Relationships among pruning time response, symptoms attributed to grape bud mite, and temporary early season boron deficiency in grapes

Abstract

In studies over a five-year period, the development of abnormal growth formerly included under “grape bud mite injury,” was found to be correlated with the effects of pruning time upon time of leafing of spurpruned vines. Pruning times (e.g., early January) that resulted in early leafing were followed by abnormal growth in early season and resulted in a 39 per cent reduction in yield over a five-year period. The effect of time of pruning upon abnormal growth occurs in the absence of bud mites, a bud-inhabiting strain of Eriophyes vitis (Pgst.). Pruning times (e.g., late March) that resulted in late leafing were followed by virtually normal growth and normal yields. Such pruning-time responses have been observed in Mataro, Muscat of Alexandria, and Malaga grape vineyards subject to abnormal growth. On Mataro vines, the period in winter in southern California during which buds responded to a nearby pruning wound by leafing very early and developing severe abnormal growth usually began about mid-December and extended through mid-January and, in some years, through the first part of February. Evidence is presented which indicates that this abnormal growth is caused by a temporary early-season deficiency of boron. Soil applications of borax were followed by alleviation of symptoms, increased yield, and elevation of boron level in leaves above the deficiency range. It is not inferred that these results show that grape bud mites can cause no injury. It is not known whether such pruning-time responses are in all cases related to temporary early-season boron deficiency, but this appears to be an excellent working hypothesis. Since pruning time responses have been recorded in northern California vineyards subject to “bud mite injury,” this suggests that this abnormal growth be re-investigated in the light of the possibility of temporary early-season boron deficiency as a causal factor.