There is no need to push the panic button about the widely popular almond plum rootstock Krymsk86 in California’s almond industry.

A tree abnormality found in some Sacramento Valley almond orchards and a few in the San Joaquin Valley (SJV) last spring has the attention of tree nut farm advisor John Edstrom and others.

“Some trees on the Krysmk86 plum rootstock, mainly the Monterey almond variety, stopped growing last spring and the foliage turned yellow,” said Edstrom, University of California Cooperative Extension, Colusa County. “It was very obvious from a distance that there was something wrong.”

As the season progressed, the yellowed leaves turned brown, burned up, and curled. None of the impacted trees is known to have died.

“The trees grew about one-half compared to normal,” Edstrom said. “The trees set the terminal bud and just stopped growing. The leaves went from green to a bronzy-brown color and then died.”

Some growers and nurserymen tried several unsuccessful remedies including sprays of kaolin-type clays to reduce leaf stress. Impacted trees were pruned back which helped the trees partially recover.

The net cause of the problem is uncertain. It could be the Krymsk86 rootstock. Edstrom’s gut says the malady was probably, in part, a seasonal aberration caused by last spring’s cool, wet spring which slowed tree development.

“The cool, wet spring likely played a significant role,” Edstrom said. “The tree flush this coming spring should answer many questions.”

Edstrom found the problem in one to two-leaf trees in about 1 percent of the trees in the dozen or so orchards he evaluated. The phenomenon was found to a lesser degree in the Nonpareil, Winters, and Aldridge varieties on the Krymsk86 rootstock.

From a distance the tree malady resembled the effects of union mild etch which is often associated with the rootstock Mariana 2624. Union mild etch causes similar leaf symptoms, but also abnormal etching at the union graft. The affliction can be found by peeling back the bark between the scion on top and the root on the bottom.  An examination of the Krymsk86 trees last spring revealed a smooth graft union.

“The big question is will the impacted trees rebound this spring and develop normally, and will the problem occur in other one-to-two leaf trees this coming spring,” Edstrom asked.