Date: Wed, June 14, 2006

In this email look for the following:  What ails them apples? (and pears?) - E Letter

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What ails them apples?

I’ve seen two significant problems with apples recently (and one on pears too). One you can’t do anything about now; the other you need to deal with – now.

Cedar apple rust is causing susceptible apple cultivars to turn yellow. Looking closer you may see yellow to orange spots on the leaves. Some of these trees are so severely affected that I expect them to defoliate and probably not bear a crop to fruition. Defoliation is not fatal (usually) but it can be alarming. And repeated defoliation or defoliation of a small tree under stress can take a serious toll.

These leaves were likely infected in the first week they were unrolling. And I don’t remember the weather then but it’s likely to have been damp.

The pathogen that causes this problem requires alternating hosts. The apple tree cannot re-infect itself. In July to August, the windborne spores will infect red cedar trees where the pathogen will spend the winter. By late winter to spring you may notice round, brown structures slightly smaller than a ping-pong ball on cedars. When its time is ripe, this sporangium will produce orange horn-like structures that produce spores that can infect apples. If you can remove these structures from all the cedars within a 4-5 mile radius, then you probably can break the cycle. If that is not practical, removing the ones you do encounter will at least improve your odds.

How can you deal with this problem? This is where I can tell you to attend one of my classes before you plant trees. Variety selection is big. I have seen in this county leaves of two varieties inches apart – one covered with spots, the other hardly touched. Lee Calhoun has grown hundreds of varieties locally and produced a list of varieties of low susceptibility. I think I have his permission to share that, but you won’t find any of these varieties at most retail outlets.

Another option is to start spraying the trees with fungicide about the time the flower buds start to show pink next spring. If you want to try that strategy, there’ s a good leaflet on management for the home orchard at http://www.ces.ncsu.edu/depts/pp/notes/Fruit/fdin002/fdin002.htm

Site selection (watch for my next series of classes) and pruning for air movement within the tree are probably more effective than spraying. And pruning every year will improve spray penetration and coverage. I hope you’re getting the idea that Integrated Pest Management is more effective than any single strategy – variety selection, site selection, pruning, spraying, …. It all goes together.

The other problem we’ve seen this year is fireblight again. Fireblight is a regular problem of apples and pears – not every year but often. The first symptoms are usually wilting stems. The foliage turns brown and often black.

This problem must be pruned out. If you don’t remove it, it continues to grow down the stem and the damage increases. Eventually it threatens the survival of the tree.

When pruning, cut at least 12 inches below any sign of injury on the stem. Sterilize your pruners after every cut to reduce transferring the bacterium on you pruners. Alcohol will do nicely. Keep an eye on it in case you didn’t get it all. It doesn’t get better unless you remove it all.

Remember my mantra that it’s always appropriate to remove dead, diseased or damaged material from the plant – the 3 Ds.

And yes, there is a spray you can use for fireblight by making several applications while the tree is in bloom – streptomycin. But when people find out the cost, they go back to wait and see and prune.

alcooke

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Al Cooke
Extension Agent - Agriculture
Chatham County Center
North Carolina Cooperative Extension Service
N C State University
PO Box 279
Pittsboro, NC 27312
919.542.8202, FAX 919.542.8246
al_cooke@ncsu.edu http://www.ces.ncsu.edu/chatham/staff/acooke/home.html