Linda Benedict, Webster, Eric P., Salassi, Michael | 2/28/2011 11:34:28 PM
Eric P. Webster, Tyler P. Carlson, Michael E. Salassi and Jason A. Bond
Red rice is one of the most troublesome weeds of rice in the South. Because of genetic similarities, controlling red rice with traditional rice herbicides has been unsuccessful.
Imidazolinone-resistant rice is tolerant to the imidazolinone class of herbicides, which effectively control red rice with no effect on the crop. This rice is sold under the trade name Clearfield.
The target herbicide for use in Clearfield rice is imazethapyr, sold under the trade name Newpath. Clearfield rice should be treated twice with Newpath at a rate of 4-6 ounces per acre per application. Because of cost and weed management concerns, research was conducted to evaluate the weed control, crop response, cost, yield and overall economic return of Newpath at various application timings and rates throughout the growing season.
Weed scientists conducted the study at the LSU AgCenter Rice Research Station near Crowley and the Mississippi State University Delta Research and Extension Center near Stoneville, Miss. The long-grain rice cultivar Clearfield 131 was drill-seeded at both locations.
The initial application of Newpath was applied at plant emergence or at one, two, three or four weeks after emergence followed by a second application of Newpath 14 days after the initial application of each treatment. Newpath was applied in four combinations:
A crop oil concentrate was added in each application at 1 percent by volume. Red rice and barnyardgrass pressure was high with 40 to 60 plants per square yard.
The economic analysis was based on the average long-grain rice price of $13 per hundredweight with price deductions based on rice grade. Actual rough (unmilled) rice market prices were adjusted by grade, and these grade price discounts can vary among rice mills.
Rough rice price deductions for grades 1, 2, 3, 4, 5, 6 and sample grade were zero, zero, $0.25, $0.55, $1.25, $1.50 and $2 per hundredweight, respectively. These price reductions are representative of actual market price discounts based on the grade of rice for sale.
Newpath was priced at $525 per gallon, and the crop oil concentrate was priced at $15 per gallon. Profitability of the herbicide programs was determined by evaluating the total value product, which was calculated by multiplying the rough rice yield by the price of rice. Net returns above herbicide cost also were evaluated using the net return (the total value product) minus the herbicide program cost.
In this study the initial application of Newpath applied at rice emergence controlled 89 percent of the red rice and 90 percent of the barnyardgrass. When the initial application of Newpath was delayed by one to four weeks after emer gence, control decreased below 60 percent. This indicates the importance of applying Newpath on small, actively growing red rice to maximize weed control.
Initial applications of Newpath applied at rice emergence resulted in a rough rice yield of 4,280 pounds per acre (Figure 1). By delaying the initial application by one to three weeks after emergence, yield was reduced an average of 1,360 pounds per acre. By delaying to four weeks after emergence, overall yield was reduced by 2,160 pounds per acre.
The rice industry measures the milling yield of rice by the percentage of whole kernels over the percentage of total kernels (whole plus broken) remaining after the hulls and bran layer have been removed through milling rough rice. When Newpath was applied at rice emergence, the milling yield was 61/69 with a rice grade of 3. Delaying the initial application of Newpath to one, two and three weeks after emergence resulted in 28, 37 and 30 percent decreases in rough rice yield, respectively (Figure 1). Milling yield and rice grade for these timings were 59/69, grade 5; 58/66, grade 6; and 61/70, grade 5. By delaying the initial application to four weeks after emergence, rough rice yield decreased by 50 percent, compared with the initial application at emergence, with a milling yield of 60/69, grade 6.
These data indicate that delaying the initial application of Newpath decreases rough rice yield because of the increase in weed competition. Results also indicate that weed control played a direct relationship on rice quality. When weed control was reduced, rice quality decreased. Rough rice yield and quality were maximized when the initial application of Newpath was applied at rice emergence.
Profitability of Newpath treatment programs can be determined by evaluating the total value product, which is the rough rice yield multiplied by the price of rice. Therefore, the effects of Newpath applied at different times on rough rice yield and quality will directly affect total value product. The initial application of Newpath applied at rice emergence resulted in a total value product of $550 per acre. Delaying the initial application to one, two or three weeks after emergence decreased total value product 38, 47 and 40 percent, respectively, compared with the program of Newpath at emergence followed by Newpath at two weeks after emergence. Delaying the initial application to four weeks after emergence decreased total value product 61 percent compared with the initial application applied at rice emergence.
Net returns above herbicide cost were also evaluated, where the net return above herbicide cost equals the total value product minus the Newpath program cost (Figure 2). However, because all Newpath rates were averaged across application timing, the average Newpath cost was $45 per acre. Applying the initial application of Newpath at emergence followed by the second application two weeks later provided a $505-per-acre net return above herbicide costs. However, by delaying the initial application to four weeks after emergence, the net return above herbicide cost dropped below $200 per acre.
The standard Newpath program of 4 ounces followed by 4 ounces per acre resulted in a rough rice yield of 2,910 pounds per acre with a milling yield of 59/69, grade 5 (Figure 3). Newpath programs that included at least one 4-ounceper- acre Newpath application resulted in a rough rice yield similar to the base Newpath program. However, when both applications were applied at 6 ounces per acre, rough rice yield was 3,380 pounds per acre with a milling yield of 62/69, grade 4. These data indicate that increasing the rate of Newpath for both applications to 6 ounces per acre increases rice yield and quality, which will directly benefit the total value product.
Because application rates varied, the costs of treatment will play a bigger role in overall profit compared with the timing evaluations. The standard Newpath program resulted in a total value product of $340 per acre. The cost was $40 per acre, which gave a net return above herbicide cost of $300 per acre (Figure 4). When Newpath was applied at 6 ounces followed by 4 ounces per acre and at 4 ounces followed by 6 ounces per acre, the total value product was $340 per acre for both treatments. However, the cost of each increased to $45 per acre and the net returns above herbicide cost decreased by 2 percent, compared with the standard program.
Newpath applied at 6 ounces followed by 6 ounces per acre resulted in a total value of $420 per acre. This program had the highest herbicide cost at $50 per acre; however, the net returns increased by 23 percent compared with the standard program.
These data indicate that the higher rates of Newpath applied at both loca tions resulted in increased profits, even though costs of treatment increased. This increase in profit was due to higher rice yield and quality, which increased total value product and overcame the additional cost of herbicide.
The effectiveness of Newpath will depend on the weed spectrum and weed densities. However, earlier Newpath applications were more effective in controlling red rice and barnyardgrass. Newpath programs evaluated in this study produced higher rough rice yields, rice quality and returns when the initial application of Newpath was applied at rice emergence. A program of 6 ounces per acre followed by 6 ounces per acre increased rough rice yield and quality.
The data indicate that Newpath application timing, averaged across various rates, increases weed control, rice yield and overall economic returns when applied early. Also, data indicate that Newpath applied at the higher rate for both applications, averaged across different timings, was more beneficial. Therefore, it may be concluded that the initial application of Newpath applied at 6 ounces per acre at rice emergence followed by a second application of 6 ounces per acre two weeks later would maximize overall rice production. Increased weed pressure, even over a short period of time, decreased rice yield.
Producers are encouraged to be aggressive and treat weed problems early in the growing season. When weeds are controlled early and the crop has minimum weed competition, rice plants produce higher yields, which in turn produce higher profits. In this study, economic returns nearly doubled when the initial application of Newpath was applied at rice emergence.
Eric P. Webster, Florence Avalon Daggett Professor in Rice Research, and Tyler P. Carlson, Graduate Research Assistant, School of Plant, Environmental & Soil Sciences; Michael E. Salassi, J. Nelson Fairbanks Professor, Department of Agricultural Economics & Agribusiness; Jason A. Bond, Associate Professor, Delta Research and Extension Center, Mississippi Agricultural and Forestry Experiment Station, Stoneville, Miss.
(This article was published in the winter 2011 issue of Louisiana Agriculture magazine.)