Tunnels eliminate sprays
But they don't prevent all diseases and pests.
Rainiers grown under tunnels.
Growing cherry trees under tunnels continues to show potential for both organic and conventional cherry production. In the last two years, Michigan State University's Dr. Gregory Lang has not applied any herbicides, fungicides, or insecticides inside the tunnels, saving money on the countless sprays that have been eliminated.
For weed control, MSU horticulturist Lang uses black woven polypropylene cloth as a weed barrier under the tree rows in the tunnels. Lang said the cloth has a triple purpose—preventing weeds and warming up the soil in the spring while conserving soil moisture later in the summer.
The tunnels are also beneficial when it comes to insect control. By leaving the tunnel plastic over the trees an extra month after harvest, Lang found that he prevented Japanese beetles from "gorging on the leaves," a problem that typically occurs from July through the rest of summer. Unfortunately, the control trees outside the tunnel were not as lucky, he said, adding that the beetle skeletonized the foliage.
"It turns out that Japanese beetles don't like the tunnels, just like honeybees don't," Lang said, explaining that he believes both insects need ultraviolet light for navigation. "The tunnels reduced Japanese beetle feeding by 90 percent in comparison to the outside tunnel control, and we eliminated three months of weekly or biweekly sprays for the beetle."
Cherry leaf spot, a key disease in Michigan, is particularly troublesome during years with lots of rain. In some seasons, Lang has observed complete tree defoliation before harvest from the disease. "By keeping rain off the cherry trees, we had no leaf spot in the tunnels," he said. "That's another spray that we'd have to do repeatedly to control cherry leaf spot if not for the tunnels."
Preliminary data also showed that incidence of bacterial canker was reduced under the tunnels.
The tunnels don't prevent all diseases, however, as in 2006, brown rot was as much of a problem inside the tunnels as outside. Both treatments in 2006 had about 20 to 30 percent incidence, Lang reported. But by switching from microsprinkler to drip irrigation and venting the sides more in 2007, they significantly reduced the humidity inside the tunnels and also reduced brown rot, he said. "We didn't eliminate it, but it was better than the outside treatment."
Lang said that so far, the tunnels have significantly reduced pesticide applications. But he noted that if cherry trees are grown under organic practices under the tunnels—something he believes has potential because of the reduced need to spray insecticides and fungicides—control methods will be needed for mites, aphids, brown rot, and mildew, such as releasing predatory mites and natural enemies of aphids, and using organic fungicides.