0 Disease Management Nightmare

Hand-Sprayer-circa-1960.jpgGraham Paul, Chemical Specialist at Sherriff Amenity looks at thirty five years of changes in our approach to disease management on turf

Turf disease control was much simpler thirty five years ago - you just treated any patches that appeared with a mercury-based fungicide and it was more or less sorted. To make life easier, there were fewer products to choose from and most had a very broad spectrum of control, so you didn't have to be particularly adept at disease identification.

Fewer re-treatments were necessary because most fungicides of this era took a long time to break down. It seems that these fungicides were controlling problems that were not evident at the time, for ten years after we stopped using mercury-based products several 'new' diseases started to appear as levels of mercury in the soil were depleted. For example, we began to see Anthracnose and the thatch eating disease Superficial Fairy Ring on a regular basis.

Regulation of pesticide use was more relaxed; spray operators didn't need a licence and there were no regulations governing the storage and disposal of used containers or unwanted product, although there were guidelines for these issued by the Ministry of Agriculture.

The Pesticide Safety Precaution Scheme was a voluntary system of product regulation of that time and, in addition, manufacturers could demonstrate the efficacy of their goods by obtaining an 'Approval number' via the Government run 'Approvals Scheme' to show potential customers that it "did what it said on the tin".

At the close of the 1970s came 'the age of enlightenment' for the Agrochemical industry. The European Community outlawed indiscriminate, persistent chemicals and manufacturers had to seek out safer alternatives. Over the next few years we saw the introduction of many new fungicides with turf recommendations, some (e.g. iprodione) have stood the test of time and are still available but others came and went.

Tighter controls on the storage, sale, use and disposal of chemicals was legislated in 1986 and has meant that pesticides present a much lower risk to the users and to the environment.

All pesticides with approval to be sold in the UK are now subject to a regular review. In this process, those wishing to secure a further period of approval may be required to submit data on the toxicology, efficacy and/or environmental impact of the active ingredients, in order to keep the products up-to-date with modern standards. The data that was sufficient to gain approval for a product 25 years ago may fall well below our current criteria. For this reason we have recently seen a large number of pesticide products withdrawn from sale.

Fortunately, it may not be all doom and gloom as we have also seen some important new products launched into our market place. In particular, there are some useful new fungicides that bring modern technology to the task of disease control. Highly active products with lower dose rates have dramatically reduced the volume of chemicals put into the environment and new modes of uptake have given a new slant to the term 'systemic'.

Traditional systemic fungicides were taken up mainly by the roots which meant that they could only be used during periods of strong growth and there was a delay of about 48 hours for the chemical to get to the leaf where it was needed. Many of the newer fungicides are taken up through the leaves, a process that requires less energy from the plant and, because uptake is possible during periods of slow growth, they can be used much later in the season.

One new family of turf fungicides known as the 'strobilurins' now has three different products in the amenity market. These have natural origins in that the basic chemical structure was developed from naturally occurring fungicides produced by wood-rotting fungi. These three products have the same biochemical action against the fungal pathogens, although there are significant differences in the way they behave inside the plant. Azoxystrobin, the first of the newcomers in this group, moves into the leaf and then gains access to the plant's xylem transport system which carries water and nutrients upwards to the leaf tips. This movement is known as acropetal penetration.

True systemic activity in the xylem system can be a definite bonus in broad-leaved vegetation where the plant grows from its extremities (the apical meristem). However, grasses grow from the base of the plan so upward movement of fungicides within the leaf will take the chemical away from the unprotected new growth at the base and could reduce the period of protection in times of active growth.

Trifloxystrobin sold under the brand 'Scorpio' has a slightly different mode of uptake to azoxystrobin in that it moves quickly into the wax layer of the leaf cuticle where it is protected from any subsequent rainfall and then moves into the plant cells without getting into the transport systems. The active ingredient is then able to move from leaf to leaf in the vapour phase to protect new leaves that emerge from the base of the plant. Bayer, who manufacture the product, refer to this mode of uptake and distribution as 'mesostemic' and claim a long period of activity - up to 56 days - together with a wide range of turf diseases controlled in many countries around the globe.

Pyraclostrobin is the third member of the strobilurin family to be launched into amenity turf. Like trifloxystrobin, it too moves into the leaf wax but has no action in the vapour phase. It is interesting that three active ingredients from one chemical family can have the same effects on the target pathogens yet behave so differently within the plant.

Another fungicide group (known as the dimethylation inhibitors) has provided three more new fungicide products that have uptake via the leaf. Two of these; myclobutanil and propiconazole, demonstrate acropetal movement within the leaf in the way that azoxystrobin does. The third product 'Lunar' is a mixture of two ingredients; an acropetal penetrant (tebuconazole) and prochloraz which penetrates the leaf but has only translaminar movement within the leaf tissues. This combination gives Lunar eradicant and protectant properties and also the best of both types of behaviour inside the leaf.

Fungicide resistance, the ability of a pathogen to adapt to a chemical and survive, has been a problem for many years. It often results from the over-use of a 'favourite chemical', especially where the product has just one mechanism of attacking the pathogen, i.e. a single site mode of action. One way to reduce the likelihood of resistance developing is to apply a mixture of fungicides with different sites of action.

This practice has been followed for many years in agricultural crop protection and is now recommended under the latest framework (Plant Protection Product Regulations) which states that resistance management issues have to be addressed and measures taken to mitigate the risks.

In the management of amenity turf there are many possibilities for tank-mixing strategies. For example you can mix Scorpio with Lunar to combine the benefits of the mesostemic, systemic and trans-laminar uptake and distribution, to give long-term eradicant and protectant action against fusarium, such a mixture now has a multi-site mode of attacking the pathogen. You should only use tank-mixtures that are backed by your BASIS registered fungicide supplier and, if you are in any doubt about a recommended mixture, ask for a signed, written recommendation.

When tank-mixing was first proposed in the amenity turf market there were cries from some ill informed sources that it "was dangerous and might even be illegal". It pleases me to see that the same voices who questioned tank-mixing have now seen the light and are themselves firm advocates of the practice.
Lunar and Scorpio are registered trademarks of Bayer.

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