Category Archives: The Garden

Fire Blight

Fire BlightFire blight, found across North America, is a disease to be reckoned with. Caused by the bacterium Erwinia amylovora, this blight affects:

  • Pears.
  • Quinces.
  • Apples.
  • Crabapples.
  • Cane fruits.
  • Roses.

The disease is most likely to appear after a mild winter and during a wet spring. Insects transport fire blight bacteria from plant to plant when the hosts are flowering.

 

Symptoms

  • Brown leaves with a singed appearance.
  • Dead leaves clinging to tree instead of falling.
  • Shoots curled downward, similar to a shepherd’s crook (see photo below).
  • Amber droplets on shoots.
  • Sudden shoot death.
  • Wet, oozing bark.
  • Fruit death.
  • Rapid plant death.

 

Fire BlightTreatment

Unfortunately, there is no effective cure for fire blight once it strikes. The best option is to cut down and burn the affected tree, bush, or canes to avoid the spread of the disease.

If you want to make an attempt to save a valuable fruit tree, you will have to prune heavily, but cautiously. Choose a dry day to work so that bacteria spread is minimized. Cut off blighted twigs and branches at least 12 inches below the sites of decay. Collect the infected wood in a plastic bag to be burned when you are finished. Sterilize your pruning tools between each cut with a strong bleach solution.

 

Fire BlightPrevention

Because pears are extremely susceptible to fire blight, growing pears on a large scale is not advised in Kansas. While you may be able to grow a few pear trees, doing so will make growing apples very difficult because of the increased disease risk. If apples are your priority, destroy all pear trees in the vicinity.

To further prevent fire blight in your orchard:

  • Select plant varieties resistant to the disease.
  • Avoid weakening the tree through excessive pruning.
  • Spray trees and canes with copper or white vinegar in the spring.
  • Keep insects in check.
  • Avoid the use of high-nitrogen fertilizer, which encourages the rapid growth of soft, disease-prone tissue.

 

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Downy Mildew

Downy MildewDowny mildew is caused by parasitic fungi of the family Peronosporaceae, a group of water molds. The resulting disease is quite common in humid climates, affecting most of the fruits, vegetables, flowers, and grasses that gardeners like to grow.

This mildew tends to overwinter in old plant matter. Unfortunately, it also has a remarkable ability to survive in the soil for long periods of time, sometimes years. It can spread via wind, rain, insects, or infected seeds and cuttings.

 

Symptoms

  • Stunted growth.
  • White to purple down on the underside of leaves and stems.
  • Pale, sometimes speckled, upper surfaces of leaves.
  • Distorted leaves.
  • Leaf drop.
  • Discolored radishes.
  • Distorted roots and flowers on beets.
  • Leathery, wrinkled grapes.
  • Mottled lima bean pods.
  • Rapid plant death.

 

Downy MildewTreatment

Treating downy mildew is difficult and not worthwhile in most cases. Destroy the affected plants immediately, taking care to avoid bringing them into contact with healthy plants. Apply lime or sulfur to the area where the affected plants were growing to kill any remaining fungus.

For perennial fruits, such as grapes, fungicides can be used to save the plants. Bear in mind, however, that this method of control is not very effective. Proactively spraying the plants before infection sets in will be necessary in the future. Organic growers can use a copper spray as a natural fungicide.

 

Downy MildewPrevention

Practicing good garden sanitation is key to preventing this disease:

  • Raise your own seedlings instead of buying transplants.
  • Plant seeds or seedlings in the garden only when the soil temperature is suitable for that particular type of plant.
  • Plant seeds at the spacing recommended on the seed packet.
  • Practice crop rotation.
  • Take steps to improve soil drainage, if necessary.
  • Do not overwater the garden.

If downy mildew is a recurring problem in your garden despite your efforts, buy only mildew-resistant plant varieties.

 

Helpful Resource

“Soil Temperature Conditions for Vegetable Seed Germination”
Useful factsheet listing minimum, maximum, and optimum soil temperatures for starting common vegetables.

 

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Cucumber Mosaic Virus

Cucumber Mosaic Virus Cucumber mosaic virus does not affect only cucumbers. It also targets:

The disease is primarily spread by aphids, but it can also be spread by cucumber beetles and on gardening tools. The virus overwinters in perennial weeds.

Cucumber Mosaic Virus

Symptoms

  • Stunted, unusually bushy plants.
  • Thin, rough, curled leaves with mottled coloring.
  • Reduced yields.
  • Small, bumpy, misshapen fruits.

 

Treatment

There is no cure for cucumber mosaic virus. Diseased plants should be destroyed immediately. Nearby weeds should be pulled and destroyed, as well.

 

Cucumber Mosaic VirusPrevention

If cucumber mosaic virus is a recurring problem in your garden, switch to disease-resistant varieties. Also try to avoid planting host species in close proximity; separate the cucumbers and the tomatoes, for instance, with another vegetable that is not susceptible to the virus, such as corn.

To break the life cycle of cucumber mosaic virus, destroy any weeds that it might hide in, particularly catnip, milkweed, and ground cherry. Also control aphids, cucumber beetles, and other potential insect vectors.

 

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Cedar-Apple Rust

Cedar-Apple Rust

Cedar-apple rust is a disease caused by fungi of the genus Gymnosporangium. It affects the following common orchard and ornamental trees, as well as the invasive eastern red cedar:

  • Apple.
  • Crab apple.
  • Pear.
  • Hawthorn.
  • Juniper.

Due to its complicated life cycle, this disease is dependent on both deciduous and coniferous trees to survive:

  1. Galls on junipers and eastern red cedars release spores in the spring in response to warm rains.
  2. Spores travel by wind, sometimes as far as two miles, to infect deciduous host trees.
  3. Spores are released from leaves of deciduous trees in the summer (typically June and July in Kansas).
  4. Spores travel by wind to reinfect junipers and cedars.
Cedar-Apple Rust

Symptoms

On deciduous trees:

  • Reduced tree vigor.
  • Round spots on leaves, with the top side yellow and the bottom brown.
  • Cup-shaped structures on leaves.
  • Yellowed leaves.
  • Leaf drop.
  • Reduced fruit production.
  • Brown spots on fruit.
  • Cracked or misshapen fruit.
  • Premature tree death.

On junipers and cedar:

  • Brown round galls hanging from branches.
  • Orange gelatinous “horns” on galls.

Treatment

Treatment consists of spraying fruit trees with fungicides designed to control cedar-apple rust. Organic producers can use copper or sulfur sprays. Garlic sprays also show promise.

Make it a habit to check your ornamental cedars and junipers from time to time and pick off all the galls.

To prevent the further spread of the disease, rake up all fallen leaves and needles and destroy them.

Cedar-Apple Rust

Prevention

Ideally, susceptible fruit trees should not be kept on the same property as cedars and junipers. For ornamental evergreens, use species that do not get cedar-apple rust if you intend to grow apples. Destroy all eastern red cedars within half a mile of the orchard if possible. A two-mile radius is even better. If this is not possible, select apple and crab apple varieties that are resistant to the disease.

Another important aspect of preventing cedar-apple rust is maintaining general plant vigor. Be sure that each tree receives enough water and nutrition.

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Brown Rot

Brown RotBrown rot is a serious disease of fruits and almonds caused by fungi Monolinia fructicola and Monolinia laxa. The fruits most susceptible to the fungus are:

  • Peaches.
  • Nectarines.
  • Plums.
  • Apricots.
  • Cherries.
  • Almonds.

However, apples and pears are infected with brown rot on occasion.

The fungus grows and multiplies rapidly in wet weather, entering plants through wounds. It survives the winter in twigs and dry, shriveled pieces of fruit called mummies.

 

Symptoms

  • Small, elliptical cankers on twigs, generally oozing.
  • Gray, fuzzy masses of spores on branches or flowers.
  • Brown, wet spots on blossoms.
  • Blossom drop.
  • Brown or gray fuzz on fruit.
  • Mummified fruit.

 

Brown RotTreatment

Cankered twigs should be pruned out during the summer.

Blossoms can be treated for brown rot starting when the first pink shows in the unopened bud. Treatment should continue through the spring if the weather is wet. Fungicides are typically used, but organic growers can spray with sulfur or copper. Spraying with organic milk also shows promise at this point in time.

Fruit that is visibly affected with brown rot must be destroyed to prevent the spread of the disease. Fungicides can be applied to the unaffected fruit as soon as it begins to ripen.

 

Brown RotPrevention

The first step in preventing brown rot is to remove potential vectors of the disease:

  • Destroy wild plums growing near the orchard.
  • Water trees at the base so that the leaves do not get wet.
  • Control insect pests.
  • Pick up all fruit laying on the ground under the trees.

Proper pruning is also an important part of preventing brown rot. If air and light can reach all parts of the canopy, fungal diseases will have a hard time gaining a foothold.

 

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Black Rot

Black RotBlack rot is a particularly unpleasant fungal disease affecting:

  • Members of the cabbage family.
  • Apples.
  • Grapes.
  • Boston ivy.
  • Virginia creeper.

Several fungi species are involved.

Note that the black rot which affects squash and pumpkins is just a phase of the disease known as gummy stem blight.

The spores of the black rot fungus spread rapidly in hot, humid weather, traveling on the wind and in splashing drops of water. They can also penetrate wounded plant tissue. The fungus overwinters on the ground and in dead or dormant plants.

 

Symptoms

  • Reduced plant vigor.
  • Stunted plants.
  • Yellow V-shaped lesions on leaf margins of cabbage crops.
  • Circular tan spots with purple border on leaves of apples, often called frogeye leaf spot.
  • Black leaf veins.
  • Yellowed leaves.
  • One-sided heads on cabbage family plants.
  • Rapid head spoilage after harvest.
  • Branch and shoot cankers.
  • Root decay.
  • Small white dots with reddish-brown ring on grapes.
  • Reddish spots on apples which grow and blacken.
  • Early ripening.
  • Rotten apple cores.
  • Mummified fruit.

 

Black RotTreatment

Treatment of vegetables is not practicable. Affected plants should be destroyed. Fungicides (copper for organic gardens) should be applied to remaining vegetables to avoid the spread of infection. Once the growing season has ended, let the soil rest for two or three years to kill remaining spores.

Grapes and apples should be treated with regular fungicide applications. Take care to remove all mummified fruit from the plants and the ground, or black rot will return in the spring. Burying mummies through cultivation is effective.

 

Black RotPrevention

Minimizing plant stress and maintaining good garden sanitation are the keys to preventing black rot:

  • Choose varieties well adapted to your area.
  • Plant in a location with plenty of sunlight and air flow.
  • Rotate garden vegetables.
  • Keep fruits well pruned to allow air circulation.
  • Do not work with plants when wet
  • Take care to avoid wetting leaves when watering the garden.
  • Control weeds.
  • Make sure plant nutritional needs are being met.

 

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Bacterial Wilt

Bacterial WiltAs its name suggests, bacterial wilt is a bacterial disease affecting cucurbits, such as:

Watermelons are rarely affected by bacterial wilt.

Note that bacterial wilt of cucurbits is different than the various bacteria-caused wilt diseases of corn.  These corn diseases are caused by different organisms and spread by different insect pests.

Bacterial wilt of cucurbits typically cannot survive or spread without the assistance of cucumber beetles.  Erwinia tracheiphila bacteria spend the winter in the digestive systems of the beetles and are then transferred from plant to plant as the insects feed during the growing season.  The bacteria take up residence in the xylem, or water transport tissue of the plant, and block up the flow of moisture.  Once a plant begins to succumb to bacterial wilt, it attracts more cucumber beetles.  The cucumber beetles then ingest more bacteria, and the cycle continues.

 

Symptoms

  • Dwarfism.
  • Rapid wilting.
  • Sudden drying out.
  • Pale, streaked leaves.
  • Excessive branching.
  • Whitish strings of bacterial slime oozing from stems when cut.
  • Excessive flowering.

 

Bacterial WiltTreatment

There is no cure for bacterial wilt.  Remove and destroy affected plants immediately.

 

Prevention

If bacterial wilt is a problem in your garden, choose resistant varieties when possible.  Unfortunately, no muskmelon varieties have been shown to resist bacterial wilt.

Because the bacteria involved are dependent on cucumber beetles for survival, any measures taken to control the beetles will greatly reduce the risk of the disease:

  • Till plant debris under in the fall to destroy insect shelter.
  • Rotate garden crops.
  • Deter cucumber beetles with floating row covers.
  • Kill cucumber beetles using handpicking, sticky traps, natural predators, or natural or chemical insecticides.

 

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Bacterial Leaf Spot

Bacterial Leaf SpotBacterial leaf spot is a disease affecting several plants of interest to gardeners:

  • Lettuce.
  • Leafy plants in the cabbage family.
  • Peppers.
  • Tomatoes.
  • Cherries.
  • Plums.
  • Peaches.
  • Nectarines.
  • Apricots.
  • Ivy.
  • Begonias.
  • Geraniums.

The disease is caused by several species of Xanthomonas bacteria.  Not all types of Xanthomonas can affect all plants.

This bacterial disease is common east of the Rocky Mountains, as it thrives on warm, wet weather.  The bacteria spend the winter in old leaves and cankers on twigs.  Bacterial leaf spot can be introduced into a previously healthy garden through diseased seeds or seedlings.

Overuse of high-nitrogen fertilizers, whether chemical or organic, tend to increase the plant’s susceptibility to bacterial leaf spot.  Plants with wounded tissue are more severely affected than healthy plants.

 

Symptoms

  • Small, angular pale green to yellow spots on leaves, particularly near tip.
  • Dry, flaky substance on leaves.
  • “Shotgun” holes on leaves that widen over time.
  • Yellowing of old leaves.
  • Premature leaf drop.
  • Sunken dark spots or cracks on fruit.
  • Fruit drop.

 

Treatment

Bacterial leaf spot is a serious problem in vegetables, as it can ruin the produce.  There is no organic cure for this disease.  Bactericides can be used, but are generally not effective.  Removal and destruction of infected plants is the best solution.

Fortunately, bacterial leaf spot is much less serious in fruit trees.  Bactericides can be used to prevent the spread of the disease, but not to treat it.  Allowing the disease to run its course is suggested, provided that steps are taken to improve orchard health and sanitation (see below).

Diseased ornamental plants should be destroyed promptly.

 

Prevention

Choosing disease-resistant plant varieties from reliable sources is the first step to preventing bacterial leaf spot.  Rotate garden crops, and space plants far enough apart for good airflow.

Because high-nitrogen fertilizer is a major contributor to the development of bacterial leaf spot, keep the nitrogen levels low.  If you are concerned that your plants may need the extra nitrogen, test the soil nutrient levels before fertilizing.

Other measures for preventing bacterial leaf spot fall into the category of maintaining garden sanitation:

  • Support plants to keep their fruits and leaves off of the ground.
  • Do not work with plants when wet.
  • Do not use overhead sprinklers in the garden.
  • Keep the weeds in check.
  • Remove plant debris in the fall.

 

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