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Another well known salt used in viticulture is the copper sulfate pentahydrate, which has a blue color, and its natural form is called chalcanthite. It is one of most common antifungal when it is mixed with lime, particularly against downy mildew, and it is named Bordeaux mixture. It is one of the rare antifungal treatments, with sulphur, allowed in organic vineyards. However, its intensive use is known to 'pollute' soils and to render some cultures difficult after several years of vine growing, as other crops are not so tolerant to high Copper concentrations in soils.

It is a known food preservative, it can be associated with sodium or potassium, among others (Fig. 3.9). Karabulut et al. [47] showed that potassium sorbate when applied on 'Thompson Seedless' grapes after harvest, at concentrations around 1%, reduced the incidence of gray mold over storage. No data was found regarding pre-harvest sprays of sorbate salts to control various fungal or bacterial diseases on grapes, but there is some potential.

Sulphur remains a very efficient and simple alternative to synthetic fungicides against powdery mildew and a recent report confirmed this fact [48]. They compared the efficacy of several compounds, such as milk, whey, canola oils and potassium bicarbonate to sulphur, and the later was most often the best blocker of powdery mildew. Whey showed some potential, however, in field trials the acceptable yield (i.e. bunches with less than 5% powdery mildew infections) was lower than when treated with sulphur. The whey compounds are mainly lactose and lactoglobulin. Why these compounds or the whey pH might have an inhibitory effect on the fungus is not discussed in the article.

3.13 Combinations

These are always interesting as they can generate additive or synergistic effects. One example has been detailed above when combining ethanol with calcium chloride during field sprays gave a better control of gray mold at harvest, and after

3.11 Sorbic Acid

3.12 Sulphur storage [32]. Elsewhere such effect was seen with ethanol and potassium sorbate [47]. Belhadj et al. [49] have tested with success the combination of methyl jasmonate and sucrose to induce accumulation of polyphenolics in grape cell cultures.

Many combinations have been tested on different fruit, giving ideas for grape future treatments. For example, Spadaro et al. [50] have tested with some success combinations of hot water, backing soda and ethanol against Penicillium expansum and Botrytis cinerea over apple storage, but the potential may be extended to grapes and field trials. Wang et al. [51] showed that the combined treatment with methyl jasmonate and ethanol resulted in a greater control of green mold due to Penicillium citrinum and also improved antioxidant capacities of bayberries. These authors reported a clear synergistic effect of the combination of methyl jasmonate and ethanol leading to approximately 10% decay in bayberries when each treatment led to 40% decay and the controls showing 80% decay. Interestingly, the combined treatments led to a better sensory appreciation of the fruit by a sensory panel than for all other treatment.

There is an infinite number of combinations, (i) as the number of potential individual treatments is great, (ii) as the combination order may vary (e.g. treatment A before treatment B, or B before A), and (iii) as the number of repeated applications over the pre- and post-harvest periods (e.g. one treatment every week over the ripening period or one treatment every fortnight). Combinatorial optimisation has an obvious interest in such approaches.

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