Disorders of Cole Crops

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu and Emmalea Ernest, Scientist – Vegetable & Fruit Crops; emmalea@udel.edu

Summer cole crop planting for fall harvest will begin soon. The following are some common physiological disorders of cole crops to note:

Black Petiole in Cabbage

Black petiole or black midrib is an internal disorder of cabbage that has been observed in recent years. As heads approach maturity, the underside of the internal leaf petioles or midribs turn dark gray or black at or near the point where the midrib attaches to the main stem. It is believed that this disorder is associated with a potassium (K) -phosphorus (P) imbalance. Proper nutrient management and choice of cultivar will help minimize this condition.

Blanching and Off-Colors in Cauliflower

Heads exposed to sunlight may develop a yellow and/or red to purple pigment. Certain varieties (e.g., Snow Crown) are more predisposed to purple off-colors, especially in hot weather. Self-blanching varieties have been developed to reduce problems with curd yellowing. For open headed varieties, the usual method to exclude light is to tie the outer leaves when the curd is 8 cm in diameter. Leaves may also be broken over the curd to prevent yellowing. In hot weather, blanching may take 3-4 days, but in cool weather, 8-12 or more days may be required. Cauliflower fields scheduled to mature in cool weather (September and October) that are well supplied with water and planted with “self-blanching” cultivars do not require tying. Newer orange cauliflower and green broccoflower varieties are less susceptible to off-colors but can still turn purple under warm conditions.

Bolting/Buttoning Due to Low Temperatures in Broccoli, Cabbage, Cauliflower, Collards and Kale

Bolting in cabbage, collards and kale, and “buttoning” in cauliflower can occur if early planted crops are subjected to low temperatures (between 35-50°F/2-10°C for 10 or more continuous days). Temperature-induced bolting responses depend on variety.

Boron Deficiencies

Cole crops have a high boron requirement. Boron deficiency results in cracked and corky stems, petioles, and midribs for most cole crops. For broccoli, cabbage and cauliflower, stems can be hollow and sometimes discolored. Cauliflower curds become brown, and leaves may roll and curl, while cabbage heads may be small and yellow.

Brown Floret (Brown Bead) and Yellowing Floret in Broccoli

Brown Floret (brown bead) (Figure 1) may be caused by heat damage during early floret development, plant nutritional imbalances or insect feeding damage (e.g., harlequin bugs). Areas of florets do not develop properly, die and lead to brown discolored areas.

 

Yellowing florets

Yellowing florets may be due to over-maturity at harvest, high storage temperatures and/or exposure to ethylene. Any development of yellow beads ends commercial marketability. Bead yellowing due to senescence should not be confused with the yellow to light-green color of areas of florets not exposed to light during growth, sometimes called “marginal yellowing”. Proper post-harvest handling and packaging will help minimize this problem.

Curd Bracts in Cauliflower

Development of curd bracts (Figure 4) or small green leaves between the segments of the curd in cauliflower is caused by high temperature or drought. Heat-resistant cultivars and proper water management can help minimize this condition.

Edema on Cole Crop Leaves

Edema is water blistering on cole crop leaves. The most common cause of edema is the presence of abundant, warm soil water and a cool, moist atmosphere. Proper water management can help to minimize this condition.

Hollow Stem in Broccoli and Cauliflower Not Caused by Boron Deficiency

This condition starts with gaps that develop in stem tissues. These gaps gradually enlarge to create a hollow stem (Figure 2). Ordinarily, there is no discoloration of the surface of these openings at harvest but both discoloration and tissue breakdown may develop soon after harvest. Some cultivars of hybrid cauliflower and broccoli may have openings from the stem into the head. Hollow stem increases with wider plant spacing and as the rate of nitrogen increases. The incidence of hollow stem can be greatly reduced by increasing the density of the plant population.

Lack of Heads in Broccoli and Cauliflower

During periods of extremely warm weather, i.e., days over 86°F (30°C) and nights over 77°F (25°C), broccoli and cauliflower can remain vegetative due to inadequate cold exposure. This can cause a problem in scheduling the maturation and marketing dates for these crops.

Premature Heading (Buttoning) in Broccoli and Cauliflower

Losses are usually most severe when transplants have gone past the juvenile stage before setting in the field. Stress factors such as low soil nitrogen, low soil moisture, disease, insects, or micronutrient deficiencies can also cause this problem. Some cultivars, particularly early ones, are more susceptible to buttoning than others.

Ricing and Fuzziness in Cauliflower

“Riciness” and “fuzziness” (Figure 3) in cauliflower is caused by high temperatures, exposure to direct sun, rapid growth after the head is formed, high humidity, or high nitrogen. When “ricing” occurs, flower buds develop, elongate and separate, making the curd unmarketable. Proper cultivar and nutrient management can help minimize this condition.

 

Head Knuckling in Broccoli and Curd Separation in Cauliflower

Both disorders are caused by exposure to excess heat during head development (Figures 4 and 5).

 

 

 

Splitting in Cabbage

Cabbage splitting mainly occurs in early cabbage when moisture stress is followed by heavy rain. Rapid growth associated with rain, high temperatures and high fertility can cause splitting. Proper irrigation and deep cultivation may help prevent splitting. There are significant differences between cultivars in their susceptibility to this problem.

Tipburn in Cauliflower, Cabbage, and Brussels Sprouts

Tipburn (Figure 6) is a breakdown of plant tissue inside the head of cabbage, individual sprouts in Brussels sprouts, and on the inner wrapper leaves of cauliflower. It is associated with an inadequate supply of calcium in the affected leaves, causing a collapse of the tissue and death of the cells. Calcium deficiency may occur where the soil calcium is low or where there is an imbalance of nutrients in the soil along with certain weather conditions (high humidity, low soil moisture, high potash and high nitrogen aggravate calcium availability). Secondary rots caused by bacteria can follow the onset of tipburn and heads of cauliflower can be severely affected. Some cabbage and cauliflower cultivars are relatively free of tipburn problems. This problem can cause severe economic losses.