"Bull vine" or "witches' broom," another form of chimera, can affect individual vines, especially in older vineyards. It also starts from single, mutated buds, but abnormal, vigorous, and unfruitful growth can eventually crowd out normal shoots. Shoot nodes are closely spaced with numerous buds, lateral shoots, and small leaves. Crowded, numerous shoots will eventually dominate the affected portion of the vine. All abnormal growth, once detected, must be removed with a pruning saw. Otherwise, within a few years of unproductive growth the vine may have to be removed. Never take propagation wood from affected vines.
The chimera, shoot fascination, also results in a malformation of shoots: The affected individual shoots are enlarged and flattened in shape as if several shoots are fused. The mutation occurs more frequently in certain cultivars and is especially common in Petite Sirah (Durif). Such shoots are usually pruned in winter and thus do not affect production.
Flaherty, D., Christensen, L.P., Lanini, W., Marois, J.,
Phillips, P., and Wilson, L.T. 1992. Grape Pest Management, 2nd
edition. University of |