AIR-BORNE FIELD SPREAD OF TULIP BREAKING VIRUS, LILY SYMPTOMLESS VIRUS AND LILY VIRUS X IN LILY AFFECTED BY SEASONAL INCIDENCE OF FLYING APHIDS AND CONTROL BY SPRAYS OF MINERAL OIL, VEGETABLE OIL, INSECTICIDE AND PHEROMONE IN THE NETHERLANDS

The mineral oil was highly effective under the conditions of moderate infection pressure (MIP) and moderately effective under high infection pressure (HIP). The vegetable oils were slightly effective under MIP and they were not under HJP. The pyrethroid deltamethrin was moderately effective under MIP, and it had hardly any effect under HIP. The pheromone was slightly effective under MIP, and its effect was comparable to that of the vegetable oils. It was not effective under HIP. It decreased the effect of the mineral oil if applied in a mixture. The pirimicarb insecticide was not effective as such under HIP, but it was in a mixture with mineral oil.

The incidence of flying aphids in May varied in relation to weather conditions. High numbers of aphids were caught in June and July and low numbers in August and September. The rates of virus infection obtained in consecutive seasonal periods were moderately high in May, high in June and July, and fairly low in August and September.

The weekly and fortnightly mineral-oil/pyrethroid sprays after the flowering of the lilies in early July were similarly effective. The efforts to increase the efficacy of the virus control in lily are discussed.

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