broccoli

4.4 PHYSIOLOGICAL DISORDERS

Broccoli crops show various non-parasitic disorders which cause tissues to die off. In some

cases, these deviations have been shown to depend mainly on heritable characters; whereas in

other cases external factors had a least marked effect.

Blindness

Plants do not form heads, but produce many shoots at ground level. This may be caused by

insects or damage to the growing point early in the plants life.

Leafy Heads

Small leaves develop and protrude through the head during high temperatures, drastic

fluctuations in day and night temperatures or improper nitrogen balance.

Broccoli buttoning

Buttoning is the premature formation of a head 2.5 to 10 cm in diameter. Buttoning can occur

anytime between seeding and almost mature plant, but usually occurs shortly after transplanting

into the field. Generally foliar growth slows after buttoning resulting in too few nutrients to nourish

the curd to marketable size. Losses are usually most severe in the early planted crop during

cold, wet seasons, when vegetative growth is affected by:

1. too much hardening of greenhouse plants

2. too little hardening of greenhouse plants

3. low soil nitrogen

4. low soil moisture

5. continued cold weather (4 to 10 0

C for day or more)

6. Other – disease, insects, micronutrient deficiency, etc.

Some cultivars, particularly early ones, are more susceptible to buttoning than others.

Lack of heads in broccoli

During periods of extremely warm weather (days over 30 0

C and nights of 25 0

C) broccoli can

remain vegetative (does not head) since they do not receive enough cold for head formation.

This can cause a problem in scheduling the marketing of even volumes of crop.

Hollow stem in broccoli

Symptoms are internal only. This condition starts with gaps that develop in the tissues, and

gradually they enlarge to create a hollow stem, sometimes from the bottom of the stalk into the

head. Ordinarily, there is no discolouration of the surface of these openings at harvest, but both

discolouration and tissue breakdown may develop soon after harvest. Avoid excessive nitrogen

 after head initiation. Dense plantings will maintain even growth rates and decrease the

occurrence of hollow stem.