Desk study to apply knowledge developed for conventional horticulture to the control of pests in organic vegetables (OF0179)

Summary in the original language of the document

This is the final report for Defra project OF0179.
The demand for organic vegetable and salad crops is likely to increase as a result of the projected requirements of the multiple retailers. The threat of yield and quality reductions due to pest damage is a major constraint to increasing the organic vegetable crop area. The aim of this project is to demonstrate how methods of pest control developed for conventional vegetable production can be adapted for use by organic growers. The project concentrates on the pest insects that cause damage to umbelliferous and cruciferous vegetable crops. Umbelliferous crops are attacked by one major pest insect, the carrot fly (Psila rosae), and two minor pests, whereas cruciferous crops are attacked by about eight major, and over 40 less important pests.
A strategy for reducing carrot fly damage in organically grown umbelliferous crops was produced. The strategy is based on the existing carrot fly forecast, on published data and on information collected previously at HRI. This includes the contribution that can be made by partial host plant resistance. Commercial breeding lines of carrots now have levels of partial resistance up to 75% and, if used in combination with late sowing, could reduce infestations by more than 90% when compared with a susceptible variety sown early.
The carrot fly forecast was adapted to predict 1) the proportion of the first generation of flies that will lay eggs on crops sown on different dates and 2) the timing of emergence of the subsequent (second) fly generation within the crop. Field experiments confirmed that late sowing is an effective method of reducing carrot fly damage. The model was modified to identify the times at which crops should be covered to reduce damage by carrot fly larvae. Previous experiments have shown that to avoid damage by carrot fly larvae, crop covers should be applied to susceptible crops before the start of fly emergence. Although third generation carrot flies may be active after the end of September, their progeny do not damage overwintering crops, so late control is unnecessary.
The strategy for reducing carrot fly damage in umbelliferous crops grown organically was evaluated in 2001. Participating growers grew plots of a partially resistant variety and applied/removed crop covers according to the carrot fly forecast. At harvest, the experimental plots, with one exception, suffered similar or less damage than the main area of crop, that had been grown according to standard practice.
A strategy for controlling the pest insects of organically-grown cruciferous crops was developed. This is based on existing forecasts for several crucifer pests. The pest forecasts were verified in a field experiment in 2000. The literature was reviewed to 1) identify crop/pest combinations where it would be advantageous to apply covers to exclude pests, 2) find simple ways of sampling crops to detect the presence of each species, and 3) indicate the best time to apply the control measures available to organic growers. Crop covers can be used to exclude many crucifer pests. However, if aphids are able to penetrate the covers then infestations may be greater than if the crop was left uncovered.
The crucifer pest control strategy was evaluated in 2001 in the organic areas at HRI Kirton and HRI Wellesbourne using forecasts for several pests and pheromone traps to monitor diamond-back moths. Plants were inspected for aphids and caterpillars. Treatments (crop covers or garlic for cabbage root fly, soft soap for aphids, Bacillus thuringiensis for caterpillars) were applied as necessary. In general, pest damage was not severe and where a large percentage of the crop was unmarketable, this was due to non-pest damage.
A workshop on carrot fly control was held at HDRA, Ryton in January 2002. As a result of this project, and the conclusions drawn from this workshop, two factsheets (carrot fly and crucifer pest control in organic crops) have been produced for publication by the HDC. Other sources of information, such as the HDC/HRI pest forecasts, will be publicised through the HDRA pest and disease e-mail group.
There is a more detailed summary at the start of the attached report document.