My makmik is roughly 12 years old. It has been well until this year. It has been regularly pruned and the last pruning was fall 2016. Never removing more than a third. Flowered well this spring but has not looked well this summer. Form the picture your u can see the condition of the leaves. Please advise a course of treatment for my tree.
Sorry to hear about your problems with your crabapple tree. This year’s cool wet spring has provided the perfect environment for fungal diseases. From your photo it appears as if your tree is suffering from cedar-apple rust.
Cedar-apple rust, caused by the fungus Gymnosporangium juniperi-virginianae, is a problem when crabapple and certain species of juniper and red cedar grow in close proximity. This rust requires two different hosts to complete its life cycle. The fungus causes brilliant yellow-orange spots or lesions on crabapple leaves and occasional lesions on the calyx end of the fruit. On cedar/juniper, the fungus produces brown to reddish-brown galls. During rainy periods as we had this spring, distinctive bright orange, gelatinous spore-horns protrude from the surface of these juniper galls. The spores are blown by the wind to crabapple trees where they infect and produce their characteristic lesions
This fungus causes leaf spots on apple and crab apple trees. These leaf spots are first yellow, then bright orange-red. They often have a bright red border and may have small raised black dots in the center of the spot. These lesions grow through the leaf and develop small, brownish, spiky projections on the lower surface of the leaf. Very infrequently, fruit may exhibit a similar infection.
The following link provides information on the life cycle of this disease along with photos: https://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-1036/EPP-7611web.pdf
Cedar-apple rust cannot spread from apple to apple or from red cedar to red cedar – the fungus must go through the two-year life cycle, alternating between hosts.
Crabapple diseases can be effectively controlled through the combined use of culture, sanitation, resistance, and fungicide sprays.
Cultural methods include maintaining tree vigor by proper planting, fertilizing, and pruning and by following general practices that help to minimize tree stress, all of which you are currently following.
Make sure to remove any affected or dead portions of the tree and remove diseased foliage or fruit, which are often sources of inoculum for the next season. Make sure to dispose of the affected foliage in the garbage and not in your compost bin. Select and plant varieties of crab apple with genetic resistance to specific diseases.
Proper selection, timing, and application of these sprays are important. Thorough coverage of all parts of the tree is necessary and sprays should be applied by a qualified arborist. To find a certified professional arborist to help you with a tree problem, visit the Ontario branch of the International Society of Arboriculture here.
The Ministry of Agriculture food and rural affairs (omfra) provides more information on the treatment of this fungal disease: https://www.omafra.gov.on.ca/english/crops/facts/cedarap.htm#cedar