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11-04-04
Question and Answer
Q. Our tomatoes have had blight the last two years.
Is there anything we can do to keep them from getting it again? -- Mrs.
George Bowen, Plymouth, Ind.
A. There are three major blights that can attack your
tomatoes: Septoria leaf spot, early blight and late blight. All are fungal
diseases spread by spores, which require dew or rain to infect the plant.
These are most severe in wet weather. Septoria leaf spot, sometimes called
Septoria blight, is caused by the fungus Septoria lycopersici and usually
appears on the lower leaves after the first fruits set. Fruits are rarely
infected. All the leaf loss reduces fruit yield and quality, and exposed
fruits are more susceptible to sunscald. The fungus is spread by splashing
water and by working among the plants when they are wet. It overwinters
on tomato and weed refuse.
Early blight, caused by the fungus Alternaria solani, appears on the
lower leaves, usually after a heavy fruit set. The spots are dark brown
to black. Concentric rings develop in the spot forming a bull's eye. The
leaf area around each target spot turns yellow, and soon the entire leaf
turns yellow and drops. Early blight fungus also infects stems and may
produce stem cankers. It occasionally attacks the fruit, producing large
sunken black target spots on the stem end of the fruit. Infected fruits
often drop before they mature. This disease is most common late in the
growing season. The fungus overwinters on old tomato vines and on weeds
in the nightshade family.
Late blight, caused by the fungus Phytophthora infestans, occurs in moist
weather with cool nights and moderately warm days. Dark-green to nearly
black wet-looking spots begin spreading in from the leaf edge. In wet
weather, the spots may have a downy, white growth on the lower leaf surface
near the outer portion of the spot. Spots also develop on the fruits.
At first, the spots are gray-green and water-soaked, but they soon enlarge
and turn dark brown and firm, with a rough surface. When conditions are
favorable, the disease may progress very rapidly.
Avoid these diseases by rotating crops. Plant tomatoes in the same place
only once in three or four years. Remove and destroy tomato vines in the
fall. Plow or rototill to bury the remaining crop refuse. Use healthy
transplants. Remove badly diseased lower leaves, as these are a source
of leaf spot fungus spores that help spread the disease.
Water at the base of the plants to avoid splashing water, which spreads
the spores. Avoid watering with overhead sprinklers in late afternoon
or evening. If the plants stay wet all night, leaf spot infections are
likely to occur.
Use fungicides when needed. These diseases spread rapidly and are difficult
to control once established. Fungicides must be applied before the disease
first appears and reapplied throughout the growing season. Chlorothalonil
fungicide, sold as Ortho Multi-Purpose Fungicide, can be applied up to
the day of harvest.
Q. I planted some roses this year and need to know how
to care for them during the winter. The Styrofoam cones are ugly! -- Barb
Wilson, Indianapolis, Ind.
A. Grafted roses require protection on the graft union
to survive winter. Keep the plants healthy throughout the growing season
by avoiding or treating insect and disease damage and watering properly.
After several freezes in the late fall, plants become dormant and winter
protection should be applied. If applied too early, the soil, rose cone
or other materials can trap moisture around the plant and encourage disease.
Pick up and remove debris, such as leaves and dead stems. If the soil
is dry, give it a thorough soaking.
The best method is to mound soil up around the plant. A 12-inch mound,
or approximately 5 gallons of soil, provides excellent protection. It
will also keep rabbits from feeding on the stems.
Prepare the plant by tying the canes up with twine. Dig the soil from
an area away from the roses, so you don't damage their roots. For further
protection, pile additional mulch, such as straw or chopped leaves, on
top of the soil mound.
Commercially available rose cones have been used with varying success.
Even with cones, some mounding is advisable. Plants must be pruned to
fit under the cone. Cut slits in the tops to provide air ventilation,
and weigh the cone down with a heavy rock or brick.
In early spring, all protection must be removed as soon as plants begin
new growth. Soil from the mounds should be placed in another area, rather
than on top of the plant's root area. Adding more soil thickness may prevent
proper aeration needed for root growth.
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