Chlorine (Cl) & Sodium (Na)

Chlorine is needed in very small amounts in fruit trees, but is seldom deficient. The more serious problem with this element is when it is in excess, leading to salt toxicity. Peach, plum and nectarine are particularly sensitive to this disorder. Leaf levels need to be kept below 0.3% to prevent the problem. The initial symptom is marginal leaf burn, followed soon after by shoot dieback, loss of productivity and poor fruit size.

In one study we conducted in a Santa Rosa plum orchard, the threshold for damage was found to be 2.6 dS/m. Therefore, extensive soil and water testing should be carried out before planting to make sure this threshold will not be exceeded. Once an orchard is established, the problem is difficult to control.

Excess sodium can lead to similar symptoms.

Further reading:
Salinity experiment in Santa Rosa plum orchard (1)
Salinity experiment in Santa Rosa plum orchard (2)
Nutrition Chapter in UC Stone Fruit Manual

Marginal leaf burn on peach leaves caused by salt toxicity