Efficacy of spirotetramat for control of blackcurrant leaf midge Dasineura tetensi (Rübs.), its effects on phytoseiid predatory mites and residues in fruits

Abstract

The blackcurrant leaf midge Dasineura tetensi is an important pest in young blackcurrant plantations as well as nurseries. Its larvae cause curling and twisting of young leaves into a distinctive leaf galls, older galls becoming necrotic. In established crops, infestation with larvae reduces bush vigour, killing out terminals and causing a proliferation of side shoots from lateral buds. In mother plantations, D. tetensi attack may cause up to 60% reduction in the growth of shoots, and in the nurseries the infested plants are weakened and do not grow to a suitable size. The objective of the work reported here was to evaluate the efficacy of spirotetramat for control of D. tetensi, its effects, on phytoseiid predatory mite populations and residues in blackcurrant fruits. Between 2012 and 2014 four field experiments were conducted in commercial blackcurrant plantations comparing three programs of spirotetramat with two reference active ingredients, thiacloprid and lambda cyhalothrin, and untreated controls. All of the products were applied once or twice against the 1st or the 1st and 2nd generations of the pest. Furthermore, the effects of the programs on phytoseiid predatory mites and the residues of spirotetramat in blackcurrant fruits were checked. The spirotetramat treatment applied once against the 1st pest generation gave 90.3-100% control of larvae of that generation, which then resulted in a 79.5-100% reduction in the 2nd generation larvae. Two treatments of spirotetramat used at the dosages 0.45 and 0.75 L ha-1 reduced larvae of D. tetensi by 87.1-100% and 96.8-100%, respectively, and its effectiveness was similar to that obtained with lambda cyhalothrin (88.0-100%) and higher than the thiacloprid treatment (34.4-85.2%). One application of spirotetramat resulted in a 24.2-35.0% reduction in phytoseiid mites approximately three weeks after treatment. Two applications of this active substance at the dosages 0.45 and 0.75 L ha-1 reduced the number of phytoseiids by 33.3-66.7% and 57.6-77.4%, respectively. Thiacloprid or lambda cyhalothrin were less selective than spirotetramat and reduced the population of phytoseiid mites by 82.8-95.0% and 77.4-97.0%, respectively, one week after each treatment. Spirotetramat gave residues well below maximum residue levels (MRLs).