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History of pear psylla resistance in Pacific Northwest to chemicals
used for its control from 1945 to 1990. Bars represent the period of
time from which the individual chemical was first used for pear psylla
control until its use was discontinued because of development of resistance
to the chemical by the psylla or because the material was withdrawn by the
manufacturer (chlordimeform, 1978).
Modified from Van de Baan, H. E. 1988.
Factors influencing pesticide resistance in
Psylla pyricola Foerster,
and susceptibility in its mirid predator,
Deraeocoris bretis Knight. Ph.D.
thesis, Oregon State Univ., Corvallis, 127 pp.)
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