What is Leaf Spot?
Leaf spots are caused by a number of fungi or bacteria that produce lesions ranging from tiny spots to large blotches on leaf surfaces.
While spots may remain small and the plant can localize the infection, even if lesions are numerous, little harm is done to the plant. However, other pathogens might expand the lesion into large blighted areas and, in severe cases, cause defoliation or premature leaf drop. The spread of leaf spot diseases is primarily through water rather than air and will persist if conditions are favorable. Generally, leaf spot diseases occur sporadically and cause little damage.
Sign and Symptoms
These spots can be circular or irregular in shape and can vary in color from tan to red, purple, brown, or black. Some spots may be two-toned or have a different colored ring around the margins or in the center of the spot. Dead tissue in the center of lesions may fall out, creating a shot hole appearance or a ragged leaf. Some leaf spot diseases produce blister-like lesions or tar spots that are quite conspicuous on leaf tissue.
Prevention - What you can do on your own
- watering in the early morning and adjusting sprinkler spray height to avoid wetting the leaves
- Space plants appropriately to reduce humidity and increase air movement.
- Collect fallen leaves before winter to reduce overwintering sites of the pathogen,
which can invade new growth in the spring.
- Where infected leaves are small, individual leaves can be removed or branches pruned where infections are localized.
Control - What you need an arborist to do
- Once symptoms are exhibited, chemical control only functions to slow any further spread – any existing leaf spots will not disappear.
- Fungicides applied in the early spring, before the disease appears, and on a regular basis throughout the season, can provide effective control.