Apple Disease - Rapid Apple Decline

The issue has been labeled 'Rapid Apple Decline' (RAD) or 'Sudden Apple Decline' (SAD) based on how fast the trees die from the first obvious symptoms to total collapse of the tree. The common denominator in all situations seems to revolve around the graft union. This situation is not to be confused with root,  crown, or collar rot diseases; or rootstock blight resulting from Erwinia amylovora infection.

RAD was named by Pennsylvania Department of Agriculture due to the rapid or sudden collapse of apple trees from the time the first symptoms appear to tree death. The diagnostic characteristics are as follows:

• A block can have a mix of dead, declining and healthy trees dispersed fairly evenly throughout a block.
• Decline is limited to young (2 - 8 yr), dwarf trees on M9 rootstocks (M9/337, M9/Nic29, Pajem, etc.) planted within the last 10 years.
• The graft union is affected: severe shedding of bark around graft union and cankers are present.
• Necrosis begins at the graft union and it proceeds up the trunk of the tree.
• Affected wood is usually solid and not spongy.
• The rootstock is healthy, as indicated by many rootstock suckers present, as well as a healthy root system.
• The leaves on the trees begin to look pale yellow, then reddish (indicating tree girdling), and within two weeks the tree can be dead.
• Trees can collapse with a full load of large fruit.
• Total collapse of the trees has been observed from May through September.
• Decline has not been observed on EMLA 9 rootstocks, other dwarfing rootstocks, or semi-dwarf rootstocks.

Tree stress, such as severe winters, drought, or herbicide injury, appear to be a predisposing factor leading to RAD; however, not all affected regions have experienced these tree stressors. To date, affected trees fitting the mysterious RAD description have not tested positive for E. amylovora, Phytophthora, phytoplasma, tomato ringspot virus, or nematode issues. Previously undescribed viruses and viroids in apple, such as apple luteovirus 1 (ALV1), citrus concave gumming associated virus (CCGaV), and apple hammerhead viroid (AHVd), have been identified; however, understanding the pathogenicity of these microorganisms and their possible link to RAD is still ongoing. Borers, such as black stem borer and Ambrosia beetles, have been associated with declining trees; however, these insects are not attracted to healthy trees, but are attracted to ethanol, which is emitted from stressed or declining trees.

Growing stronger, healthier trees that withstand stresses is the best action to help try to prevent RAD: irrigation; painting trunks white to limit southwest injury; yearly foliar and soil tests to be sure nutrients are balanced; planting trees in well-drained areas or using raised beds; reduce weeds; season-long disease and insect management; and protect graft unions from rodent damage.