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Plant Disease: Tips to Identify & Prevent Fungus

 
A high level of rainfall can be damaging to your plants and lawn. Increased rainfall, combined with heat and humidity, can cause the development of landscape diseases and problems—fungus being a main culprit. Learn about some of the common types of foliage fungus and how you can prevent and stop them from spreading.
A high level of rainfall can be damaging to your plants and lawn. Increased rainfall, combined with heat and humidity, can cause the development of landscape diseases and problems—fungus being a main culprit. Learn about some of the common types of foliage fungus and how you can prevent and stop them from spreading.

Common Fungal Diseases in Plants

Black Spot

Black Spot fungus can be identified by the black spots it produces on leaves, typically, in early spring. It thrives in hot and humid conditions and when leaves stay wet for more than six hours. As seasons evolve and temperatures rise into the 70s, the disease quickly progresses and doesn't slow down until temperatures reach above 85°F.

Powdery Mildew

Powdery Mildew is one of the most common foliage diseases and is easily identifiable by the white powdery blemishes it produces on the surface of leaves. It is rarely fatal for plants, but produces stress and weakness by inhibiting the photosynthesis process. This is especially a problem in edible crops. A decrease in photosynthesis causes a lack of flavor and sweetness in fruits and vegetables.

Scab - Apple

Apple scab produces round olive-green spots that over time turn dark brown to black. It is common for the spots to grow together along leaf veins. It is spread when the fungus from dead leaves ejects spores into the air that are carried by the wind and deposited onto developing leaves. The warm rainy weather in spring and summer can cause repeated disease cycles and increase the severity of the disease.

Rust Fungus

Rust fungus gets its name from the reddish, orange blister-like spots that form on the surface of leaves. It is spread by the wind, watering or by rainfall, and needs wet surfaces to cause infections. This type of fungus most often occurs in mild, moist conditions. Once infected, foliage will curl, wither and experience stunted growth.

How to Treat Plant Diseases

If your foliage has been infected with fungus, a fungicide can be used to help control and prevent it from spreading. There are many "chemical" pesticides (including fungicides) for domestic and commercial use. There are also organic fungicides available to prevent plant diseases with active ingredients such as sulfur, bicarbonate, copper and oil.

Note: Scroll right to view complete table

Pesticide Fungal Diseases Description
Sulfur Fungicides Prevents powdery mildew, rust, rose black and other fungal diseases It prevents fungal spores from developing so it must be applied before the disease develops to be effective.
Copper Fungicides Kills fungi and bacteria Special care must be taken to prevent it from damaging the host plant. Young foliage is especially sensitive to copper, so a diluted formula should be used to avoid damage to the plant.
Oil Fungicides Minimize the spread of fungal diseased Controls the insects that transmit fungal diseases. Neem oil, at 70% concentrate, kills the eggs of many insect pests, powdery mildew spores, and virus vectors.
Bicarbonates   Have been used as a fungicide since 1933. Ammonium bicarbonate and potassium bicarbonate are the best kinds to use because they provide potassium and nitrogen to plants. Baking soda is an alternative but its use without oil is ineffective. When used without oil its sodium component tends to build up and becomes toxic to plants.


Some plants are sensitive to certain types of fungicides so it is important to always reference the product label of a fungicide for its safe and recommended use.

How to Prevent Fungal Diseases in Plants

There are simple steps you can take to prevent the growth of fungus and help your foliage flourish.

In spring, remove debris from around plants before they begin budding. This will allow for air circulation and prevent a buildup of excessive moisture.

View some innovative rakes that help make plant bed maintenance much easier >

Pruning should be done to thin out closely packed foliage. Treat pruning and trimming tools with a 1:10 bleach solution after using on foliage infected with fungus.

View the latest and greatest pruning tools >

When watering plants, do so in the morning so excess moisture will evaporate during peak sunlight hours. Also remember to water the soil and not the foliage.

Check out our vast offering of Tree & Plant Irrigation products >

Types of GEMPLER'S fungicides

Safer 3-in-1 Insecticide and Fungicide

  • Mixture of potassium salts of fatty acids and sulfur
  • Targets earwigs, grasshoppers, harlequin bugs, leafhoppers, squash bugs, psyllids, and more
  • Tackles plant diseases such as powdery mildew, blight, leaf spot and more
  • Sulfur Fungicides

Safer Neem Oil Insecticide and Fungicide

  • OMRI listed and compliant for use in organic gardening
  • Safe for indoor and outdoor use
  • Applications including ornamentals, trees, shrubs, foliage, vegetables, fruits and nuts
  • Oil Fungicides
True GG,GH,GI,GJ,GK