Effects of horticultural oils on the photosynthesis, fruit maturity, and crop yield of winegrapes

The effects of horticultural oils on grapevine photosynthesis, fruit maturity, and crop yield components in field experiments were evaluated. Three applications of a 1.5% (v/v) oil/water emulsion were made to Chardonnay and Cabernet Sauvignon vine canopies at 6200 L/Ha (Chardonnay) and 2440 L/Ha (Cabernet Sauvignon) in 1998 using several horticultural oils. Net assimilation rates (NAR) and fruit soluble solids concentrations (SSC) were reduced in both cultivars by all oils, as compared to the control. In addition, berry weights, cluster weights, crop per vine, and vine pruning weights were all reduced by oil treatments to Chardonnay vines. Experiments in 1999 sought to determine if reduced spray volumes or applications to only the fruit zone minimized reductions in NAR and SSC. Chardonnay and Cabernet Sauvignon were treated twice with JMS Stylet-Oil(TM) (1.5%) using 5600 L/Ha or 1870 L/Ha applied to the whole canopy or 930 L/Ha applied only to the fruit zone. The NAR of 5600 L/Ha-treated Cabernet Sauvignon was significantly lower than the NAIR of 1870 L/Ha oil-treated vines on three of four subsequent measurement dates. The NAR of Chardonnay in either the 1870 or 5600 L/Ha whole canopy oil treatments was significantly lower than the NAR of the water treatment at all measurement dates. Oil application to only the fruit zone (930 L/Ha) reduced the negative impact on NAR. Cabernet Sauvignon fruit SSC was consistently reduced by the 5600 L/Ha and 1870 L/Ha treatments, relative to the water-treated control. Similarly, the SSC of Chardonnay fruit in the 1870 and 5600 L/Ha treatments was consistently reduced compared to controls. Oil effects on fruit pH and titratable acidity were occasionally observed. While horticultural oils may serve as effective fungicides, our results highlight the potential negative impacts they can have on fruit composition and fruitfulness if used excessively.