CropAlert Net Form of Net Blotch October 2011

CropAlert Net Form of Net Blotch October 2011

A severe outbreak of the net form of net blotch (NFNB) was detected in a crop of barley growing in the Wimmera region of Victoria.

NFNB can cause grain yield losses as high as 70 percent, if infection goes untreated, in susceptible varieties. Growers need to be aware that there is a risk of infection from NFNB. They are advised to closely monitor crops with the view of applying a foliar fungicide if the disease is detected prior to ear emergence.

More than one application of a foliar fungicide may be required to manage NFNB and protect the upper leaves from infection, if the infection is detected before ear emergence.

It is suggested that growers monitor crops for the remainder of the season and apply foliar fungicides as needed. There are several registered products available. Contact local agronomists or resellers for further information on fungicide control.

What to look for

The net form of net blotch is different from the more common spot form of net blotch. Net form starts as pinpoint brown lesions, which elongate and produce fine, dark brown streaks along and across the leaf blades, creating a distinctive net-like pattern.

Symptoms of the spot form of net blotch develop as small circular or elliptical dark brown spots becoming surrounded by a chlorotic zone of varying widths. The spots do not elongate into the net-like pattern

This is the first significant recording of NFNB in Victoria for more than a decade, and highlights the risk associated with growing susceptible varieties. This situation also places other varieties with resistance under pressure as it increases inoculum, and therefore the opportunity for mutation and the emergence of new virulent pathotypes.

The majority of varieties grown in Victoria have adequate resistance to this disease. Even though conditions in Victoria are conducive to this disease, the widespread use of varieties with either complete or partial resistance to this disease has kept it under control.

Be aware that going into next season NFNB can carry over on seed and stubble. It can therefore be an issue in most paddocks regardless of paddock history.

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