Effects of Topping on Marketable Yields in Several Cultivars of Brussels Sprout (Brassica oleracea var. Gemmifera)

In New England, Brussels sprouts are grown primarily for direct market, and are harvested and marketed on the stalk. Many cultivars are available, but published comparisons to guide grower choice are lacking. In Brussels sprout production, removal of the apical meristem (topping) has been shown to increase yields in once-over harvests. However, recommendations regarding topping vary widely and the effects of this practice on currently available cultivars have not been studied.  The objective of our study was to compare yields, performance, and response to topping for several Brussels sprout cultivars. Experiments were conducted in 2013 and 2014 in Durham, NH at the NH Agricultural Experiment Station. Seeding and harvest occurred on 3 June and 6 Nov. in 2013, and on 12 May and 19 Oct. in 2014. We grew nine cultivars in each year, with five grown in both years. A split-plot design with four replicates was used, with cultivar as the main factor and topping as the split plot factor, and experimental units of six plants. For topping treatments, apical meristems were removed when basal sprouts first reached 1.25 to 2.5 cm diameter. This resulted in earlier topping dates in 2014 (4 Aug. through 23 Sept.) than in 2013 (10 Sept. through 18 Oct.). Number and weight of marketable sprouts were assessed for each stalk. For each plot, we estimated the percentage of sprouts that were too large, too small, and that showed Alternaria symptoms. We observed significant differences between cultivars for all measured traits. The effects of topping were variable, and appeared to be associated with maturity date. In 2013, topping either significantly increased or had no effect on yields, depending on cultivar. However, in 2014, topping increased yields for some cultivars, had no effect on others, and decreased yields for others. Taken together, our results suggest that topping has the potential to increase marketable yields for several cultivars, but that topping far in advance of harvest (60 d.) may negatively impact yields in terms of weight and number of marketable sprouts, and reduces stalk length.