I have been trying to determine what has been the cause of decline and death of several large Chinese Pistache trees on CSUChico campus. There have been no signs of Armillaria fruiting bodies, although some other trees have had them, especially maples. Examining the wood, there is an expanding, irregular pattern of darkened, discolored heart wood. The leading edges of expansion (looking in cross section) are aligned with the major root flare lobes at the root crown. There is no soft rot. There is also a streaking discoloration beyond the heart wood, that looks like dark flecks in the sap wood (in cross section). The branches of mature trees became sparse and died over a course of years. On the largest tree, half the tree has green leaves and no fruit, while the other half has lots of fruit on the dwindling branches that remain. I am wondering if this could be verticillium wilt. I do not currently have access to laboratory services to do a culture. The soils may be too wet/compacted around these trees, which are in lawns. Some root disturbance is undoubtably in their history. The trees have not been on a regular program of fertilization or aeration. Does anyone here have experience with a similar situation? I'd like to see what others think about this.
