Boron is an essential plant nutrient required in small quantities. It is relatively immobile in plants, so is taken up throughout the season.
Symptoms first appear in new growth. Young leaves become light green at their base and lose their shape (top right photo).Older leaves become twisted and distorted.Flowers become distorted and malformed with short petals that fold inwards.Young petioles are irregularly thickened and darkly banded with dying pith. In severe cases petioles split and young bolls are shed. Mild deficiency can produce rank growth and parrot beak bolls.
Toxic concentrations of boron result in leaf cupping, chlorosis and death of leaf tissue in localised spots.
Deficiencies can occur through leaching so may be more common on sandy soils.Prolonged dry periods can reduce soil boron availability.
Boron Toxicity leaf underside