are inevitable and it is
important to rotate your crops (do not plant tomatoes in the same place every
year, in fact every 3 years is best) and buy varieties that are resistant.
A last resort option is to “solarize” your soil. This only
works in hot, sunny climates. In late spring, cover the infected area with
CLEAR 5 mil plastic. Secure the edges with weights, or bury edges with dirt.
That’s it! Leave the cover there for at least 2 months. This will kill all soil
diseases, insects and eggs, weeds and weed seeds; however, keep in mind it will also kill
beneficial insects, soil microbes…everything. Your soil will be dead, but it
will be free of diseases. After you have solarized your soil, you will need to
introduce lots of compost and earthworm castings to bring it back to life.
