Transcend offers better apple scab control

Improved apple scab control has been achieved with the help of a special adjuvant in an Agrovista trial. Transcend has the ability to ensure that fungicides reach leaf surfaces early in the season when the leaves are still very small and hairy and very prone to infection.

Agrovista fruit agronomist Paul Bennett told the company's spring fruit seminar that even at early green cluster stage the leaves in the centre of the buds are very difficult for fungicide sprays to fully reach.

He explained that Transcend combines two types of adjuvant - a silicon and an oil - that provide the best of both worlds. It contains 80% methylated soybean oil and 15% complex silicon.

Silicons are "super wetters" that are very good at wetting leaf surfaces to provide better spray coverage but tend to over-wet so that the spray can flow off the edges of the leaves. On the other hand oil reduces surface tension on leaf surfaces resulting in better fungicide absorption and rain fastness.

"One thing that's always bothered me about scab control is that early in the season the target is so small and difficult to wet," maintained Bennett. "Even at the early green cluster stage the leaves in the centre are not easy to get at.

"You also tend to see lots of spray droplets sitting in the ends of the leaf hairs and that makes me wonder how much spray actually gets down to the leaf," he added.

Transcend's efficacy was clearly demonstrated last year in the trial in a 3.66m by 1.52m Jonagold orchard near Wisbech that's proved particularly scab prone. Three treatments were applied, one to each plot, at 200l/ha after scab infection events, as predicted by a computer model, from bud burst to mid-bloom. The crop is most prone to infection at the latter the stage.

Dithianon provided by BASF was used at 500g/ha in one plot, 750g in another and at 750g plus 250ml of Transcend in the third.

Leaf scab was assessed on 100 extension shoots from each plot at harvest time. Those from the 500g and 750g plots had 24 per cent and 20 per cent scab respectively compared with only 4 per cent from the 750g plus Transcend treatment - a significant improvement said Bennett.

As a result of the better scab control achieved with the use of Transcend the winter scab carryover on leaf litter should be reduced, he reckoned.

He said that there was very little or no fruit scab in any of the plots. It probably would have been worth applying the treatments up to the end of petal fall but when adjuvants are used beyond very early fruitlet stage there is a risk of fungicide residues unless their rate is halved.

 


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