Mar 11, 2016
First scab spores of 2016 season detected

The first scab spores of the season have been detected; however, there is no scab infection risk until green tissue is present and there is an infection period. Since trees are pushing due to the warm weather the last several days, now is a good time to apply dormant copper sprays to manage diseases.

No green tip yet on Gala. Photo: Kari Peter
No green tip yet on Gala. Photo: Kari Peter

Winter isn’t technically over; however, apple scab says otherwise.

Cornell University’s Dave Rosenberger reported in a recent blog post about finding the first mature apple scab spores in the Hudson Valley on March 7.

Needless to say, I broke out in a cold sweat upon reading this news.  I had just finished my winter meetings four days prior; the last thing on my mind—and anyone’s mind—was dealing with apple scab right now. However, if it was occurring in New York, we needed to know what was going on in Pennsylvania.

Well, folks, it’s time to face the music – scab spores are maturing quickly and have started to disperse: We detected 65 spores from our overwintering samples on Wednesday, March 9.

Mass panic need not occur

As far as I know, no green tissue is present right now, so there is no threat of infection. The other critical factor is a significant wetting event, and that has not occurred yet either. Similar to what was reported in New York, to find mature spores in Pennsylvania now isn’t surprising since the temperatures over the last two months would have favored early maturation of the ascospores.

Thanks to the warm weather this week, green tip will be here before you know it. I’ve kept a very close eye on the trees at the Fruit Research and Extension Center every day this week and they aren’t moving as fast as I had dreaded. Consequently, now is the time to get on those dormant copper sprays on apples and pears for fire blight and scab; and on peaches for bacterial spot and peach leaf curl.

You want to aim for 2 lb/A of metallic copper, so pay attention to the percent metallic copper equivalent listed on the label of the copper you use. If the weather pushes us to green tip by the weekend, you will have a layer of protection on your trees before the forecasted rains occur if green tissue starts peeking through. If the weather cools down, along with the progression of the trees, applying another copper spray later wouldn’t hurt either, especially if rain occurs to wash off the first copper spray.

For commercial growers:

For more resources, visit the Penn State Tree Fruit Production website.

For specific recommendations for disease management, visit The Disease Control Toolbox via the Tree Fruit Production website.

When controlling for disease, weather and tree growth conditions need to be monitored at a local level within one’s own orchard. Before chemical products are applied, be sure to be in compliance by obtaining the current usage regulations and examining the product label. Product information can be easily obtained from CDMS.

For the home gardener and backyard grower:

If you have questions about fruit trees growing in your backyard, please contact your county Extension office and ask for Master Gardeners:

Kari Peter, Penn State University


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