ISHS Acta Horticulturae 533: VIII International Symposium on Timing Field Production in Vegetable Crops
STRATEGIES FOR CONTROLLING CARROT FLY WHILE MINIMIZING PESTICIDE INPUTS |
| Authors: | J. Davies, R. Collier |
| Keywords: | Psila rosae, pest management, chemical control |
| Abstract:
Carrot growers in the United Kingdom are looking for ways to reduce their reliance on organophosphorus insecticides for carrot fly control. Possible options include the use of pyrethroid insecticides, either as seed treatments or foliar sprays, cultural techniques such as the manipulation of sowing and harvesting dates to avoid carrot fly attack, and the use of film covers or fine mesh netting to exclude carrot flies from the crop. This paper describes recent work on possible components of a future strategy for carrot fly control, and on the appropriate times to target them. A tefluthrin seed treatment was evaluated for control of first generation carrot fly in a field experiment in 1996. It was compared with seed treated with chlorfenvinphos and untreated seed. The insecticide was applied to the treated seed at a rate of 5g ai/100,000 seeds and the seed was sown on four dates between 16 April and 16 May. At harvest on 22 July, the two earliest sowings suffered considerable damage, even when the seed had been treated with insecticide. The results suggest that tefluthrin seed treatment may not be sufficiently effective to control the first generation of carrot fly adequately, particularly if pest pressure is high. There were no statistically significant differences between the chlorfenvinphos and tefluthrin seed treatments. In another experiment in 1991, polypropylene film covers applied to carrots to exclude adult flies reduced carrot fly damage. Crop damage increased between the first harvest on 18 November 1991 and the second harvest on 20 January 1992. Delaying covering until just before, or part way through, the second generation of carrot fly gave poorer control than covering from sowing, the effects being most evident at the time of the second harvest. In a final experiment in 1995, polypropylene covers were applied to carrots at sowing and then removed at two-week intervals from mid-July onwards, to identify the most damaging period of attack by the second generation of carrot fly. Severe crop damage occurred when the covers were removed during July and early August, at the start of the second generation. In contrast, carrots exposed to attack beyond mid-September suffered little damage, even though high numbers of flies were captured on sticky traps. Growers are being encouraged to concentrate their insecticide programs during the first part of the second generation of carrot fly, since carrot flies are caught from late July to November. This study, and work done on sampling first instar carrot fly larvae at HRI Wellesbourne suggest that second and third generation flies emerging after the end of September do not cause significant damage, even on late-harvested crops. | |
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