What Causes Brown Spots on Plants?
The ideal garden--whether it be vegetable or flower--consists of perfectly formed flowers or fruits and symmetrical green leaves. However, that's rarely the case. Brown spots are not an uncommon sight in any type of garden, and the causes of these spots can vary between plants. Therefore, it's important to know exactly what you're dealing with so that you can treat your affected plant accordingly.
Watermelon Bacterial Fruit Blotch
Symptoms of watermelon bacterial fruit blotch are most noticeable in seedlings and young watermelon plants. The leaves appear to have oily spots on them, and as the disease progresses the leaves begin to die, forming brown spots and patches. In some cases, the spots do not form until the watermelon becomes more mature and begins to form fruits. If the disease sets in when the plant it older, the leaves will develop small, dark lesions that can be difficult to see. Once the watermelon fruits begin to develop, the bacterial infection will set in and appear as a dark-green stain on the rind. The flesh of the watermelon isn't infected, but will rot once the rind is damaged. Watermelon bacterial fruit blotch is spread through contaminated seeds, which then grow into seedlings and come in contact with other plants.
Rose rust is a fungal infection that is spread by spores, which can quickly cover a wide area with as simple a delivery device as the wind. In the first stages of infection, orange pustules will form on the bottom surface of the leaves. These will soon become noticeable on the upper surface of the leaves, in the form of spots that range in color from yellow to reddish-orange to brown. Rose rust is commonly found in the Western United States. It thrives in cooler weather, but can be controlled by careful, thorough and prompt removal of all infected leaves. Once the growing season is over, leaves should be completely removed.
Leaf spot is a generic name for a fungal disease that can afflict almost any shade tree and whose telltale symptom is brown spots on leaves. Size and shape of the spots vary depending on what type of fungus has infected the tree. The color of the spot can also vary--it is frequently brown, but can also be light brown or tan. In many cases of fungal infection, there is no real damage done to the tree. Oftentimes the leaves will not die or fall prematurely; however, the affected leaves can be removed, which will help slow the spread of the fungus. In some cases, fungicide can be used effectively, and in some cases a badly infected tree should just be replaced.