Diseases
APPLE SCAB
Apple scab is one of the most serious diseases of Apple and ornamental Crabapple trees. Disease development is favored by wet, cool weather that generally occurs in spring and early summer. Both leaves and fruit are affected. Symptoms first appear in the spring as spots (lesions) on the lower leaf surface, the side first exposed to fungal spores as buds open. This is followed by early defoliation. This early defoliation weakens trees and makes them more susceptible to other problems.
Apple scab is caused by a fungus. This fungus survives the winter in the previous year’s diseased leaves that have fallen under the tree. In the spring, the fungus in old diseased leaves produce millions of spores. These spores are released into the air during rain periods in April, May and June. They are then carried by the wind to young leaves, flower parts and fruits. Once in contact with susceptible tissue, the spore germinates in a film of water and the fungus penetrates into the plant.
The disease continues to develop and spread throughout the summer. Because a film of water on leaves and fruit is required for infection to occur, apple scab is most severe during years with frequent spring rains.
The primary form of control for apple scab is done with fungicide sprays. Timing and proper application technique are essential. To ensure coverage of newly emerging tissues and to replace the chemical as it is lost to weathering, fungicides must be re-applied on a regular schedule. This consists of at least three(3) treatments, spraying every 7 to 14 days as weather permits during springtime.
Applying fungicide to apple scab infested trees is very important for their health and beauty. There are other things you can do that can help them:
- Proper health care such as mycorrhizae or fertilizer treatments.
- Supplemental watering during dry periods keeping in mind not to wet the foliage as this can contribute to spreading the fungus.
- Pruning to allow more air and light into the interior of the tree.
- Picking up leaves that have apple scab to help keep the fungus from spreading.
DIPLODIA TIP BLIGHT
Austrian, Scots and Mugo Pines are most commonly affected by this disease in Chicagoland. Red and Eastern White Pines are less likely to be infected. Browning of needles at the tips of shoots is the first symptom that is noticed. It causes the tips to deform into a bent shape called a “shepherd’s crook”. As the disease progresses it can cause cankers. Branches can become girdled and die.
Diplodia tip blight is caused by a fungus. The fungus overwinters in infected cones, shoots and needles. Spores are released in the spring during rainy periods. It frequently starts on lower branches and moves upward as spores are spread by splashing rain and wind.
Control of diplodia tip blight requires 3 sprays with fungicide during springtime. These sprays must be timed to occur first when buds begin to open, the second when candles are half grown, and the third when candles are fully expanded.
Other things to keep in mind to help control the spread of this disease is to avoid pruning and wounding trees when they are most susceptible from late spring to early summer. Avoid overhead watering which spread spores. When pruning out infected tips, sterilize tools with 70% alcohol between cuts. The best way to control this disease is to not plant susceptible pines.