Grant Funds Frost Research
17th June 2009
Katnook Estate's Hans Loder has sought funding to collate a "User's Guide" to frost protection. Following the severe frosts of spring/summer 2006 in south-east Australia and the catastrophic effects on crop production in these areas, frost protection has received significant attention of late. This guide is intended for south east viticulturists and growers, to help them make informed decisions in relation to frost - risk assessment, irrigation plant, irrigation equipment and management practices.
Hans Loder is Katnook Estate's technical officer and collated the “User’s Guide”on frost protection in viticulture, which focused on frost protection by the use of overhead irrigation. The following summary was written by Katherine Lindh in the May edition of "Australian Grapegrower and Winemaker."
“We wrote the report as we (at Katnook Estate) decided there was room for improvement in our knowledge of frost events and hoped that a better understanding would subsequently help us identify shortcomings,” he said. “So, it came about that we proposed a frost trial, converting systems to reduced precipitation rates (to better match observed minimum temperatures) and new site frost management guidelines, which included a degree of automation.
“It was at this stage that we approached the South East Natural Resources Management Board (SENRMB), who as part of their “innovation grants” program, were able to assist in funding our trial, with a condition being development of the ‘user’s guide’,” he said.
According to a media release from Melbourne University in March 2008, frost damage accounts for an average of $33 million dollars a year in lost viticultural production in South Australia and Victoria alone. A survey by the Phylloxera and Grape Industry Board of South Australia (2007) also stated that for the Coonawarra region in 2006, frost accounted for an approximate 70% loss of production.
Loder said the results from the report showed that the use of overhead irrigation for frost protection, which functions by the release of latent heat at the point of freezing, remains a good option for management.
“The heat is released into the vine tissue, preventing freezing and disruption of plant cells, while also releasing some into the surrounding air,” Loder said. “While overhead irrigation is an extremely effective and relatively energy efficient form of frost protection, room for efficiency has been identified in Coonawarra, in the form of a reduction in precipitation rates and improved irrigation management.”
Loder said the factors that determine frost events and their prevention, may vary from region to region. The report states in coastal areas, the relatively warm ocean temperatures ameliorate those on land by reducing extremes in temperature and humidity, while the distance from the Equator and elevation above sea level are major cooling influences.
“Coonawarra experiences only mild frost conditions based on its relative proximity to the coast,” Loder said. “An average of only six frost events per season, and an absolute minimum for the last 25 years of -3.6oC attest to this.”
“In temperate latitudes such as is the case for the Coonwarra, low pressure systems are generally characterized by a ‘frontal’ line, along which there is a more or less sharply defined boundary between air masses of tropical and polar or sub-polar origin. Between the trough of a low pressure system and the central zone of the next high pressure system, a stream of cold air generally exists, indicated by strong winds, clouds and/or showers. As the ‘front’ passes, conditions may rapidly change with an encroaching high, clearing clouds and decreasing wind all favouring the likelihood of a frost event,” he said.
Loder said although irrigation is a good method for frost protection, effective management comes with a combination of techniques.
“Ultimately, good site selection is the best frost protection strategy,” he said. “If this, combined with “passive” protection methods, is inadequate to reduce the risk of damage to an acceptable level, then it is necessary to apply “active” methods of frost protection such as overhead irrigation.”
“Use of overhead irrigation is a proven method which has a relatively low energy and labor requirement, along with being quite versatile. For example, depending upon the site, systems can be setup to accommodate for specific observed minima.
“Needless to say, there are negative aspects to this management method, including the prerequisite of a reliable source of water and the potential for water logging. Furthermore, it’s ironic that in seasons where the winter and spring conditions are dryer (and water less available), the potential for frost increases. It is important to emphasise that good site selection is the best protection method.
For many regions throughout Australia, the start of next season will again bring with it the risk of frost and frost damage.
“Although I’m definitely not claiming to have a great understanding of meteorology, if average rainfalls eventuate this winter, there is similarly a likely chance for an average number of frosts for each region. Turning this around, a dry soil profile is inducive to frost, so if low winter and spring rainfall conditions combine with a dominance of high pressure systems over southern Australia at the start of the grapegrowing season, it would certainly make me wary of the potential for a higher than average number of frost events.
“In a nutshell, just like the latent heat which is released by irrigation water freezing on the vines, it is soil moisture which ultimately stores the suns radiant heat during the day and releases it to the sky in the evening.” Loder said.
