Dec 27, 2017

Fertilization boosts sweet cherry health

Bacterial canker, San Jose Scale, poor plant nutrition and some exceptionally hard winters are all part of sweet cherry orchard decline, and foliar applications of nitrogen fertilizer in September continue to be a solid tool to help maintain tree health and improve winter survival.

“These early fall applications help accelerate cold acclimation and make the trees more winter hardy,” said Greg Lang, professor in Michigan State University’s (MSU) Department of Horticulture.

Cherry leaves turning color in the fall indicates the photosynthetic enzymes and chlorophylls are being broken down and nitrogen in the form of amino acids is being remobilized back into the tree tissues.

“When you remobilize nitrogen back into the tree trunk and roots, this tissue becomes storage areas for nitrogen,” Lang said. “In a way, the tree is fertilizing itself.”

“The nutrients for that first flush of green growth in the spring all come from storage reserves in the tree,” Lang said. “In high density cherries on dwarfing rootstocks, you’ve got a very small tree on very small rootstocks that has very little storage capacity for nitrogen reserves.”

“We’ve seen improved winter hardiness from these foliar applications,” said Nikki Rothwell, MSU Extension specialist and coordinator of MSU’s Northwest Michigan Horticultural Research Center at Traverse City, Michigan. “In high-density sweet cherries, that are irrigated, spoon feeding with these smaller amounts of fertilizer has been shown to be very beneficial.”

Research at MSU’s Northwest Center has found foliar fertilization with nitrogen in the fall improves the winter hardiness of tart cherries as well as sweets.

The recommended program is two foliar applications of a three percent urea solution seven to 10 days apart. “There isn’t a critical time frame,” Lang said. “Make both applications in September, starting as early as Sept. 1.”

The nitrogen content of cherry leaves typically drops during senescence in the fall to half the nitrogen content of the growing season, as nitrogen is remobilized into the spurs and other parts of the tree for storage over winter. Foliar applications increase the amount available for remobilization. This boosts spur nitrogen levels which helps produce larger spur leaves in the spring.

The foliar fertilizer is applied late enough that it doesn’t stimulate new growth. “Most of these nutrients are translocated into the trees so you’re not going to jump start growth when the trees are trying to go to sleep for winter,” Rothwell said.

Cherry leaf spot defoliation, an early frost or any other cause of premature leaf drop reduces the amount of nitrogen remobilization. This often leads to reduced cold hardiness and spring growth potential.

— Dean Peterson, FGN correspondent