Apple tree suffering from RAtD
as seen in late July

 Apple orchards throughout the Northeast witnessed a spate of Rapid Apple-tree Decline (RAtD) in the past few years. It was particularly onerous in 2023 in Massachusetts. In orchard blocks that otherwise had been healthy and productive, too many trees were turning yellow and ultimately collapsing and dying. Upon close inspection, it was evident that often a significant “sloughing” off of the bark all the way down to the cambial layer was observed, mostly on the exposed shank of the rootstock. (See pic at end of this blog post.) Among other trunk cankers, this failure in the rootstock shank bark was most frequently observed. RAtD has been rather widely reported throughout the Northeast, and is a generalized symptom of what has been hypothesized to be the result of one (or more?) of causations: fire blight infection of the rootstock, cold injury, herbicide injury, alternating periods of drought and too wet, viruses, and/or general apple tree stress. Because the cause of RAtD is likely one or more of these factors which can be hard to pin down, going forward a strategy needs to be in place that might help manage (hopefully prevent?) the risk of RAtD in Northeast apple orchard blocks. Suggested best management practices from an Extension perspective to help reduce the risk of RAtD include:

• Plant only on your best sites – used to be reserved for stone fruit, however, now be thinking of new plantings of apples on only your best sites too. For example, if you even think it might be too wet (soil), it is too wet! Don’t do it! Or put drainage in, plant on berms.
• Consider planting on berms – again a recommendation for stone fruit, but berms can be a more favorable environment for apple roots too, less wet feet during periods of excess rain. A foot high and three to four feet wide? Yes, can present some management challenges, mowing, etc. But get those roots a bit “higher” in the ground. (But see plant deeper below.)
• Paint tree trunks white – soon after planting, and maintain throughout the life of the orchard if practical. White latex paint – full strength is OK – can prevent sunscald to trunks, deter rodents and borers.  Once a common practice that seems to have lost favor, but needs to be resurrected.
• Plant deeper – but not too deep of course. Used to be “just roots in the ground,” which could leave a long portion of rootstock shank above ground. That might be more susceptible (less cold hardy?) to cold damage. Leave just two or three inches of rootstock shank above ground if practical.
• Rootstock choice – makes a difference, M.9 and some of the Geneva rootstocks have exhibited RAtD. Jason Londo at Cornell has shown some hardiness differences in Geneva rootstocks, but the verdict is still out on that. Although G.41, even though it has other modest faults, appears to be particularly resistant to winter temperature swings. M.9 is not the most cold-hardy rootstock out there given its British (not too cold there) origin, and is fire blight susceptible. (But it is still a good workhorse if you can manage fire blight.) B.9 and B.10 have field resistance to fire blight and have shown less (maybe) RAtD than other rootstocks. Just saying.
• Plant virus-free trees – certified virus-free scion and rootstock. With the slowdown in planting, maybe nurseries have an opportunity to up their game and provide virus-free trees for sale across the board? It will take some time, but sure bet they (should be?) are working on it. Or are they? It’s a bit of an unpopular topic amongst them.
• Herbicides – be careful with herbicides. Systemic herbicides (glyphosate, glufosinate-ammonium) in particular. Avoid hitting the tree trunk and root suckers with those. (Paraquat too!) Shield tree trunks if you insist on overlapping contact herbicide sprays. The white paint may help here too.
• Fire blight – has to be managed aggressively if using M.9 rootstock in particular. Geneva rootstocks are resistant, the B.’s may be field resistant. Even with these rootstocks it’s important to manage fire blight aggressively in the scion/variety.
• Borer infestation – black stem borer has been observed in trees under stress, and under the “sloughing’ bark of rootstock shanks. This is not good and may be contributing to Rapid Apple tree Decline. Consider an insecticide – whole orchard, or trunk directed – effective on borers.

Black stem borer infestation as evidenced by pin hole(s) and sawdust
underneath where the outer bark has separated

• Irrigation – probably a no-brainer here, drought stress is likely to exacerbate Rapid Apple tree Decline. Monitor soil moisture and use the Apple Irrigation tool in NEWA.
• Limit tree stress – over-cropping trees in their formative years may put stress on the trees, and make them more likely to succumb to other stressors like cold injury, drought, etc. Grow trees through the 2nd leaf then start modest cropping in the 3rd and 4th leaf. Monitor nutrition status but avoid over-fertilization with nitrogen which may promote later hardening off. (Not to mention bitter pit.)
• Soil health — yes, it is a buzzword lately. Has some merit. Avoid compaction. Incorporate organic matter, cover crops ideal. Check pH. (Should be 6.5 to 7.) Test for soil borne pathogens? Nematodes, phytophthora, southern blight, replant disease. Fumigate? If you have any or all of the above, if it is available to you. More relevant the farther south you go and on sandy soil.

The good news it seems the progression of RAtD in Massachusetts (and hopefully elsewhere) in 2024 has slowed. Still, the above best management practices are recommended for any new apple planting in 2025 and beyond.

"Sloughing-off" of outer bark down to cambial layer is often observed with RAtD