BASF new blight fungicide Resplend reveals its rainfastness

Even if rainfastness may not appear to be top of the agenda for potato blight fungicides this season, such products must be highly rainfast and weather proof, as the majority of the crop is irrigated and spray intervals must be kept tight throughout the programme.

"Farmers need blight fungicides that make the most of available spray days and give them the best opportunity to keep to their planned spray intervals, which for most growers is now 7 days. When blight control falls down, it is usually due to the lengthening of the spray interval, planned or otherwise. So being able to utilise every spraying opportunity is vital if blight is to be kept at bay. But farmers need to be confident that when they apply a blight fungicide, it stays on and gets into the plant and is not washed off. If there is also re-distribution across the leaf to improve coverage, then so much the better,” says Phil Brown, Agronomy Manager for BASF.

Phil reports that research and development work on the new blight fungicide Resplend (300 g/litre ametoctradin + 225 g/litre dimethomorph) reveals its superior rainfastness. “In fact it looks to be one of, if not the best in trials, when compared with cyazofamid, mandipropamid or fluopicolide + propamocarb, all of which have excellent reputations for rainfastness when applied to a dry leaf. In tests where 20 mm and 40 mm of water were applied after fungicide application and blight levels assessed 7 days later, Resplend reduced blight substantially. In the worse case scenario where 40 mm of water was applied within one hour, the untreated had close to 80% foliar blight, whereas the Resplend plots had 17% blight, the fluopicolide + propamocarb treatments had 26%, mandipropamid 21% and cyazofamid 20%” (See graph at end of release).

Phil explains that the rainfastness of Resplend is largely due to the lipophilic nature of one of its actives, ametoctradin. “With high affinity for leaf wax, ametoctradin binds tightly to the wax on the leaf’s surface where the pathogen infects the plant, becoming rainfast within an hour and becoming highly resilient to wash off. By forming a stable layer on the leaf surface, it provides a protective shield through adsorption on the wax layer.”

"Ametoctradin is also redistributed under the influence of moisture, to expand the leaf area that is protected. If the first application of Resplend gives 100% leaf coverage and is followed by alternating cycles of wet and dry, caused by either dew, rainfall or irrigation, the area of the leaf protected will increase by a further 50% after 2 cycles and by a further 100% after 4 cycles. The suspension concentrate formulation of Resplend also has relatively small particles, with more than 50% of particles being less than 2 microns, which adds to its excellent coverage of the foliage.”

Peter Clare, MD for Cheshire-based distributor Environmental Crop Management Ltd, has to contend with high rainfall and hence high blight pressure every year. “Growing early and maincrop potatoes in an area with consistently high rainfall and a history of regular potato blight means that a prescriptive approach of weekly spray intervals is the only realistic way forward,” he says.

"Not only do we have high rainfall, but we have had A1 and A2 blight for 15 years. So we start spraying early, maintain tight weekly spray intervals and continue protection right to the end, including a fungicide at burning off.”

He looks for fungicides with good rainfastness. “This is essential for growers with large areas to treat and high disease pressure to cope with. They need to be able to take advantage of every available spray window. We had the opportunity to try out Resplend last year and decided to test it from the middle of the programme onwards, due to its strength on tuber blight, its curative activity on late infections and its impressive rainfastness. As far as we were concerned Resplend worked well, controlling several late infections.”

Phil Brown, Agronomy Manager for BASF, explains that Resplend, which contains ametoctradin and dimethomorph, offers protectant, locally systemic and translaminar activity with options for use at rapid canopy, stable canopy and senescence. “It is a mancozeb-free option which may appeal to some sectors of the industry. It has demonstrated in trials that it can stack up well against any of the key blight fungicides in terms of both foliar and importantly tuber blight as well as rainfastness.”