We saw the same problem for the first time last spring in small blocks of 5th leaf Redmax/Bud 9 and Mor-Spur/M26 after an "average" Montana winter. Symptoms and conditions were very much as described in the other cases. We've thought possibly some latent, atypical fireblight infection was the cause. It's somewhat comforting, therefore, to read these posts. Thanks.
Tom Moss Rollins, Montana ________________________________ From: Dave Rosenberger <da...@cornell.edu> To: apple-crop@virtualorchard.net Sent: Fri, April 9, 2010 6:44:14 AM Subject: Re: Apple-Crop: sickness in the Pioneer Mac block Hello, Mark -- The symptoms you describe sound exactly like a problem that appeared on Marshall McIntosh trees in New York and New England soon after that strain of Mac was introduced. On the Marshall Macs, the problem also appeared when trees were about 5-7 yr old. No one ever made a definitive diagnosis of the problem, but there was some evidence that trees at this stage (could we call them adolescents?) were particularly susceptible to winter damage following years that allowed them to grow late into the fall. Some folks in MA thought that fire blight might have been involved, but I think that hypothesis was mostly discarded. I thought that perhaps Botryosphaeria dothidea was involved in some of the die-back, perhaps by extending the cankers beyond the tissue that would have died from winter-kill, but I never proved that hypothesis either. Many growers in the Hudson Valley attacked this problem by apply a dormant copper spray in spring just as they would have done for fire blight, and I believe that some of them also used a copper spray in late fall. The problem disappeared after the copper sprays were applied, but we never had a controlled trial and it may well be that the problem would have disappeared without the copper applications. Folks have continued to plant some Marshall Macs and I've not seen this problem in later plantings. Thus, it seems that it was probably a combination of "adolescent" tree age and weather conditions that contributed to the problem. Hello all, In 08 a neighbor with a 5 yr old Pioneer Mac block on G30 saw extensive amounts of die-back in his trees, starting with trees hanging onto their leaves going into late fall. Spring of 09 showed that the most vigorous trees were affected to the greatest degree with whole limbs, leaders and some entire trees dying. Everything looked good in the spring of 09 in our orchard, which is 7 yr old P-Mac on M26. We wondered if our neighbor had a problem because of G30. Many "experts" looked at his trees and the consensus was "winter injury". In early October we harvested our block and noticed nothing of concern (except scab). In mid-November we saw trees throughout the block with dark leaves that refused to fall. The most vigorous trees seem to be the most affected. Whole limbs seem to die from the tip to or near the truck. Leaders often turned dark brown down to just above the lower scaffold limbs. Trunks below this point are mostly unaffected. Most trees seem to be O.K. at this point in time but nearly 20% of the block has some degree of this malady. None of our other varieties have this problem. Does anyone have experience with this sort of situation? Any ideas would be appreciated. Mark Evans, Northwest Michigan -- ************************************************************** Dave Rosenberger Professor of Plant Pathology Office: 845-691-7231 Cornell University's Hudson Valley Lab Fax: 845-691-2719 P.O. Box 727, Highland, NY 12528 Cell: 845-594-3060 http://www.nysaes.cornell.edu/pp/faculty/rosenberger/
