Plants were grown in Speedling polystyrene trays in a greenhouse for six weeks and transplanted to a field at the Virginia Tech Horticulture Farm near Christiansburg on July, 25 1990. About 15 g of fertilizer (10N-4.3P-8.3K) were placed beneath each plant during transplanting, and a soil drench consisting of 9N-19.4P-12.5K fertilizer (4 g/liter) plus the insecticide, Diazinon (0.7 g/liter), was applied at a rate of 250 ml per plant after transplanting. Plants were set in double rows 30 cm apart with an in-row spacing of 60 centimeters. Each cultivar was transplanted into double rows 15 m long in an unreplicated block. Overhead irrigation was applied as required and fungicide and insecticide treatments were applied in accordance with recommended procedures (Anon. 1990). On Nov. 30, 127 days after transplanting, 10 to 12 plants of each cultivar were randomly harvested. The unharvested plants were evaluated periodically throughout the winter to assess holding ability and freeze tolerance.
'Dolmic', 'Golfer', and 'Rider' produced a significant percentage of large, loose sprouts. Large sprout size may be a characteristic of these cultivars or an indication of excessive nitrogen fertilization. 'Boxer', 'Lunet', 'Royal Marvel', and 'RS88032' exhibited excellent sprout quality. However, 'Royal Marvel' was the only high-yielding cultivar with excellent sprout quality. 'Royal Marvel' yielded 17.9 t/ha, about 14% greater than the average yield for Brussels sprouts in the United States (Lorenz and Maynard 1988).
Brussels sprouts are slow to mature and are known to be susceptible to a wide range of insect pests. An early season infestation of diamondback moth (Plutella xylostella L.) did considerable damage and required the application of insecticides. However, after the first killing frost in October, insects were no longer a problem and many of the later maturing cultivars, such as 'Lunet' and 'RS88032', matured in near perfect condition without further use of insecticides. The cultivar 'RS88032' matured in late December, after the harvest data in Table 1 had been collected. The optimal harvest date for 'RS88032' should have been on January 1.
Brussels sprouts characteristically have a long storage life if maintained under optimum conditions. In this study, Brussels sprouts were stored at 3°C and greater than 90% relative humidity for two weeks with no reduction in quality.
Plants remaining in the field throughout the winter were assessed for cold hardiness. As of Jan. 1, an estimated 90% of the sprouts for all cultivars were still marketable. During the month of January, the percentage of unmarketable sprouts for 'Prince Marvel', 'Dolmic', and 'Royal Marvel' increased as the outer leaves began to yellow. On two occasions in mid-January, temperatures dropped below -10°C. This resulted in freeze damage to exposed sprouts near the bottom of all plants that had dropped their lower leaves. Sprouts protected by foliage near the top of the plant were not damaged. In early February, plants were exposed to -12°C. The exposed sprouts received more damage, but surprisingly, many of the sprouts protected by foliage sustained only minor damage. In mid-February, most plants began to decline, and few marketable sprouts remained after this date. The winter of 1990-91 was uncharacteristically mild, and the Brussels sprout harvest period could be significantly reduced in other years with colder winters.
The sprouts of some cultivars are very difficult to remove from the plant by hand. Large scale production is extremely tedious and time consuming without mechanical harvesting equipment. Intact stalks can be cut at soil level and fed through a sprout stripper which removes the sprout from the stalk. Multitrade Inc. (P.O. Box 58, 1610 AB Bovenkarspel, the Netherlands) markets a sprout stripper that attaches to a tractor's three-point hitch and runs off power takeoff. The Multitrade Brussels sprout stripper sells for $4,352, including shipping charges from the Netherlands. More sophisticated and expensive harvesters are made by Mali-Ploeger B.V. of the Netherlands and are distributed in the United States by Agro Gold Inc. (Route 1, P.O. Box 299 B, Homer, IL 62849).
|Marketable weight (g)|
|Plant height (cm)||No. marketable |
|47.1||46.1||283||6.1||30.2±0.8 x 22.5±0.5||Light green, solid sprouts were produced on tall, late maturing plants. Sprout quality was high, but plants were not highly productive. Matured 125 days after transplanting. Very difficult to hand harvest.|
|35.6||35.0||324||9.3||36.4±0.5 x 26.2±0.7||Small plants produced large sprouts that were not solid. Matured 115 days after transplanting. Very difficult to hand harvest.|
|47.3||33.8||331||9.8||35.5±0.6 x 29.4±0.3||Sprouts were large, light green, and lacked uniformity. Some sproutswere large and not solid Sprouts held well on the plant and were easily hand harvested.|
|37.6||40.6||232||5.7±0.2||27.9±0.2 x 22.4±0.3||Very attractive small, dark green, solid sprouts were produced on short plants. Sprout quality was very high but productivity was low. Late maturing sprouts held well in the field and tolerated cold weather.|
|39.4||46.7||348||7.4||32.9±0.7 x 24.7±0.6||Large, light green sprouts were produced on medium sized plants. Plants were very productive. Sprout quality was somewhat lacking, because the sprouts were not solid. Matured 125 days after transplanting. Easy to hand harvest.|
|Prince Marvel |
|36.6||45.9||324||7.1||32.4±0.7 x 25.9±0.3||Small sprouts were produced on compact plants. Both plants and sprouts have distinct red leaf veins. Sprouts near the top of the plant developed slowly. Suitable for hand harvest 180 days after transplanting.|
|38.6||39.7||308||7.7||32.7±0.5 x 26.5±0.6||Sprout size was variable. Many sprouts were large but not solid. Sprouts held well in the field. Suitable for hand harvest.|
|49.9||38.4||258||6.7||30.3±1.0 x 29.4±0.3||Very large late maturing plants. Later harvests in mid-Dec. produced yields in excess of 300 g per plant. Performed well under cool conditions and held well in the field. High quality, uniform sprouts were light green in color. Difficult to hand harvest.|
|Royal Marvel |
|38.1||49.1||358||7.1||32.7±0.3 x 23.8±0.4||Similar to 'Prince Marvel'. Short compact plants produced uniform, high quality sprouts. Easily hand harvested 115 days after transplanting.|