Control SFNB with correct spray timing

GroundCover Live and online, stay up to date with daily grains industry news online, click here to read more
Image of Dr Mark McLean

Dr Mark McLean says growers can effectively control the spot form of net blotch by applying fungicides between GS31 and GS47, when the crop produces the most biomass.

PHOTO: Victorian DEDJTR

Growers are urged not to be complacent when it comes to managing spot form of net blotch (SFNB) and to use foliar fungicide sprays at the right time to lessen the impact of the disease.

In very susceptible (VS) barley varieties, SFNB caused up to 25 per cent in yield and quality losses during 2014. Historically, yield losses of up to 44 per cent have been observed.

Victorian Department of Economic Development, Jobs, Tourism and Resources (DEDJTR) plant pathologist Dr Mark McLean says the disease’s prevalence is caused by:

  • growing susceptible varieties in intensive barley production;
  • one to two-year rotations between barley crops;
  • retention of SFNB-infected stubble; and
  • the ‘right’ climatic conditions (up to six hours of moisture at temperatures between 10ºC and 25ºC).

“The majority of barley varieties sown in Victoria are susceptible to SFNB,” Dr McLean says.

Hindmarsh represents about 41 per cent of barley production in Victoria, but it is VS to SFNB. Gairdner is also susceptible and Scope is moderately susceptible (MS).

“This is resulting in an abundance of SFNB inoculum being produced annually, which is just floating around the atmosphere and infecting new crops every year.”

SFNB colonises stubble over summer and disease development starts at the beginning of the new season when fruiting bodies grow. Dr McLean says growers should be out inspecting stubble for these black fruiting bodies towards the end of April and in early May.

“One of the interesting things to consider is there isn’t a great deal of difference between the barley resistance in the varieties grown in the previous season compared with how much inoculum will be present in the following year,” Dr McLean says.

“For example, Barque, which is moderately resistant (MR) to SFNB, compared with Dash, which is MS, basically produced the same amount of inoculum in the following season.

“In this intensive barley system where we’ve got a lot of susceptible varieties, it really doesn’t matter if we put the occasional resistant variety in the rotation, it’s still going to get colonised by SFNB.If you want to reduce inoculum levels, it would be best to avoid growing barley in successive years in the same paddock.”

The disease has started to spread in barley crops in lower-rainfall regions, such as the Mallee. In 2014, Dr McLean ran a trial with BCG in Quambatook, Victoria, researching varieties with varying susceptibilities to SFNB. The results showed that where there was average to above-average crop yield potential and favourable climatic conditions, SFNB reduced grain yield by between six and 11 per cent in VS varieties such as Hindmarsh and SY Rattler.

“When we looked at grain quality, we found a three to 13 per cent reduction in retention, or grain plumpness, and zero to seven per cent increase in screenings,” Dr McLean says.

For this reason, SFNB is more of a concern to growers trying to produce malting barley because the disease can reduce grain quality. In the majority of cases during a trial in the Wimmera between 2005 and 2011, varieties infected with SFNB had retention losses from five to 13 per cent.

Dr McLean says the best option for growers to control SFNB is to avoid VS varieties and, if infection occurs, apply registered fungicides during stem elongation, between GS31 and GS47, when the crop puts on the most biomass.

“That is when we will get the most penetration out of our fungicides,” he says. “If we spray too early, we just get reinfection and if we go too late, we miss the boat. This is what we have found from our trials over seven years, which have shown that targeting sprays at GS31 and/or GS39 provides the greatest suppression of SFNB. However, what that has also shown is that it doesn’t completely eliminate SFNB – we’re still getting up to about 15 per cent infection, which is enough to cause yield loss.

“That tells us we probably need to be looking at the two-application approach at GS31 and GS39 in a severe season conducive to SFNB.”

More information:

Dr Mark McLean
03 5362 2313

mark.mclean@ecodev.vic.gov.au

End of Ground Cover issue 116 southern edition
Read the accompanying Ground Cover Supplement:

Ground Cover Supplement issue 116 – Foliar fungal diseases of pulses and oilseeds

GRDC Project Code DAV00129

Region South