Potential production challenges with ornamental cabbage and kale

Be prepared this season by recognizing some of the common ornamental cabbage and kale disorders and pests.

Photo 1. Ornamental cabbage exhibiting marginal tip burn caused by excessive fertilization.

Photo 1. Ornamental cabbage exhibiting marginal tip burn caused by excessive fertilization.

Ornamental cabbage and kale

Ornamental cabbage and kale (Brassica oleracea var. acephala L.) are produced commercially during the summer and fall along with other crops such as asters, chrysanthemums, pansies and other cold-tolerant bedding plants. Greenhouse and outdoor ornamental cabbage and kale growers can encounter production challenges, which we discuss in this article.

Lower leaf chlorosis or purpling and leaf loss

Lower leaf yellowing (chlorosis) and leaf loss may be attributed to two cultural conditions: water stress and excessive or deficient fertility.

Ornamental cabbage and kale are often transplanted during summer months for fall sales. During this time they may experience water stress, thus resulting in lower leaf yellowing and loss. Additionally, high substrate electrical conductivity (EC), in addition to excessive drought stress, can also cause lower leaf loss and root death. To prevent this from occurring, growers must provide plants with adequate moisture and maintain substrate EC between 1.0 and 2.5 mS/cm (PourThru method). Appropriate container size selection, substrates with increased water holding capacity and automated irrigation systems are recommended to prevent these problems.

Fertilizer recommendations vary for ornamental cabbage and kale production. Excessive fertilization greater than 250 parts per million (ppm) nitrogen (N) will prevent intense coloration and can also cause marginal tip burn (Photo 1).

However, contrary to popular belief, discontinuing fertilization will not enhance center head and color development. Rather, it can result in chlorosis (Photo 2), purpling of lower leaves (Photo 3) or loss of lower leaves (Photo 4). During periods of active growth, it is recommended you provide 150 to 250 ppm N, while maintaining a substrate pH between 5.5 and 6.2.

Ornamental cabbage

Photo 2. Ornamental cabbage deficient of nitrogen exhibits lower leaf chlorosis.

Ornamental kale

Photo 3. Ornamental kale deficient of phosphorus exhibits lower leaf purpling.

Ornamental cabbage and kale with lower basal leaves.

Photo 4. As a result of discontinuing fertilization, ornamental cabbage and kale can drop lower basal leaves.

Temperature

Ornamental cabbage and kale are typically grown outdoors, but can be grown in greenhouses. High temperatures during production can cause excessive stem elongation (Photo 5). Plants exposed to night temperatures between 45 and 50 degrees Fahrenheit for two to three weeks will develop full color without lower leaf chlorosis, purpling or leaf loss (Photo 6).

Stems of ornamental cabbage and kale.

Photo 5. High temperatures during production can excessively elongate stems of ornamental cabbage and kale. As a result of increased growth, plants will exhibit lower leaf yellowing (chlorosis) due to the lack of fertility and water.

Ornamental cabbage with dark foliage.

Photo 6. Ornamental cabbage and kale will develop darker foliage color as temperatures decrease. Ornamental cabbage ‘Glamour’ exposed to temperatures of (A) 68 F, (B) 65 F, (C) 60 F and (D) 50 F for two weeks developed darker foliage color.

Pests

Ornamental cabbage and kale are prone to a number of insects and diseases. The most common pests, especially with outdoor production, include aphids (Photo 7), caterpillars, flea beetles (Photo 8), whiteflies, slugs and snails (Photo 9). The most common diseases of ornamental cabbage and kale include Alternaria leaf spot, black rot, club rot, downy mildew, fusarium yellows, rhizoctonia stem rot and root rots caused by Pythium and Phytophthora. Therefore, while using a substrate that holds sufficient moisture helps prevent lower-leaf loss, the substrate should also be allowed to dry out somewhat between irrigation events.

Aphids on cabbage leaf.

Photo 7. Aphids found on the underside of ornamental cabbage leaves.

Flea beetle leaf damage.

Photo 8. Flea beetle damage on ornamental cabbage leaves.

Snail on ornamental cabbage leaf.

Photo 9. Snails can often cause damage on ornamental cabbage leaves.

The following e-GRO Alerts contain information on ornamental cabbage and kale production challenges:

W. Garrett Owen is a PhD candidate at Purdue University, Department of Horticulture and Landscape Architecture, and Roberto Lopez is an assistant professor and Extension specialist in MSU’s Department of Horticulture.

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