What is the POINT of run-off?

Is there a ‘Point’ of run-off? I could be accused of playing with words, but the fact is that there is a ‘Point’ and we shouldn’t exceed it.

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point of run off

Is there a ‘Point’ of run-off? I could be accused of playing with words, but the fact is that there is a ‘Point’ and we shouldn’t exceed it.

As professional pest managers, one of the most used tools in our kit bag is hand spraying, and more specifically residual spraying. The skills required to apply residual sprays could be considered as fairly straight-forward. Firstly, we need to measure, then mix our residual product of choice with water into the tank, pump it up and pull the trigger. But there is so much more to it than that. In this article I’ve focused on the application to surfaces, because this is where many issues can occur for the less experienced.

Unlike other industries that also spray-apply products such as turf managers, farmers, spray painters and even concreters, pest managers are faced with a unique challenge when it comes to application. That is surface (target) variability. In virtually all the other industries, the target surfaces are uniform and consistent, but for pest managers, that it is almost never the case.

Golf courses are a perfect example of consistent surface conditions that allow the course superintendents to calibrate, then apply products with sophisticated boom sprayers. The way they apply a particular product on a fairway is quite consistent on each and every fairway on the course.

However, the conditions faced by pest managers are constantly variable, such as surface porosity (liquid holding capacity); orientation (vertical and horizontal) and the presence of non-target surfaces (e.g. windows, electrical hazards).

Using a low set home as an example, within just a 2-3 m2 area on the exterior there are multiple things you need to consider:

  • Where does the product need to be applied (or not)?
  • What to do around the electrical fittings?
  • How much spray will the porous bricks absorb?
  • How quickly do I need to spray over the non-porous Colorbond and painted soffits?
  • How will the vertical and horizontal surfaces behave?
  • Where is each pass of the sprayer going?

 

Thankfully, with appropriate industry training and on-the-job experience, pest managers can make these computations ‘on the fly’ to apply products successfully. But what is it we’re trying to accomplish?

Firstly, let’s look at a product label such as Temprid. Most product labels distinguish different spray volume rates for porous (10 L/100 m2) and non-porous surfaces (5 L/100 m2). The volumes on the label are a guide to the likely ‘carrying capacity’ of the two different surface types before run-off occurs.

A good way to manage spray applications on different surface types is to consider the proportion of each surface type on the job (porous vs non-porous) and select the one that is the most prevalent. In the majority of cases, this will be the non-porous rate. If the majority of surfaces are porous, or when power equipment is being used, then the porous rate will be the preferred option.

The reason for selecting one mixing rate on a job site is that as pest managers, we have to compromise. It’s not common practice to mix up a tank and do all the porous surfaces then mix up another tank to do the non-porous surfaces. We make this decision and adjust the application volume ‘on the fly’. An exception to this would be larger commercial sites with expanses of each type of surface.

The Temprid label also mentions not to exceed the ‘Point of Run-off’.

Run-off is the term used to describe the point at which a given surface will no longer ‘hold’ liquids on its surface and the liquid will run-off. Pest managers tread a delicate balance between applying enough product to ensure good coverage and control of pests, but not to use too high a spray volume that the product runs-off surfaces. This is where experience plays its part. As pest managers we see what’s in front of us and consider all of the decisions we need to make resulting in some areas not being treated at all (non-target) and varying application speed across different surface types. Spray solution soaks into bricks and masonry readily, so the speed across these surfaces can afford to be slower before a product runs-off, whereas painted walls and Colorbond requires faster movement to prevent the same from happening.

Consequences? Two of the main issues caused by excessive run-off are off-target contamination and surface marking and staining.

Where a treatment runs-off and drips onto surfaces that are not meant to be treated, high concentrations and pooling of the spray solution can end up on these surfaces. This run-off can mean insecticide residue is found on surfaces where it shouldn’t be and can result in many issues in commercial and domestic accounts if workers, homeowners and pets come into contact with these off-target residues.

Tech Tip 1: Be especially careful when applying to dirty surfaces as run-off will further concentrate these deposits causing runs and other aesthetic issues. Particularly on domestic jobs, consider advising homeowners early to wash down their home prior to the treatment to avoid this issue. If concerned, test areas and if necessary, discuss with the client if you feel run-off will be difficult to manage in some areas.

Tech Tip 2: Run-off can result in streaks and marking of paint surfaces, particularly those recently applied that have not yet aged or fully cured. Pay particular attention with dark paint colours and those that are facing the sun at the time of application, as these situations are the most likely to show marking from over application – even from plain water!

Case Study – Furniture Factory

 

A number of years ago, I received a complaint about an application of a suspension concentrate in a furniture production warehouse. The pest manager hand sprayed a number of areas, but some run-off from the pallet rack frames containing the raw furniture timber supplies had occurred. After a period of time, the liquid dried out with little or no evidence of the run-off occurring. The factory continued to produce furniture over the next week or so, but when the items were finished in colour stain, marks were visible all over the furniture. A subsequent investigation showed that the run-off a week earlier had caused a change to the timber and the way it took the stain, and as a result, a substantial claim against the pest manager ensued.

It was later proven that it was in fact water that was responsible for the damage and the addition of the suspension concentrate played no part in the damage. However, as we all know, things are never black and white. Water from rain during delivery or other spills do occur from time to time and the normal procedure is to pre-sand timbers before staining to prevent this problem from occurring. If the pest manager was able to prevent the run-off or at worst report the situation to the factory manager, action may have been taken to minimise the claim, but in this case production staff converted all the raw furniture to stained furniture before reporting and the claim was therefore greater than it should have been. The moral to the story – always stop if you suspect off-target application and notify accordingly.

Residual spray applications may look simple but the skill and knowledge to do them properly is deceptively high. Always survey your site before starting to help identify potential hazards and challenges that you may be confronted with. And if in doubt, discuss these concerns with the client before pulling the trigger.

 

Happy Spraying!

For further information:

Jeff Einam

(m) 0418 390 803