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 o 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 name. This substance may contaminate both foliage and fruit and is a nuisance at harvest time late August.
The substance provides predator protection whilst the aphids, in small colonies, feed on young leaf buds and shoots. Infestations are spread mainly by crawling from tree to tree, or can be blown from one tree to another in the right conditions. Alford D 2000, mentions the presence of some winged forms appearing in July but these are generally uncommon, several hatchings of flightless aphids take place during the summer. Immature aphids seek shelter lower down in cracks of bark or near the ground in the shelter of the roots and other foliage.
In the autumn and become dormant till the following spring, the old seasons adults die out as winter approaches. Control measures for Woolly Aphid; include physical treatments on fruit trees of a tar oil wash that can be used in early to mid-winter when the plants are dormant. In summer Malathion can be used against the young nymphs. Greenwood P, Halstead A (1997). Another more environmentally friendly approach is to wrap grease bands around affected trees trapping the grubs as they descend the trees looking for places to hibernate close to the tree base or on the ground in autumn, these bands can then be removed in November and burned.
In southern England a Biological control was introduced in the 1920’s in the form of a small parasitic wasp, Aphelinus. If these are present in the woolly aphid colonies then the use of pesticides should be carefully limited as not to affect damage the wasp populations. Buczacki, Harris1998. Though there is little empirical information to quantify the damage done by Woolly Aphids, there is a threat to the overall health and vitality of fruit trees, especially young trees. The damage Woolly Aphids cause goes on to cause cankers and resulting poor crops.
Ultimately affected trees would need to be replaced or at least the damaged branches pruned out causing lost production. DiseasesBotrytisDiseases are caused by various infectious means, fungi, bacteria or sub-microscopic organisms, commonly called ‘virus-like’ organisms. These organisms causing disease are known as pathogens. There are over 100,000 species of fungi they differ from plants as a group as they retrieve nutrients by digesting extracellularly. By secreting enzymes into material they then reabsorb and digest the mixture.
Most fungi are able to produce sexual and asexual spores, thus they are readily able to multiply quickly given the right conditions. Pathogens develop in different ways, some only cause a mild located problems, for instance simple spots on leaves. Whilst others totally smother and rot the plant material, ultimately destroying the whole plant, its fruits and seeds. Botrytinia, more often referred to as botrytis, is one such potentially devastating grey mould fungi. It is a particular problem to soft fruit growers and vineyards worldwide.
The spores of botrytis are constantly present in the air, the fungus forms black, seed-like resting structures (sclerotia) in dead plant tissue which can carry the fungus through periods when host living plants are scarce. Botrytis spores were seen to survive 30 weeks in the pruning of vines in Hawkes Bay New Zealand (Philip. A etal 2007) Under the right conditions spores drifting from the host dead material will attack living plants. The right conditions may include for instance when the plant is damaged spores are then able to enter the wound, or in in damp humid conditions spores will attack the fruits and or flowers of plants.
Sometimes the spores enter the plant flowers lying dormant until fruits are formed and begin to ripen. As the sugar levels rise during ripening the fungi is able to thrive and rapidly form grey mould on the fruits surface. Glass houses and polytunnels offer botrytis the warm humid conditions that help the fungi thrive, it is therefore important to make sure there is always adequate ventilation in covered growing environments to limit the spread. There are a number of types of botrytis; the most common being botrytis cinerea.
Like all botrytis it enjoys damp humid conditions, it not only infects soft fruit which easily rot, the spores will enter the cracks in woody barks on the stems of raspberries and gooseberries causing die-back. Left untreated the plants will need to be completely removed and burnt. Some other types of commonly found botrytus include B. elliptica, this affects Lilly bulbs if kept in damp conditions. B paeoniae particularly affects Peonies, infecting the joints of lower leaves where they join the stems, turning them brown and mould appears at ground level. B. allii, is a common problem affecting stored onions throughout Europe.
Seen after about 10 to 12 weeks in store, bulbs soften and brown patches appear. Preventative dust treatment for this form can be made to onion ‘sets’ prior to planting. B. fabae common on broad beans, chocolate brown spots appear on the leaves mainly on up facing surfaces. Results usually in brown patches turning black and bean pods become infected at which point grey mould appears on the pod. To control botrytis in temperate climates, the cold of a winter will help prevent this life-cycle process, and greatly reduces the multiplication of the botrytus fungi.
However, most species produce toughened ‘overwintering spores’ as climates cool and it is the prevention of the development of these combine with the frost of a winter that will give a higher degree of success in controlling fungal outbreaks in forthcoming seasons. In considering the use of antibacterial chemicals to combat fungi, it should be remembered that the repeated use of such chemicals may lead to the development of mutated and stronger bacterial types which may then cause problems for humans and other life forms.
The economic impact of botrytis cinerea is huge; for example, damage to grapes in vineyards in France amounts to 15-40% of harvests depending on climatic conditions. Worldwide the damage estimated in vineyards accounts for 20% of harvests, and their cost is estimated at 10-100 billion Euros per year. Estimated losses for other crop losses are believed to be in the region of 20-25% of the strawberry crops in Spain, and 20% of cut flowers in Holland. www. Genescope. cns. fr Apple Scab (Venturia inaequalis)
Blackish Brown scabby patches develop on fruits and similar greenish brown spots develop on leaves. Fruit may become covered with scabby patches and may crack or split, these splits and cracks then become infected with a secondary problems such as brown rot. Trees affected usually lose their leaves early. The cause in both cases is a closely related is a fungus, this overwinters on young stems and also on the fallen effected leaves and any fruit left on the orchard floor. The lack of pruning resulting in overcrowded branches in damp seasons is thought to encourage this disease.
Controls for Apple Scab; simple controls suggested by Buczacki & Harriss1998, would be to improve hygiene, “to rake up leaves where possible and burn, this breaks the overwintering cycle of the fungus lying dormant on infected leaves”. Prune out trees regularly, especially where they are overcrowded. Pay particular attention to the removal of scabby and swollen shoots. Greenwood P and Halstead A 1997. There are commercially available anti fungal sprays which may combat scab, Sovran (kresoxim-methyl) from the BASF Company and Flint (trifloxystrobin) from the Novartis Company. Though all these measure may have limited effect as with botrytis, fungal apple scab spores are carried in the wind and in orchard situations they can carry from tree to tree. (RHS Apple Scab)
Adams C. Bamford K & Early M. 2012 Principles of Horticulture. Oxon UK: Routledge Alford D 2000, Pest and Disease Management Handbook. Blackwell Science Ltd. Oxford Baily,A. Chandler, D. Grant, W. Greaves J. Prince G. Tatchell M. 2010 Biopesticides Pest management and Regulation, Oxford: CAB International Botrytis Reaserch Website – www. Genescope. cns. r http://www. genoscope. cns. fr/spip/Botrytis-cinerea-estimated-losses. html [accessed 18 October 2012] Buczacki, S. Harris, K. 1998. Pests Diseases & Disorders of Garden Plants, London: Harper Collins Canadian Phytopathological Society http://phytopath. ca/journallinks. shtml [accessed 27 November] Flint,M. L and Vanden Bosh, R 1981. Introduction to Integrated Pest Management, New York: Plenum Press Greenwood P and Halstead A 1997. The royal Horticultural Society. “Pests and Diseases”. The Complete guide to preventing, Identifying & Treating Plant Problems.
Dorling Kindersley London Philip A. G. Elmer Themis J. Michailides 2007 Epidemiology of Botrytis cinerea in Orchard and Vine Crops Netherlands: Springer Netherlands http://apps. rhs. org. uk/advicesearch/Profile. aspx? pid=165 [accessed 25 September 2012] RHS Apple Scab http://apps. rhs. org. uk/advicesearch/profile. aspx? pid=81 [accessed 25 September 2012] http://apps. rhs. org. uk/advicesearch/profile. aspx? pid=193 [accessed 25 September 2012] RHS Wooly Aphid http://apps. rhs. org. uk/advicesearch/Profile. aspx? pid=724 [accessed 25 September 2012]
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