Apple scab and cedar-quince rust are both diseases that can affect your trees in the spring. The cool, damp conditions are a breeding ground for fungal growth. Both infections begin as yellow coloring on leaves. Maybe you’ve seen this on your trees in the past. As a homeowner, here’s what you need to know, how to prevent it, and what to do if it happens.
Apple scab is a fungal disease that affects crab apple, apple, pear, and serviceberry trees. It can infect both the leaves and fruit on the tree. It may look akin to or co-occur with fire blight, tent caterpillars, and cedar-apple rust. Apple scab over-winters in leaf litter on the ground. The disease spores release in the spring when conditions become favorable for infection.
Leaves are most susceptible to infection during development but can be infected at any time. Cloudy, cool, damp weather is favorable for rapid fungal growth. In the spring, this weather coincides with leaf development.
Leaves can show signs of infection within days but generally will begin to show signs in mid-summer. It starts as a yellow spot that grows and ruptures to reveal a black lesion, turning some leaves yellow. Lesions have undefined boundaries, creating a water-colored appearance. Leaves will drop early and can cause defoliation by early August in severe years. Repeated years of heavy infection can stress trees but it’s almost never fatal.
To treat an apple scab infection, consult a local arborist. They have the tools and the knowledge to treat these infections in a safe and efficient manner. Treatment will consist of two applications of a foliar spray of fungicides. The second application will occur between a week and two weeks after the first.
For low-tolerance trees, the arborist may apply up to three more applications. These will protect new tissue that wasn’t present at the time of the first two applications. For most trees, the two applications should result in good control on all infected leaves. New leaves that develop after flowering and fruit set will not be protected. In this case, some amount of apple scab can develop.
Cedar-quince rust is a fungus that affects cedars, junipers, and trees that belong to the rose family. Quince, pear, apple, hawthorn, and crab apple trees are all potential hosts of this disease. It can look like and co-occur with cedar-apple rust and hawthorn leafminer.
Cloudy, cool, damp weather is favorable for rapid fungal growth. In the spring after it rains, galls put out wind-borne spores which move to Rosaceae hosts and infect developing leaf, shoot, and fruit tissues. Leaves can show signs of infection within days, but generally will begin to show in mid-summer. Infection appears as small, pale yellow spots with defined margins on the upper surface of leaves. Leaf spots will enlarge and turn orange-red over time. Heavy infection combined with other stresses can cause early leaf drop.
As with apple scab, consult an experienced arborist to treat a cedar-quince rust infection. The treatment consists of four applications of a fungicide foliar spray. Proper application should provide good control of cedar-quince rust.
The only way to prevent an infection is to act before you actually see any issues. As a homeowner, there are a few steps you can take to prevent an infection. This alone won’t prevent infection but will help to keep conditions unfavorable for fungal spores.
If you suspect that your trees have become infected with either apple scab or cedar-quince rust, contact the arborists at Vineland Tree Care. We’ll help you determine the proper treatment and provide a free estimate.
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