ACROSS Australia, apple crops can now be protected from Alternaria fruit spot and leaf blotch with Dragon 700WG (dithianon) – a proven fungicide in Australian apple orchards.
Announcing this important registration, Crop Care regulatory affairs manager Bronwyn Vorpagel said with increasing incidence of Alternaria disease in Australian apple orchards, and limited registered fungicides for its control, Horticulture Australia (HAL) and Apple and Pear Australia Limited (APAL) had funded research into the disease and its potential control with existing orchard fungicides.
In Queensland trials, Ms Vorpagel said that a 700WG formulation of dithianon had proved very effective for reducing Alternaria leaf blotch symptoms, defoliation and fruit spot.
“A Crop Care application to APVMA for registration of Dragon 700WG for this purpose was approved in June 2014. Already used by Australian orchardists against black spot/apple scab and bitter rot, Dragon 700WG can now be used at the same registered rate for Alternaria management – the only dithianon (Group M9) fungicide registered for this purpose in Australia,” Ms Vorpagel said.
Queensland Department of Agriculture, Fisheries and Forestry (QDAFF) now rates Alternaria leaf blotch and fruit spot alongside apple scab as the most significant apple diseases in Queensland.
Affecting apple leaves and fruit mid to late season in high spring/summer rainfall areas, Alternaria can cause significant fruit loss, with the disease progressing from leaf infection to fruit spotting.
Aternaria leaf blotch was first reported in the 1990s and fruit spot in 2003 – both around Stanthorpe in Queensland’s Granite Belt.
By the mid 2000s, Alternaria fruit spot was considered a significant pathogen, particularly of the higher-value apple varieties Gala, Pink Lady, Fuji plus Red Delicious.
Alternaria has also been a problem in NSW orchards around Bilpin, Picton and Orange; in Western Australia when warm, wet weather favours the disease; with some reports of Alternaria-like symptoms also in South Australia and Victoria.
Research by QDPI&F plant pathologist Christine Horlock and colleagues reported that the Alternaria species impacting on Queensland, NSW and WA orchards were widespread in all major Australian apple-production areas.
The research confirmed Alternaria leaf blotch caused significant premature leaf defoliation as early as January, with the majority of Alternaria fruit spots appearing two to four weeks prior to harvest.
Another Queensland Government/HAL-backed study by University of Queensland PhD student Dalphy Harteveld confirmed symptoms of leaf blotch developing from November to February, and fruit spot peaking in January and ongoing up to harvest in February.
Since 2001, research into managing Alternaria – including registration of suitable fungicides – has been undertaken by QDAFF and NSW Department of Primary Industries (NSWDPI) with HAL and APAL funding.
These trials led to emergency-use permits for late-season use of specific fungicides.
Data from two QDAFF and private research company field trials on susceptible varieties demonstrated that Dragon 700WG would be effective in reducing the number of infected leaves later in the season, preventing premature defoliation and reducing the number of fruit spots.
Combined with good orchard hygiene to reduce accumulation of Alternaria-infected litter, Ms Vorpagel said researchers concluded that:
An effective, registered fungicide remained the most important factor in symptom reduction.
The best timing for applying fungicide to control Alternaria leaf blotch and fruit spot in apples was during flowering and early fruit development stages before any symptoms appeared.
She encouraged Queensland and NSW apple growers with significant Alternaria infection last season to use preventative measures this season.
“Using a broad-spectrum fungicide like Dragon 700WG several times during early-mid growing season for apple scab/black spot will reduce Alternaria in the orchard,” she said.
“After the black spot season, growers should make further approved fungicide applications to manage Alternaria fruit spot in Gala, Pink Lady and Red Delicious varieties – especially from eight weeks prior to harvest up to the recommended WHP.”
With WA Alternaria outbreaks associated with higher-than-average spring/summer rainfall, she advised WA growers to make fungicide applications on the basis of weather.
“Even with average rainfall, orchards with a history of Alternaria infection should be treated with Dragon 700 WG in a protectant program. “
Similarly, she advised growers in other states to monitor for leaf blotch if spring/summer rainfall occurred, and to begin a preventative fungicide program at the earliest sign of leaf infection to protect fruit.
Ms Vorpagel said Dragon 700WG label instructions for Alternaria were to apply as a foliar spray during flowering and early fruit development, with applications every 10-14 days – using the shorter spray interval if weather favoured disease development.
“Dragon 700WG is a multi-site protectant fungicide – Group M9 for resistance management,” Ms Vorpagel said.
