(Updated January 28th 8:43 pm see below)
The first post to my new blog! It is something I have been thinking about doing for several months now. I have several timely topics that I would like to write about over the next few months before things start to get busy in the field by mid April. Hopefully, I’ll get to all of them.
The topic for my first post came to me unexpectedly January 23rd while attending the Crop Life Canada Sask Council meeting in Saskatoon. Clark Brenzil is the Provincial Weed Specialist for the Saskatchewan Ministry of Agriculture and I have heard him speak many times on technical weed issues such as updates on weed herbicide resistance. However the feature topic of this most recent presentation was a bit different (for me anyway). Clark presented on crop injury arising from herbicide residue contamination in Sprayer systems. I say systems because Clark believes much of puzzling chemical injury of canola crops comes not from contamination of sprayer tanks but sprayer plumbing.
I was interested in this topic immediately because I have seen (unfortunately) this many times with my own customers. I have always been certain that the cause was sprayer contamination because you usually could see a line in the field of differing crop damage between the first and second tank fills. However the puzzle always was that my customers and their hired men are usually very careful about rinsing and cleaning between operations and particularly when changing herbicides.
Clark singled out Invigor canola treated with Liberty as being the most frequent for this type of incident. There are two main reasons for this: canola is a crop which is very sensitive to chemical residues, and Liberty acts much like a detergent and is capable of breaking the bonds which cause chemical contaminants to stick on the plastic surfaces in the plumbing of the sprayer. In the majority of cases it is believed to be group 2 chemistry (and occasionally group 4) involved in the contamination.
While listening to Clark an analogy came to mind of Tupperware type food storage containers when they get covered in a film of oily, fatty substances from margarine, salad dressing, etc. Often (in our dishwasher anyway) these containers need to be pre-washed before going into the dishwasher otherwise the oily film will still cover the surface of the container when it comes out of the machine after being washed. And so to is it with spray solutions / suspensions containing oily adjuvants as sticking agents. The plastic surfaces of the PVC plumbing fixtures in most sprayers are vulnerable to this type of contaminating chemical residue bond – particularly after the sprayer has been sitting parked overnight or longer with no clean out or agitation. According to Clark, this residue can stay bound in the sprayer (even after multiple cleanings and/or several thousand acres sprayed of a different herbicide) until the right circumstances converge with a Liberty operation to strip these bound residues from plumbing fixtures and contaminate the contents of a sprayer tank.
For many (myself included) It seems logical that a sprayer should only need to be cleaned when switching to a different product but Clark offers a compelling case that it is these very situations (not cleaning – allowing sprayers to sit for periods and not doing cleanout) which underlie most residue contamination incidents. He goes even further and suggests that perhaps layers of residue can accumulate with each sprayer stoppage if there is no clean out or agitation.
The circumstances for these incidents seem to fit into 3 predominant scenarios:
- Damage occurs on the outside round and area the where the first tank is sprayed out. Damage diminishes with each subsequent tank until eventually it disappears all together. Clark believes the chemical mixing / filling sequence in this scenario is that the Liberty is added to the spray tank very early in the process resulting in highly concentrated Liberty being circulated into the system which is very effective in stripping the contaminant from the plastic surfaces in the plumbing. This process is replicated over subsequent tanks until the residue (and crop injury) eventually disappears.
- No damage evident with the first tank but shows up with the second tank onward. The chemical mixing / tank filling process is believed to be slightly different in this scenario from the first. Here Clark believes that the Liberty is being added late in the filling process and that the tank is perhaps not being adjitated. Nothing is going into the plumbing during filling therefore the first tank is not being contaminated ergo there is no crop damage. Once the sprayer and adjitation is stopped to fill the second tank the Liberty in the lines has the opportunity to act on any contaminant hung up in the plumbing. Tank content contamination occurs once the adjitation is started again and is then sprayed out over the second tank and on causing crop injury. There is a diminishing effect over subsequent tanks similar to scenario #1.
- A single “catastrophic” tank in mid operation causing all of the damage. Here there may be several tanks prior and several tanks after with no symptoms of crop damage. It is suggested that initially sprayer agitation is continuous through each fill not giving the Liberty a chance to sit idle in the lines and strip the residue out of plumbing and contaminate the tank contents. Then the sprayer is perhaps stopped at the end of a work day (or an interruption) for a significant length of time with no clean out. This is the opportunity for the Liberty in the lines to remove bound up residue and contaminate the content of the next tank.
In late, wet springs like we had in 2013 farmers are under more time pressures and have greater weather related interruptions in spraying operations. If sprayers are not cleaned out in these interruptions because there is no change of chemical, then we have the situations which Clark believes could give rise to both the residue hang up (possibly in multiple layers) and the residue removal with Liberty.
There was no type of cleaning “fix” offered by Clark to resolve this type or problem. As well, when Clark reviewed the article he expressed concern that the issue of plumbing vs tank residues could be a bit of a red herring. The real take home message should be to take preventative steps to avoid the circumstances which cause the problem in the first place – which is sprayers sitting idle without clean out or periodic agitation. Clark related a farmer’s comment: “I guess I should be cleaning my tank as often as I shower” to which Clark suggested was “probably right on as long as the person has socially acceptable personal hygiene habits.”
Update January 28th, 8:43 pm – Twitter exchange involving Grant Laroque, Clark Brenzil and myself on a suggested cleaning strategy if contamination (such as discussed in the post) is suspected: