Whats Causing Top Dieback in Mulberry?

Q. What is causing the “big hurt” on mulberry trees? There was considerable damage to most trees in recent years. What caused so many dead branches this and last year?

Sooty canker disease 

A. Mulberries are solid performers in the hot desert if they get enough water and are pruned properly. I am not endorsing their planting; they use a lot of water and the male trees release large amounts of allergenic pollen, a huge health problem for many residents.

Battle of the Sexes

            The female trees are not “outlawed” in southern Nevada. The male, or fruitless mulberries, are. Female trees can be planted and will produce fruit without male trees because of large amount of airborne pollen produced every year from existing male trees.

Bowl of purple and white mulberry fruit in Tajikistan. Many countries I visited call the fruit "toots".

Sooty Canker Disease

            We see an increasing number of mulberries with dead branches in the tops of the trees. Most of this is “sooty canker” disease. This fungal disease spreads from tree to tree on poorly sanitized pruning equipment, birds and insects.

Sooty canker disease on ash. Looks the same on mulberry.

            It also infects other trees besides mulberry including ash, poplar, apple and many others. Frequently, the health of infected trees was “compromised” in some way making them susceptible to an otherwise weak pathogen.

            What compromises the immunity of otherwise vigorous trees growing the desert? Usually its water; a lack of it causing them to be stressed. The disease organism is transported to this weakened tree on pruning tools, or perhaps by birds or insects. This pathogen enters the tree through open wounds caused by pruning equipment, fresh openings left by dropping leaves, or through the flowers.

Consider this scenario: 

Sanitize pruning equipment before pruning

a landscape converts from large, established trees and lawns to a desert landscape; the lawn is removed and drip irrigation is installed; large established trees do not get enough water and limbs begin dying; landscapers remove limbs with unsanitary tools; the trees become infected; disease spreads because the tree’s health is compromised due to a lack of water.

            Simple solution? Sanitize pruning equipment.