Circulating spray mix through a tank-rinse nozzle maintains nematode concentration
Many horticultural commodities, such as turfgrass and nursery crops, include the application of live nematodes as part of their annual spray program. In 2013 we performed preliminary research into the claim that a grower's nematode applications were becoming less effective. In the course of the investigation, it was discovered that the nematode concentration (i.e. dose) sampled from the spray gun was diminishing over the course of the application.
After eliminating potential sinks in sprayer plumbing (e.g. filters, strainers, etc.) it was hypothesized that the nematodes were adhering to the interior of the poly tank. As the level of spray mix dropped this could reduce the concentration. To test the hypothesis, we installed a tank-rinse nozzle to sparge the inner walls of the tank throughout the application and re-suspend any stranded nematodes (Figure 1).
Figure 1 - (A) Tank-rinse assembly mounted through tank lid with a flow-regulating valve. (B) Close up of tank-rinse nozzle. (text version)
A high capacity roller pump (Pentair series 1700C) was installed to operate the tank-rinse nozzle (Pentair Proclean Tankwash) during spraying (Figure 2). It was installed through a bulkhead fitting in the tank fill lid. During testing it was discovered that the tank-rinse nozzle shunted too much flow and pressure to maintain flow to the spray gun. A valve was installed behind the tank-rinse nozzle to restrict flow to the point where it gently rinsed the inner walls of the tank, restoring flow and pressure to the spray gun.
The 200 L tank was inoculated with a stock solution containing 25 million nematodes (125 nematodes / ml). 20 L of the spray solution was sprayed into a bucket every 10 minutes, whereupon 1 L of spray solution was immediately removed and 1 ml volumes were sub-sampled for counting (Figure 3).
Figure 2 - (A) Installing a high-capacity roller pump. (B) Tank-rinse nozzle, with valve, installed through tank lid. (C) Control manifold installed to plumb the return, the tank-rinse nozzle, spray gun and boom. (D) The entire installed system. (text version)
Figure 3 - (A) Nematodes, as-shipped, in a sponge. (B) Suspending nematodes for tank mixing. (C) Counting nematodes. (D) Undiluted, healthy nematodes in water via microscope ocular. (text version)
In the first trial, nematode counts (and overall viability) dropped by >40%. It was assumed the damage was caused by prolonged circulation through the roller pump. In subsequent trials, the sampling duration was reduced to 10 minutes (more realistically reflecting the time it took the grower to apply 200 L in the field). The tank was rinsed and re-inoculated for each trial. 1 ml samples were drawn from the spray gun, which operated continuously, with and without the tank rinse nozzle in operation.
Univariate analysis confirmed data normality and a GLM procedure was conducted for analysis of variance. Results indicate that nematode concentration dropped by >15% without tank-rinse with minimal nematode damage observed. With the tank-rinse nozzle engaged, the concentration still declined slightly, but significantly less (<5%) (see graph below).
The results suggest that a tank-rise system preserves nematode concentration throughout an application and may lead to more efficacious applications.
Horticultural Crops Ontario, Ground Covers Unlimited, Pentair (Hypro), Nemapro and Behrouz Ehsani are gratefully acknowledged for making this research possible.
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