Southeastern U.S. Vegetable Crop Handbook - 2023 - 32

c. Do the symptoms point to cultural problems? Look for
the following:
(1) Nutrient deficiencies. (A soil test from good areas
and poor areas should be done as well as analysis of
nutrient content of leaf tissue from the same areas.)
* Nitrogen-light green or yellow foliage. Nitrogen
deficiencies are more acute on lower leaves.
* Phosphorus-purple coloration of leaves; plants
are stunted.
* Potassium- yellow or brown leaf margins and
leaf curling.
* Magnesium-interveinal chlorosis (yellowing between
veins) of mid level or lower leaves.
* Boron-development of lateral growth; hollow,
brownish stems; cracked petioles.
* Iron-light green or yellow foliage occurs first
and is more acute on young leaves.
* Molybdenum- " whiptail " leaf symptoms on cauliflower
and other crops in the cabbage family.
(2) Chemical toxicities.
* Toxicity of minor elements-boron, zinc, manganese.
*
Soluble salt injury-wilting of the plant when
wet; death, usually from excessive fertilizer application
or accumulation of salts from irrigation
water.
(3) Soil problems. (Take soil tests of good and poor
areas.)
* Poor drainage.
* Poor soil structure, compaction, etc.
* Hard pans or plow pans.
(4) Pesticide injury. (Usually uniform in the area or
shows definite patterns, and more than one plant
species, such as weeds, are often symptomatic.)
* Insecticide burning or stunting.
* Weed-killer (herbicide) burning or abnormal
growth.
(5) Climatic damage.
* High-temperature injury.
* Low-temperature (chilling) injury.
* Lack of water.
* Excessive moisture (lack of soil oxygen).
* Frost or freeze damage.
(6) Physiological damage.
* Air-pollution injury.
* Genetic mutations (this is rare).
In summary, when trying to solve a vegetable crop problem,
take notes of problem areas, look for a pattern to the symptoms,
trace the history of the problem, and examine the plants and soil
closely. These notes can be used to avoid the problem in the future
or to assist others in helping solve their problem. Publi cations
and bulletins designed to help the grower identi fy specific
vegeta ble problems are avail able from Extension.
AIR POLLUTION INJURY
The extent of plant damage by particular pollutants in any given
year depends on meteorological factors leading to air stagnation,
the presence of a pollution source, and the susceptibility of the
plants.
Some pollutants that affect vegetable crops are sulfur dioxide
(SO2), ozone (O3), peroxyacetyl nitrate (PAN), chlorine (Cl),
and ammonia (NH3
).
Sulfur dioxide. SO2 causes acute and chronic plant injury. Acute
injury is characterized by clearly marked dead tissue between
the veins or on leaf margins. The dead tissue may be bleached,
ivory, tan, orange, red, reddish brown, or brown, depending on
plant species, time of year, and weather conditions. Chronic injury
is marked by brownish red, turgid, or bleached white areas
on the leaf blade. Young leaves rarely display damage, whereas
fully expanded leaves are very sensitive.
Some crops sensitive to sulfur dioxide are: squash, pumpkin,
mustard, spinach, lettuce, endive, Swiss chard, broccoli,
bean, carrot, and tomato.
Ozone. A common symptom of O3 injury is small stipple like or
flecklike lesions visible only on the upper leaf sur face. These
very small, irregularly shaped spots may be dark brown to black
(stipplelike) or light tan to white (flecklike). Very young leaves
are normally resistant to ozone. Recently matured leaves are
most susceptible. Leaves be come more susceptible as they mature,
and the lesions spread over a greater portion of the leaf with
successive ozone exposures. Injury is usually more pronounced
at the leaf tip and along the margins. With severe damage, symptoms
may extend to the lower leaf surface.
Pest feeding (red spider mite and certain leafhoppers) produces
flecks on the upper surface of leaves much like ozone
injury. Flecks from insect feeding, however, are usually spread
uniformly over the leaf, whereas ozone flecks are concen trated in
specific areas. Some older watermelon varieties and red varieties
of potatoes and beans are particu larly sensitive to ozone.
Peroxyacetyl nitrate. PAN affects the under surfaces of newly
matured leaves, and it causes bronzing, glazing, or silvering on
the lower surface of sensitive leaf areas.
The leaf apex of broadleaved plants becomes sensitive to
PAN about 5 days after leaf emergence. Since PAN toxicity is
specific for tissue of a particular stage of development, only
about four leaves on a shoot are sensitive at any one time. With
PAN only successive exposures will cause the entire leaf to develop
injury. Injury may consist of bronzing or glazing with little
or no tissue collapse on the upper leaf surface. Pale green to
white stipplelike areas may appear on upper and lower leaf surfaces.
Complete tissue collapse in a diffuse band across the leaf
is helpful in identifying PAN injury.
Glazing of lower leaf surfaces may be produced by the feeding
of thrips or other insects or by insecticides and herbicides, but
differences should be detectable by careful examination.
Sensitive crops are: Swiss chard, lettuce, beet, esca role,
mustard, dill, pepper, potato, spinach, tomato, and canta loupe.
32
2023 Vegetable Crop Handbook for Southeastern United States
Southeastern U.S. Vegetable Crop Handbook - 2023

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