Controlled environment experiments showed that velvetleaf plants grown under drought stress or low temperature (LT) treatments had greater leaf epicuticular wax (ECW) deposition compared to plants grown in soil with moisture at field capacity (FC) or a high temperature (HT) regime. Light intensity did not affect ECW deposition; however, increasing light intensity decreased the leaf ECW ester content and increased the secondary alcohol content. Plants grown at an LT regime or under FC had leaf ECW with fewer hydrocarbons and more esters than those grown at an HT or drought stress regime. Velvetleaf absorption of acifluorfen increased as light intensity decreased for plants grown in adequate soil water content, while the opposite was true for drought-stressed plants. Velvetleaf absorption of acifluorfen was approximately 3 and 10 times greater, respectively, with the addition of 28% urea ammonium nitrate (UAN) in comparison to crop oil concentrate (COC) or no adjuvant, regardless of the environmental treatments. Plants absorbed more acifluorfen when subjected to the LT regime in comparison to the HT regime when UAN was the adjuvant, while the opposite was true when COC was the adjuvant. Velvetleaf absorption of acifluorfen was not affected by drought stress when COC or no adjuvant was used and varied between studies when UAN was used. Velvetleaf absorption of bentazon was greatest for plants grown under HT/FC or high light/FC treatments and least with plants grown under HT/drought stress or low light/drought stress treatments, regardless of the adjuvant. However, bentazon absorption was higher with the addition of an adjuvant and for plants grown at a high light intensity or FC condition compared with medium to low light intensity or drought stress treatments.

Controlled-environment experiments were conducted to determine giant foxtail epicuticular wax (ECW) deposition and fluazifop-P absorption under different environmental conditions and with two adjuvants. Drought stress and low temperature increased leaf ECW content, whereas low light intensity decreased ECW content compared with medium light intensity. Drought stress conditions decreased the fatty acid and primary alcohol content of ECW and increased the hydrocarbon content compared with field capacity. Compositional changes would make the ECW more hydrophobic and reduce leaf wetting by herbicide spray. Increasing air temperature decreased the aldehyde content of ECW, whereas decreasing light intensity increased ECW fatty acid and aldehyde content while decreasing primary alcohols and esters. Compositional changes under low light intensity would make the ECW more hydrophilic and increase leaf wetting by a herbicide spray. Drought stress reduced fluazifop-P absorption regardless of the temperature but could not further reduce fluazifop-P absorption under low light intensity. Fluazifop-P absorption by plants under low light and drought stress conditions was similar to plants under low or medium light intensity and field capacity conditions. Similarly, the rate of fluazifop-P absorption was less under drought stress and low light conditions. Fluazifop-P absorption was greater when crop oil concentrate was added compared with 28% urea ammonium nitrate or no additive. Crop oil concentrate, added to the herbicide solution, overcame reduced fluazifop-P absorption under the low light conditions and in one of the two drought stress regimes but could not overcome reduced fluazifop-P absorption with the high temperature regime.