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University of Minnesota Extension

Broccoli trials test which varieties can stand up to disease and heat stress

Researchers Natalie Hoidal and Charlie Rohwer in a field of broccoli. Each of them hold heads of broccoli in their hands.
Natalie Hoidal and Charlie Rohwer at the Southern Research and Outreach Center

Disease pressure and climate change pose significant challenges to growing broccoli in the Midwest. For the past two summers, Extension researchers have been conducting trials with growers across the region to identify broccoli varieties that can survive disease pressure and heat stress.

Since 2018, black rot (Xanthamonas campestris pv. campestris) and Alternaria (Alternaria spp.) have become common causes of disease on farms and in gardens, with some growers reporting 80-100% yield losses. Especially for organic growers, planting varieties that tolerate these pathogens can be a powerful tool for disease management.

We conducted broccoli trials at the Southern Research and Outreach Center (SROC) in Waseca, where we inoculated plots with black rot (Xanthamonas campestris pv. campestris). We also partnered with 88 farmers and gardeners to conduct mini trials at their farms and gardens.

Our goal was to screen for varieties of broccoli with tolerance to the pathogens black rot and Alternaria, as well as environmental challenges like warm fall nights and high heat in the summer.

June-planted broccoli

In 2021, broccoli varieties in Waseca produced mostly high-quality, marketable heads. Of the 17 varieties, 16 produced marketable heads 97-100% of the time. In 2022, many broccoli varieties planted in Waseca did not perform well due to high disease pressure and heat stress.

Varieties that we recommend based on high performance in both research station and grower trials include Wolfman, Green Magic and Eastern Crown.

Late-planted broccoli

Asteroid, Imperial, Luna, Monty, Diplomat, Abrams and Eastern Crown are all varieties that growers liked. Of these, Eastern Crown, Diplomat, Imperial and Abrams had the best disease tolerance in 2022. During seasons when disease pressure is expected to remain low, these varieties could all be good choices.

Our new report outlines the results of the 2022 trial with overall takeaways and variety recommendations from 2021 and 2022. Tables and charts in the report will help growers select from these varieties according to preferences for timing, color, head size, etc.

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