Controlling multiple heading and transplant shock in lettuce
Multiple heading, or ‘blindness’ is a physiological disorder affecting up to 20% of lettuce crops. It is most prevalent in NSW and Queensland during summer months, but can occur any time.
Blindness refers to loss of the apical shoot. The result is a lettuce that is deformed and unsalable. The causes of blindness are unclear, although a range of factors are suspected to increase risk. Blindness occurs when lettuces are still young seedlings, although the disorder is often not apparent until after planting and development.
In some cases the young plants can recover. However, further stress exacerbates the situation. Transplanting lettuces while they are still small minimises damage to the developing roots and allows the plants to establish quickly. However, young plants are fragile and difficult to handle. Transplanting when lettuces are further developed means they are more robust, but inevitably damages roots and can result in ‘transplant shock’, where the plants fail to establish well and thrive.