Subject: Tomato diseases FAQ

From: [email-masked]
Date: 3 Apr 95 16:26:12 -0500

Here's one of the FAQs from sunsite.unc.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.

Kay Klier  Biology Dept  UNI [email-masked]