High tunnels have the potential to provide specialty crop growers with the ability to extend the growing season and moderate the environment with respect to precipitation and temperature. This can translate to increased income from increased marketable yields and improved produce quality. High tunnels play an important role in the local food system of Kentucky. There are over 1,000 high tunnel across the state of Kentucky. High tunnel production is nuanced and growers face unique production challenges from pests and diseases. One of those particular challenges is plant-parasitic nematodes, specifically the root knot nematode. Root knot nematodes invade plant roots and cause root galling. This impairs root function which causes reduced water and nutrient uptake. Root knot nematodes have a very wide host range, including nearly all vegetable crops. They can significantly impact yield and thus, profit margins for the grower.

Grafting is a management method that involves combining the desirable fruit characteristics of one plant (called the scion) with the desirable root characteristics of another plant (called the rootstock). Desirable root characteristics include plant-parasitic nematode resistance. Very few growers in KY are familiar with grafting and even fewer growers actually utilize grafting in their production system.

In response to a Knox county high tunnel tomato grower having repeated issues with root knot nematodes, an on-farm trial was conducted in 2019. The Knox county ANR agent, Wayne Kirby, contacted the vegetable specialist, Rachel Rudolph, about assisting the largest commercial vegetable grower in Knox county with this issue. The grower was interested in a collaborative project that would not only help him and his production system, but would also help other growers across the state. In the trial, we evaluated three different tomato rootstocks on the same scion against non-grafted tomatoes in the grower’s high tunnel. Tomato yield and root knot nematode population densities were part of the evaluation. 

At the end of the season, the grafted tomatoes yielded 28% more on average compared to the non-grafted tomatoes. One particular tomato rootstock yielded 33% more compared to the non-grafted tomatoes. The grower sold the tomatoes for $2 per pound. At this price the grower made over $15 more per plant on the best performing grafted plants compared to the non-grafted plants. In 2019, when calculating the increased yield of all the grafted plants compared to the non-grafted plants, this resulted in an increased gross profit of over $1,600. The grower can fit approximately 405 plants in his high tunnel. If all the plants were grafted with the best performing rootstock, he could potentially increase his gross profit by approximately $6,300. Root knot nematode population densities were also lower in the roots and surrounding soil of the grafted tomatoes compared to the non-grafted tomatoes. During the course of the trial, the grower and his farm assistant learned to graft, began grafting their own tomatoes, and have planted grafted tomatoes on other parts of the farm. This positive experience has helped forge strong Extension relationships between the grower, agent, and specialist, as well as increased profits for a commercial vegetable grower, and provided new information and data to share with other Kentucky vegetable growers across the state.