June 23, 1997
DIAGNOSING VEGETABLE PROBLEMS
by Stephen Reiners, Associate Professor Of Horticultural Sciences,
Cornell University, New York State Agricultural Experiment Station, Geneva, NY
Geneva, NY - "What's wrong with these plants?" is a phrase growers
repeat over and over as the growing season progresses. Often with some
common sense and a thorough knowledge of a field's recent history, it's
easy to find the answer. The following are guidelines that both growers and
consultant may find useful in diagnosing problems.
- Identify the symptoms.
- Determine if there is a pattern to the symptoms. Do the affected plants
sit above a low spot, poor drainage area, or an area with obviously
compacted soil? Does the pattern correlate with current field operations?
- Trace the problem's history.
- When were symptoms first noticed?
- What rates of fertilizer and lime were used?
- What pesticides and/or herbicides were used?
- What were the weather conditions like before you noticed the problems -
cool or warm, wet or dry, windy, cloudy, sunny?
- Examine the plant carefully to determine if the problem seems to be
caused by insects, diseases or management practices.
Insects. Look for their presence or feeding signs on leaves, stems
and roots. Sometimes it's easier to find insects early in the morning or
toward evening.
Disease. Look for dead areas on roots, leaves, stems and flowers.
Are the plants wilting even though soil moisture is plentiful? Are
the leaves spotted or yellowed? Are there any signs of bacterial or
fungal growth (soft rots, mildew, spores, etc.)? Look for virus
symptoms-are the plants stunted or do they have obvious growth
malformations? Are all the plants showing symptoms, or are just a few
scattered around the field?
- Could there be nutritional problems? The following is a list of
characteristic deficiency symptoms for the major and minor nutrients.
- Nitrogen: Light green or yellow older foliage.
- Phosphorus: Stunted plants and purplish leaves.
- Potassium: Brown leaf margins and leaf curling.
- Calcium: Stunted plants, stubby roots. (Causes blossom end rot of
tomatoes, tip burn of cabbage, brownheart of escarole, celery
blackheart, carrot cavity spot).)
- Magnesium: Yellowing between veins of older leaves.
- Sulfur: Yellowing of hew leaves, stunted plants.
- Boron: Growing points die back and leaves are distorted.
- Copper: Yellowing of leaves which become thin and elongated, causes
soft onion bulb with thin scales.
- Iron: Light green or yellow foliage on youngest leaves.
- Zinc: Rust-colored spots on seed leaves of beans, green and yellow
striping of corn, yellowing of beet leaves.
- Manganese: Mottled yellow area appearing on younger leaves first.
In beets, foliage becomes deeply red.
- Molybdenum: Distorted, narrow leaves, some yellowing of older
leaves; whiptail leaf symptoms in cauliflower.
- Could there be a nutrient toxicity? Boron, zinc, and manganese may be a
problem here. Soluble salt injury may be seen as wilting of the plant even
when the soil is wet. Burning of the leaf margins is usually from excessive
fertilizer. Soil problems such as compaction and poor drainage can severely
stunt plants.
- Could soil problems be to blame? Soil compaction, poor drainage, etc.
- Could pesticide injury be at fault? Pesticide injury is usually uniform
in the are or shows definite patterns. Insecticides cause burning or
stunting. Herbicides cause burning or abnormal growth.
- Could the damage be caused by environmental conditions? High or low
temperatures, excessively wet or dry, frost or wind damage, or even air
pollution? Ozone levels may rise as hot, humid weather settles in for long
stretches. Look for irregularly shaped spots which may look similar to
feeding of mites and certain leafhoppers. Ozone flecks are usually
concentrated in specific areas of the leaf, while feeding damage from
insects is spread uniformly across the leaf.
- Contact: Linda McCandless, Communications Services
- Telephone: (315) 787-2417
- e-mail: llm3@cornell.edu
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