“If the tank mix is not approved by the manufacturer, there is no guarantee of performance or safety
stressing that further guidance should be sought from the supplier or manufacturer to see whether mixing is possible. “There’s really no need for those in amenity to be cautious of tank mixing,” Allbutt reiterates. “Section 4.5 is clear about what can and cannot be done. The only way to be competent is to either take the necessary training, or the easier option being to just consult the code of practice,” he adds. When approaching tank mixing, each
product needs to be correctly calibrated for that particular mix, he continues, and the correct dose rate and water volume should always be applied. “One of the products should be applied with a greater volume of water and the end user should always use the greater water volume stated. After calibration, each product must then be measured and mixed separately in the required volumes. “Introduce each into the tank separately, rinsing thoroughly before mixing the next - the process of emptying and rinsing must always be followed when mixing another product. The most crucial point to remember with tank mixing is to use the mix immediately. “The water acts a buffer between the two products, but it doesn’t last forever,” cautions Allbutt. “Good tank mixing is also very weather dependent, planning the event in a steady way is vital. The job must be finished and there cannot be anything left in the tank.” With literally hundreds of chemical permutations possible in a tank mix, however, a foolproof system is needed urgently.
A leading horticultural chemicals
manufacturer has developed software that it plans to roll out to end users within the next eighteen months. While available to its area sales managers, who can advise councils on what chemicals will and will not mix, the method of delivering the programme is still to be finalised.
Meanwhile, the Compatibility Test
remains the usual form of assessing whether or not chemicals will mix physically. Scientifically, it may appear a little ‘Heath Robinson’ but, in the absence of another method, is still the preferred option.
Mixing incompatible chemicals can
wreak havoc in more ways than one though.
A chemical reaction, or precipitation, may occur to create a viscous or glutinous mass that can block spray nozzles, which are growing increasingly advanced in their technology, rendering them inoperable.
Also, the effectiveness of, say, a selective weedkiller, when mixed with a fertiliser for a single application, needs to be evaluated beforehand. If not, the risk is that one or both chemicals may not function to their intended performance level.
Local authorities and the private sector
alike should be aware of the pitfalls, believes Mark De’Ath, who sits on the Amenity Forum. “It should be beholden on councils to know what the parts of the job entail, rather than leaving responsibility solely to the contractor. “Time is money. If a contractor can perform two operations in one run, so much the better for the council,” argues De’Ath, who is also operations director for Headland Amenity Ltd, which
supplies chemicals to the sports and amenity sector.
But he concedes that, unless they are
aware of all the regulations, it is difficult to develop documentation to highlight potential problems.
Another issue is aggravating the
problem, he believes. EU law banning what were once widely used pesticides is forcing contractors to change the way they service councils. Since the residual pesticide, Diuron, was banned at the end of last year, contractors are unable to undertake weed control work “in a planned fashion”. “Increasingly, all weed control work is being squeezed into March, April and May, and labour is in short supply.” That, in turn, puts pressure on them to mix more chemicals in the same tank, he adds.
It is vital to mix chemicals in the right sequence, he cautions. “Powders first then liquids. The unwelcome outcome of mixing a selective herbicide and soluble iron is “pretty well known in the trade”, De’Ath says, “but incompatibility also includes the effect that spraying will have as well as the physical reaction of mixing.”
“Using a fertiliser with immediately available nitrogen in combination with a herbicide, in hot weather, could scorch turf,” he explains. “Wait for cooler weather or use a slow-release fertiliser.” Placement compatibility also presents potential problems, he goes on. If a product needs to stay on the leaf for it to be effective, but the tank mix is at too weak a concentration, because of another chemical that relies on soil penetration for its effect, the active agent may also run off to ground.
of the resultant mix” Stuart Staples, Technical Manager, Scotts Professional
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