High tunnel tomato production at Untiedt’s Vegetable Farm in Minnesota. Photo courtesy of Untiedt’s Vegetable Farm

by Gail March Yerke

Joining the trend of large conferences and events moving to online formats, the Minnesota Fruit and Vegetable Convention presented its educational programs and trade show through a virtual platform for their 2021 conference. The annual two-day event is jointly sponsored by the Minnesota Fruit and Vegetable Growers Association (MFVGA) and Minnesota Apple Growers Association (MAGA). This year’s program took place Jan. 14 and 15 and offered educational sessions presented by growers and industry specialists along with researchers and educators from the universities of Michigan, Ohio State, New Hampshire, Minnesota, Maine, Vermont, Purdue and Cornell.

One of three workshops on high tunnel production at the conference was hosted by Natalie Hoidal of University of Minnesota Extension and Paul Nelson of Untiedt’s Vegetable. Their presentation included plant spacing, best growing practices, disease and pest management and irrigation. Besides extending the season, benefits of this growing method offers protection from severe weather, impacts the insect population and offers higher and more consistent yields.

First introduced by the USDA-NRCS, the High Tunnel Initiative began as a pilot program for farms in 2010. While there is no comparable grant program in place currently, additional funding continued in later years to help farms get their start in this type of production. Today there is high tunnel production in all 50 states, with crops including herbs, fruits and vegetables.

At 31.4 pounds per person, tomatoes rank second in annual vegetable consumption per person in the U.S., according to the latest USDA Economic Research Service report, and high tunnel production has increased across the country to help meet that demand. Unlike growers who are just joining this trend, high tunnel production systems have been in use at Untiedt’s Vegetable Farm for over 30 years, adapting growing techniques from their educational travels to farms in Europe and Mexico.

High Tunnels at Untiedt’s Vegetable Farm

With 30 acres in high tunnels alone, Untiedt’s Vegetable Farm located in Waverly, MN, produces more than 30 different crops in the covered production style. They grow 10 acres of tomatoes in the three-season-style, 24-by-500-foot tunnels. Paul Nelson said that the coverings are removed at the end of each growing season because of Minnesota’s snow loads. A portion of the side material can be raised in warmer weather for increased ventilation and lowered during the early or late season to help with frost protection. Their tunnels do not have heating systems or fans for ventilation. They set five-foot aisles for determinate tomato varieties to allow row plantings to be accessed from either side for maintenance and harvest. Landscape fabric covers aisles between rows of plants and each tunnel in their production plan covers about a quarter of an acre.

“We grow both determinate and indeterminate varieties, with about 80% of the crop determinate,” Nelson explained. All of their tomato plants are grafted, with rows of determinate varieties planted 24 inches on center. Tomatoes are planted every two weeks during the growing season. Weeds are managed manually and the drip irrigation system is walked daily to troubleshoot any watering issues. “Tapes can get plugged, accidently cut or even damaged by deer walking through the tunnels,” he said. On average, tunnels are irrigated every other day with additional watering during hot spells.

“We can do tissue and sap analysis every two weeks during the growing season,” he said. The first week, Nelson sends samples to the lab. The following week nutrients are adjusted and applied based on those lab findings. The process is repeated throughout the summer to measure the success of nutrient applications.

When it comes to nutrients, Nelson said they opt for in-season application rather than applying a heavy fertilizer at planting. “Our plants are spoon-fed all summer long, giving them just what they need when they need it,” he explained. Untiedt’s high tunnel staffing includes separate crews assigned to growing, irrigation, pruning and harvesting.

Insect & Disease Control

Different insect populations are found in tunnels compared to field crops. “The two-spotted spider mite is common because its natural enemy is rainfall. In a tunnel you have taken that away,” he said. “Citrus thrips and western flower thrips are also a problem for us.” Biocontrol products are not an option on tomato crops, according to Nelson. “Tomatoes are one of the few things we don’t use biocontrols on because of the fine hairs on the plants. There are issues with the beneficials walking the plants to find the pests.” He explained that biocontrols are successful with and used on many of the other crops they grow.

One of the more aggressive tomato diseases that impacts tunnel production is Clavibactor michiganensis. It is highly transmittable and can impact an entire tunnel in just a few days. Also known as ring rot, it’s bacteria that cause damage to both the plant’s vascular system and fruit. It can be spread by tools, handling plants or even clothing and shoes. When identified, it’s important to sequester the tunnel so that staff do not go into other areas after working there. Hands should be washed with a water/peroxide solution, tools disinfected and clothing washed before wearing again in other tunnels. It can be managed when staff is trained and procedures are followed to reduce transmission of the disease.

With high tunnels it’s important to remove all vegetation at the end of the grow cycle. After frost, tomato plant vegetation is moved to an above ground compost area and fruit goes into a “bury pile.” Neither compost area is reintroduced as organic matter in any of the high tunnels. “We don’t want to incorporate any possible disease for the following season. We want it all cleaned up,” Nelson said. Plant stakes are disinfected before being reused the following spring. If a tunnel has had any sign of disease, the walls of the tunnel are also disinfected.

High tunnel production offers both advantages and challenges for farms considering this crop option. “We tend to be a very hands-on type of farm here,” said Nelson. “We keep trying new things each season.” With 30 years of experience in this method of fruit and vegetable production, Untiedt’s Vegetable Farm offers high hopes for continued success for high tunnels.

According to MFVGA President Beth Nelson, more than 200 growers participated from the U.S. and Canada. Nelson said that feedback was positive on the new online format. Attendees could easily log on and attend various breakout sessions, visit the trade show and interact with speakers and other attendees in chat rooms following each session.

More than 35 live workshops covered new varieties, crop troubleshooting and production tips for orchards, fruit and vegetable crops, high tunnel operations and apples. Trends in general agriculture marketing and agritourism were also presented. Recorded program content is available until April at MFVGA.org.