Article 20227 of rec.gardens:
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From: klier@iscsvax.uni.edu
Newsgroups: rec.gardens
Subject: Tomato problems FAQL
Message-ID: <1993Jul22.171936.15049@iscsvax.uni.edu>
Date: 22 Jul 93 23:19:36 GMT
Organization: University of Northern Iowa
Lines: 339


 Here's a first draft of a tomato disease FAQ, with "cures"
restricted to "organic" (sensu lato) means.  As always, questions,
comments, additions, brickbats, etc., should be sent to me.

Kay Klier      klier@iscsvax.uni.edu
                     _________________

         Common tomato diseases and problems

General comments: there are many cultivars that are resistant to
common tomato problems:  often after a name you'll see a series
of letters like "VFFNT", which means this cultivar is resistant
to verticillium wilt, fusarium races 1 & 2, nematodes, and
tobacco mosaic virus.  These resistant cultivars are good choices
if you must grow tomatoes in the same area year after year.  If
you can, rotate growing areas every 3 years, and don't grow
related crops (eggplant, potato, pepper, in the same areas in
your rotation).

Practice good sanitation.  Keep the weeds out, the rotten
tomatoes and old plants picked up and composted, etc.  If you
smoke tobacco, both you and your tomatoes will be better off if
you quit (tobacco mosaic virus is a major problem for the
tomatoes), but if you must smoke or chew tobacco, wash your hands
thoroughly before handling tomato plants.

Finally, grow several cultivars of tomatoes.  When you don't put
all your eggs in one genetic basket, you stand a much better
chance of getting a good harvest.


                            Insects:
Colorado Potato Beetles:
Oval, hard-shelled adult beetle is about 1 cm (3/8") long, with
alternating black and yellow stripes on wing case.  Larvae are
sluggish, red, humpbacked grubs with two rows of black spots on
each side of the body.  Foliage feeders, may strip plants if
population is large.  Control by 1ft of loose mulch under plants,
interplanting with flax, marigolds, garlic, snap or bush beans.
Eggplant and black nightshade (Solanum ptycanthemum = S. nigrum
of American authors) are favored foods and can be used as trap or
lure crops.  Handpick adults and crush yellow eggs found on
underside of leaves of tomatoes.  Other controls: Bacillus
thuringensis var. San Diego, Thripobius semiluteus, pyrethrins,
or rotenone/pyrethrin mixtures.

Corn earworm (=Tomato fruitworm, bollworm):
More of a pest in the south... 3.5 cm (1.75 ") long green, brown
or pink moth caterpillar with light stripes along sides and back.
Eats holes in fruits and buds.  Handpicking or rotenone for
control, or pheromone traps, Bacillus thuringensis, ryania, or
insecticidal oils.

Cutworms:
Several species, usually gray or brownish grubs up to 3 cm (1.5")
long.  Mainly a spring problem.  Control: Clean cultivations,
collars of plastic, tin, juice cans, or paper wrapped around stem
at planting.  Bacillus thuringensis.

European Corn Borer:
Occasional pest.  Moves to tomatoes if nearby corn dies.

Flea beetles:
Many species, most notable for leaving small "pepper holes" in
leaves.  Garlic spray reputed to control the beetles.  I've never
had major damage from them.

Psyllid yellows:
A disease caused by feeding of tomato or potato psyllid nymphs,
due to a toxin released in feeding.  These look like fringed
scales that change from yellow to orange to green.  Older leaves
thicken and roll upward at the base; veins may turn purplish.
Younger leaves may curl.  Plants may be dwarfed, stems and
petioles may be skinny.  Control by removing ground cherry and
other solanaceous weeds.

Tobacco Hornworm:
Similar to tomato hornworm, but green and black horn.  Same
controls.

Tomato Hornworm:
Larvae of a species of Sphinx moth.  Green caterpillar, to 6 cm
(4") long, with white diagonal side stripes and a prominent red
horn on the head.  Handpick.  Bacillus thuringensis  will kill
hornworms, but I do not recommend this: several species of Sphinx
are pollinators of endangered native orchids, or are endangered
themselves  Braconid wasp parasites are becoming commercially
available, again, I feel these should not be used because they
are non-selective killers.  Handpicking is easy and effective, or
you can make exclosures of netting around plants.
Dill makes a good trap crop.  Rotenone and Trichograma wasps are
other controls.

Whitefly:
Tiny, white flying insects that fly up to make a cloud when an
infested plant is disturbed.  Control: Insecticidal soaps,
Encarsia formosa (a parasite), yellow sticky traps, row covers,
insecticidal oils, or rotenone/pyrethrin mixtures.  (You need at
least 300 sq inches of sticky trap per 8 tomato plants.)

                     Physiological Problems
         ("diseases" caused by culture and environment):

Blossom drop:
Usually caused by dry soils, and drying winds, but may be caused
by sudden cold spells, heavy rains, N overdose, or heavy
infections by bacteria or fungi.

Blossom end rot:
See Calcium deficiency below.  End of fruit away from stem gets
soft, mushy.  Generally caused by a combination of drought and
drown water availability, calcium mobilization problems.  Cure:
mulch to smooth out soil water availability; water in drought
periods.  See also Calcium deficiency below.

Fruit crack:
Surface cracks in fruits near stem end caused by rapid growth
during periods of good moisture and high temperatures.  Cracks
can radiate around stem or encircle "shoulders" of tomato.  May
vary in depth.  No cure, but even moisture (mulch!) will help
prevent periods of slow and rapid growth.  Pick fruits with
rapidly developing cracks early (not fully reddened) to prevent
Early Blight and other fruit rots.

Leaf roll:
Rolling begins on lower leaves and proceeds upwards until most
leaves are affected.  Plants may lose leaves, particularly on
staked plants.  Seems to be caused by heavy pruning or deep,
close cultivation.

Sunscald:
Occurs when green tomatoes are exposed to sun, most commonly in
hot, dry weather on plants with leaf spot diseases or other
defoliation.

Boron deficiency:
Blackened areas at tip of stem, which is stunted.  Abnormally
bushy looking plants.  Terminal shoots curl, yellow and die.
Fruit of severely affected plants may darken and die in patchy
patterns.  Cure: a handful of borax (not boraxo soap!) worked
into the soil around each plant.

Calcium deficiency:
Thick woody stems, slow growth, yellow upper leaves (not yellow
lower leaves seen in N, P or K deficiency), weak, flabby plants.
Blossom end rot of fruit.  Cure: Correct Ca/Mg balance,
(dolomitic
limestone and a little Epsom salts help), mulch to retard plant
water fluctuations that seem to bring on blossom end rot.

Copper deficiency:
Stunted root and shoot growth, blue-green curled, flabby leaves,
few or no flowers.  Manure is an easy cure; copper salts can be
used with great caution (in too high a quantity, they can kill
plants.)  Bordeaux mixture applied at fungicidal rates will work.

Iron deficiency:
Spotted white areas on new leaves and upper parts of stem.  New
shoots may die if severely deficient.  Apply chelated iron, dried
blood, manure, or sewage sludge.

Manganese deficiency:
Very slow growth; light green leaves with dead patches ringed in
yellow.  Few flowers or fruit.  Use manure.

Nitrogen deficiency:
Very slow growth of plants, followed by progressive pale green
color moving from tip and young leaves back to more mature
leaves.  Leaves are small, thin, perhaps with purple veins.
Stems eventually brown and dry off.  Flower buds yellow and drop.
Apply N immediately.

Too much nitrogen:
Rapid growth, with many bright, light green leaves; poor
flowering and fruiting.  Stop fertilizing immediately with N, add
P and K.

Phosphorus deficiency:
Slow growth, purple tinged small leaves that feel fibrous.  Fruit
set delayed.  Add P.

Zinc deficiency:
Very long, narrow, yellowed leaves mottled with dead spots.
Manure is simplest cure.

                         Fungus diseases
Most can be treated with Bordeaux Mixture, Kocide micronized
copper, copper dust, and sulfur sprays and dusts.

Anthracnose:
Primarily affects ripe fruit, causes a slight, sunken spot rot
(early symptoms are a round sunken spot on the fruit skin, about
2-4 mm diameter).  Most prominent in hot Augusts with high temps
and humidity or heavy dews.  Fungus can overwinter on vines, or
can be seedborne.  Rotations and treating seeds with 122oF water
for 15 minutes can help control.  Also Bordeaux mixture.

Botrytis fruit rot:
More of a problem with greenhouse tomatoes when grown cool in
humid conditions.  "Water soaked" spots in the fruit that enlarge
rapidly and become covered with powdery grey spores.  Raise heat,
reduce humidity.

Buckeye rot:
Large, dark brown soft spots on greenhouse fruits.  Mulch plants,
sterilize soils.

Damping off:
Seedlings suddenly "pinch in" at the soil line and keel over.
Well drained, sterile soil for sowing is the key to control.

Early blight:
Irregular brown spots with a "bullseye" pattern on lower leaves
of plants.  Spots enlarge to 4-9 mm (0.25 - 0.5"), then coalesce.
Affected leaves turn brown, drop.  Stem spotting and stem
girdling or fruit rot (near stem) may occur late in season.
Rotation and good sanitation practices (including removing
horsenettle, jimsonweed, groundcherry and nightshade) are
recommended controls.  Also Bordeaux mixture.

Fusarium wilt: ("yellows")
One of the most common and damaging diseases.  Generally not
damaging unless soil and air temperatures are high in much of the
season.  Slight yellowing of a single leaf, or slight wilting of
the lower leaves is followed by an overall yellowing.  Brown
discoloration of vascular tissues in stem or petioles of wilted
leaves is common.  Choose Fusarium resistant cultivars, grow in
clean soil, rotate crops, destroy vines at end of the summer.
Nematode infection increases risk of fusarium infection.

Ghost Spot:
Same fungus as Gray mold.  Small whitish rings, 1-3 mm diameter,
on green tomatoes.  Warmer, drier conditions control.

Gray Leaf Spot:
More common in SE states.  Also on peppers, eggplants, ground
cherries, etc.  Dark brown spots on underside of leaves in warm,
humid weather.  Affected leaves turn yellow, wither, drop.
Serious infections will keep plants from fruiting.  Bordeaux
mixture will treat.

Gray Mold:
Heavy gray growth on dead leaves or stems at the base of the
plants.  Tan markings appear on stems, gray spots on live leaves,
and gray or yellow soft spots on the fruits.  Usually a spring
disease that will let up in higher temperatures or lower
humidities.

Late Blight:
Severe defoliation following irregular greenish-black,
watersoaked spots on older leaves.  In humid weather, there may
be a white, downy growth on spots.  Plants may look "frosted".
Fruits can be affected at any stage; lesions are large, dark,
firm, rough patches.  Most common at night temperatures of 40-
60ooF, day temps of 70-80.  May spread from infected potato
plants.  Bordeaux mixture will treat.

Leaf Mold:
Usually greenhouse disease, but sometimes outdoors.  White spots
appear on surface of older leaves, enlarging and yellowing.  With
humidity, patches become velvety and olive-green.  Control with
good ventilation, temperatures > 60oF.

Septoria leaf spot (Septoria blight):
Common in Atlantic, Central states, and Southern Plains states.
Most severe in rainy seasons, crowded patches.  Usually not seen
before mid-July.  Older leaves have many, small, watersoaked
spots, usually 1-2mm diameter.  Leaves may drop, and progressive
defoliation may occur.  Clean cultivation, clean up at the end of
season, and staying out of wet tomato patches (you can spread the
spores) help.  Can be treated with Bordeaux mixture.

Soil rot fungus:
Also a Pythium rot, like damping off.  Slightly sunken brown
spots on fruit, outlined with concentric rings.  Spots enlarge,
and may break open.  Keep tomato vines and fruits off soil.

Spotted wilt:
Numerous small, dark, circular dead spots on younger leaves.
Stem tips may be dark streaked and die back.  May kill plants;
survivors will have yellowish leaves and fruits with concentric,
circular marks.  Disease can be shared with lettuce, tomato,
celery, spinach, peppers and potatoes.

                       Bacterial diseases

Bacterial canker:
Usually first symptoms are wilting of margins of lower leaves,
often on only one side of leaf; leaves curl upward, turn brown,
wither and die.  Petioles remain attached to stem, which helps
distinguish this from Fusarium and Verticillium wilts.  Plants
may have a single affected shoot, though dying will continence up
the stem, and pith becomes yellow and mealy.  Open stem cankers
develop.  Fruit may be affected with small raised, white dots 2-4
mm diameter, which later become white birdseyes with brown
centers.  Fruit may be stunted or deformed.  This is a seedborne
disease, commonest in home-saved or uninspected seed.  Can be
prevented by a 25 min seed soak in 122oF water, or fermenting the
seeds in crushed tomato pulp 96 hours, or soaking in 50-50
mixture of vinegar and water for 24 hours.

Bacterial spot:
Common in rainy seasons.  Small dark, greasy-looking leaf spots
may be followed by flower drop and/or water-soaked spots 2-4 mm
diameter on young green fruits.  Soil borne disease.

Bacterial wilt:
Commonest in southern states.  Rapid wilting and death of entire
plant without yellowing or spotting of leaves.  Stem cross-
sections of wilted plants will be dark, watersoaked and have a
grayish exudate when squeezed.  Institute 5 year rotations,
avoiding including pepper, tobacco, eggplant or potatoes in
rotation.  Remove affected plants as soon as problem is noticed.

                         Virus diseases:

Curly top: (western yellow blight)
Caused by the same virus as curly top of sugar beets.  Seems to
be carried by beet leafhopper.  Main symptoms are curling and
twisting of leaves of affected plants.  Prevention is planting at
times that may avoid high leafhopper populations, or excluding
insects with row covers.

Mosaics:
Common mosaic, tobacco mosaic, Aucuba mosaic and cucumber mosaic
can all infect tomatoes.  Mottles areas of light and dark green
on leaves, sometimes appearing puckered, or malformation of
leaflets, or yellow mottling of leaves, or stunted yellow, bushy
plants can be seen with these diseases.  Control by avoiding
handling plants (esp. by people who handle tobacco), removing
perennial weeds, esp. pokeweed, catnip and milkweeds.  Aphids can
transmit mosaic viruses.   Seedlings can be dipped or sprayed
with milk at least twice if they are suspected of being infected.

OK, folks, what have I forgotten?


Kay Klier  Biology Dept  UNI