Blackcurrant gall mites in Latvia: resistance of cultivars and efficacy of acaricides

Gall mites (Cecidophyopsis spp.) are one of the most important pests in blackcurrants. The growing of resistant cultivars together with proper application of acaricides can limit the blackcurrant gall mite spreading and associated damage. The screening of cultivars for resistance to blackcurrant gall mites was done in collection plantings of the Pure Horticultural Research Centre (Pure HRC) and Latvia State Institute of Fruit-Growing. Plants were observed in spring at the beginning of vegetation. The evaluation was done visually by estimating the amount of damaged buds. It was noticed that the damage severity increased with the age of planting. Cultivars 'Black Dawn', 'Bogatyr', 'Chernecha', 'Gracia', 'Kipiana', 'Krivia', 'Orlovia', 'Partizanka', 'Seyanets Golubki', 'Shirayevskaya', 'Vakariai', and 'Yadrenaya' showed the best resistance to gall mites. Trials on efficacy of acaricides were carried out in 2009 and 2010 in blackcurrant plantations in southern Latvia - 56°25’36.48 N, 23°43’24.63 E. Mainly the blackcurrant cultivar 'Öjebyn' was observed. Acaricides Kumulus DF (a.i. sulphur 80%) in dosages 4.8 and 6.0 kg ha-1 and Tiovit 80 WG (a.i. sulphur 80%) in dosage 1.0 kg ha-1 were tested for control of blackcurrant gall mites. The acaricides were applied twice in the autumn of 2009 (24.08.: BBCH 91- terminal bud developed and 23.09.: BBCH 92 - leaves begin to discolour); three times in the spring of 2010 (12.04.: BBCH 51 - 53 (buds closed), 27.04.: BBCH 53 - 55 (bud burst) and 11.05.: BBCH 54 - 56 (first flower buds visible beside unfolded leaves)); and twice in the autumn of 2010 (09.08.: BBCH 91 and 20.08.: BBCH 92). The research results show that both tested products, Kumulus DF in dosage 6.0 kg ha-1 and Tiovit 80 WG in dosage 1.0 kg ha-1, can limit blackcurrant gall mite populations.