Jacques Bouwer
SAKATA
Temperature can play a critical role in the vegetative growth, head formation and quality of brassica crops. Stress from extreme temperatures triggers hormonal and metabolic changes across various growth stages, and plants can respond differently depending on their developmental stage.
Cold temperatures
Cold stress is most damaging to young plants and seedlings, reducing photosynthesis and slowing metabolic activity. The stomata close, causing lower evaporation and decreased water loss, but it also negatively affects photosynthesis as CO₂ intake gets limited.
Symptoms of cold stress often include:
- dull, bluish leaves with slight wilting,
- reduced leaf expansion, and
- thicker, tougher leaf tissue.
The practical impact for farmers can include:
- slower growth and delayed maturity,
- lower early biomass affects scheduling for varieties grown for the fresh market, and
- young seedlings may stall during cold snaps, requiring several days to recover, depending on the severity.
Hot temperatures
Heat stress in seedlings can trigger a drastic increase in proline. Proline is a natural stress relief compound that strengthens cell walls and helps the plant to tolerate stress. However, prolonged heat still suppresses photosynthesis and reduces carbohydrate production. Heat stress reduces the photosynthesis activity, which can cause smaller head formation, premature buttoning, loose heads and bracts (small leaves pushing through the head).
The practical impact for farmers can include:
- early heat disrupts plant frame size, reducing head quality later, and
- shortened maturity periods, causing overlapping harvests and bottlenecks in supply planning.
Pest pressure
High temperatures speed up pest life cycles. Diamondback moths, for example, can complete their cycle in less than 7 days during ideal warm conditions. This rapid turnover increases population size and causes resistance to specific active chemicals to build up faster than anticipated.
Management strategies:
- Constant rotation of the active chemical sprayed.
- Shorten spray intervals as temperatures rise.
- Adopt integrated pest management (IPM) practices to reduce reliance on chemicals.
Disease pressure
Warm, moist conditions allow fungal spores and bacterial pathogens to multiply quickly. This causes high disease pressure, making management extremely difficult and can increase the risk of disease breakdown.
Best practices for farmers:
- Monitor fields closely and identify symptoms early.
- Spray preventatively when temperatures start to get more ideal for disease development.
- Maintain good air movement through correct spacing and field hygiene.
Temperature extremes, cold and hot, pose significant challenges to brassica production. This can have direct effects on plant physiology as well as intensifying pest and disease pressure. Successful management requires proactive monitoring, adaptive scheduling and integrated pest and disease control strategies to maintain yield and quality.
DISCLAIMER: This information is based on our observations and/or information from other sources. As crop performance depends on the interaction between the genetic potential of the seed, its physiological characteristics, and the environment, including management, Sakata gives no warranty, express or implied, for the performance of crops relative to the information given, nor do Sakata accept any liability for any loss, direct or consequential, that may arise from whatsoever cause. Please read the Sakata Seed Southern Africa (Pty) Ltd Conditions of Sale before ordering seed.