Computerworld 1996 March/Computerworld_1996-03_cd.bin/idg_cd3/aplikace/domacnos/wgarden1/diseases.txt

Text File | 1995-03-06 | 30.8 KB | 700 lines

                             Ascochyta blight

  This blight like other blights can be minimized through crop
rotation. Also, seed grown in the west is less likely to cause
blight.
_________________________________________________________________

                              Asparagus rust

  Asparagus rust appears as reddish or brownish spots on the
stems and leaves of Asparagus. The spots release a cloud of
spores when brushed or rubbed. The disease will certainly cause
poor quality shoots and often will kill the plant. The problem
usually occurs in damp areas, because the spores need moisture to
germinate.
  Plant resistant varieties, such as Mary Washington, in a well
drained area to prevent the problem. Control the disease with
applications of a fungicide, such as Zineb or chlorothalonil.
_________________________________________________________________

                             Bacterial blight

  Bacterial blight occurs as large brownish spots with a yellow
edge on plant leaves. Decaying of the plant often follows.
  Select seed grown in the west as a preventative measure and
reframe from working in the garden when the plants are wet, as
this can spread diseases.
_________________________________________________________________

                             Bacterial canker

  A canker is a fungus disease which will cause an infected area
or lesion on a plant stem. The plant will often die above the
infected area, because the canker restricts the flow of water
through the stem.
  Diseased plants are most often removed and destroyed; however
the diseased area could be cut out. Sterilize any tools used to
remove a canker with denatured alcohol. This will prevent in
spreading the disease. As a preventive measure, crop rotation is
recommended.
_________________________________________________________________

                              Bacterial spot

  Leaf spots can be caused by either bacteria or fungi. They come
in a variety of colors, shapes, and sizes. Leaf spots caused by
bacteria has a water-soaked appearance. Fungi cause leaf spots
with a small black dot in the center. One of the most common leaf
spots encountered in the garden is a bacterial leaf spot, which
is 1/16 to one inch in diameter and dark to tan in color.
  Crop rotation will help to discourage the problem. Also, select
treated seed or resistant varieties. Remove any infected leaves
promptly and apply Maneb or chlorothalonil fungicides. An organic
approach is to dust the leaves with lime.
_________________________________________________________________

                              Bacterial wilt

  Wilting occurs because of a lack of moisture in a plant.
Bacteria introduced into a plant creates a thick white substance
that restricts the flow of moisture in a plant. This problem
eventually kills the plant. The bacteria is carried by certain
pests that overwinter in or near the garden area. Corn can be
attacked by flea beetles that carry the bacteria. Cucumbers and
watermelons are affected by cucumber beetles, such as the striped
and spotted cucumber beetles that carry the bacteria. Cucumber
leaves are the first to be seen to wilt, followed by wilting of
the vines.
  Control the pests that carry the bacteria and you will control
the bacteria. A preventive measure is to keep a clean garden at
the end of the growing season. This will keep the pests from
having a home to overwinter in. Control outbreaks of the pest
during the season with the proper pesticides or organic methods.
_________________________________________________________________

                                 Black leg

  Black leg appears as the blackening of the stems at the base of
the affected plant. This problem is caused by fungi and bacteria.
It is a problem amongst potatoes, brussels sprouts, cabbage, and
cauliflower. The cabbage family of plants will also have leaves
which turn purplish in color, in addition to the base of the
stems turning black. Potato plants will have small leaves at the
top of the plant which curl inward.
  Remove infected plants promptly. Crop rotation will help also.
Black leg most often occurs in heavy wet soils, so planting in a
well drained soil is recommended. Planting whole seed potatoes
could be to your advantage also. Seed potatoes infected by the
disease are not always obvious to the eye, so buy seed potatoes
from an area that has not been affected by the problem. Planting
infected seed potatoes could cause the disease to spread.
_________________________________________________________________

                                 Black rot

  Black rot affects many of the crucifer family of plants
including cabbage, cauliflower, and brussels sprouts. The leaves
of affected plants will develop wedge-shaped areas yellow in
color. Plants will have black or discolored areas inside the
stem.
  Plant in a well drained location to discourage rotting.
Purchase plants that are certified as being disease free, such as
those that are grown in the far west. Also, purchase seed that
has been hot water treated. Remove and destroy diseased plants to
prevent the spread of the disease. Frequent crop rotation is
advisable.
_________________________________________________________________

                                  Blight

  Blight is a generalized term to cover a wide variety of
diseases which affect plants and are caused by fungi and
bacteria. The problem does not necessarily cause the leaves to
wilt and drop off, but does often cause browning of the leaves
and death of the plant.
  Removal of an infected plant is suggested to hamper the spread
of diseases, as well as crop rotation.
_________________________________________________________________

                              Blossom end rot

  Tomatoes are the most commonly affected plant of blossom end
rot, but the problem can happen to other plants as well. The
blossom end of the fruit will become brown when the fruit is one
third to one half mature. The affected area of the fruit may
become depressed or concave. Blossom end rot is basically a
deficiency of calcium. Too much or too little water is what
causes the plant not to acquire the proper amount of calcium.
Also, too much nitrogen fertilizer can cause the plant to grow
too fast and not get the calcium that it needs.
  There are several things that can be done to help with this
problem. The first thing to do is to make sure that the pH is
about 6.5. Steady growth and not rapid growth is preferred. The
same holds true for watering...not too little and not too much.
As a rule of thumb the garden requires about one inch per week.
Be particularly attentive to proper watering after the plant
blossoms, as this is the most likely time for the problem to crop
up. Should you try to save an affected plant, try spraying the
plant with calcium chloride.
_________________________________________________________________

                                 Club root

  Club root causes a plants root system to become swollen and
disfigured. It affects members of the Mustard family, such as
cabbage and brussels sprouts. Wilted leaves and stunted growth is
likely to occur. The disease is caused by a fungus-like organism
called a slime fungi. The disease can remain alive and
destructive in the soil for several years.
  A preventative measure is to raise and maintain the soil pH
above 7.0. Crop rotation is also recommended. When purchasing
seedlings, inspect the plants for any signs of the disease before
purchasing.
_________________________________________________________________

                                 Corn smut

  Corn smut is a fungus that creates massive numbers of black
spores. Left unchecked the problem can wipe out an entire corn
crop. It appears as a boil-like area on various parts of the corn
plant including the tassels, stalks, and ears. The boils are
usually greenish-white in color. These will eventually burst,
releasing numerous spores. The plants will become stunted and
disfigured. The disease overwinters in the soil and on old
infected corn stalks.
  Crop rotation can be helpful. Remove any boils before they
burst and spread the disease. Infected plants should be removed
and burned. Never use old infected stalks in your compost, as the
disease can remain active for several years.
_________________________________________________________________

                                 Crown rot

  Crown rot or Southern stem blight is a fungus disease that
attacks the plant on the stem at or just above the soil level.
The problem my first be noticed as a white fungus growing at the
base of the stem or on organic matter laying on the surface of
the soil surrounding the plant. Eventually, sclerotia will
develop in the mold. These are small seed-like bodies which are
light tan to dark brown in color. The leaves of affected plants
will turn yellow and wilt. The plant, as well as surrounding
plants, will die.
  Crop rotation may be somewhat helpful, but removal of affected
plants and the soil surrounding the plants is highly recommended.
Soil removal is important, because the disease can remain in the
soil for over a year. Making sure that all organic matter is
plowed under will give the fungus less places to develop.
_________________________________________________________________

                                Damping off

  Damping-off disease is caused by fungi that live in the soil.
The problem causes young seedlings to turn brown, wilt, and die.
The fungi can attack the seedlings shortly before or shortly
after emerging from the soil. This is a common problem when
starting young plants in trays.
  There are several ways to combat damping-off including the
following. Purchase seed which have been treated for the disease.
Either sterilize the soil or use a sterile growing media. One
such
fumigant is called Vapan. Vermiculite and sphagnum moss make an
excellent sterile growing mixture. Also, provide adequate
drainage for the seedlings as this encourages the problem. If
growing the seedlings inside, keep the humidity down. High
humidity is known to create a good environment for fungi. In the
garden a well drained soil and crop rotation is important.
_________________________________________________________________

                               Downy mildew

  Downy mildew is not actually a true mildew at all. Unlike true
mildews which grow on the surface of leaves, downy mildews
originate from within the tissues of the affected plants. Downy
mildew appears as yellow, white, gray, or purplish patches on
mainly the underside of leaves. The patches are actually the
spores of the fungi affecting the plant. Downy mildew can also be
seen on stems and fruit. Lima beans, for instance, will develop a
white downy mildew on the pods and eventually turn into black
patches of mildew. This is a particular problem during long wet
periods. Affected leaves will often not develop properly and fall
off the plant.
  Infected plants and diseased leaves which fall off the plant
should be removed and destroyed. Crop rotation and adequate water
drainage are also helpful. One control of the downy mildew is the
chemical zineb. An organic solution to the problem is dusting
with lime, flour, or sulfur.
_________________________________________________________________

                               Early blight

  This fungi causing disease affects potatoes, peppers,
eggplants, and particularly tomatoes. It first appears as dark
brown or black spots with rings similar to a "target" design. The
disease first strikes the lower leaves and then may spread to the
upper leaves. The infected leaves will wilt, yellow, and often
die. Sometimes the problem will spread to the stems and fruit.
  Crop rotation is important, as the disease can remain in the
ground for about three years. Use seed that has been hot water
treated. Treat your own seed with Thiram. Early blight is
encouraged by moisture, warmth, and humidity; so provide adequate
drainage and ventilation. Control outbreaks of the disease with a
fungicide, such as chlorothalonil or Maneb. An organic approach
would be to simply remove and destroy infected plants to prevent
spread of the disease. Also, avoid working the garden after
watering to reduce the chance of spreading diseases. Water early
in the morning to give the plants time to dry off.
_________________________________________________________________

                                 Fruit rot

   The rotting of fruit can occur through damage inflicted by
insects, garden tools, or simply the fruit laying on a warm,
moist soil. These conditions will give bacteria and fungi an
opportunity to develop. Fruit may become discolored, slimy, soft,
and foul smelling. Overmature fruit can also develop fruit rot.
  A number of things can be done to discourage fruit rot
including the following. Control pests to reduce injury to fruit
and spread of diseases. Be careful when working the garden with
garden tools. They can inadvertently create open wounds. Keep
fruit up off of the soil by staking or mulching. Do not allow
ripened fruit to remain on the vine. Crop rotation and proper
drainage are also important. Control outbreaks of fungi-causing
diseases with the proper fungicide.
_________________________________________________________________

                       Fungus and Bacterial diseases

  Fungi and bacteria can cause a wide variety of problems.
Bacteria are minute plants which can cause rotting, wilting, and
the forming of galls. Fungi, which are usually visible to the
naked eye, cause rusting, spotting, mildewing, and damping-off.
Both are generally encouraged by moisture, warmth, and humidity.
  Control these problems with the proper fungicide or by removing
and destroying diseased plants. Purchase disease-free or treated
seeds and plants. Crop rotation, staking, mulching, and adequate
soil drainage are also important.
_________________________________________________________________

                               Fusarium wilt

  Fusarium wilt is a common problem amongst beans, peas, cabbage,
sweet potatoes, tomatoes, and watermelon. The disease, which is
caused by fungi, will at first cause the lower leaves to curl
downwards. Latter, the leaves will yellow and the plant will
become stunted. A cross section of the lower stem will reveal
dark brown streaks running lengthwise.
  Purchase wilt-resistant varieties of seeds and plants. Do not
plant in a soil that has been infected by the disease. Crop
rotation will naturally help.
_________________________________________________________________

                            Internal black spot

  This disease is one of many affecting potatoes. Prevent this
problem by not overfertilizing the plant with nitrogen.
_________________________________________________________________

                                Late blight

  Late blight is a fungus causing diseases which affects potatoes
and tomatoes. It most often occurs in long wet periods of
weather. The disease first manifests itself as dark green or
black water-soaked spots. Occasionally the affected leaves will
have a white powdery mildew on the underside of the leaves.
Leaves will droop and appear as though they have been scalded or
frost bitten. Fruit will develop rot and decay.
  Use of the proper fungicide is helpful, but infected plants are
usually removed to prevent spread of the disease. Preplan by
selecting certified, disease-free seed and plants.
_________________________________________________________________

                                Leaf blight

  This is a disease which affects carrots. Crop rotation can be
helpful to inhibit spread of the disease. Also, purchasing hot-
water treated seeds is recommended.
_________________________________________________________________

                                Leaf Spots

  Leaf spot diseases are caused by fungi and bacteria. Infected
leaves have spots which appear as dead tissue. These spots can be
yellow-green, tan, or black. The problem is particularly noticed
on plants whose leaves are to be consumed, such as turnip greens.
The spots will sometimes first appear as dark green water soaked
spots. The spots are generally 1/16 to 1 inch in diameter.
  Remove infected leaves promptly and follow up with an
application of fungicide, such as Maneb or chlorothalonil. Also,
crop rotation can be a good preventative measure.
_________________________________________________________________

                                Lettuce rot

  Lettuce rot is caused by the lower leaves coming in contact
with the soil. The rotting of the lower leaves will often spread
to the rest of the plant.
  Prevent this problem by applying a layer of sand around the
base of the plant. This will improve drainage and keep the leaves
from laying on the moist soil which encourages rotting.
_________________________________________________________________

                                  Mildew

  Mildew is a fungus. The term mildew includes powdery mildews,
which are true mildews, and downy mildews, which are false
mildews. True mildews lie on the surface of the affected plant
and feeds on the plant through tiny suckers. False mildews are
living on the internal fibers of a plant and appear on the
surface of the plant. Mildews come in a variety of colors, but
true mildews are generally white in color and occasionally black.
  Prevent mildew by planting in a sunny, well-drained area.
Plenty of air flow and ventilation will also discourage the
growth of mildew.
_________________________________________________________________

                                  Mosaic

  Mosaic is a disease caused by a virus. Mosaic can infect beans,
peas, corn, cucumbers, melons, peppers, and tomatoes. Infected
plants are generally stunted. The leaves of affected plants will
have light and dark green areas. This mottled appearance is due
to the virus attacking the chlorophyll in the leaves. This will
inhibit the plant from creating its own food and cause other
disastrous side effects, including distortion of the leaves and
fruit.
  Crop rotation is a good preventative measure. Purchasing
disease free, certified seed and plants is also a plus. In
addition, control aphids which may carry the virus. One common
mosaic is tobacco mosaic which affects tomato plants. The virus
is spread by gardeners that smoke. Always wash your hands
thoroughly before handling tomato plants if you smoke.
_________________________________________________________________

                                 Neck rot

  The rotting of the necks of onion plants will be less likely a
problem with the stronger flavored onions than the milder ones.
_________________________________________________________________

                                 Nematodes

  Nematodes are tiny worm-like creatures invisible to the naked
eye. They live and feed off of plant leaves, stems, and roots.
This and the laying of eggs in the tissue of the plant will cause
knots and stunted growth.
  Control this parasite through crop rotation and garden
sanitation. The use of organic fertilizers and mulches will
encourage beneficial organisms, such as fungi and bacteria, to
multiply. These beneficial organisms will feed on the nematodes.
Also, planting marigolds will help to repel nematodes.
_________________________________________________________________

                              Payllid yellows

  This is a disease of tomato plants. Cultivating the soil will
help.
_________________________________________________________________

                                 Pink rot

  This rotting of onions is bred in moist soil. You can help to
prevent this problem by planting bulbs in a well-drained soil.
_________________________________________________________________

                              Powdery mildew

  Powdery mildew is a true mildew and appears as a powdery or
felty white growth on the surface of affected plants. The problem
most often occurs during periods of high humidity. This mildew
feeds on the plant by means of tiny suckers, draining the plant
of important nutrients.
  Preventative measures of controlling mildew includes providing
adequate ventilation and drainage. Applications of sulfur can
help to control the problem on beans and peas. Benomyl,
karathane, and chlorothalonil may be applied to vine crops, such
as melons and squash.
_________________________________________________________________

                                Rhizoctonia

  To prevent this problem from happening to your potatoes, plant
the potato seed shallow in a thick bed of mulch. This will assist
the plant in developing faster. Crop rotation is also a good
preventative measure.
_________________________________________________________________

                                 Ring rot

  This disease of potatoes is easily spread by garden tools that
have come into contact with infected plants. Thoroughly clean
garden tools to keep this from happening.
_________________________________________________________________

                            Root knot nematode

  Nematodes are tiny worm-like creatures invisible to the naked
eye. They live and feed off of plant leaves, stems, and roots.
This and the laying of eggs in the tissue of the plant will cause
knots and stunted growth. In general plant production, quality,
and fruit quantity are reduced. Root knot nematodes are one of
the most common nematodes. They are particularly prevalent in the
southern states where the temperatures are warm and winters are
mild. They can remain in the soil for quite some time where these
conditions are met. Examine the roots of plants that are
suspicioned to have this problem. Take note that knots on the
roots of bean and pea plants may not necessarily be nematode-
caused. These plants have root nodules which contain beneficial
bacteria. These beneficial nodules can easily be removed, whereas
the galls created by nematodes are not.
  Control this parasite through crop rotation and garden
sanitation. The use of organic fertilizers and mulches will
encourage beneficial organisms, such as fungi and bacteria, to
multiply. These beneficial organisms will feed on the nematodes.
Also, planting marigolds will help to repel nematodes.
_________________________________________________________________

                                 Root rot

  The fungus which causes this disease will first appear as red
or reddish-brown areas on the lower stem and roots of infected
plants. These discolored areas eventually spread to the entire
stem and root system. Plants infected by this disease may turn
yellow, droop, or die. Stunted growth and pod development are
also some of the symptoms.
  Control this disease through crop rotation and by purchasing
treated seed. Additional control methods for rot are as follows.
Provide adequate drainage, as too much moisture encourages rot.
Keep the proper balance of pH and fertilizers. Use a fungicide,
such as Capan, or a soil fumigant, such as Vapam. Use a nitrogen-
rich fertilizer, but be cautious. Peas produce their own nitrogen
and too much nitrogen could cause the plant too produce all vine.
_________________________________________________________________

                                   Rust

  Rust fungi produces spores which appears as reddish-orange
spots on the leaves of affected plants. These areas of orange are
easily rubbed off when brushed. They can often cause great damage
to some crops.
  Control the disease by applying a fungicide, such as
chlorothalonil or Zineb. An organic approach to the problem is
dusting the leaves with lime.
_________________________________________________________________

                                   Scab

  This disease occurs as wart-like growths on the foliage and
fruit of infected plants. On the tubers of potato plants, the
scab can appear as either indented or raised areas of growth.
  Naturally, crop rotation can help in the control of this fungus
disease. Keep the pH level low. Too much alkalinity will only
encourage the growth of scab. For organic gardeners this means
not to use wood ashes where scab has been a problem. Sulfur is
said to be an effective control also.
_________________________________________________________________

                                   Scurf

  Scurf, also known as Soil rot or soil stain, is a disease
afflicting sweet potatoes. The fungus, which can remain in the
soil for several years, causes brown or brownish-black spots on
the tubers. The disease causes the harvested potatoes to shrink
in storage. This is particularly a problem in heavy soils.
  Control scurf by planting seed potatoes which are certified
disease-free. If heavy soil is a problem, adding sand to the soil
will benefit soil texture. Also, keeping the soil pH below 5.5 is
recommended.
_________________________________________________________________

                              Seldom bothered

  This simply means that the selected plant either has no
diseases or that any diseases that do affect it are of little
consequence.
_________________________________________________________________

                            Septoria leaf spot

  Septoria leaf spot is a fungus disease which affects tomato
plants mainly in the eastern and mid western states. The disease
occurs during very wet periods. The fungus appears as water-
soaked spots on the lower, older leaves. These circular spots,
usually no more than 1/8 inch in size, eventually turn gray with
dark edges. As the disease progresses it will spread to the upper
foliage of the plant. All but the topmost leaves may fall off.
Even if this does not kill the plant, the lack of foliage may
cause the fruit to get sunscald or develop improperly. Advanced
stages of the diseases may reveal tiny dark dots in the gray
spots which are spores of the fungus.
  Control the problem by crop rotation, deep cultivation, and
weeding of the garden area. Weeds belonging to the nightshade
family should especially be destroyed.
_________________________________________________________________

                                   Smut

  Smut is a fungus which produces massive amounts of black
spores. The disease can kill the plant or cause stunted growth.
  Control this disease with crop rotation and removing any
infected plants. Also, remove any spore boils before they burst
and spread the disease. If setting out plants, use healthy sets.
_________________________________________________________________

                               Spotted wilt

  Spotted wilt is a virus which is carried by insects called
thrips. The disease is a serious problem amongst tomatoes and
peppers. Plant death or poor setting of fruit can occur. The
young leaves of affected plants curl downwards. Leaves, stems,
and fruits may develop dark purple streaks. Also, leaves may have
yellow, parchment, or dead-like spots. On the fruit of tomatoes
yellow blotches will appear.
  Control this disease by controlling the thrips which carry the
virus. Methods for controlling aphids are as follows. Weed in and
around the garden where the thrips live. Apply insecticides, such
as Malathion 50% or Diazinon 25% at the recommended rates. A
good organic solution is to apply a shiny mulch around the plant.
Shiny surfaces have been known to repel the pest. This shiny
mulch could be aluminum foil or black plastic mulch which has
been spray painted with an aluminum colored paint.
_________________________________________________________________

                             Stem anthracnose

  This disease is the most common disease afflicting lima beans.
The fungus first appears as reddish blotches on the pods of the
bean. These blotches may completely cover the pods and cause the
pods to drop off of the plant. Advanced stages of the disease
will turn the reddish blotches to gray or brown. Red streaks in
the veins of the underside of the leaves may appear, as well as
reddish spots.
  Control this disease by purchasing western grown seed or seed
that has been hot-water treated. Crop rotation is very important
also. Do not save seed affected by this problem, as the disease
can be carried by the seed. Try not to work in the garden when it
is wet. This is another way in which diseases are spread.
_________________________________________________________________

                             Verticillium wilt

  Verticillium wilt is a fungus disease which affects tomatoes,
potatoes, and eggplants. Initially the lower, older leaves yellow
and droop. These lower leaves will fall off and the disease will
spread to the rest of the plant. Often only the leaves at the
tips of the plant remain. Of course this causes stunted growth of
the plant and its fruit. In the case of tomatoes the fruit will
remain small and undesirable.
  Since this disease is soil-born tomatoes, potatoes, and
eggplants should not be planted where these same plants have been
grown before. Remove any infected plants from the garden
immediately and destroy them.
_________________________________________________________________

                                  Viruses

  Viruses cause a variety of problems including yellowing of the
leaves, curling of the leaves, blocking of a plant's vascular
system, stunting growth, and killing the plant. Viruses are
spread by other infected plants and pests which transmit the
disease. Pests that feed on the sap of an infected plant can go
on to feed on a healthy plant and transmit the virus through its
saliva.
  Controlling pests is one of the best ways to control viruses.
Always use disease free plants and remove any diseased plants
from the garden immediately. Also, avoid working in a wet garden.
This is another way diseases are spread. Sanitize garden tools
with denatured alcohol to keep from spreading diseases.
_________________________________________________________________

                                 White rot

  This rotting of horseradishes is controlled by keeping the
garden area free of wild horseradishes.
_________________________________________________________________

                                Yeast spot

  Yeast spots are recognized as grayish brown spots on the seed
of lima beans. The yeast fungus enters the bean pods by puncture
wounds made by stink bugs.
  Control the disease by controlling the pest.
_________________________________________________________________

                                  Yellows

  This disease of cabbage is controlled by purchasing disease
resistant varieties.
_________________________________________________________________