NOVEMBER
2004
By
Beverly Shaw
Advanced
Master Gardener
Purdue University
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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.
11-4-04
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