Question
Hello,
 I live near the Il. and Wis. border. I have a crabapple tree thats about 40 feet across and when it blooms it looks amazing. But soon after blooming, any new leaves on the tree seem to be deformed with brown spots on them and buy the end of may I`m raking leaves and the tree becomes somewhat bare. This has been going on for about 5 years or so. I don`t know the specific name of the tree. It has a deep pink color to the blooms and the fruits are no bigger that a half of an inch. Do you know what the problem is and how can I treat it. Thank you for your time.

                                  Mike

Answer
Sounds like a leaf spot more then likely Frogeye Leaf spot or apple scab.

Frogeye Leaf Spot of Crabapple. Pathogen: Botryosphaeria obtusa
This leafspot disease is a minor problem on most crabapples, although a few exhibit considerable leaf yellowing and leaf drop in some locations, including 'Madonna' and 'Professor Sprenger.' During moist spring weather the fungus infects leaf tissue and causes small roundish brown spots with purple borders. In some cases spots enlarge developing irregular lobes that, when they enclose the original roundish spots, cause a "frogeye" symptom. Blackish pimple-like fungal fruiting bodies may develop inside the lesions.

In addition to the leaf yellowing and defoliation that can occur on particularly susceptible cultivars, black rot cankers can develop on stems over the years, especially on crabapples weakened by winter injury and other environmental stresses. In the rare cases when fungicides are warranted, begin sprays at budbreak.

Prevention and Treatment: Remove and discard dead branches and diseased fruit, called mummies, where the fungus overwinters.

Apple Scab
This common fungal disease is a serious problem on many flowering crabapple varieties, causing spotting of the leaves, premature defoliation, and unsightly corky spots on the fruit. Spots on the new leaves appear olive-colored and velvety. Later, the infections appear as olive-green or brown circular spots, with raised or puckered leaf tissue underneath. Scab spots may appear on leaves anywhere on the tree.

When severe infections take place, the leaves yellow and the tree may lose almost all its leaves by midsummer. Typical fruit lesions are distinct, almost circular, rough-surfaced, olive-green spots, which later turn brown to black.

The apple scab fungus, Venturia inaequalis, overwinters in old, infected, fallen leaves. In spring, the fungus produces spores which land on crabapple foliage or fruit and infect the plant if the tissue surface is wet for several hours. The fungal infection results in leaf lesions, where more spores are produced to begin additional cycles of infection throughout the growing season. Secondary infection may also occur from spores produced on scab lesions found on the twig growth of extremely susceptible crabapples such as Malus 慉lmey,?M. 慔opa,?and M. x purpurea 慐leyi.?

Control: Use scab-resistant varieties in new plantings. Scab infection on established trees may be prevented by three to five applications of fungicides at 10 to 14 day intervals starting as soon as bud growth appears and continuing until mid June. Scab is most severe during wet growing seasons.

Both are controlled with fungicides sprayed at bud break and then 3-5 applications at 10-14 day intervals.  


A fertilizer is suggested, apply 2 - 3 pounds of actual nitrogen per 1,000 square feet of root zone area. Use a fertilizer like 20-5-10.

Example; a bagged fertilizer with an analysis of 20-5-10 (Nitrogen - Phosphorus - Potassium) apply 2 pounds nitrogen per 1,000 square feet which translates into 10 pounds of the 20-5-10 fertilizer spread beneath the trees over an area measuring 31.5' x 31.5' or its equivalent.