Horticulture Pests & Diseases
A pest is any organism that reduces the availability, quality or value of a human resource including our crop plants. Flint,M. L and Vanden Bosh, R 1981. Four pests have been researched, although Flint and Van den Bosh describe any detrimental organism as a pest, in this report we will treat pests as those which breathe and move. Under the sub heading Pests I have chosen to look at Greenhouse White Fly and Woolly Aphid. In this report horticultural diseases are those which are less animate and more closely reminiscent of viruses and growths. Under the sub-heading of Diseases I have chosen to research Botrytis and Apple Scab.
PestsGlasshouse white fly (Trialeurodes vaporariorum)
The Glasshouse white fly commonly known as the greenhouse whitefly is a primary pest of many fruit, vegetable and ornamental crops, frequently found in glasshouses and other protected horticultural environments. White flies are sap-feeding insects, about 2mm in length when fully grown, with four wings coated in wax, they live on the undersides of leaves. When disturbed they fly up in a small cloud if the plants are heavily infested. Infestations will cause plants not to flourish, reducing vigour and yields, in the case of a tomatoes crop for instance a loss of 25% in yield could be experienced without intervention. (The Canadian Journal of Plant Pathology). White flies usually lay around 200 eggs at a time, on the undersides of leaves and when these hatch the small scale-like nymphs excrete a sticky “honeydew”, as they feed which falls onto the leaves below forming a black sticky substance a little like sticky soot. If conditions are right they will breed continually all year round. Development from egg to adult takes around three weeks at 70 degrees or four weeks at 60 degrees. Buczacki, Harris 1998. These pests need warmth and as such are rarely a problem outdoors; they are a particular problem to house plants and indoor glasshouse growers. To control Glasshouse whitefly ensure that areas are kept clean and clear, this also applies to outdoors around the glasshouse in summer. White fly can use weed foliage in summer outdoors to continue their reproductive cycle. Common methods of physical control in the glass house are the use of simple yellow sticky paper traps hung just above the plants to catch the adults. Biological control can be achieved through the use of a tiny wasp parasite called Encarisa Formosa, however they need warm conditions and time to build up numbers. Insecticidal soaps are also used to control whitefly numbers without affecting the Encarsia formosa. Other pesticides permethrin, bifenthrin, primiphos-methyl and pyrethrum are all dangerous both to human and beneficial parasitic wasps. These should only be used in cases where numbers of white fly have become uncontrollable. Applications should be made at five day intervals. Greenwood P and Halstead A (1997)
Woolly Aphid (Eriosoma lanigerum)
This aphid attacks a number of woody plants including ornamental Malus, Pyracantha and is a significant pest to apple growers and orchard owners in the UK. Woolly aphids are insects that unlike most other aphids suck sap from woody stems rather than the foliage. Blackish brown in colour, they cause galling of the wood, not normally be very damaging to more mature trees but is a serious problem on young saplings. They are particularly fond of attacking the thinner bark areas on trees. This means that numbers thrive in new orchards but they also find the thin bark around freshly pruned branches an easy entry point making them just as big a problem in old long established orchards. Affected shoots often develop soft, lumpy growths in the bark as a result of woolly aphid feeding. Such shoots are easily spotted during winter pruning. Sheltering from winter in the cracks of bark low on the trunk the young become active in March and April. They begin to secrete a waxy wool material hence their...
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