Think of cherry leaves as the engine that converts gas to energy in your car.
Now if you can imagine the stress put on fruit trees that lose their leaves, you’ve got a picture of what’s occurring in many orchards across Leelanau County.
Two diseases that cause leaves to drop prematurely on cherry trees are having banner years due mainly to a wet spring, according to cherry grower and retired county extension director Jim Nugent. The disease combination is causing headaches for county growers.
“It’s a bad combination if you get the cherry leaf spot on top of the virus,” Nugent said. “That’s kind of a double whammy … leaves are important because they are the energy collector.”
The diseases have struck at once before. Nugent recalled another wet spring in the early 1990s that took a toll on cherry trees. One grower who did not spray an orchard with fungicide lost all his trees during the rough winter that followed.
But that was the exception rather than the rule. Cherry trees can usually sustain even a heavy loss of leaves one year and still produce a crop, perhaps on the small side, the following season, Nugent said.
The diseases converging on county orchards are:
• Cherry Yellow Virus. During most seasons it’s a sleeper, causing some damage but nothing dramatic. Growers have no spray or other method to combat it, so they try not to let minimal infestations interfere with sleep. It survives year after year, building up in older orchards of mostly tart cherries.
“Every year we see some virus leaf drop, but it varies greatly. This is one of the worst years I’ve seen,” Nugent said.
Over the past week to two weeks some cherry trees have lost leaves. But the disease rarely completely denudes trees and is unnoticeable to passersby.
• Cherry Leaf Spot. A fungus, it’s one of the main targets of spraying underway in county orchards.
“This year we’ve had a lot of wet weather, so there has been a lot of pressure caused by cherry leaf spot. It mostly affects tarts. Sweets can tolerate more infections in the leaves before they cause leaves to yellow and drop. It’s been a tough year to control cherry leaf spot,” Nugent said.
The disease can defoliate whole orchards. During heavy infestations growers spray to keep leaves green and producing glucose at least through harvest.
Wet weather is also conducive to the life cycle of spotted-wind Drosophila (SWD), an invasive fruit fly of East Asian origin that also hurts production.
“At this point the tarts aren’t ripe enough to be susceptible but sweets are getting there. This is the kind of year that I would expect pressure from SWD. If we get a dry spell, though, it won’t be an issue,” Nugent said.
Leelanau grows more cherries than any other county in America. Past Department of Agriculture surveys have shown that about 60% of county orchards were planted in tarts, but the gap has narrowed as growers pull tart cherry trees due to poor monetary returns.
Some 4.02 inches of rain was recorded in April at the research station, which is located in Bingham Township, compared to an average of 2.8 for the month. May precipitation was also higher at 3.5 inches compared to a 2.9 inch norm. June has been dryer, however, at .53 inches compared to an average of 1.74 inches through June 18.
Sweet cherries bloom and are ready to harvest a few days before tarts. The sweet cherry harvest begins in early July in Leelanau County.
