Symptoms and Signs
Trees with lemon sieve tube necrosis go through a cyclic decline. About 4 or 5 years after planting, the older food-conducting sieve tubes near the bud union die. Several years later, younger sieve tubes also die, severely restricting food transport to the roots. Many feeder roots die, fruit ripen prematurely, shoots grow poorly, and some leaves turn yellow and drop. The dieback stimulates new cambium and phloem production, and the tree recovers temporarily. Once the new sieve tubes also become necrotic, the decline process starts again. Only a microscopic analysis can reveal the collapsed sieve tubes.
Comments on the Disease
Lemon sieve tube necrosis is an inherited disorder of lemon trees in coastal areas. Eureka bud lines and Frost Lisbon lemons are affected. In some areas the disease is less severe, and in the San Joaquin and Coachella valleys, lemon sieve tube necrosis does not result in noticeable decline.
Only certain bud lines are affected by this inherited disorder. Eureka lemons that have this disorder could potentially die in 8 to 15 years. Before planting this variety, obtain the most recent recommendations from your farm advisor.