—by Matt Milkovich
Placing nets over trees during bloom can successfully set a target crop load in Michigan without the use of chemical thinners, according to trials led by Michigan State University.
Setting a crop by limiting pollination is always a tricky proposition in Michigan, where spring frosts during and after bloom can severely reduce crop loads on their own. But in an organic system, which needs alternatives to chemical thinning sprays, the utility of nets could outweigh their potential pitfalls. After MSU trials were conducted in his orchard, longtime Michigan organic apple grower Jim Koan thinks so.
“I’m sold on netting,” he said. “It did an unbelievable job thinning.”
Mokhles Elsysy led the trials, first as a research assistant in the lab of tree fruit physiologist Todd Einhorn and now as an assistant professor. In addition to Koan’s organic orchard, trials were held in conventional blocks at Schwallier’s Country Basket and MSU’s Clarksville Research Center. The work was funded by the Sustainable Agriculture Research and Education program, Elsysy said.
The MSU team imported the anti-hail/insect exclusion netting from an Italian company, but Elsysy said growers can buy suitable nets and equipment domestically. For multiple seasons, nets were placed over a few trees at a time at each site. In a larger-scale trial last season, they placed nets over rows.
Elsysy said results were consistent regardless of scale or growing method. The nets — deployed at 30 percent and 60 percent king bloom — controlled fruit set such that yields were similar to the chemically thinned control trees in the conventional orchards. Yields also resembled those of the organic orchard control, where Koan used his standard lime sulfur and oil to blossom thin.
When they looked at other factors that might have been influenced by the nets, they found few concerns. Fruit quality attributes and vegetative growth were similar. Nets excluded codling moth males, and fewer San Jose scale males were captured under them. Woolly apple aphids and flower thrips, however, were more abundant under the nets.
Nets also protected against hail in 2024. At Clarksville, the non-netted Gala trees had 11 percent hail damage, while netted trees had 2 percent damage. Netted trees also had less hail damage at Koan’s orchard, Elsysy said.
Nets have shown they can save organic growers time and money in the long run. The MSU team will test nets again, placing them before dormancy break to see how well they can mitigate early spring frosts, the researcher said.
Nets were placed over about an acre of Koan’s organic trees last season. The cost and labor involved in setting them up made him skeptical about adopting nets long term. But Koan was “totally amazed” at the results, he said. The nets were “a touch better” at managing crop load than his typical method of using lime sulfur and oil. His netted apples ended up bigger and redder, with no insect damage, he said.
One of Koan’s biggest costs as an organic grower is mating disruption of codling moth and oriental fruit moth. Mating disruption requires labor and doesn’t provide complete control, often requiring supplementary virus sprays. But with nets keeping the bugs out, he doesn’t have to use mating disruption, he said.
Nets aren’t cheap, but after the initial installation, all you have to do is roll them up in fall and roll them back down in spring. They pay for themselves after a few years, he said.
Koan plans to eventually place nets over all of his high-density blocks. Doing so won’t be simple. Nothing is in organic farming, he added. The netted blocks will probably push pests into his older, freestanding blocks, which are too big for netting. He’ll have to find ways to enhance beneficial insects in those older blocks.
“In an organic orchard, every input has positive and negative consequences,” Koan said. “I’m not sure of the negative consequences of netting yet.” •
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