Plant NutritionNutritional Disorders
Iron deficiency
Description: Emerging leaves bright yellow in colour,
often with veins remaining green giving a net pattern.
Leaves can entirely bleach and develop necrotic spots.
Roots may brown and die.
Control: If leaves are not totally bleached they will recover with application of iron. For fast corrective action, apply iron sulphate. To prevent, keep soil pH to 5.5-6.0 and apply a balanced fertiliser containing Fe such as Osmocote Exact or Osmoform, or apply Osmocote Coated Fe.
Magnesium deficiency
Description: Yellowing of old leaves, beginning with
leaf margins occurs, in between veins. A green arrowhead
shape may remain in the centre of the leaf. When severe,
necrosis may occur.
Control: Prevent occurrence by applying a balanced fertiliser containing Mg such as Osmocote Exact or Osmoform, or supplement with Micromax Micronutrients or Magrimax slow release magnesium. For fast corrective action, apply magnesium sulphate.
Nitrogen deficiency
Description: Pale, weak, disease-prone seedlings.
In mature plants chlorosis and dropping of older
leaves, the rest of the plant light green in colour.
Sometimes, abnormal reddening of leaves and stems occurs. Reduced growth
and performance.
Control: Apply Peters water soluble fertiliser as a drench or foliar spray for a fast response. To prevent N deficiency, use Osmocote or Agroblen controlled release fertiliser of the appropriate longevity and at the correct rate for the crop. Use potting mix with a low NDI.
Phosphorus toxicity
Description: Initially necrosis of the margins and tips of older leaves. Older leaves drop and chlorosis of younger leaves occurs. May cause plant death in severe cases. Common in Proteaceous plants and some other natives.
Control: Heavy soils such as clay loams will tie up Phosphorus. Use controlled release fertilisers such as Osmocote and only apply zero P or low P fertilisers such as Osmocote Plus low P.