Organic Tomato Trials Compare Yield and Quality

By Blake Jackson

A two-year organic tomato evaluation was conducted at Penn State’s Russell E. Larson Agricultural Research Center in central Pennsylvania during the 2024–2025 growing seasons.

Six determinate Late Blight-resistant cultivars were compared: Defiant, Galahad, Iron Lady, Mountain Gem, Mountain Merit, and Stellar. The field previously used synthetic inputs was transitioned into an organic plasticulture system with raised beds, drip irrigation, and fertigation.

Plants receive organic nutrients through granular fertilizer before planting and weekly liquid fertigation throughout the season.

Transplants were planted in early June, spaced 1.5 feet apart with 10 feet between rows. Annual ryegrass was used for weed suppression, and all plants were trained using the Florida Weave system.

Copper fungicide was applied weekly beginning in early September to manage Early Blight and Septoria Leaf Spot, and Entrust insecticide was used in 2025 to manage Brown Marmorated Stink Bug.

Tomatoes were harvested weekly from early August through early October, sorted into marketable and unmarketable categories, and further sized into small, medium, large, and extra-large. Most unmarketable fruit were affected by cracking or Raincheck, while Defiant showed elevated Yellow Shoulder issues, likely linked to potassium demand.

The trial used a randomized complete block design with four replications, and statistical analysis was used to compare cultivars each year.

Across both years, Late Blight was not observed. Mountain Merit served as the comparison standard. ‘Stellar’ consistently produced more marketable fruit than Mountain Merit, while other cultivars showed mixed performance.

Medium-sized fruit made up the largest category overall. Both Stellar and Defiant produced more medium fruit by number and weight than Mountain Merit.

Extra-large fruit were rare, and none of the cultivars consistently outperformed the standard. Large fruit production was similar across all cultivars. Mountain Gem produced more culls than marketable fruit, while Iron Lady, Defiant, Galahad, and Stellar produced more unmarketable fruit than Mountain Merit.

Photo Credit: gettyimages-bastetamn