Broccoli Trials – What a Difference a Year Makes

Gordon Johnson, Extension Vegetable & Fruit Specialist;

In an effort to diversify, Delaware growers are seeking to expand broccoli production in the state. Delaware is located in the southern portion of the Mid-Atlantic region and with a changing climate, much of the state is experiencing warmer fall weather conditions and more variable spring weather. At the same time, there has been an effort to breed more heat tolerant broccoli varieties for Eastern U.S. production.

A 2-year study was conducted to evaluate available commercial broccoli varieties, especially those with heat tolerance, for late spring, late summer, and fall harvests in high density plantings under Delaware conditions.

In 2017 there were 22 varieties in the 2 spring trials. Seeds of each variety were planted in the greenhouse on February 22 and March 8, 2017. Plants were transplanted to the field on April 3 for planting 1 and April 17 for planting 2. The soil was a Hammonton loamy sand. Plots were 7’ long with 4 rows wide with 1’ between rows and 1’ between plants (28 plants). The experimental design was a randomized complete block with 4 replications.

Yields were promising in spring 2017 trials. Eastern Crown had the highest marketable yield with 467 boxes per acre and 9 % cull. Both Luna and Sakata 6316 also yielded over 400 boxes per acre (452 and 429 respectively). Yields of other varieties tested were below 400 boxes per acre in trial 1. In the April 17 planting, Millennium significantly outyielded all varieties with 641 boxes per acre and 0 percent culls. Other varieties yielding over 400 boxes per acre were Eastern Crown, Emerald Crown, and Sakata 6316 (488, 423, and 406 respectively). Iron Man, Gypsy, Everest, Emerald Jewel, Emerald Crown, and Diplomat had the highest ratings for head evenness.

In Fall of 2017 broccoli varieties were transplanted on July 27 and August 16. These trials experienced severe disease conditions (Alternaria, black rot) and commercial yields were not obtained. Disease ratings indicated that most varieties were susceptible, but Lieutenant and Burney had significantly more marketable heads than other varieties.

In 2018 there were 23 varieties in three spring and two fall trials. Transplanting dates were April 3, April 16, and April 30. Spring weather conditions were extremely variable and yields were low (below commercial levels). In the early April planting best yielders were Green Gold and Diamante (only 269 and 261 boxes per acre respectively). In the mid-April planting, best yielding varieties were Millennium and Eastern Crown but yields were very low and marketable heads were 34.8% and 29.5% respectively. In the late April planting top yielders, Bejo 3019 and Luna, only produced 215 and 201 boxes per acre respectively.

For the summer planting, varieties were transplanted on July 30 and August 20, 2018. The July 30 planting experienced high temperature conditions during early September and had severe disease pressure (black rot, Alternaria). No commercial yields were obtained. This mirrored the low yields found in commercial fields throughout the region with late July plantings.

In contrast, many varieties did well in the August 20, 2018 planting. Diamante, SVBL 2036, Eastern Crown, Emerald Crown, Hydra, Virgo, Diplomat and Lieutenant all had commercial level yields above 400 boxes per acre.

These studies indicated that variable weather conditions and extreme events associated with climate change (heat, heavy rainfall) and heavier disease pressure will limit the expansion of broccoli growing seasons in Delaware. Further on-farm cooperator research will be conducted in 2019 on broccoli adaptability.