Crown Symptoms of Regrowth Dieback

Abstract

Symptoms in the crowns of Eucalyptus obliqua and E. regnans trees affected by "regrowth dieback" are reevaluated and amplified using tree climbing, tree felling, and optical study methods. A distinction is made between the dying upper branches and the lower crown of dieback-affected trees. Declining branches showed an increase in mortality or absence of growing shoots, naked buds, and accessory buds with increase in dieback severity. Mean distance between leaf scars indicated that growth rate of shoots was slowed before death. With increase in dieback severity of a branch, leaf size and leaf area index were reduced. Leaves on dieback-affected branches showed increased chlorosis and reddish colors. There are common features linking dieback-affected shoots with shoots showing mild "witches brooming."Twiginhabiting insects are considered of only secondary importance. There was no evidence of any culturable microorganism from the vascular system. The symptoms could be the result of water deficits and high leaf temperatures. Alternatively, the symptoms are suggestive that microbes such as a virus or more especially a mycoplasma are involved.