BARLEY growers are being reminded to monitor crops for disease after net blotch emerged in several parts of the State.
Spot Type Net Blotch (STNB) and Net Type Net Blotch (NTNB) have been discovered in areas such as Wongan Hills and Corrigin and down to Frankland and Kojaneerup in the past month.
In many cases the diseases were found in barley regrowth or volunteers, but some Planet and Rosalind barley seeded this year has also reportedly been susceptible.
Net blotches being found on barley volunteers or regrowth is a good indicator that conditions are ripe for the disease and that barley on barley seedlings are at risk of infection.
Both STNB and NTNB are stubble-borne diseases, with the fungus carried from season to season on infested stubble.
The closer new crops are sown to stubble, the greater the risk of infection occurring at early growth stages.
STNB lesions develop as small circular or oval dark brown spots with yellow edges.
Infections can occur following about six hours of leaf wetness at temperatures between 10-25 degrees Celsius.
Primary inoculum comes from airborne spores, which are produced on stubbles from previous crops.
Risk of infection in seedling to tillering growth stages is greatest in barley regrowth and continuous barley which are exposed to infected barley stubble.
STNB occurs across the State but is most damaging in south coastal and neighbouring medium to high rainfall regions where it can have severe yield and quality effects.
NTNB lesions appear on leaves as thin brown streaks or blotches that may enlarge up to several centimetres in length.
Darker longitudinal and horizontal lines sometimes develop in the lesions, creating a net-like appearance.
NTNB infection and spread is favoured by wet conditions and it is most evident following periods of rainfall.
It will cause the greatest yield loss in paddocks that are re-sown to barley without a break crop as the fungus is stubble borne.
Spores produced on stubble are spread by wind to initiate infections in new barley crops.
Seed infection is rare and is considered of minor importance in spreading disease.
Barley varieties that are susceptible to STNB or NTNB that have not been treated with a registered seed dressing against net blotches and are sown into in a high risk situation (barley on barley) are particularly vulnerable.
Department of Primary Industries and Regional Development plant pathologist Kithsiri Jayasena has been monitoring the disease prevalence in the south of the State and said it seemed that Planet was an issue as well as Rosalind.
"When we have warm conditions, moisture and high humidity it is conducive for both STNB and NTNB," Mr Jayasena said.
"The main thing is to use an integrated disease management system when going to crop.
"Variety selection, clean seeds and plant nutrition are key things to manage to try to reduce the prevalence of these diseases.
"When selecting cropping paddocks it is important to carry out good weed control, managing the green bridge is very important.
"Also if barley is going on barley or next to a barley crop from last year, then it is a high risk situation and needs to be managed."
Mr Jayasena said one weapon in growers' arsenal was the use of fungicides.
"If these diseases are appearing in crops now a foliar fungicides can be applied to control them," he said.
"Applying a fungicide spray is necessary in medium to high rainfall regions where disease threatens crops with high yield and quality expectations, particularly if the barley crop has been sown into or adjacent to last year's barley stubble."
Application of a registered foliar fungicide prior to stem extension (for example, tillering) can reduce disease levels but may still require a follow-up fungicide later in the season.
In low rainfall areas, fungicide applications are most likely to result in a yield response to STNB when the disease pressure is high and there is reasonable spring rainfall or stored soil moisture.
The choice of a single-spray or two-spray strategy depends on the environment in which the crop is growing.
In high rainfall environments it may be necessary to apply two sprays, such as at early stem elongation stage with a follow-up spray three to four weeks later.
While in medium rainfall regions, consider one well timed spray between late stem elongation and early flag leaf emergence (Z33-39) to protect leaf 2 (flag-1).
Under high disease pressure, best results may be obtained by using the maximum recommended rates.
"When applying fungicides growers must be aware that they need to avoid resistance building up," Mr Jayasena said.
"The same product shouldn't be used more than two times in one season."
Mr Jayasena said plant nutrition was also an important consideration in reducing the risk of STNB or NTNB.
"Potassium is a particularly important in this situation," he said.
"Potassium is one of the macro elements that make the plant cell walls much harder and good plant nutrition is a good management practices to try to avoid the diseases."
In some cases net blotch has caused up to 45 per cent yield loss in crops.
