Leaf Spots on Shrubs Sometime Cause Unnecessary Worries

Leaf spots that occur on shrubs often alarm gardeners. In some cases the concern is justified, but in others this is only a minor problem or no problem at all.

Most leaf spots are caused by fungi and are gray, brown or almost black in color. Depending upon the causal agent, individual spots can range from tiny up to one-fourth inch in diameter. Some fungal leaf spots have definite patterns, depending upon the species. There are those that have gray centers with dark margins and are often referred to as frog-eye spots. Others have alternating shades, yielding a target board appearance.

There are a few of the leaf spot diseases that are caused by bacteria. Though similar to fungal leaf spots, bacterial leaf spots are generally smaller, very dark in color and sometimes shiny in appearance.

Excessive numbers of spots on individual leaves can be detrimental to a plant’s health because the affected parts can no longer photosynthesize. Heavy spotting can also cause affected leaves to prematurely fall from the plant.

Three things are necessary for leaf spots to infect plant leaves: 1) The fungus or bacteria must be present; 2) A susceptible plant must be available and, 3) there must be favorable environmental conditions for the development of the disease pathogen.

Controlling Leaf Spots

_ Don’t bring infected plants home with you. Inspect plants before purchasing and obtain only spot free shrubs. Many microscopic spores are contained within an individual spot and these can be rapidly spread to other susceptible plants within the landscape.

_ Avoid those shrub species that are prone to repeated infection by the leaf spot organisms.

_ Many of the leaf spot organisms require a film of water on the foliage for several hours in order to germinate and infect. Good watering practices can therefore help to reduce the incidence of disease. Water during the early morning hours so that the leaves dry off quickly. Avoid daily watering when possible. The more frequently the foliage is wetted, the more likely the plants will become infected. If possible, water the root zone of the plants without wetting the foliage.

_ Hand pick spotted leaves promptly if only a few are present. These infected parts should be destroyed or removed from your property. Do not place them in the compost pile.

_ A fungicide can sometimes be helpful in controlling leaf spots. The challenge when using one is to positively identify the causal organism and then select a product that is labeled for control on that particular plant species. Thorough spray coverage and timeliness of applications are extremely important.

Question of the Week: I recently saved some seed from a watermelon that was purchased from a local farmer. If I plant them next spring, will they yield the same kind of watermelon?

Answer: Most locally grown watermelons are hybrids. Though the seed will probably germinate and grow, odds are you won’t harvest the same kind of melon.

In the case of watermelon, the plant breeder incorporates desirable characteristics from several different parents. Selection is made for taste, texture, earliness, disease resistance and other characters. Through crossing these are incorporated in such a way that the best comes forth with the first planting of hybrid seed.