Norflurazon for Weed Control in Arizona Cotton

W.B. McCloskey and L.J. Russo


Norflurazon has long been registered for use in cotton in the Southeastern U.S. but prior to the 1993 season was not registered in Arizona. Arizona cotton production areas are characterized by coarse textured soils containing less than 1 percent organic matter that have low adsorptive capacity. Pre-plant incorporated norflurazon applications at rates required for adequate purple nutsedge (Cyperus rotundus) control in these soils causes cotton injury and stand loss because norflurazon is readily available for uptake by cotton seedlings. During the 1992 and 1993 cotton season, field experiments were conducted in Arizona to evaluate the efficacy and crop safety of split applications of norflurazon where pre-plant incorporated applications were followed by post-emergence incorporated applications. In general, the experiments included a control (no herbicide application) and 0.5, 0.75, 1.0 and 1.25 lb active ingredient (a.i.)/A of norflurazon applied pre-plant incorporated followed by a postemergence application at 1.5, 1.25, 1.0 and 0.75 lb a.i./A, respectively, to yield a total application rate of 2 lb a.i./A. The post-emergence applications of norflurazon were made when the cotton was 3 to 4" tall. The spray solution was directed in the area between crop rows and was followed by incorporation with a rolling cultivator or knives and sweeps. Irrigations following the post-emergence norflurazon applications resulted in further incorporation and movement of norflurazon into the crop row. During the 1992 season, it was observed that pre-plant incorporated combinations of norflurazon and prometryn provided good control of annual morningglory (Ipomoea species). Thus, experiments similar to the nutsedge experiments described above were conducted in 1993 to investigate the use of pre-plant incorporated (PPI) applications of norflurazon for morningglory control.

The PPI applications of norflurazon at 0.5, 0.75, 1.0 and 1.25 lb a.i./A resulted in 29, 49, 58 and 76% control of purple nutsedge for about six weeks after which the degree of control declined. Rates 1.5 to 2 times the labelled rate for a particular soil type caused cotton injury in several experiments in the 1993 cotton season although no injury was observe in the 1992 season. Data collected 71 and 21 days after the PPI and post-emergence (POST) applications, respectively, showed that the 0.25+1.75, 0.5+1.5, 0.75+1.25 and 1+1 (PPI+POST) lb a.i./A treatments resulted in 85, 85, 76, and 73% control of purple nutsedge, respectively. Nutsedge control declined throughout the season with the 0.5+1.5, 0.75+1.25, and 1.0+1.0 lb a.i./A split applications all resulting in about 27% control 3 month after the POST applications (4 months after the PPI applications). Since late season nutsedge control is relatively poor, several years of norflurazon use combined with other herbicides with activity on nutsedges and with a competitive cotton crop would probably be required to lower nutsedge population densities. No norflurazon injury was apparent after the post-emergence applications except in one study conducted on a sand where 1.5 lb a.i./A applied POST caused some injury and yield loss. Every row furrow irrigation within a week or two of post-emergence norflurazon applications enhanced purple nutsedge control in the crop row. Nutsedge control was relatively poor in the experiments where irrigation was delayed for several weeks after the post-emergence norflurazon applications and in fields where fewer irrigations were used to produce the cotton crop.

Tank mixes of norflurazon with prometryn (0.5 + 1.0 lb a.i./A) or with prometryn and trifluralin (0.5 + 1.0 + 0.5 lb a.i./A) provided 95 to 98% morningglory control 30 days after treatment (DAT). In contrast norflurazon alone at 0.5, 0.75 and 1.0 lb a.i./A resulted in 41, 60 and 76% control 30 DAT. The percent of the plant canopy in the plots that was morningglory was visually estimated 77 DAT. The canopies in the control plots were 94% morningglory (i.e., almost no cotton was visible) 77 DAT whereas the plots treated with mixtures of norflurazon with prometryn (0.5 + 1.0 lb a.i./A) or with prometryn and trifluralin (0.5 + 1.0 + 0.5 lb a.i./A) had canopies that were about 15% morningglory. When norflurazon was mixed with prometryn, increasing the rate of norflurazon to 0.75 or 1.0 lb a.i./A did not increase the level of morningglory control. The norflurazon-prometryn mixture appeared to be synergistic when compared to the grower treatment of 1.0 lb a.i./A of prometryn mixed with trifluralin or the norflurazon alone treatments in this experiment.

Reprinted from Proceedings of the 1994 Beltwide Cotton Conferences pg. 1706
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998