PROTECTING PLANTS FROM THINGS THAT PREY ON THEM - Continued
Treatment for some of the common plant diseases.
The following advice (mostly adapted from Whetzel and Stewart) covers
the most frequent types of fungous disease appearing to the home
gardener. Many other kinds, however, will almost certainly attract his
attention the first season if he looks closely. The standard remedy is
bordeaux mixture; but because this material discolors the foliage the
carbonate of copper is sometimes used instead. The treatments here
recommended are for New York; but it should not be difficult to apply
the dates elsewhere. The gardener must supplement all advice of this
character with his own judgment and experience, and take his own risks.
Apple scab.--Usually most evident on the fruit, forming blotches and
scabs. Spray with bordeaux, 5-5-50 or 3-3-50; first, just before the
blossoms open; second, just as the blossoms fall; third, 10 to 14 days
after the blossoms fall. The second spraying seems to be the most
important. Always apply before rains, not after.
Asparagus rust.--The most common and destructive disease of asparagus,
producing reddish or black pustules on the stems and branches. Late in
the fall, burn all affected plants. Fertilize liberally and cultivate
thoroughly. During the cutting season, permit no plants to mature and
cut all wild asparagus plants in vicinity once a week. Rust may be
partially controlled by spraying with bordeaux, 5-5-50, containing a
sticker of resin-sal-soda soap, but it is a difficult and expensive
operation and probably not profitable except on large acreage. Begin
spraying after cutting as soon as new shoots are 8 to 10 in. high and
repeat once or twice a week until about September 15. Dusting with
sulfur has proved effective in California.
Cabbage and cauliflower diseases.--Black-rot is a bacterial disease;
the plants drop their leaves and fail to head. Practice crop rotation;
soak seed 15 min. in a solution made by dissolving one corrosive
sublimate tablet in a pint of water. Tablets may be bought at
drug stores.
Club-root or club-foot is a well-known disease. The parasite lives in
the soil. Practice crop rotation. Set only healthy plants. Do not use
manure containing cabbage refuse. If necessary to use infested land,
apply good stone lime, 2 to 5 tons per acre. Apply at least as early as
the autumn before planting; two to four years is better. Lime the
seed-bed in same way.
Carnation rust.--This disease may be recognized by the brown, powdery
pustules on the stem and leaves. Plant only the varieties least affected
by it. Take cuttings only from healthy plants. Spray (in the field, once
a week; in the greenhouse, once in two weeks) with copper sulfate, 1 lb.
to 20 gal. of water. Keep the greenhouse air as dry and cool as is
compatible with good growth. Keep the foliage free from moisture. Train
the plants so as to secure a free circulation of air among them.
Chestnut.--The bark disease of chestnut has become very serious in
southeastern New York, causing the bark to sink and die and killing the
tree. Cutting out the diseased places and treating aseptically may be
useful in light cases, but badly infected trees are incurable, in the
present state of our knowledge. Inspection of nursery stock and burning
of affected trees is the only procedure now to be recommended. The
disease is reported in New England and western New York.
Chrysanthemum leaf-spot.--Spray with bordeaux, 5-5-50, every ten days
or often enough to protect new foliage. Ammoniacal copper carbonate may
be used, but it is not so effective.
Cucumber diseases.--"Wilt" is a disease caused by bacteria that are
distributed chiefly by striped cucumber beetles. Destroy the beetles or
drive them away by thorough spraying with bordeaux, 5-5-50. Gather and
destroy all wilted leaves and plants. The most that can be expected is
that the loss may be slightly reduced.
Downy mildew is a serious fungous disease of the cucumber known among
growers as "the blight." The leaves become mottled with yellow, show
dead spots, and then dry up. Spray with bordeaux, 5-5-50. Begin spraying
when the plants begin to run, and repeat every 10 to 14 days throughout
the season.
Currant diseases.--Leaf-spots and anthracnose are caused by two or
three different fungi. The leaves become spotted, turn yellow, and fall
prematurely. They may be controlled by three to five sprayings with
bordeaux, 5-5-50, but it is doubtful whether the diseases are
sufficiently destructive on the average to warrant so much expense.
Gooseberry powdery mildew.--The fruit and leaves are covered with a
dirty white growth of fungus. In setting a new plantation, choose a site
where the land is well underdrained and where there is a good
circulation of air. Cut away drooping branches. Keep the ground
underneath free from weeds. Spray with potassium sulfide, 1 oz. to 2
gal.; begin when the buds are breaking and repeat every 7 to 10 days
until the fruit is gathered. Powdery mildew is very destructive to the
European varieties.
Grape black-rot.--Remove all "mummies" that cling to the arms at
trimming time. Plow early, turning under all old mummies and diseased
leaves. Rake all refuse under the vine into the last furrow and cover
with the grape hoe. This cannot be too thoroughly done. The disease is
favored by wet weather and weeds or grass in the vineyard. Use surface
cultivation and keep down all weeds and grass. Keep the vines well
sprouted; if necessary sprout twice. Spray with bordeaux mixture,
5-5-50, until the middle of July, after that with ammoniacal copper
carbonate. The number of sprayings will vary with the season. Make the
first application when the third leaf shows. Infections take place with
each rain, and occur throughout the growing season. The foliage should
be protected by a coating of the spray before every rain. The new growth
especially should be well sprayed.
Hollyhock rust.--Fig. 212. Eradicate the wild mallow (Malva
rotundifolia). Remove all hollyhock leaves as soon as they show signs
of rust. Spray several times with bordeaux mixture, taking care to cover
both sides of leaves.
Lettuce drop or rot.--This is a fungous disease often destructive in
greenhouses, discovered by the sudden wilting of the plants. It is
completely controlled by steam sterilization of the soil to the depth of
two inches or more. If it is not feasible to sterilize the soil, use
fresh soil for every crop of lettuce.
Muskmelon diseases.--"Blight'" is a very troublesome disease. The
leaves show angular dead-brown spots, then dry up and die; the fruit
often fails to ripen and lacks flavor. It is caused by the same fungus
as is the downy mildew of cucumbers. While bordeaux has proved effective
in controlling the downy mildew on cucumbers, it seems to be of little
value in lessening the same disease on melons.
"Wilt" is the same as the wilt of cucumbers; same treatment is given.
Peach diseases.--Brown-rot is difficult to control. Plant resistant
varieties. Prune the trees so as to let in sunlight and air. Thin the
fruit well. As often as possible pick and destroy all rotten fruits. In
the fall destroy all remaining fruits. Spray with bordeaux mixture
before the buds break, or self-boiled lime-sulfur.
Leaf-curl is a disease in which the leaves become swollen and distorted
in spring and drop during June and July (Fig. 213). Elberta is an
especially susceptible variety. Easily and completely controlled by
spraying the trees once, before the buds swell, with bordeaux, 5-5-50,
or with the lime-sulfur mixtures used for San José scale.
Black-spot or scab often proves troublesome in wet seasons and
particularly in damp or sheltered situations. While this disease attacks
the twigs and leaves, it is most conspicuous and injurious on the fruit,
where it appears as dark spots or blotches. In severe attacks the fruit
cracks. In the treatment of this disease it is of prime importance to
secure a free circulation of air about the fruit. Accomplish this by
avoiding low sites, by pruning, and by removal of windbreaks. Spray as
for leaf-curl and follow with two applications of potassium sulfide, 1
oz. to 3 gal., the first being made soon after the fruit is set and the
second when the fruit is half grown.
Yellows is a so-called "physiological disease." Cause unknown.
Contagious, and serious in some localities. Known by the premature
ripening of the fruit, by red streaks and spots in the flesh, and by the
peculiar clusters of sickly, yellowish shoots that appear on the limbs
here and there (Fig. 215). Dig out and burn diseased trees as soon as
discovered.