CANCELED - Management Strategies for Potential Herbicide-Resistant Weeds in Cotton in the San Joaquin Valley California- CANCELED

Abstract

Glyphosate-resistant (GR) weeds are changing the Roundup Ready (RR) cotton (Gossypium hirsutum L.) production system throughout the US cotton belt. This phenomenon has compelled cotton producers in the San Joaquin Valley (SJV) of California to search for options before the onset of this problem. One such option could be the combined use of pre-emergence (PRE) residual and postemergent (POST) herbicides. We hypothesized that PRE herbicide applications may reduce the density of weeds at initial application of glyphosate in RR cotton production systems. Further, this may also be an effective weed seedbank management strategy. Therefore, the objectives of this study was to compare the efficacy of some POST and PRE herbicides applied at 15 and 35 days prior to planting cotton (DPP) on weed control, and to assess their deleterious effects on the crop.

Once the crop established, crop injury and stand loss evaluations were taken in May and June. Monthly weed density evaluations were taken from May to September. In both years, the PRE treatments did not cause crop injury or stand loss. Final plant mapping was taken before defoliation. In both years, the crop was harvested in October. It is not determined if the PRE treatments incorporated did an excellent job of controlling weeds or weed pressure was just low. The data for both years showed that weed pressure was nonexistence. None of the treatments affected (P>0.05) weed densities, stand loss, crop injury, and final plant mapping. Although, the treatments applied at 35 DPP had no effect on lint yield, differences occurred between the treatments for lint yield when they were applied at 15 DPP.