Adjuvants are OK despite anomalies
APPARENT anomalies in a set of adjuvant trials should not detract from the overall message that fungicide performance may be boosted by using such products.
That is the reaction of Headland Agrochemicals John Teague after an examination of results from two years experiments with the firms sticker/spreader spray additive Guard.
The work, by Nigel Metcalfe of Yorks-based NDSM, examined the impact of adding the standard rate of Guard to a range of fungicides – used mainly as mixtures – at full or three-quarters dose.
The results found that when taken as a whole Guard gave useful benefits, marginally increasing control of mildew and in some cases septoria, and lifting margins by as much as £27/ha (£10.90/acre) in one instance.
However, there were some odd results, the most significant involving three-quarter rate mixtures of cyproconazole and chlorothalonil. In 1995 on Buster, when Mr Metcalfe acknowledges septoria pressure was low, adding Guard to a full rate mix of the two chemicals raised yield by 0.11t/ha (0.9cwt/acre). But doing the same at the three-quarter rate trimmed output by 0.85t/ha (7cwt/acre).
A similar result had been obtained with the same mixtures on Riband a year earlier when disease pressure was greater, S tritici affecting an average of 6.8% of the older leaf area in early May.
Then Guard added to the full dose cyproconazole/chlorothalonil mixture raised output by 5%. But using it with the three-quarter rate mix decreased yield by 4.7%, reports Mr Metcalfe.
However, over the full range of treatments in 1994 the use of Guard saw a 9.4% increase in output. And even in 1995 it gave an overall yield lift of 0.35t/ha (2.8cwt/acre), the figures show.
"The overall trend is for an improvement in performance," comments Mr Teague. He is hard put to account for the apparent quirks in the trials, but says results from small plot work always need interpreting with caution.
"There was clearly something odd going on last year. And dont forget that there was a severe drought and very little disease anyway. You can always get rogue results."
Guard helps provide more even chemical distribution and faster drying on leaves, he maintains. As such it might have been expected to have improved the performance of a mainly protectant fungicide like chlorothalonil. "It was an odd result because on full rate it clearly worked."
Despite the trials, Headlands aim with the product is not to encourage growers to cut fungicide doses, says Mr Teague. "We are selling it so that the chemicals can do a better job nine times out of 10. We are very confident we are on the right lines." *