Guignardia bidwellii (black rot)

Control of grape black rot is frequently necessary to prevent crop losses of susceptible species of Vitis and cultivars grown in areas where the weather conditions are favourable to the pathogen. Black rot is not difficult to control if the cultural and chemical practices outlined are followed.

Species of Vitis and cultivars within species differ in their susceptibility to black rot. Some species of Vitis, in increasing order of resistance to black rot, are as follows: V. vinifera (very susceptible), V. arizonica, V. californica, V. labrusca, V. rubra, V. monticola, V. coriacea, V. aestivalis, V. rupestris (St. George), V. cinerea, V. berlandieri, V. cordifolia, V. riparia and V. candicans (very resistant) (McGrew, 1976).Resistant cultivars such as Mars (Moore, 1985), Suwannee and Conquistador (Mortensen, 1983), Venus (Moore and Brown, 1977), Saturn (Moore et al., 1989) and Sunbelt (Moore et al., 1993), are recommended for fresh fruit and wine production in the USA. A survey of 12 cultivars grown in the Friuli region of north-eastern Italy showed that only Cabernet Sauvignon was resistant (Rui et al., 1987).In the grapevine cv. Blue Lake, resistance could be controlled by two heterozygous genes (Mortensen, 1977).

Cultural practices that open the canopy are beneficial because they increase air circulation and improve spray coverage. Good weed control beneath the vines also enables plants to dry more quickly during wet weather.It is very important to remove overwintering mummified berries attached to the vine and to destroy them. Where feasible, cultivate the vineyard before bud-break to bury the mummified berries.Prune the vines each year during the dormant period and select only a few strong, healthy canes. If only a few leaf lesions appear in the spring, remove these infected leaves.

A fungicide spray programme to control black rot is largely practised in many vine cultivation areas, mainly in a number of European countries (France and Italy, for example) and the USA.Preventive applications should begin at bud burst or when shoots are 10-16 cm long and continue until the berries contain about 5% sugar. Sodium bicarbonate was tested in Russia and reduced black rot infection by 5-7 times (Chernyak, 1978). Sodium ethylphosphite also gave good control of a severe attack of black rot (Chazalet et al., 1977).Mancozeb, captan, dichlofluanid, folpet, maneb, propineb and zineb could be used as protective fungicides (Barbe, 1984). The efficiency of copper is not clear (Slack and Brown, 1974; Boubals, 1984).Some translaminar or systemic fugicides such as triadimefon (Spotts, 1978; Pearson and Goheen, 1988), fenarimol (Spotts, 1977a; Roussel et al., 1981), myclobutanil (Orpin et al., 1986), hexaconazole (Heaney et al., 1986) and difenoconazole (Bolay et al., 1994) applied after infection, showed good curative activity against G. bidwellii. A new strobilurine fungicide, azoxystrobine, showed excellent preventive and curative properties against black-rot in France (Bugaret et al, 1998) and also in Italy (Politi, 1998). Benomyl has also been used in the past (Hopkins, 1974; Slack and Brown, 1974).

A microprocessor programmed to predict grape black rot infection was evaluated in the USA in the field. It effectively determined infection periods and was used to time curative fungicide applications (Spotts, 1977; Ellis et al., 1986). In France, a forecasting model has been described (Acta, 1991).In several countries, integrated protection of grapevine is used and G. bidwellii has been included in this new approach in Italy (Grande, 1986), Switzerland (Viret, 1996) and Australia (Gadoury and Seem, 1991).