Posted: July 30, 2007
A recent research project shows that much has yet to be learned about the science of fungicide application
A producer-driven research project recently evaluated a number of spray systems in their ability to control schlerotinia white mould on dry bean crops. The project, conducted by the AgTech Centre in Lethbridge, Alberta, focused on Lance WDG, a foliar fungicide increasingly being used to tackle the disease as other options disappear from the marketplace.
Project manager Brian Storozynsky says the results of the project offer some useful information for producers seeking advice on how to get value from a growing number of spray technology choices. "However, the most conclusive point gathered from the results is that there is no 'magic bullet' solution to tackling white mould on dry beans," he says.
The bottom line, says Storozynsky, is that the jury is still out on the cost-effectiveness of Lance WDG, which producers have described as being more expensive than some previously available solutions. "Although Lance WDG appeared to be less effective in preventing white mould than previously available fungicides, the sprayed plots always produced better yields than the untreated checks.
"That said, the cost-effectiveness of the product is still dependent on fundamentals such as looking at individual environmental and cost factors."
Conducted on the request of the Alberta Pulse Growers Commission, the project examined which specific types of spray deposition and penetration would enhance the effectiveness of Lance WDG. It focused on broadcast spraying equipment, the efficiency of a number of commonly used nozzles and air assisted sprayers, and sprayer volume rates. Disease index (a measurement of disease severity) of white mould on these sites was then compared to plots that were not treated with any fungicide. Yield rates were also measured.
For the 2006 season, two commercial fields of Othello dry beans were studied. One was a 26 ha (65 ac) bean crop planted two kilometres south of Taber, Alberta in a north-south direction and irrigated with a central pivot system. A 24 ha (60 ac) bean crop near Cranford, Alberta was also planted in a north-south direction and irrigated with a wheel move system.
At both sites, each application of Lance WDG was applied at 770 kg/ha (312 g/ac). The Cranford site received the recommended two applications. However, the grower and the AgTech Centre decided to cancel a second application on the Taber plots as the crop canopy was too advanced and soil conditions too wet for AgTech's sprayer equipment.
The nozzles tested included both high and low pressure air induction venturi nozzles, two types of twin venturi nozzles, two air assist systems and one extended range nozzle used as reference. "Many nozzle technologies are used in conjunction with each other and currently, twin nozzles and spraying angles are the topic of many questions," explains Storozynsky.
Any advantages of one nozzle over another seemed to be arbitrary and ultimately statistically insignificant. "At some sites the high pressure twin fan system resulted in the least amount of white mould. But on some others, the air assisted systems appeared to be the most effective. For the most part, however, all of the nozzles seemed to be equally effective."
At the Taber site, average disease index between the nozzle types ranged from 63 to 81. Plots sprayed with the air assist system, flat fan nozzles and air assisted flat fan system resulted in the lowest disease indexes of 63, 67 and 69 respectively.
Meanwhile, the Cranford site yielded almost completely different results, ranging in average disease index from 14 to 21, with the twin venturi, low pressure venturi, extended range flat fan and high pressure venturi resulting in the lowest disease indexes of 14, 16, 17 and 17 respectively. An example of this overall inconsistency is the fact that the low pressure and twin venturi nozzle types had the highest average disease indexes at the Taber site and the lowest at the Cranford site.
Nozzle type did not appear to make a difference in terms of yield. "At Cranford, the twin venturi was the nozzle type that resulted in the lowest disease index, so you'd think it would also result in the highest yields. As it turned out, it had the lowest yields compared to all the other nozzle types."
Plots were sprayed at three different spray volumes: 112, 224 and 336 L/ha (10, 20 and 30 gpa, respectively). "Many growers believe low water rates do not provide the coverage and penetration needed and higher water rates would probably benefit foliar fungicides, so we set the volumes to reflect that range," says Storozynsky.
However, water volume rates appeared to have little significant influence over white mould prevalence. "The trends we saw suggest that spraying with low water rates does just as good a job as high water rates."
At application rates of 112 L/ha, disease index averaged 14. In most cases, disease index was significantly higher on the untreated checks than those applied with Lance. Under 112 L/ha, the disease index of untreated checks was 36.
Doubling the rate to 224 L/ha increased disease index minutely with an average of 16. Untreated check plots averaged 26. Plots sprayed at a rate of 336 L/ha showed the highest average numbers of disease index at 22. Untreated check plots had an index of 37.
Although Lance WDG was generally found to be a less effective fungicide for treating white mould than previously available fungicides, yield in the treated checks was consistently higher than in the unsprayed plots.
At the Taber site, one application of Lance WDG at a rate of 770 kg/ha (312 g/ac) on a crop of dry beans at the 40 to 70 percent flowering stage reduced white mould disease index by nine and increased net seed yield by 21 percent compared to the untreated checks. Meanwhile, at the Cranford site, two applications of Lance at the same rate on dry beans 30 to 60 percent into the flowering stage reduced disease index by 45 and increased yield by 15 percent.
"Even on the site with the high disease index, we still had a yield increase of 400 lb/ac over the untreated checks," says Storozynsky. "At the same time, we had another site with a significant reduction in disease and a 400 lb/ac increase in yield. The end result for yield is the same."
Providing information that can help farmers make better management decisions on purchases or use of technology is a goal of the AgTech Centre. Results of AgTech's machinery evaluations, applied and scientific research, and information on its development of innovative agricultural technologies are available to producers. For more information, contact the AgTech Centre at (403) 329-1212.
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