In this study on the air-borne viruses in Lilium, mainly lily symptomless virus (LSV) and tulip breaking virus (TBV), various factors involved in the efficiency of control are dealt with. The incidence of LSV was reduced very substantially from the old 100␛ate. TBV occurs at fairly low rates. Lily virus X (LVX) and cucumber mosaic virus (CMV) occurred at low level in the last decade. The symptoms of TBV to induce the roguing of diseased plants became less important, if the ELISA-testing of bulbs before bulk propagation by the scaling of bulbs and by tissue culture procedures was effectively applied. The reduction in bulb yield and the relative reduced quality of cut flowers indicate the need for virus control. The virus spread as affected by the elimination of virus source plants strongly became dependent on the ELISA-testing. The speed of spread was generally experienced to be differentially rapid over the season, while a range of c. 25 aphid species were able to transmit LSV and TBV. The chemical control of spread is efficiently done by the routine spraying of mineral oil plus pyrethroid. Terpenoids were not effective. Some effect was observed from a pheromone, plant oil, and -pinene polymer emulsion. Deltamethrin and zetamethrin sprays were most effective. The non-chemical control by the polymer web coverage of crops proved impractical under field conditions. The factors in the chain of control which have a weak impact, e.g., delayed elimination of TBV-diseased plants in the field if the ELISA-bulb testing prior to planting is routinely unapplicable in varieties of L. longiflorium and Oriental hybrids, or strong impact, e.g., testing of bulbs by ELISA of a large part of the assortiment of cultivars, chemical control of virus spread, and rapid propagation procedures, on the efficiency to improve the health situation in the lily culture were indicated.
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