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.