The problem with camera/spot-spray systems that nobody wants to talk about - Part 2

Last week I wrote to you about what happens when you switch your spot spraying system from side safety (multiple nozzles) to single spot, that your application rate for isolated nozzles could drop off by up to half or even more depending on nozzle height, size and angle.

Today’s topic is the opposite. What happens when groups of adjacent nozzles engage in single spot mode?

Some sprayers are single spot ONLY. They do not have a side safety or multi nozzle option. They include Weedit, WeedSeeker and more recently Carbon Bee.

All of these and the other familiar camera based systems can be retro fitted on to conventional trailed or SP sprayers. Yes those same sprayers that may have rate management systems based on nozzle spacing alone.

As explained last week, the single spot rate per hectare is calculated on the spray width (or footprint) of the isolated nozzle. That is derived from the nozzle angle and its height above the ground. As there is no overlap factored in, you can expect the nozzle to be about twice the size of your blanket spray or side safety nozzle.

At ARAG/ASJ and Fantastic Nozzles, we have added an extra dimension to the formula by introducing target zone rates. We measure the percentage volume of the nozzle output in the area immediately under each nozzle. Explained in detail here;

Spot-Spray Calculator

So what does happen when two or more nozzles engage? The rate applied basically doubles. Not exactly but you will get the point without the need to write down a pile of formula’s again.

Is this a bad thing? Well let me quote Brendan Williams of Weedit fame who you probably all know;

Dave, we spot with knockdown herbicides with little residual activity and extremely wide ranging rates so over applying rates is inconsequential. In fact in most cases it’s highly desirable. Big weeds over 250cm with Weedit will always get two adjacent nozzles firing and be overdosed by about 60-70%. So big weeds get overdosed that’s generally considered a good thing.

Incidentally, Weedit also calibrate according to target zone rates tested and measured in Holland, ours in Italy ;)

So, If your spray rate controller is only capable of calculating blanket rates (based on nozzle spacing), the only way to maintain the correct rate of say 100 l/ha for isolated nozzles is to force a minimum pressure of 3BAR for pressure regulated systems or alternatively to set up for the full blanket rate, even for 06’s, 08’s or 10’s as are required on 50cm spacings.

Be happy about overdosing where groups of adjacent nozzles engage. That is just a fact and currently there is no way around it if single spot is your intention.

In summary;

• Switching from Side safety to single spot halves the rate (approximately) unless you step up to the correct size/angle nozzle,
• Where multiple nozzles engage in single spot mode the rate between them doubles (approximately), and
• If your spray controller works on nozzle spacing only and not spray width, set up for a blanket rate for the single spot nozzle you have on board. Even if is a BIG figure. It is a reliable way to guarantee you are applying the correct rate when isolated nozzles fire without overlap.

Lastly, I am aware that applying unintentionally low rates like when switching from multi to single with small nozzles or where there is a failure to maintain pressure and duty cycle to isolated nozzles, can and often does work. My responsibility though is to provide accurate information to help you comply with label rates. The 'it works' argument is only good until the time that it doesn’t.

Any questions, just call.

Dave

08 6102 5886