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Crop Science Abstract -

Growth and Physiological Response of Alfalfa to Diazinon and Methoxychlor Insecticides1


This article in CS

  1. Vol. 16 No. 2, p. 190-192
    Received: June 3, 1975

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  1. D. D. Wolf,
  2. G. R. Buss and
  3. R. L. Pienkowski2



An effective insecticide must control insects with minimum adverse influence on the plant. During a cultivar performance study, a commercial insecticide containing diazinon [0,0-diethyl 0-(2 isopropyl-6-methyl-4-pynimidinyl) phosphorothiorate] and methoxychlor [l,l,l-trichloro- 2,2-bis= (p-methoxyphenyl)] was applied to alfalfa (Medicago sativa L.) as a control for alfalfa weevil (Hypera postica Gyllenhal). A phytotoxic response was noted and several experiments were conducted to elucidate the nature of the toxicity. Weevil control by the insecticide was satisfactory, but total nonstrnctural carbohydrate concentration (TNC) in tap roots decreased and growth rate of shoots was not increased when compared with check treatments during 2 weeks following insecticide application. Greenhouse studies indicated that the diazinon component was phytotoxic and caused a reduced growth rate for at least 5 days. Carbon dioxide exchange rate and TNC concentration in leaves were reduced by nearly 50% for several days following application of the insecticide. Hay yields were increased by control of the insects but yield increase might have been greater if a nonphytotoxic insecticide had been used. Diazinon should not be recommended for use on actively growing plants until it has been shown that the beneficial effects out weigh the risks of phytotoxicity.

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