Organic Late Blight Indeterminate Tomato Cultivar Evaluation

Methods

This study took place in central Pennsylvania at Penn State's Russell E. Larson Agricultural Research Center in Pennsylvania Furnace during the 2024–2025 growing seasons. In previous years, the experimental field had been managed with synthetic fertilizers and pesticides.

We evaluated seven indeterminate tomato cultivars (see the table below). Four-week-old transplants were planted in early June into a plasticulture system with raised beds covered in embossed black plastic mulch. Each bed had two drip irrigation lines: one for irrigation and the other for fertigation. Each test plot had six plants spaced 1.5 ft apart within rows, with 10 ft between rows. Plants received 1–1.5 acre-inches of water weekly. Before bed formation, we applied an organic granular fertilizer (Fertrell Blue N 5-1-1) at a rate of 150 lb/acre N. During the season, we fertigated weekly with 2 lb/acre N using an organic liquid fertilizer (Alaska Fish Emulsion 5-1-1).

Indeterminate Late Blight-resistant cultivars evaluated in an organic production system in Pennsylvania Furnace, Pennsylvania, at Pennsylvania State University's Russell E. Larson Agricultural Research Center

To manage Early Blight and Septoria Leaf Spot, we applied a copper-based fungicide (Kocide 3000) weekly beginning in early September. Brown Marmorated Stink Bug was managed with an insecticide (Entrust; applied only in 2025), which was also applied weekly starting in early September. Annual ryegrass was planted between rows for weed suppression, and plants were trained vertically using the Florida Weave system.

We harvested tomatoes weekly, once they had fully turned red, starting in early August and continuing until early October. After each harvest, we sorted the fruit into marketable and unmarketable categories, counted, and weighed them.

Marketable tomatoes were then sized into four categories:

• Small: less than 2 inches across
• Medium: 2 to 2.75 inches
• Large: 2.75 to 3.5 inches
• Extra-large: more than 3.5 inches

Most unmarketable fruit had Radial or Concentric Cracks or Raincheck. A few had other issues, such as Blossom End Rot, Zippering, or Tomato Pox and Fleck ('Rose de Berne' 2024 only).

We used a randomized complete block design for the experiment, with each cultivar replicated four times. We collected data from six plants per cultivar per replication. Data were pooled and analyzed using GLIMMIX with means separated at P ≤ 0.05 using Tukey's Honestly Significant Difference test. All year * cultivar interactions were significant; therefore, data were analyzed separately by year using the mixed procedure, with means separated at P ≤ 0.05 using the pdiff function.

Key Findings

We didn't see Late Blight during the two years of testing.

 We used 'Mountain Rouge' as the standard for comparison.

'Beef Maestro' was the sole cultivar that outperformed 'Mountain Rouge' in terms of marketable yields, both in number and weight. Fruit from 'Beef Maestro' was red at maturity. For markets demanding pink fruit, none of the cultivars evaluated consistently produced higher or lower marketable yields, by number or weight, than 'Mountain Rouge'. They are, therefore, all good options.

Most cultivars produced a large amount of unmarketable tomatoes. Specifically, four out of the seven cultivars (excluding 'Strawberry Fields', 'Big Beef', and 'Beef Maestro') in 2024 and all seven in 2025 produced higher unmarketable yields by number compared to marketable ones. By weight, six out of the seven cultivars (excluding 'Strawberry Fields') in 2024 and all seven in 2025 produced higher unmarketable yields compared to marketable ones.

Some causes of unmarketability were cultivar-specific. For instance, fruit with pronounced blossom-end scarring was noted in 'Abigail,' while Tomato Pox and Fleck (observed only in 2024) were associated with 'Rose de Berne. ' In early harvests, we noted Blossom End Rot across all cultivars in 2024 only. The greatest cause of culled fruit was Concentric and Radial Cracking, as well as Raincheck.

'Rose de Berne', 'Damsel', 'Mountain Rouge', and 'Abigail' produced more unmarketable fruit by number and weight than marketable yield over both study years. Seed companies describe 'Abigail', 'Rose de Berne', and 'Strawberry Fields' as having minimal Cracking or resistance or tolerance to Cracking. The volume of rainfall we experienced likely exceeded the tolerance of these cultivars to Cracking.

Very few tomatoes were extra-large. No cultivar consistently produced higher or lower yields of extra-large fruit by number or weight than 'Mountain Rouge'. Other cultivars than the ones we evaluated may be better options for extra-large fruit.

Most fruit was large- and medium-sized. 'Strawberry Fields' consistently produced higher yields of large fruit by number and weight, and 'Beef Maestro' by number than 'Mountain Rouge'. These are red-fruited cultivars. We noted that 'Beef Maestro' produced a blocky fruit compared to the other cultivars, and 'Strawberry Fields' produced very uniform fruit. Among pink-fruited cultivars, none produced yields of large fruit by number or weight that were different than 'Mountain Rouge'.

'Strawberry Fields' consistently produced more medium-sized fruit, both in number and weight, than 'Mountain Rouge'. Among pink fruited cultivars, none consistently had yields of medium fruit by number and weight that differed from 'Mountain Rouge'.

None of the cultivars evaluated were described by seed companies as small-fruited, and very few fruit were categorized as small. None of the cultivars evaluated consistently had yields of small fruit by number or weight that were different than 'Mountain Rouge'. Other cultivars than the ones we evaluated may be better options for small fruit.

Bottom Line

For higher marketable yield of red tomatoes, consider 'Beef Maestro'. For pink fruit, all the cultivars evaluated are good options.

High rates of culls due to Cracking and Raincheck were common due to excessive rain in the fall.

For extra-large and small fruit, consider cultivars beyond the ones we evaluated.

Consider 'Strawberry Fields' for large-sized and medium-sized red fruit by number and weight.

 'Beef Maestro' is another option for large-sized red fruit by number.

For large- and medium-sized pink fruit, all the cultivars evaluated are good options.

Acknowledgments

This work was only possible because we belong to a strong community of people who helped us succeed. Chris Sánchez prepared the field for planting, assisted with setting up and cleaning up after every harvest, planted and maintained the cover crop, and handled all post-harvest field cleanup. Austin Kirk supported field operations, ensuring we were well-equipped for success. Chris Igo, Harvey Gilbert, Jeanie Kim, Tim Damico, Dave Wolfgang, Ann Shallcross, Leigh Steingraber, Tara Mather, Michal Stump, Dan Kottloski, Karen Kottloski, and Darlene Bachmann planted the field, assisted with the weekly harvests, and made Thursday morning harvests enjoyable.

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