[Arid_gardener] Re: Tomatoes: White Flies and Wilt

[dergartenarzt]

----- Original Message -----From: <l007r at yahoo.com>
> Tomato plant:  I planted a tomato plant three weeks ago.  The leaves start
> to turn yellow and dry in the center of the leaf to brown. Also, there at
> very small white fyling insects on the leaves.  The plant wants to grow,
> but turns pail green and is stalled out.  Any recomendations?

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Your description suggests either a whitefly invasion or verticillium wilt

Whiteflies cane be a serious pest at this time of year when the the flies'
habitat in the cotton fields is destroyed due to defoliation in preparation
for picking.  The whiteflies then move into urban areas where there is still
al lot of foliage.  The damage is done by the larvae feeding on the plants'
leaves. The leaves can turn yellow, appear dry, or fall off plants.  The
usual suggestions for control are to knock  the larvae off the plant with a
water spray or use either commercial insecticdal soap or a homemade
preparation of 1/4 teaspoon of liquid dish washing detergent in a gallon of
water.  Many chemical insecticides are also labelled for whitefly control
but these are broad spectrum that will also kill off the whitefly predator
insects and should not be used.  The plants need to be checked regularly
because the whiteflies move in in swarms almost every day.  Yellow sticky
traps will attract the adult whiteflies and may help to reduce populations
but will not be helpful if the whitefly larvae are already on the plants.
For more information, see also the fact sheet at
http://cals.arizona.edu/maricopa/garden/
and follow the links to  >Index >Whitefly
http://cals.arizona.edu/maricopa/garden/html/t-tips/bugs/whitefly.htm

Verticillium Wilt is probably the most common tomato disease.  It occurs
with when soil temperature drop below 85 deg F.  According to the AZMET
sites, current soil temperatures at 4 inches vary from high 70s to low 80s.
From:

http://www.hort.uconn.edu/IPM/veg/htms/wilttom.htm

"It often begins with wilting during the hottest part of the day and
recovers at night. Leaves may turn yellow, starting at the edges and between
the veins, and spreading inward. Usually both sides of the leaf are
affected. Leaflets may also show a characteristic V-shaped or fan-shaped
yellowing, with the widest part of the V on the leaf edge. The narrow part
is on the interior of the leaf, but not necessarily bordered by the veins.
The yellowed areas will eventually turn brown and die. Generally, older
leaves are affected first. Symptoms progress up the plants until only a few
leaves remain on the top of the plant. Generally both sides of a plant are
affected equally. Plants affected when young may be stunted. Plants often
show no symptoms until they are mature and bearing"

Once the plant is infected, there is no control.  One prevention method is
to plant resistant varieties.  Seed catalogs will indicate this in the
description but usually the information is not available for nursery stock.
Another suggestion is a 3-4 year crop rotation with plants that are
unaffected byb the wilt.  Soil sterilization as described at
http://ag.arizona.edu/gardening/news/articles/12.8.html
may also help.  see also
http://cals.arizona.edu/pubs/crops/az1034.pdf

Olin Miller
Master Gardener Volunteer, Maricopa County AZ
http://home.att.net/~millero/ValleyOfTheSunGardeners.htm