At some time, most farm advisors have wondered whether their clients are getting all of the spray residues out of their spray lines and what this might be doing to the following crop. Nobody wants a crop failure complaint! Do Sprayer Hose Materials Differ in their Residue Risk?
At Eureka! we have investigated spray line residues a number of times but the information is confidential to the clients who funded it. However, last week I read a new scientific article from Gary Cundiff’s work with the Mississippi State University which I can talk about. This article builds on Gary’s interesting PhD thesis from a couple of years. I reference the article at the end of this article and recommend that you read it.
In this new, three year study, the Mississippi State University team used dicamba as their test herbicide and soybean as the sensitive crop to evaluate damage from residues sticking to spray hoses.
Five hose brands were compared that covered four material types (colors in Upper Case refer to hoses in the photo below):
- synthetic rubbers (BLACK)
- synthetic plastic polymers (polyvinyl chlorides [PVC]) (YELLOW)
- PVC plus polyurethane blends (GREEN & GREY) and,
- polyethylene blends (BLUE).
Due to the diversity of PVC/polyurethane blends two versions of this material were tested. Collectively these four materials make up a large proportion of spray hoses.
Figure 1. Five sprayer hoses used in the Mississippi State University Study
The five different hoses listed above were filled with label rates of dicamba for 48 hours before being emptied and then being: (1) not washed, (2) washed with water or, (3) washed with a 1% ammonia solution. The ammonia solution is recommended on many dicamba labels around the world including some in Australia.
The hoses were then filled with a label rate of glyphosate for 24 hours before being emptied into containers where a sample was collected for analysis and the rest was used to spray glyphosate resistant soybeans. These soybeans would not be damaged by the glyphosate but could be damaged by any dicamba residues.
The results were averaged across multiple sites and multiple years which reinforces that they are sound.
The article reports that the worst performing hose material was the synthetic rubber which retained 17 ppm dicamba when not washed out (enough to reduce soybean height after 28 days by 36%) and this fell to 11 and 16 ppm respectively when washed with water and ammonia solution (which still resulted in a 29% reduction in height).
The best performing was the polyethylene blend hose material which retained just 4 ppm of dicamba residue when not washed out (which resulted in a 13% reduction in soybean height). This demonstrates that the simple process of emptying the hose of the original dicamba solution resulted in five times more residues being stuck in the synthetic rubber hose than this polyethylene hose. The residue level in the polyethylene hose fell to less than 1 ppm when washed with either water or ammonia. This level of residue did not significant damage soybeans.
The next best was the PVC (synthetic plastic polymer) hose material which retained about 11 ppm dicamba residue when not washed (which resulted in a 23% reduction in height) falling to about 3 ppm when washed with water or ammonia (which resulted in 7 – 15% reduction in height).
The two hoses made from PVC/polyurethane blends retained 17 and 13 ppm dicamba residue when not washed (which resulted in a 30% reduction in soybean height) falling to 5 to 10 ppm when washed with water or ammonia (which resulted in 11 – 21% reduction in height).
A scanning electron microscope was used to compare the inside of the hoses both before and after being used. These scans showed imperfections in the new PVC polyurethane and synthetic rubber hoses. They hypothesized that this allowed more dicamba to adhere to the wall of these hoses and made it more difficult to wash off. The researchers also claimed that the inner wall of the polyethylene-blend hose material was smooth and free of imperfections and so could be expected to allow less dicamba to adhere to its walls.
The take home message
Be very careful about what material you recommend your clients to use in their spray hoses and how you recommend that they clean it.
Reference
Cundiff, G., Reynolds, D. and Mueller, T. (2017) Evaluation of dicamba persistence among various agricultural hose types and cleanout procedures using soybean as a bio-indicator. Weed Science 65 (2): 305 – 316
If you would like your spray hoses tested under similar conditions by our highly experienced team, please contact the friendly Eureka! AgResearch team on (03) 9369 4177 or if calling from NZ +61 39369 4177, and ask for Anthony Flynn.
Written By: Anthony Flynn
© 2017 Eureka! AgResearch Pty Ltd