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Apple Scab and Crabapple

Question of the Week

Apple Scab and Crabapples

Olive-colored spots and yellowing leaves on crabapple leaves are classic symptoms of apple scab infections. Q. We planted `Candied Apple' and `Indian Summer' crabapples and `Macintosh,' `Cortland' and `Red Delicious' apple trees around our home five years ago. Theyíve all made good growth since then and this year they were covered with beautiful flowers. During the past several weeks, however, a lot of leaves on all of the trees have started turning yellow and falling off! Are all of our trees dying?

A. No, your trees arenít dying! The cool, wet spring we experienced this year created ideal conditions for a severe outbreak of apple scab on susceptible varieties of all kinds of apple trees. Unfortunately, all of the crabapple and edible apple varieties youíve planted are highly susceptible to this disease!

Heavily infected leaves first develop dark, olive-colored blotches that gradually spread over the leaf surface (above at right). Other infected leaves will turn yellow and misshapened before falling from the tree beginning in mid-June. Severely infected trees may lose all their leaves by late summer!

Fortunately, though your trees may look bad now - and may look worse by summerís end - apple scab infections are rarely severe enough to kill even a moderately healthy tree.

While itís too late to reduce the infection of your trees this year, there are several things you can do to reduce the problem in future years.

First, prune your trees to open their branch canopy. This will improve air circulation and light penetration, drying leaf surfaces more quickly after spring rain showers and heavy overnight dew.

And, if you decide to plant more apple and/or crabapple trees in the future, an increasing number of new introductions are totally resistant to apple scab.

Scab-resistant edible apple varieties include: `Prima,' `Priscilla,' `Sir Prize,' `Freedom,' `Liberty,' `Jonafree,' `Enterprise,' `Goldrush,' `Redfree,' `Pristine,' `Williams Pride,' `Novamac' and `Nova Easygro.'

Meanwhile, for a list of crabapples with both excellent scab resistance and outstanding ornamental characteristics click here.