‘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
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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.
Sherriff Amenity The Pines, Fordham Road, Newmarket, Suffolk, CB8 7LG. Tel. 01638 721888
www.sherriffamenity.com 17
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