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Getting the timing right for net blotch fungicides

By Mark McLean, DEDJTR Victoria.

NBFSpot form of net blotch (SFNB) can reduce grain yield and quality if it becomes severe. Check crops early in the growing season and be prepared to apply a foliar fungicide if necessary.

Application of foliar fungicide is an important management tool that can provide effective suppression if applied in a timely manner. The best suppression of SFNB comes from applying foliar fungicides during stem elongation (GS31-34) and flag leaf emergence (GS37-39) growth stages. One application may be sufficient during seasons with a dry spring, while two applications may be required during seasons with average or above average rainfall during the spring months.

Growers can incorporate fungicides with post-emergent herbicides, but are encouraged to only do so when crops are nearing stem elongation stages as applying fungicide too early is generally not effective.

Generally only varieties that are rated as Susceptible (S) or Very Susceptible (VS) will benefit from a foliar fungicide application. Moderately susceptible (MS) or better varieties are much less likely to suffer yield loss, so fungicide application is only recommended where disease levels are severe.

Spot form of net blotch is a sexually reproducing pathogen which means its virulence toward varieties may change to some degree over time. Growers should consult their respective state based Cereal Disease Guide for up-to-date resistance ratings of barley varieties.

Spot form of net blotch has occasionally been more severe in some moderately susceptible barley varieties such as Scope and Buloke than what their rating would suggest. This was the case in areas such as Loxton and Cleve in South Australia and Swan Hill in Victoria during 2013 where environmental conditions were favourable for SFNB late in the season, when crops were maturing. Management using fungicides may have provided some improvements in these situations, however, they are generally uncommon.

For more information on management of this disease see DEDJTR’s Net blotches of barley

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