Technical
visible. In these instances you need a fungicide that will quickly move around within the leaf, to seek out and stop the infection.
The timescale for action does depend on the level of infection, the virulence of the pathogen, the health of the turf plant and the prevailing weather conditions but, generally, we are talking hours or, at best, a couple of days. It demands genuine systemic movement from an active that can be taken up and move around within the plant leaf. If you applied a contact or local penetrant at this stage, it would primarily only target pathogen activity on the leaf surface. This can effectively protect from new infection from spores landing on the leaf, but offers little recourse to disease activity already in the plant.
Also, consider the speed of the active
uptake and how quickly it can move through the leaf - especially in cooler spring conditions. All systemic actives need some growth to aid movement but some, such as propiconazole, are taken up and move faster than others in cool weather. Furthermore, if you get an active that
is taken up by the roots and crown, it can give a continuous resupply of fungicide through the plant for weeks. Indeed, any active that subsequently exudates from the leaf tip after cutting may be washed down and reabsorbed to recycle the fungicidal properties, such as azoxystrobin in Heritage Maxx and Headway.
In trials, azoxystrobin treated bentgrass and fescue turf has been shown to retain consistent high levels of active in clippings removed for six weeks or more after application, which demonstrated the fungicide was being replenished through the leaf throughout this period. In comparison, trifloxystrobin was present in the clippings at only low levels for only six days after application, and no evidence in new growth thereafter. Biokinetic studies have shown up to 98% of trifloxystrobin was locked into the lipophilic wax layer on the plant leaf surface, with minimal local movement through the leaf, whereas true systemic actives move smoothly and consistently through the leaf.
Contact cut off
With contact products bound onto the leaf surface, as the leaf grows and is cut off, the fungicide protection is removed. With a fine turf surface cut at 4mm, for example, spring growth of 0.5mm a day could see 50% of the product applied cut off in four days, and all removed in just a
week. Furthermore, as the plant puts on new growth from the base of the leaf, the new growth will be completely unprotected - where disease can be most prevalent and where damp conditions are conducive to infection. When we look at appropriate fungicide actions for different periods of the year, then it points towards systemic in the summer when the turf is growing and contact+ activity in the winter, when it’s not. But, to refine that recommendation, we are seeing good results from assessing soil temperatures as a guide to growth potential and fungicide selection. When soil temperatures are consistently less than 7°C, growth will typically be slow or zero and you will get the best out of contact+ activity to give long-lasting results. As temperatures rise above 7°C and turf begins to grow in the spring, or slows down in the autumn, a cool weather systemic will provide the necessary movement to protect the slow growing turf. As temperatures continue to warm up, and when they reach 12°C or more, you can also employ the full systemic actives to maintain clean surfaces right through the season.
Covering a multitude of conditions
Weather conditions in early spring and late autumn often pose a real dilemma for fungicide selection. Warm days that get plants photosynthetically active, are often followed by cold and even frosty nights. That puts extra stress on turf and that can make it more vulnerable to disease infection.
It’s a time of the year when multi- active fungicides can have a highly effective role to cover all the eventualities of changeable conditions. The key is to ensure that you have both the systemic and contact facets required in the one product; two relatively immobile contact or local penetrant actives won’t give the systemic movement required when the turf starts to grow. Also, ensure that the multi-active as a whole is providing more active and protection than if the individual components were used alone. When conditions are tough and stressful, it is even more important to have sufficient fungicide on and in the leaf to prevent attacks.
FEBRUARY/MARCH 2013 PC 127
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