ENVIRONMENT AFFECTS COTTON AND VELVETLEAF RESPONSE TO PYRITHIOBAC

Growth chamber experiments evaluated the influence of ambient temperat ure and soil moisture on cotton and velvetleaf response to pyrithiobac . Additional studies determined the basis for observed plant responses to C-14 pyrithiobac. Cotton injury from six times the normal dosage w as < 20% at 2 wk for all temperatures and soil moistures. Pyrithiobac injured velvetleaf less at lower soil moistures. Both species absorbed more C-14-pyrithiobac at 30/28 or 35/33 C than at 25/23 C. Cotton abs orbed more herbicide than velvetleaf at all temperatures and soil mois tures, Velvetleaf translocated < 16% of absorbed C-14 out Of the treat ed leaf while cotton translocated < 3% of absorbed material. At warmer temperatures, velvetleaf translocated less C-14 when soil was dry (-1 .0 MPa) than when plants were watered to field capacity (-0.03 MPa). T his decreased absorption and translocation may affect pyrithiobac acti vity on velvetleaf growing in dry soil. Translocation differences did not fully explain whole plant effects. The metabolism difference may a ccount for cotton tolerance.