ROCK ISLAND, Wash. — Mechanical pruning works well on Cosmic Crisp apple trees by the fourth year and cutting the tips of one-year old limbs controls growth better than limb bending.
Those were main points growers learned at a Washington State University field day at Sunrise Research Orchard south of Rock Island, Sept. 27.
Cosmic Crisp is the new WSU-bred apple tree the industry is starting to plant in a big way with plans for the first apples to hit grocery stores in the fall of 2019 and quickly ramp up thereafter.
Promoters say cosmic Crisp is a great eating apple with great flavor and good crispness and firmness that consumers will love more than Honeycrisp, one of its parents. It stores well without storage disorders such as water core, internal browning and superficial scald that hampers other varieties.
Perhaps it’s only negative is vigorous growth causing too much spacing between fruit, called blind wood, resulting in fruit on outer edges rather than closer to tree trunks where desired.
Stefano Musacchi, WSU tree fruit physiologist, “now believes that’s better controlled by cutting the tips of one-year-old limbs and cutting tips in subsequent years rather than by bending limbs down,” said Karen Lewis, WSU Extension tree fruit specialist. Musacchi calls it click pruning. Bending limbs down actually creates more blind wood, according to a tip sheet the scientists wrote for growers.
Apple trees produce the plant growth regulator auxin in their stems and shoot tips inhibiting bud formation. Cutting limb tips or girdling or notching every foot of a trunk on two-year-old trees interrupts auxin flow allowing more buds to form where desired.
The tip sheet gave equal credence to spindle and biaxial (two trunks off a one) tree structure for good fruit coloring and automation and mechanization of pruning and harvest while European V is more problematic for mechanized pruning and harvest.
“At the end of the day, Cosmic Crisp responds well whether vertical or angle (V),” Lewis said. “Growers need to put the math to it (what’s profitable) and their ability. They’ll do what they know.”
Musacchi is now experimenting with a fourth tree structure, what he calls top grafting which is grafting Cosmic Crisp onto stumps of other varieties above their rootstocks to develop three trunks, she said.
Lewis has focused a lot on mechanical pruning, also called hedging. Mechanical pruning in June eliminates blind wood by producing buds closer to stems and produces higher quality fruit, she said.
“We’ve also noticed that in the first couple of years when hedging the tree responds vigorously (more growth), but in the fourth year it settles down and gives you the tight narrow canopy you’re looking for,” she said. But it can result in smaller fruit which is something to consider, she said.