Screenhouses Boost Marketable Yields for Farmers

( Koon-Hui Wang, University of Hawaii )

What can a screen do for agriculture? A lot more than you think, based on research lead by Dr. Koon-Hui Wang, associate professor and chair of the Department of Plant and Environmental Protection Sciences with the University of Hawaii. 

Insecticide-resistant pests are an increasing bane for farmers. 

“This issue started with farmers dealing with fruit flies, also called melon flies, which are very problematic to cucurbit crop production,” Dr. Wang says. Cucurbits are a family of plants that include cucumbers, melons and other gourds. 

The commercial high tunnel screenhouse next to the small DIY 17-mesh screenhouse.

At night the fruit flies crawl inside the fruit and lay eggs. Then the eggs hatch and the maggots grow inside the cucumber. Over the years, fruit flies have developed resistance to the bait.

One Hawaiian farmer went overseas to visit some producers outside of the U.S., Dr. Wang says, and he saw that farmers were solving this fruit fly problem with 17-mesh screen. This farmer began working with an extension agent to import the screen and build a screenhouse. They sewed the screens together to create panels big enough to cover a structure. 

The farm coach of the farmers' training program shows the success of their steak tomatoes with no fruit fly damage.

In 2014, The College of Tropical Agriculture and Human Resources’ (CTAHR) Cooperative Extension Service (CES) began testing screenhouse prototypes, from commercial systems to do-it-yourself models. 

“Our main purpose is to try to get it at a cheaper cost to the farmer so they can afford it,” Dr. Wang says. “The majority of the farmers in Hawaii, about 80% of them are smaller than 50 acres, and they are vegetable growers. So we want to find materials that are cheaper and affordable for them.”

The cucumber screenhouse using the commercial frame but replaced with 17-mesh insect netting now accepted by NRCS AMS program.

Farmer response has been overwhelmingly positive. Dr. Wang says many farmers were close to giving up on cucumber and zucchini production, but the screenhouses have given them the ability to grow these crops again. They’ve also found it helpful to protect tomatoes from fruit flies and prevent the diamondback moth on kale and cabbage.

In the feedback CES received, one farmer wrote, “I loved the screenhouse. The zucchini and tomato fruit were pest-free, and aphid pressure was manageable.” Another noted, “The pepper in the screenhouse has no fruit fly or pepper weevil, both of which cause nearly 100% devastation in the field. These are cryptic insects that can’t be managed by contact type insecticides.” 

Growing buckwheat as an insectary plant inside the screenhouse to attract parasitoids into the screenhouse.

Growers reported a 50% reduction in insecticide use to manage fruit flies, caterpillar aphids, whiteflies and thrips. CES research trials showed up to a five-fold increase in marketable yields in nonpollinated cucumber, kale and zucchini. Since the inception of this project, CTAHR CES had constructed about 24 screenhouses on farming systems in Hawaii through grant funding. Through their findings based on local needs, NRCS has contracted for the installation of 187 commercial high tunnels in Hawaii through federal cost share programs.

Finished constructing a DIY screenhouse (15 x 30 x2 foot) with the help of master gardeners in 2.5 hours.

Dr. Wang says she can see the application of screenhouses on the mainland U.S. to manage insect pressure. While farmers in Hawaii opt for screenhouses without the plastic  it can retain too much water and tends to sag after a rainy day, and farmers must install air-conditioning to manage climate in Hawaii —in cooler parts of the U.S. plastic screens on more traditional greenhouses may help extend growing seasons. 

Check out the AgDay report on screenhouses here: