Evaluation of Puma (Fenoxaprop) for
A field experiment was conducted in 1998 to determine the efficacy of Puma and Hoelon for littleseed canarygrass control in durum wheat. The herbicide treatments consisted of three rates of Puma, 0.83, 1.24, and 1.66 oz a.i./A, and one rate of Hoelon, 6.8 oz a.i./A, that were applied at two application timings. The early-postemergence (EPOST) applications when canarygrass had 2.2 leaves per plant did not result in commercially acceptable control due to water stress. Increasing rates of Puma applied mid-postemergence (MPOST) when canarygrass had 5 leaves per plant provided increasing canarygrass control (70 to 90%) with the two higher rates of Puma providing commercially acceptable control. The two highest rates of Puma also resulted in better weed control than the commercial standard, Hoelon, which did not provide commercially acceptable weed control. No herbicide injury symptoms were observed on the wheat at any of the evaluation dates. Grain yield also increased as the rate of Puma applied MPOST increased and yields overall reflected the degree of weed control observed earlier in the season. These data indicate that the combination of Puma applications that killed or stunted emerged canarygrass combined with later season crop competition that suppressed stunted and later emerging canarygrass plants was sufficient to protect grain yields. The highest yielding Puma treatment was equivalent to 4150 lb/A compared to the Hoelon and control treatments which yielded the equivalent of 2753 and 1946 lb/A, respectively.
Littleseed Canarygrass (Phalaris minor) has become increasingly widespread in Arizona wheat fields because it is difficult to control. Canarygrass seedlings in wheat can be easily identified by their thin leaf blades compared to wheat. In addition, when the leaf blades are broken or crushed at the soil level the base of the leaves turn a distinctive reddish color. In recent years, only one herbicide, Hoelon (diclofop), manufactured by AgrEvo has been registered in Arizona for canarygrass control in wheat. The degree of canarygrass control achieved with Hoelon has been variable when 1 to 2 leaf canarygrass seedlings were treated. Canarygrass seedlings with 3 or more leaves are not adequately controlled by Hoelon (Tickes, 1993). Canarygrass is an effective competitor against wheat. Tickes (1997) found that canarygrass infestations of 20 to 40/ft2 reduced wheat yields 30 to 40% and canarygrass densities of 100/ft2 reduced yields 50 to 60%. AgrEvo and University researchers have been testing the experimental herbicide Puma for canarygrass control in wheat for several years and the product is near registration. The active ingredient of Puma, fenoxaprop, is in the same chemical family as Hoelon (diclofop) but fenoxaprop is much more toxic to wheat than Hoelon. A non-herbicidal safener mixed with fenoxaprop provides satisfactory crop tolerance and is part of the formulated product, Puma. Fenoxaprop can also be tank mixed with broadleaf herbicides such as 2,4-D and MCPA to provide crop safety because these herbicides reduce the activity of fenoxaprop in wheat. The research reported here was conducted to evaluate the efficacy of Puma for littleseed canarygrass control in wheat grown in central Arizona.
Materials and Methods
A field experiment was conducted in 1998 on the Paloma Ranch west of Gila Bend, AZ in southwestern Maricopa County to determine the efficacy of Puma for littleseed canarygrass control in wheat. The DuraKing cultivar of durum wheat was planted in dry soil about 1.5 inches deep using a drill in a level basin on January 2, 1998. The field was flood irrigated shortly after planting to germinate the crop seed. This irrigation also initiated the germination of canary grass seed. The herbicide treatments consisted of three rates of Puma, 0.83, 1.24, and 1.66 oz a.i./A, and one rate of Hoelon, 6.8 oz a.i./A, that were applied at two application timings. Thus, there were a total of nine treatments including the control that were replicated three times and arranged in a randomized complete block design. Individual plots were ten ft wide by thirty feet long. The herbicides were applied using a CO2 pressurized backpack sprayer and a boom with six TeeJet 8003VS nozzles on nineteen inch centers operated at twenty one psi that sprayed about fifteen gallons of water per acre.
The first set of treatments were applied early-postemergence (EPOST) twelve days after planting (DAP) on January 14th when the wheat averaged about three leaves per plant and the canarygrass averaged 2.2 leaves per plant. No crop oil concentrate (COC) or other adjuvants were added to the herbicide spray solutions applied EPOST. The field was dry at the time of application and was not irrigated until January 27, 1998. The second set of treatments were applied mid-postemergence (MPOST) 32 DAP on February 3rd when the wheat averaged about nine leaves per plant and was tillering and the canarygrass averaged five leaves per plant (the range was four to six leaves/plant) and also was beginning to tiller. For the MPOST applications, the plots were split in half and the south half of each plot was sprayed without adding any COC to the spray solution. After spraying the south half of all of plots in a treatment, the remaining spray solution was measured and COC (Herbimax) was added at a rate of 1 pt/A before spraying the north half of the plots in that treatment. The MPOST applications were made between 1100 and 1200 hours. It began to rain at the study site at 1800 hours and rained until early the following morning for a total rainfall accumulation of 0.46 inches.
The efficacy of Puma on canarygrass was evaluated on February 3rd, February 23rd, and March 24th by visually estimated the percent reduction of canarygrass biomass in herbicide treated plots relative to control plots. Injury of the wheat by Puma was also evaluated on these dates but no injury symptoms were ever noted. In general, except for the 0.83 oz a.i./A rate on March 23rd Table 1 there was no difference between halves of the plots so only one efficacy value was recorded per plot. Canarygrass control by Puma was also evaluated on May 13th by estimating the percent reduction in canarygrass inflorescences in treated plots relative to the control plots. A five foot wide strip in the center of the plots was harvested on June 7th using a Massey-Ferguson small plot grain harvester. The grain from each plot was collected in a five gallon bucket, weighed using a Tri-Coastal Industries LPC-4 hanging scale, and saved in paper bags. On June 9th, the seed from each plot was cleaned in a thresher to remove trash and debris not previously removed by the harvester. The weight of cleaned grain ranged from 89.5 to 93.1% of the initial total harvested weight for each plot with little differences between treatments. Thus, only cleaned seed weight data is presented in this report. An analysis of variance was conducted and treatments means were separated using DuncanĚs New Multiple Range Test at P=0.05.
Results and Discussion
The early-postemergence (EPOST) herbicide applications did not result in commercially acceptable control of littleseed canarygrass at the first evaluation on February 3, 1998 with 62% control in the best treatment, Puma at 1.66 oz a.i./A Table 1. The soil surface was dry at the time of the EPOST applications and soil samples collected with a soil probe revealed that the soil profile was fairly dry. The field was not irrigated for almost 2 weeks following the EPOST applications. Thus, the canarygrass was water stressed and not actively growing at the time of application, or following the applications, and did not physiologically response to the herbicides resulting in poor weed control. Increasing the rate of Puma increased canarygrass control with the highest rate, 1.66 oz a.i./A, resulting in better weed control than the commercial standard treatment, Hoelon Table 1 Canarygrass control declined following the initial evaluation such that there was no statistically significant difference in the number of canarygrass inflorescences between any of the EPOST treatments on May 13, 1998 Table 1. This decline in control was probably due to early water stress and the recovery of treated canarygrass plants as well as the continued emergence of canarygrass following the first post-planting irrigation on January 27, 1998. There also were no yield differences between EPOST treatments and the untreated control Table 1 indicating that there was no economic benefit from the herbicides that could pay for the cost of the chemical application.
Increasing rates of Puma applied mid-postemergence (MPOST) provided increasing control of canarygrass with the two higher rates of Puma providing commercially acceptable weed control at the February 23rd evaluation date Table 1.. The two highest rates of Puma also resulted in better weed control than the commercial standard, Hoelon, which did not provide commercially acceptable weed control Table 1. The herbicide injury symptoms on canarygrass were chlorotic leaves and stunted canarygrass plants followed by dead plants at later evaluations in the superior treatments. No herbicide injury symptoms were observed on the wheat at any of the evaluation dates. The poor control provided by Hoelon was probably due to the relatively large size of the canarygrass at the time of treatment (about 5 leaves per plant). The efficacy rating for the MPOST Puma treatment at 0.83 oz a.i./A on March 24th was significantly greater, 92% versus 70%, for the half of the plot in which COC was added to the spray mix Table 1 footnote 2. However, this increase in efficacy did not result in any detectable differences in the percent reduction of canarygrass inflorescences in the two halves of the plots. In general, there were no differences in efficacy between halves of the plots across MPOST treatments and only one efficacy rating was recorded per plot.
All of the herbicide treatments applied MPOST resulted in better weed control than similar treatments applied EPOST Table 1 probably because the canarygrass was not water stressed at the time of application in contrast to the conditions during the EPOST applications. The weed control provided by the MPOST applications remained fairly constant for the remainder of the season Table 1. The weed control estimates based on the number of canarygrass inflorescences in the plots reflected the degree of weed control observed earlier and for the Puma treatments the percent reductions in the number of inflorescences increased with increasing Puma rate Table 1. Similarly, wheat yield increased as the rate of Puma was increased and yields overall also reflected the degree of weed control observed earlier in the season. These data indicate that the combination of herbicide applications that killed or stunted emerged canarygrass and crop competition from the wheat that suppressed stunted and later emerging canarygrass was sufficient to protect crop yield. All of the MPOST treatments yields were greater than the EPOST treatment yields with the Puma treatments having almost double the yield of the corresponding EPOST treatments. The highest yielding Puma treatment was equivalent to 4150 lb/A compared to the Hoelon and control treatments which yielded the equivalent of 2753 and 1946 lb/A, respectively.
In conclusion, Puma is clearly a superior herbicide for canarygrass control in wheat compared to Hoelon. It is more active and controls larger canarygrass plants, up to six leaf plants that were beginning to tiller. This greater efficacy provides greater application flexibility. This study demonstrated that in dry planted wheat, the optimum application time for Puma is after the first post-planting irrigation and before canarygrass exceeds six leaves/plants. While Puma applications to larger canarygrass plants may still result in acceptable control, the wheat was rapidly growing, averaged nine leaves/plant, and was tillering at the time of the MPOST applications. This suggests that later applications might result in poorer control because the greater size of the wheat could cause poor herbicide coverage on the canarygrass. The maintenance of weed control following the MPOST applications suggests that even if earlier applications were made to non-water stressed canarygrass, the later application timing was superior because more canarygrass was emerged at the time of application. Thus, the first post-planting irrigations should be timed to allow Puma application to non-water stressed plants before the canarygrass exceeds six leaves/plant and the wheat exceeds about nine leaves/plant.
The data from the MPOST and EPOST applications of Hoelon indicate that for this herbicide there is a trade off between treating small, water stressed, canarygrass seedlings (2.2 leaves/plant) and non-water stress plants (5 leaves/plant). The yield data suggest that it is better to spray Hoelon on non-water stressed canarygrass that is too large at the time of application than to spray small seedlings that are water stressed. Canarygrass control could be substantially improved by irrigating dry planted wheat earlier after planting so that Hoelon could be sprayed on non-water stressed canarygrass that was still small (two to three leaves/plant).
This is a part of publication AZ1059:
"1998 Forage and Grain Agriculture Report," College of Agriculture, The
University of Arizona, Tucson, Arizona, 85721.