The mysterious "red spot disease" that appears on yellow varieties in orchards both in the wild and where mineral fungicides are employed has been a quandary for some of us for years. That the lenticels in the skin of the fruit become colonized by an opportunistic organism seems apparent. It was recently suggested in a communication elsewhere that Botryosphaeria dothidea fungi are the principle culprit, but this would actually be early symptoms of white rot (also known as bot rot) evidenced by “red halo spotting” around initial lesions. What we are dealing with here (eventually I hope to post a photo!) is something else… but we can reckon some of the causation and proceed from there.

Rick Leadbeater of Gould Hill Orchard downstate of me contributed this understanding: Red spots can be the result of things you've done or not done. Without lab data to confirm presence of a pathogen the “damage” may be physiological. If the spot usually surrounds a lenticel in the skin (check with a hand lens) then it's often a result of something you've done. Untimely application of foliar amendments or various harsh pesticide sprays (sulphur, Ca or Cu amendments, etc applied at higher temperatures or near freezing) can produce that effect some years - whatever you add that could be absorbed through the skin or burn the skin of the fruit when environmental conditions predispose the fruit to damage. Either of the above is the likely if there is also any russeting on the fruit. The other extreme is what you didn't do. You may need to find a more gentle, efficacious fungicide if a pathogen is confirmed. If your fruit has a Calcium deficiency (you need tests to confirm that – just because soil tests look good, that doesn’t mean the fruit actually gets enough) it often shows up as red spots that later may get corky. Correcting that is often a several year project.

I said in the post on sulfur’s negative impacts that skin growth can be aggravated by mineral fungicides or at the very least “good guy colonization” perturbed by the use of mineral fungicides. A chemical strobilurin like Pristine in the late cover sprays seems to address this “unknown problem” in IPM orchards. But we do see red spot on yellow apples in the wild, and now the disturbance around the lenticel is caused by water fluctuations or other environmental factors that vary from year to year. Red spotting in a commercial organic orchard is generally worse than in the good wild years, thereby justifying the view that something we did here is indeed part of the story. My intent is to “be better” and continue with neem and microbe sprays though middle and end of August, especially on later varieties like Honeygold and Tolman Sweet where red spot disease is far more prevalent in this orchard. Somehow, when things are looking good in early August, I lay back on the spray intentions and then regret it in one way or another come harvest.