FRUITAND
VEGETABLES
FRUIT
The information and recommendations in this newsletter are applicable to
North Carolina
and may not apply in other areas.
Between May 5 and May 8, five potato plant samples were diagnosed with ozone injury in North Carolina. Plants were collected in Sampson, Chowan, Columbus and Washington counties indicating that the injury is widespread. Ozone causes dark brown spots or patches of dead tissue between the veins of leaves of susceptible cultivars. Symptoms are most severe on the underside of mature leaves while the youngest and oldest leaves are much less susceptible to injury.
Red potato varieties are typically more sensitive to injury than
other varieties. Plants will usually recover over time unless high
levels of ozone occur again. High levels of ozone recorded in
Raleigh during mid to late April are indicative of concentrations
throughout much of eastern North Carolina. The timing of these
high concentrations corresponds with the timing of ozone injury in
the field. Ideal conditions for ozone injury are high
concentrations of ozone (caused by sunlight reacting with
precursors in the air) and moist, cool conditions which tend to
make plants sensitive to ozone. Injury will typically appear 3 to
5 days after exposure, depending on ozone levels. The extent of
injury throughout North Carolina is being determined so stay posted
for further developments. As we move into the summer, look for
ozone injury on other sensitive crops (e.g., snap beans, pinto
beans, soybeans, tomato, cotton, okra, tobacco and watermelon).
I have received numerous samples with low temperature injury. Low temperatures (at or near freezing) can kill plant tissue and mimic symptoms of plant disease. It is important to be able to distinguish between the two. Especially sensitive to low temperatures are plants with new, tender growth. Transplants coming out of the greenhouse are also very susceptible. In the field, cold air will collect first in low lying areas and damaged crops will often correspond with topography.
Look for the following symptoms: crinkled leaf veins, water-soaked
vascular tissue, blisters or raised epidermis. Injury from low
temperatures can be fatal or minor depending on the crop, its stage
of development, temperature and its duration. Also, secondary
organisms will eventually colonize dead tissue.
Web page last updated on May 19, 1997 by Stephen J. Toth, Jr..
