I’m not sure if this fire blight or Phytophthora – this problem and the pictures look very familiar to what I’ve been observing the last 5 years in PA (this is my frame of reference since I started in 2013).
Another pathogen to keep in mind that is often linked to this sort of mystery tree death/decline is Botryosphaeria spp., either B. dothidea or B. obtusa, – white rot or black rot. However, this pathogen is not THE cause of the decline. These fungi are everywhere and typically don’t create any hassle for the tree: These are relatively weak fungal pathogens and they will not cause tree death when the tree is healthy. They take advantage of weakened, stressed trees – this is when you have tree death. What I have observed is something is going on in the graft union area. We have been isolating Bot pathogens fire blight and Phytophthora have been ruled out. The next question is: what ultimately weakened/stressed the tree to make it susceptible to these weak pathogens. We have been studying this rapid decline problem in PA since 2013ish…and there are (still) more questions than answers, I’m afraid. I wrote about this late 2016: https://extension.psu.edu/apple-disease-rapid-apple-decline-rad-or-sudden-apple-decline-sad There is not much to add to the above other than we discovered a previously undescribed virus. However, we do not know what connection, IF ANY, this virus has to the decline issue. It is very difficult to prove cause and effect with a virus that infects a woody plant; however, we’re trying. I believe the decline issue is a complex of things occurring (Winter injury? Drought? Herbicide? Rootstocks prone to stress (ie M9)?Etc.), not just one issue. Kari Peter, Ph.D. Assistant Research Professor - Tree Fruit Pathology Department of Plant Pathology and Environmental Microbiology Penn State Fruit Research and Extension Center 290 University Dr., P.O. Box 330 Biglerville, PA 17307-0330 Office: 717-677-6116 Ext. 223 Fax: 717-677-4112 E-mail: ka...@psu.edu<https://webmail.psu.edu/webmail/shell.cgi?timestamp=1362517824> Twitter: https://twitter.com/drtreefruit From: apple-crop-boun...@virtualorchard.com [mailto:apple-crop-boun...@virtualorchard.com] On Behalf Of wincowg...@centurylink.net Sent: Sunday, July 22, 2018 10:09 PM To: Apple-crop discussion list Subject: [apple-crop-2] Photos of dying trees-fireblight- Doug Doug-I looked at the photos you attached and the last photo, #22301at the base just above the rootstock- has long verticle cankers (sunken areas in the bark) and verticle cracking in the bark. Combined with the tree colapsing it sure appears to be fireblight. However you also appear to have significant damage to the rootstock just belowe the graft union when you blow the picture up. Its weedy and from the angle cannot see how much is comprimised. I had emailed you a list of questions on this list but I didnt get a response. The purpose was to try and narrow down whats going on. You have had much advice, from many on the list. The main question is what rootstock is your planting on? If is a suceptable stock with a suceptable root then you have double trouble.The fireblight can run right to the root causing tree colapse. With those cankers visible in the lower trunk this looks like what you have. My guidance to growers with this combination, suceptable stock with suceptable root is take the tree(s) out. You also indicated these were in clusters, again sounds like fireblight, the inoculumn moves to the trees next door and take it out. The soil born disease phytophora can cause a similar looking tree colapse, but will not have the cankers in the trunk. Also is is born in the soil water and usually runs down a row if there is any slope. There are many good labs, both univ and private that can id both fireblight and phytophora if the get live tissue samples. You need to confirm what you have so you can plan control programs. I would certain
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