Tomato Grafting for Improved Vegetable Production in Kentucky High Tunnels

High tunnels are passively heated and cooled temporary structures used to extend the growing season for high value crops. They provide protection from the weather and serve as a moderately controlled environment. High tunnels have the potential to provide the grower 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. Nearly 900 high tunnels have been installed in the state of Kentucky (KY) since the inception of the High Tunnel System Initiative within the Natural Resource Conservation Service Environmental Quality Incentives Program (NRCS EQIP) in 2012. High tunnel production is nuanced and growers face unique production challenges from pests and diseases. One of those particular challenges are 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. High tunnels were intended for the production of specialty crops which include vegetables. Rotating to a non-host crop would be extremely limiting for high tunnel growers and would most likely mean that they would earn a significantly lower profit. Tomatoes are the most high-value crop grown in high tunnels in KY and the most common high tunnel crop. Infection of root knot nematodes into plant roots also opens up wounds in the roots that increase the likelihood of infections by soilborne pathogens, such as Verticillium or Phytophthora. This can be devastating for a tomato crop. Several KY high tunnel growers have already observed issues with root knot nematodes. In 2018, 11 different vegetable samples from nine different counties were submitted to the UK Plant Disease Diagnostic Lab. Ten of the nine samples were from crops grown in a high tunnel. These were submitted by agents that have previous experience with root knot nematode damage and knew to pull the plants up and look at the roots. Many agents and growers do not think to look at the roots. Damage by root knot nematode often looks like some other problem. There are fumigants and nematicides labeled for use on tomatoes. However, they are either not permitted for use in high tunnels, are extremely costly for growers, or are only moderately effective against plant-parasitic nematodes. There is a need for another management technique that is both affordable and effective. Grafting is a management method that growers could incorporate into their production system. Grafting 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 and disease resistance, stress tolerance, and vigorous root systems. Grafting is used both in the United States and around the world to improve plant development, vigor, quality, and yield. However, very few growers in KY are familiar with grafting and even fewer growers actually utilize grafting in their production system. Not all rootstock is resistant to root knot nematode and not all rootstock will be suitable for KY high tunnel production. The right rootstock for KY high tunnel production needs to be tested and evaluated. Additionally, both northern and southern root knot nematode has been observed in Kentucky. The resistant rootstocks are only resistant to southern root knot, not northern root knot nematode. However, it is not known how extensive the plant-parasitic nematode issue is in Kentucky, nor is it known which nematode species are the most problematic for vegetable growers. A survey of soil and vegetable plants around the state needs to be conducted in order to ascertain the extent of the issue (how many plant-parasitic nematodes are present and where) and identify the most abundant, problematic species in vegetables. Many agents rely on the specialists to go to their counties and provide information to the growers. This is not a sustainable form of information exchange as there are far fewer specialists than there are county agents. Additionally, the county agents are living and working in their communities and can better assess the needs and wants of their growers. Agent education and training on grafting will be conducted in order to better disseminate grafting information and techniques as well as the existence of plant parasitic nematodes and the damage they can have on vegetable crops. Trainings on tomato grafting will be provided to extension agents in a manner in which the agent will then feel capable of creating workshops for training growers how to graft.