Assessment of disease and effects on yield - Australasian Plant ...

328 John Brotun <strong>and</strong> Philio Keane
20.5 Plant <strong>disease</strong> surveys
Another statistical approach to assessment <strong>of</strong> crop loss involves the use <strong>of</strong>
questionnaires to assess <strong>disease</strong> (<strong>and</strong> pest) incidence or severity. Results <strong>of</strong>
farmers' assessments <strong>of</strong> <strong>disease</strong> can be related to the yields eventually obtained.
Appraisals <strong>of</strong> <strong>disease</strong> <strong>and</strong> yield-loss are <strong>of</strong>ten <strong>of</strong> limited value because <strong>of</strong> the
difficulty <strong>of</strong> obtaining information concerning the prevalence <strong>and</strong> severity <strong>of</strong>
<strong>disease</strong>s over large areas. For this reason there is a special need for an
increased use <strong>of</strong> plant <strong>disease</strong> surveys. The information obtained from plant
<strong>disease</strong> surveys enables the relative importance <strong>of</strong> different <strong>disease</strong>s to be
determined, which in turn enables rational allocation <strong>of</strong> resources for research
as well as control <strong>and</strong> eradication programs.
Disease surveys are also necessary to establish: (i) the geographic distribution
<strong>of</strong> pests, pathogens <strong>and</strong> their various pathotypes, (ii) the rate <strong>of</strong> spread <strong>of</strong> newly
introduced pests <strong>and</strong> pathogens,
<strong>and</strong> pests <strong>and</strong> (M
(iii) the presence <strong>of</strong> other hosts <strong>of</strong> pathogens
'breakdowns'in
<strong>disease</strong> resistance used in crop plants.
20.6 Fufther reading
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Phgtopathologg 54, 1 305- r 3 I 9.
Beaumont, A. (1954). Tomato leaf mould: spraying trials in Lancashire <strong>and</strong> Yorkshire,
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British Mycological Society (1948). The measurement <strong>of</strong> potato blight. Transactions oJ the
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(1976). A netu model to measure gield Losses cantsed bg stem rust in spring tuheat.
Technical Bulletin 307, Agricultural Experimental Station, University <strong>of</strong> Minnesota.
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Close, R.C., Gaunt, R.E., Harvey, I.C., McCully, A.J., S<strong>and</strong>erson, F.R. <strong>and</strong> Teng, P.S. (1977).
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Gollifer, D.J. <strong>and</strong> Brown, J.F. (1974). Phytophthora leaf blight <strong>of</strong> Colocasiaesculentain the
British Solomon Isl<strong>and</strong>s. Papua Neu; Guinea Agrtcultural Journal2s, 6-f l.
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root rot <strong>of</strong> subterranean clover caused by Fi.rsanum aDenaceum <strong>and</strong> Pgtlium spp. Soil
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James, C. (1971). Amotnual oJassessmentkegsJor plant<strong>disease</strong>s. Canada Department <strong>of</strong>
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James, W.C. (f 974). <strong>Assessment</strong> <strong>of</strong> plant <strong>disease</strong>s <strong>and</strong> losses. Annual Reuieu-t <strong>of</strong>
Phgtopathotogg L2, 27 48.