Common Urban diseases

Fungus,Wilt/Blight & Mildew

 Science has always confirmed: a successful garden begins with healthy soil,

Ninety percent of all garden failures are caused by unhealthy soil.

Anthracnose: is a fungus disease reported quite often in Idaho.  It seems more common when there is a wet spring.

Leaf symptoms:  tan spots that develop purple rims. Leaves may also have necrotic veins and leaf margins, and large necrotic blotches. In some cases shot holes appear. Infections often progress down the petioles of blighted leaves into shoots, resulting in trunk cankers in trees.

Prevention and control:

Trees and plants receiving good care will be better able to withstand anthracnose. Maintain by watering well during periods of drought. Mulching can help to reduce watering needs as well as protect trunks from mechanical injury. Avoid overhead watering to minimize the chance for leaf infections.

Effective control is possible only if the disease is detected before extensive dieback occurs. Always rake up fallen leaves and dispose of all fallen twigs to reduce spreading. Remove succulent branches as they form to prevent trunk canker formation. Avoid high nitrogen fertilizers which stimulate succulent branching. Trees with poor vigor may be bolstered by applying a balanced fertilizer in early spring.

Powdery Mildew causes a white powdery growth on the upper surfaces of leaves and on the stems of infected plants. Infected areas are often stunted and distorted and may drop prematurely from the plant. Powdery mildew is caused by the fungi Erysiphe cichoracearum and Sphaerotheca fuliginea. Infection can occur when temperatures are between 50 and 90 °F, during dry weather with high relative humidity. The disease can be a particular problem on late-planted squash.

     Downy mildew is one of the most important leaf diseases of     cucurbits. Typically, symptoms begin as small yellow areas on the upper leaf surface. As lesions expand, they may become brown with irregular margins. Affected areas may grow together, and the entire leaf may wither and die. Infected plants also develop a gray mold on the lower leaf surface. The fruit is not affected, but in the case of cantaloupes, it will be less sweet. This disease is caused by the fungus and is favored by moist conditions.

What should you do now that the tree or plants are infected?

a)     Prune and dispose of diseased twigs and branches, rake up all fallen leaves and twigs and burn it. Disinfect all pruning tools with a mild solution of bleach and water with a few drops of dish soap. Dip the tool after each cut. Any open areas left from the cuttings should be lightly coated with the solution.

b)     Apply a chemical garden fungicide. Ortho Daconil, Bonide garden & ornamental fungicide, or a general lawn and garden fungicide---please read all directions carefully and used as directed.

c)     Or you may use other organic alternatives to chemicals such as:

·         Barriers: A light spray of vegetable oil or highly refined horticulture oil coats leaf structures and acts as a barrier to fungal diseases, especially rusts and mildew.

·         Plant products: Garlic can be used as a potent broad-spectrum insecticide and it has fungicidal properties when blended with water, strained and applied to the leaves. The same is true of compost tea*.

·         Baking Soda: Actually this may come closer to killing off fungus than most fungicide. It’s also nontoxic. Mix 2 teaspoons per gallon of water, adding a few drops of dish soap to help the solution stick to the plants.

·         Bonide - Tomato And Vegetable 3 In 1 or Lilly Miller - Cueva Copper Soap Most of these organic solutions have to be applied at least every 10 days during growing season.

·         Copper: Copper is a powerful fungicide but it can cause more damage to plants than sulfur. And it too can be toxic to gardeners. The most familiar copper-based fungicide is Bordeaux mixture.

·         Sulfur: It works great but can cause a number of problems. It's mildly toxic to soil organisms and can cause respiratory problems in humans if inhaled. And at temperatures above 85 degrees it can burn plants.

Fungicides should be used only to supplement a cultural control program. Applications of chlorothalonil, mancozeb will protect against leaf infections. Apply 3 or 4 sprays during leaf expansion in the spring, at 10-14 day intervals. If conditions are favorable for disease development later in the growing season, additional fungicide applications may be beneficial.  

Bacterial Wilt

The main symptom of this disease is severe wilting of the vines, followed by rapid death of the plant. The disease is caused by the bacterium Erwinia tracheiphila, and at first may only affect a few vines on a plant. However, as the disease progresses, more leaves wilt, and eventually the entire vine is affected. Bacterial wilt is most severe on cucumber and cantaloupe and less severe on squash, pumpkin and watermelon. There is no chemical solution. The bacteria are carried from plant to plant by striped or spotted cucumber beetles. The beetles spread the wilt bacterium by feeding on infected vines and then feeding on healthy plants. Bacterial wilt can be reduced in your garden if the beetles are kept under control at the first sign of activity. Insecticides that control striped and spotted cucumber beetles in the home vegetable garden include carbaryl and esfenvalerate  Bees pollinate many of these vegetables, so spray all insecticides in the late afternoon. Apply all chemicals according to directions on the label.

If you have any problems or questions, please contact the Elmore County Extension at 587-2136 ext. 509

or email: elmore@uidaho.edu