Tank Mixing

The growing stigmatisation of pesticides by the European parliament, coupled with its firm focus on sustainability, has fostered what some say is an overly cautious attitude towards their application.

In today's compensation culture, the public sector, for example, is fearful of any repercussions following inappropriate application of pesticides, or other chemicals, on its sportsturf and amenity areas.

But, financial constraints on public and private sectors alike are also driving the search to deliver the most cost-effective solutions possible, and that can put pressure on contractors and other service providers to find ways to optimise the time they spend servicing sportsturf and amenity areas.

Tight budgets and timescales can put pressure on managers, departments or contractors to fast track spray application of chemicals by mixing them into a single tank or container.

Contractors, chemicals manufacturers and suppliers are stepping up their campaign of awareness-building among buyers and end users, in a bid to ensure that neither health and safety nor efficacy is compromised in the current economic climate.

Trials are underway to evaluate integrated vegetation management programmes (IVMPs) as one way to merge the application of a raft of substances, including wetting agents, fungicides and fertilisers.

Results will enable programmes to be set up that clearly identify what chemicals can be applied from the same tank, and in what concentrations, to optimise disease resistance and nutritional input.

If conducted correctly to the appropriate guidance, tank mixing can enhance turf management and weed control programmes, saving time, money and waste, while in some instances boosting the effectiveness of each constituent.

Yet the method is raising concerns among industry commentators, chemicals' suppliers and end users about the need to highlight how important it is to follow guidance to the letter to avoid potential health hazards and damage to turf, machinery and equipment.

Leading safety consultant, Jon Allbutt, for one believes the benefits of tank mixing are simply not being capitalised upon, especially in local authority markets. "Not enough is being done to promote its advantages. If it's known that tank mixing can kill a particular weed more effectively than by using normal methods, it is an obvious choice," he states.

"I would encourage groundstaff and greenkeepers in private and public sectors to seriously look into tank mixing as an alternative to their normal methods." But, the method certainly is no job for "amateurs", he stresses, and should never be approached in a "casual" way, "but that should not deter people from doing it".

Tank mixing involves blending two or more pesticides or other chemicals in the same tank. In the amenity sector, where a wide selection of insecticides, fungicides and herbicides can be applied, the crucial aspect of mixing is to check which can live happily in the same container, as not all do by any means.
Clear guidance is available to reduce the risk of mishaps, Allbutt explains. "An operator cannot make a tank mix unless he has the approval from the manufacturers of the products being used, as the mixing of ingredients that are not chemically compatible can have adverse effects - yet some are still under the impression that free mixing of products is an acceptable practice."

Before attempting any mix, operators and/or end users need to investigate whether it's chemically possible to do so - a process not to be undertaken when time is tight and deadlines are looming, warns Allbutt - one reason why he believes the amenity sector has grown more cautious about the method, in contrast to agriculture, where it is much more widely applied.

"There's a high risk of chemical incompatibility with tank mixing that could have potentially disastrous results and, more likely, something will not mix than will, and the user often might not know what mixes are or are not suitable."

Allbutt puts the lack of industry knowledge down to the level of risk involved with the method, a factor confirmed by councils across the UK that have decided to move away from tank mixing in recent years.

"We hardly do any tank mixing anymore, largely due to the likelihood of things going wrong," states Mark Dempsey, support services manager for Calderdale District Council.

"A few years back we were left with big problems after leaving selective herbicide in the tank for too long. We had terrible trouble trying to clean the machine afterwards." Although it's "rare" for local authorities to make a mistake like this, Dempsey maintains, "we want to ensure it doesn't happen again".

In erring on the side of caution, Calderdale has followed the trend set by a growing tally of other northern councils and kept the bulk of its pesticides applications in-house. Bradford, Sheffield, Leeds and Newcastle are reportedly contracting out, and southern authorities are said to be far more "contractor-driven".

"We use a contractor for some jobs, particularly when it makes more time and financial sense to do so - for example with our sportspitches - and have worked with several," explains Dempsey.

Although some councils fight shy of tank mixing, commentators report a growing trend among authorities that do spray in-house towards applying a more complex cocktail of chemicals in one hit.

That way, they aim to save time and money for both in-house and outsourced work, and reap the benefits of a more concerted, co-ordinated programme of treatment for sportsturf and amenity areas.

Manufacturers are understandably alert to the potential dangers of inappropriate tank mixing, and usually provide comprehensive guidance on their packaging about what chemicals within their product range can be combined, following completion of all the necessary tests for compatibility.

Difficulties can arise when end users want to mix chemicals supplied by more than one source. Manufacturers prefer their customers to use their own brands, because they cannot give a categorical assurance that differing ones are compatible, they argue.

Those wishing to buy from several sources are left in the dilemma of being forced to train up staff to a level of competency to choose for themselves how they mix chemicals or play safe and purchase from one supplier, who can give them the assurances on compatibility that they seek.

The safe option, some say, is to scrap tank mixing in-house, leaving it to the expertise of contractors or, as councils are pursuing, seeking organic or greener options to the applications of chemicals, especially at a time when EU legislation is starting to bite and tried and trusted pesticides have been banned.

Adherence to any one option shows no national trend, however. Some believe in tank mixing, others do not. The more worrying common thread, say Allbutt and others, is the lack of knowledge on correct mixing.

"Tank mixing is a pretty common practice," a spokesperson from a leading turfgrass research body confirmed, "but contractors complain that councils do not know what they are doing, and that they are increasingly being asked to undertake unreasonable tasks."

The onus for ensuring compatibility usually should rest with the contractor, argues one major operator that serves councils and private clubs and amenity sites across the UK and Ireland.

"It's better for local authorities to leave such a specialist service to specialist providers, because only those who deal with chemicals every day will know which can be mixed in the tank," argues Alan Abel, technical director of Complete Weed Control.

There are some definite 'don't dos', he adds: "You really do not want to be mixing 2,4-D selective weedkiller with glyphosate for example, because you are left with scum floating on the top of the surface."

A wish to mix fungicides and iron is also common. "The two do not go together," Abel stresses. However, because of the compatibility issue, those requiring total weed control are becoming accustomed to multiple runs of glyphosate, he adds.

The code of practice for using plant protection products, issued by DEFRA, the Pesticide Safety Directorate and the Chemicals Registration Directorate, outlines exactly what should and shouldn't be done when tank mixing.

"It's the standard reference, the industry Bible," states Allbutt. The code states that 'any person using a pesticide in the UK cannot use it unless they are competent to do so', with Section 4.5 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.
The issue of legality is an important one to consider, stresses Stuart Staples, Technical Manager for Scotts Professional, adding that fines and insurance problems might arise if operational guidelines are not followed.

Area sales managers would generally advise councils on what products could and could not be mixed. "However, contractors are taking more of a lead on this, but we would know what products are compatible legally and chemically."

"Advice from the Pesticides Safety Directorate (PSD) states that there are only two approved types of tank mix - convenience and positive. In order to make a recommendation for either type of tank mix, additional data or information is needed by the PSD to give label approval for the tank mix.

If the tank mix is not approved by the manufacturer, there is no guarantee of performance or safety of the resultant mix, he stresses.

"For the convenience tank mix, the supplier must be able to produce a Compatibility Assurance Statement to show that the two products can be safely mixed. If there is a claim of improved or similar efficacy by tank mixing, or improved or similar efficacy with reduced rates of one or more of the active ingredients, this then becomes a Positive Tank Mix.

If this is being recommended as an approved mix, he continues, "additional efficacy data must be on the label to back up these claims".

If a tank mix is recommended as an approved mix and used without the above data, "this could be illegal and will have implications for insurance liability".

The PSD has stated that, if a company is recommending reduced application rates, it would request that the company produces data to back the claims made, he concludes.

New ways of formulating mixtures, ready made for end users, are taking the industry in a new direction, however. "A tank mix should be undertaken to enable a better job to be done," believes David Senior, technical manager for Vitax Amenity, which supplies a range of chemicals, fertilisers and application equipment to the industry.

"The method is far more common in agriculture where it is used to tackle a specific problem. In amenity, there is little point in tank mixing two products with similar modes of action."

"Products are increasingly being formulated and packaged as a mixture of different chemicals, whose actions have been tested thoroughly and whose effects have been evaluated. Bringing such mixtures to market is the way forward."

The Amenity Forum has been one of the key players in the recent EU thematic strategy talks, with the clock now ticking for the industry to meet the targets set to come into force in two years' time. "The hope for us is that we'll be able to continue using pesticides responsibly in the future. What we don't want is prohibition of pesticides," insists Allbutt.

The overall results have been welcomed by industry leaders who feel a national action plan, to bring in a coherent strategy to reduce pesticides use, was needed.

The latest EU targets will mean both the amenity sector and local authorities will have to be more sparing with what products they use, keeping waste to a minimum.

Tank mixing could well be a good way of carrying out a number of tasks in one application and, Allbutt believes, despite the potential risks involved, councils are in a good position to successfully reintroduce mixing more widely.

"We have the leading amenity industry in the world, and a number of major chemical manufacturers who are more than willing to offer guidance and advice to those who want to get the best out of tank mixing, and not fall foul of its pitfalls."