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Fungus Plant Diseases

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Fungi are parasites that do significant damage to plants and particularly cultivated plants. Roughly 80 percent of all plant diseases come from fungi. Fungal spores are spread by agents such as water and wind to other plants. They develop in humid conditions and are often microscopic, growing on both living and dead plant tissues. Fungal diseases can be seen at any time of year, but mostly occur during fruiting.

Early Blight

Early blight is a common fungus that can cause serious crop damage and typically attacks potato and tomato plants. Caused by the fungus Alternaria solani, it first appears as brown spots on older, lower leaves and then spreads onto a leaf’s surface. This blight causes a leaf to turn yellow and then wither and die. The stem, fruit and upper part of a plant eventually become infected. Improving air circulation and disinfecting pruning shears helps control the disease.

Brown Rot

Brown rot is the most common plant fungal disease that affects the fruits and blossoms of fruits including peaches, apricots, almonds, cherries and plums. It's caused by the fungi Monilinia fructicola and overwinters in fruit on trees, in addition to fruit on the ground. This fungus first infects blossoms and then grows into branches, causing cankers that kill twigs. Wind, rain and insects carry brown rot spores to both open and unopened blossoms, as well as young shoots. Promptly remove and destroy all infected plant parts to prevent further infection.

Black Spot

Black spot is a fungal disease that attacks the leaves, stems and fruits of plants. It begins with feathery circular black spots first developing on a leaf’s upper surface. A bright yellow halo usually surrounds these spots with infected leaves turning yellow and then falling off prematurely. Purplish-red scratches may also appear. Apply preventative fungicides before leaves develop spots.

Apple Scab

Apple scab is a serious fungal disease affecting apples and ornamental crab apples. This fungus attacks leaves and fruits. It creates light yellow or olive-green marks on a leaf's upper surface with dark, smooth spots on lower surfaces. Other signs include tan scabby spots on leaves that are sunken. These spots grow larger, turning brown as they mature. It's helpful to water during early morning or late evening hours to allow leaves time to dry before an infection can occur.


Anthracnose, caused by the fungus in the genus Colletotrichum, is a severe disease able to destroy a harvest in only a few days. It mostly occurs in the eastern regions of the United States. Symptoms include an infected plant developing water-soaked dark scratches on leaves, stems or fruit. Centers of the scratches usually are covered with masses of pink, jellylike spores, often during warm, moist weather. This fungus overwinters in seeds, garden debris and soil. Wet cool weather encourages its development with the best temperature for its continued spore growth between 75 and 85 degrees Fahrenheit. Applying copper or sulfur sprays weekly to infected plants helps control the disease.

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