Foliar fungicides such as Headline appear to reduce levels of foliar disease in alfalfa, public research trials conclude. But only 25% of trial comparisons have shown higher yields and improved forage quality has been minimal, say two University of Kentucky (UK) Extension specialists.
Paul Vincelli and Ray Smith have tracked results from public field trials evaluating strobilurin fungicides since 2010. That’s when Headline was labeled for control of foliar diseases on all alfalfa production – for seed, hay and haylage – with a 14-day pre-harvest interval.
In the December 2013 edition of UK’s Forage News, Vincelli, a plant pathologist, and Smith, a forage agronomist, reported results from 42 trial comparisons. Strobilurin fungicide “very commonly reduces” levels of foliar diseases in alfalfa in humid regions of the U.S, they noted.
But the fungicide was associated with increased yield in only 11 studies and almost always in first or second cuttings.
“This may be because the fungus that causes spring black stem and leaf spot, which is most active in these earlier cuttings, is highly sensitive to Headline,” wrote Vincelli and Smith. “If considering the use of fungicide, best results will be obtained by applying during the growth phase of the forage for the first or second cutting.”
The researchers were surprised that forage quality was only minimally improved with fungicide applications. “Leaves represent high-quality forage, and we would expect that improved health would translate to improved forage quality.”
Continued research is “advisable,” they say, since several of the growing seasons in which the studies were conducted were unusually hot and dry. “Results economically favorable to fungicide use could occur in wet growing seasons.”
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