Gordon Johnson, Extension Vegetable & Fruit Specialist; email@example.com
There is a demand for local, spring-harvested broccoli in our region. However, growing spring broccoli to commercial standards is a challenge due to heat effects during head formation which causes defects such as brown bead, uneven heads (knuckled), loose heads, and premature flowering. This renders heads unmarketable. Spring plantings also have shown limited head holding ability as temperatures reach into the 90s.
Temperature variability is the main challenge for spring broccoli. Broccoli is a cool season plant and is best adapted to areas with consistent temperatures during head development where days are warm, not hot, and nights are cool. On Delmarva, high temperatures during head initiation in the spring leads to abnormal floret development. Temperatures more than 88°F can cause damage to florets in sensitive varieties.
More heat tolerant varieties have been developed and were tested in 2017 spring trials. There were 22 varieties tested in two 2017 spring trials. Plants were transplanted to the field on April 3 for planting 1 and April 17 for planting 2. Plots were harvested from the May 31 to June 19 in planting 1 and June 8 to June 26 in planting 2. Plots were harvested as crown cuts. Target head size was 4+ inches in diameter and heads were cut 1 inch below the lowest floret attachment. Data collected included marketable and cull head number and weight, crown diameter, crown height, head uniformity ratings, head evenness ratings, hollow stem incidence, and brown bead ratings. Descriptive characteristics included color and dome shape.
Uneven floret development and brown bead in a variety with most heads unmarketable.
In the April 3 planting, Eastern Crown had the highest marketable yield with 467 boxes per acre and 9 % cull. Luna also yielded over 400 boxes per acre (452). Yields of other varieties tested were below 400 boxes per acre in trial 1. In the April 17 planting, Millenium significantly out yielded all varieties with 641 boxes per acre and 0 percent culls. Other varieties yielding over 400 boxes per acre were Eastern Crown, and Emerald Crown (488 and 423 respectively). Gypsy and Iron Man had the most uniform marketable heads. Destiny, Eastern Crown, and Green Gold had the highest ratings for brown bead. Diplomat, Gypsy, and Imperial had significant hollow stem. Iron Man, Gypsy, Everest, Emerald Jewel, Emerald Crown, and Diplomat had the highest ratings for head evenness.
For a full report on the 2017 trial go to http://extension.udel.edu/ag/vegetable-fruit-resources/vegetable-small-fruits-program/variety-trial-results/
Broccoli trials are being repeated in 2018 with later planting dates to better assess varieties under heat stress.
Broccoli marketable yields and cull percent, UD-REC, Georgetown, Spring 2017, April 17 planting (heat stressed).