and Integrated Pest Management - part - usaid

166 I'I:S'1CIDFMANAGIFMI'NT AND IPM INSOUIViEASI' ASIA
Table 6. Conventional critical levels for major cotton pests in the Philippincs. a
Pest Days after
phuming
Sampling
unil b
Critical level
lollworm 28-56 terminal less than 17 out of 20
larvae uninfested
56-112 terminal less than 18 out of 20
uninfested
56-126 2nd branch less than 18 out of 20
uninfested
Lealhopper 28-112 3rd leaf less than 10 out of 20
uninfested and undamaged
"Critical levels for minor pests are provided on the field technician's sampling
cards. Sampling is optional. 'Terninal: top 20 cmn of plant main stern, 2nd
rmnch: the secor; aranch below the plant terminal, 3rd leaf: Third leaf below
)lant lip.
Table 7. ('oiparison of treatment decisions using peg.-board and technician's
sampling cards in the same colton fields."
Decision not to spray Dec ision to spray
Peg-board 13.1% 86.9%
Sampling card 19.2% 80.8%
"bascd on 99 independent samples each.
populations (termed farmers' friends) in pest management decisions. Table 7
shows how the two sampling nethods compare with regards to spray decisions.
Oi the assumption that the sanplcd fields really needed treatment (more
than 80% d(cidCd so inl both techniques), the decisions not to spray were
obviously erroneous. However, both systems were originally based on
sequential sampling plans designed to tolerate an error of 20% in order to reduce
the number of samples needed (Sterling 1976b). In any case, the basic critical
levels have been determined conservatively, i.e. to result in a treatment decision
earlier than a truly "economic" threshold level would prescribe. This means that
the apparently erroneous decisions not to spray in Table 7,even if implemented,
would not lead to an economic loss. Farmers and technicians alike are extremely
sensitive to such crrors. It was found to be considerably easier to allow a few
more spray decisions to inspire confidence in the system, and then gradually
acquaint the users with the principles of integrated pcst management.