Orchard Covers Work To Keep out Rain and Prevent Disease

Retired Michigan State University Professor of Horticulture Greg Lang speaks from experience — 20 years’ worth — when it comes to orchard covers and covering systems. His pride and joy, multi-leader sweet cherries, are no strangers to the added protection.

Speaking on behalf of the Northeast Tree Fruit IPM Working Group, Lang offered several tips on protected stone fruit production:

Types of Orchard Covers

Pole and cable tent structures tend to be the least expensive, he says. They can be movable or fixed and have different types of venting.

“Some of the things to be thinking about are how much heat is trapped under those covers in a hot climate. That can be a detriment. In a cool climate that can be a benefit if you’re trapping heat,” Lang says. “If you’re trying to advance bloom in the spring, you want to trap heat. If you’re trying to ripen fruit in a less stressful environment, you don’t want to trap heat. So, there’s always pluses and minuses based on what your main criteria are for having the covers.”

Among high tunnels, the most common structure is the three-season, multi-bay, single-layer plastic tunnel as compared to the four-season, stand-alone single-bay, double-layer plastic tunnel that is often used in year-round vegetable production. Multi-bay high tunnels are generally less expensive than single bays per area covered. Three-season tunnels are left uncovered in the winter, as the structures are not engineered to withstand snow loads.

“If it’s a single layer of plastic, typically, for orchards, the heat retention is appreciable but not necessarily significant other than a degree or two when it comes to spring frosts,” Lang says.

Greenhouse-like automated structures can open and close based on inputs, such as weather station sensors. While offering the most manipulation options, they are the most expensive. “They are more labor friendly, but you pay for the up-front installation costs,” Lang says.

Potential Benefits of Covers

Cherry growers are almost always seeking to exclude rain to prevent rain cracking. Additional advantages of stone fruit covers include altered ripening times, frost protection, diminished disease, reduced wind bruising, bird protection, and the capability to harvest and prune in any weather.

“Those are all the different factors you need to think about going into whether a covering system is going to be economically viable,” Lang says.

Generally, when growers protect their stone fruit from rain, they wind up protecting those crops from most bacterial diseases, Lang says. “We can eliminate pretty much all the bacterial diseases that we’ve learned about as being important in a variety of stone fruits,” he says.

The fungus for cherry leaf spot can essentially be eliminated upon the elimination of rain splattering onto leaves, Lang says. However, brown rot occurs at approximately the same incidence as with no covers at all, Lang says. “We can reduce or eliminate some fungal diseases but not all. We found that we do need to continue our fungicide sprays for brown rot whether we’re under a cover or not,” he says.

On the other end of the spectrum, mildew tends to increase in the dry environment of a rain exclusion system, according to Lang. “That’s a typical disease out West in places like arid Washington. It’s not that typical in the East, but when you put a cover up, it can become quite prevalent,” he says.