Handbook of invertebrate pest control in ornamental glasshouses

In the artificial environment we create, in a glasshouse, we are concerned with pest incidence from two points of view. One is the problem associated with pathogenic transfer; such as is often exhibited by the aphid in transferring various viruses from an infected plant to an otherwise healthy specimen. The consequent results may cause, in severe cases, loss of a valuable plant. Secondly, in the ornamental sense, we have the nuisance value. A plant, grown for its botanical interest, or simply its ornamental attributes, may be made unsightly by either the physical presence of a pest or, more commonly, the signs of damage left by that pest. Nature has created a balanced ecosystem; there is order. Man, in his desire to produce crops and modify the environment, tampers with and upsets this balance. Commonly through production of one or a number of similar crops, the pest species present are simplified to be those that "plague" that crop. This simplification will lead to instability and consequently often severe fluctuations in the pest species present. Under glasshouse conditions, where an ornamental crop is being produced, it is frugal to talk of economic threshold levels and the like. Undoubtedly, we are concerned with producing the best possible crop. We are concerned with visual aspect, "the ornamental value". For this reason chemicals may need to be used from time to time to check pests. Such use of chemicals if often justifiable. Concern should, however, be expressed at the apparent indiscriminant use of chemical therapeutants. All too often Parks Departments are found to apply chemicals regularly; so regularly, in fact, that some crops are being treated as often as twice a week. This is not necessary. Very often these departments are at fault in their basic husbandries. Of prime consideration is hygiene. This does not only mean sweeping the glasshouse floor, removing dead foliage and flowerheads, along with the annual spring clean. What this also includes is adequate soil sterilization, proper disposal of all infected and diseased plants, and total glasshouse hygiene. Many pests are introduced into the glasshouse as either eggs or young larvae, and often adults, in the soil. Effective means are available to provide for soil sterilization either as heat or chemical. Once in the glasshouse these pests may rapidly multiply. Emerging adults may seek refuge in litter, gravel or in foliage plants often grown beneath the benches. Furthermore, eggs, if not deposited in pots or on potted plants, may be laid on host plants growing beneath the benches. Thus, the problem may be complicated and recur later. Any plants noted as being badly infected should be disposed of. Often the case may arise where a valuable plant is infected with one or a number of pests. This plant should be treated with in the appropriate manner until such time as it is clear of any infection. With the means available today for sterilising soil, the knowledge of both plant and glasshouse hygiene, coupled with our awareness of chemical therapeutants, there should be no need to apply chemicals as often as has, in some instances, been the case.