University of Tasmania
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Mechanism of selectivity of diquat solutions in poppy. (Papaver somniferum L.)

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posted on 2023-05-26, 02:20 authored by Barnes, CD
The current mechanisms of herbicide selectivity in poppy (Papaver somniferum L.) were examined in glasshouse and field experiments. Through measurements of contact angles of diquat solutions it was established that poppy, and the weeds fumitory, fat hen and field poppy are 'hard' to wet, whilst shepherds purse, wild radish, spear thistle and curled dock are relatively 'easy' to wet. It was revealed that diclofop-methyl has properties characteristic of a weak surfactant, compared with Agral¬¨vÜ, a finding supported through measurements of dynamic surface tension. The structure of the surface wax on the adaxial surface of poppy, field poppy, fumitory and fat hen leaves are described as seen under the scanning electron microscope. Chemical analysis of these waxes are also given. It appears the wax of fumitory and fat hen are influenced by application of ethofumesate. Chemical analysis shows that ethofumesate can inhibit the deposition of primary alcohols, long chain aldehydes and alkanes on the developing leaves of fumitory and fat hen, making these plants more susceptible than poppy plants to future applications of diquat + diclofop-methyl. Field trials conducted on the east and north-west of Tasmania, highlighted the difficulties that exist in extrapolating results from glasshouse experiments to field conditions. Measurements of spray retention and efficacy, revealed that plant responses to applications of diquat treatments were influenced, in addition to ethofumesate, by environmental conditions. Plant responses at both sites demonstrated that the inert ingredients of the commercial formulation of diclofop-methyl, would, in admixture with diquat produce the same result compared with the current diquat/diclofop-methyl treatment

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