Yard Plant Disease Control


Chemical Treatment for Leaf Spot – Copper-based fungicides may help control bacterial leaf spot if applied in late spring. Fungicides containing chlorothalonil and thiophantate-methyl work to control both cercospora leaf spot and anthracnose. Dilution rates for chlorothalonil-containing fungicides range from 1.4 teaspoons to 2 teaspoons per gallon of water, depending on the product. For fungicides containing thiophanate-methyl, the dilution rates is usually 1 tablespoon per gallon of water. Apply them every 10 to 14 days as needed. For more severe infections, apply at shorter intervals. Follow all directions on the label when using chemical fungicides.

Two types of fungal diseases can infect hydrangeas — cercospora leaf spot and anthracnose. Cercospora leaf spot (Cercospora hydrangea) begins as brown or purple spots on the leaves at or near the base of the plant. The circular spots are often small and scattered and usually measure 1/8 to 1/4 inches in diameter. Spots on the bigleaf hydrangea develop tan or gray centers surrounded by brown or purple halos. Leaves may eventually turn yellow-green and fall off. Anthracnose is caused by the fungus Colletotrichum gloeosporioides. It produces large brown spots on leaves that eventually develop lighter brown or tan centers. The spots may also appear on blossoms and may appear angular if bordering a vein. Bacterial leaf spot in hydrangeas is caused by the pathogen Xanthomonas campestris and affects primarily Hydrangeae quercifolia, Hydrangeae arboreacens and Hydrangeae macrophylla. Like cercospora leaf spot, the disease first manifests itself on the lower leaves of the plant in the form of purple to reddish spots. As with anthracnose, spots bordering veins become angular.

Oak Tree


Magnolia Frescati – Below is from here.

Leaf Spot Diseases
Leaf spot diseases are caused by varying strains of fungi. Leaf spot diseases cause brown or yellow irregular discolorations on the foliage of magnolia trees. In severe cases, these discolored leaves may fall from the branches prematurely. Generally, leaf spot diseases can be tolerated if the magnolia tree is healthy.

Bacterial Blight
Leaf discoloration and distortion, cankers, wilting, stem dieback and premature leaf dropping are a few of the common symptoms of bacterial blight. Regularly pruning during dry seasons will help provide good airflow between the branches. Chemical control is generally not recommended and is not a reliable method to controlling bacterial blight.

Verticillium Wilt
Verticillium wilt appears as yellowing on the leaf margins and between veins of magnolia leaves. The infected leaves wilt, die and prematurely fall from the magnolia. This fungal disease begins at the tops of leaves and works its way back toward the tree branches. Verticillium wilt is not present in cool temperatures; the first signs of the fungal disease won’t be visible until the weather warms. There is no acceptable fungicide control to treat verticillium wilt. However, cultural control will help prevent this damaging fungal disease from attacking the magnolia. Planting magnolia trees in disease-free soil greatly reduces the chance of verticillium wilt. You can sterilize the soil before planting with solarization to kill pathogens living in the top several inches of the soil.

Powdery Mildew
Powdery mildew is a contagious fungal disease that infects plants such as magnolia trees. Powdery mildew appears as a powdery or fuzzy white growth on leaves and branches. This fungus causes the tree’s foliage to discolor, wilt and fall off the branches. Shade and mild temperatures between 60 and 80 degrees promote powdery mildew growth and — unlike other fungal disease — moisture is not required for this fungus to grow. Applying fungicide — such as horticultural oil, potassium bicarbonate or neem oil — will help control powdery mildew.

Sooty Mold
When the magnolia is infested with pests — such as aphids, spider mites and mealybugs — they will secrete honeydew over the leaves and stems of the tree. This substance is sticky and causes the black, velvet-like fungus called sooty mold to grow. Sooty mold threatens the life of the magnolia only in rare occasions where the growth covers entire leaves, blocking sunlight needed for photosynthesis. Before the sooty mold will go away, the pests secreting the honeydew must be dealt with. Predatory insects — such as predatory wasps, ladybirds and lacewings — will feed on these pests naturally. Alternatively, thoroughly apply neem oil to the magnolia to chemically control these pests. Once the pests are gone, the sooty mold will go away. For a faster approach, use a water hose to wash the fungus off the surface.

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