40 • Disease & Pest Control • C&CI May 2013
Coffee rust on a farm in Cauca, southwestern Colombia (photo: Neil Palmer, CIAT)
The coffee leaf rust uredinium showing arrangement of spores that spread the disease (courtesy: PLoS ONE)
said that, in the short term, “we need to resume phytosanitary treatments that have been neglected, particularly those using preventive copper-based fungicides. We need to develop epidemic monitoring systems on a plot, production zone and country level, in order to forecast the risks and target fungicide applications more effectively over time.”
Integrated
management Dr Avelino also said that training of technicians and producers needs to be stepped up. “In the short and medium term, integrated management systems will have to be adopted, in which shade will necessarily play a major role. In the medium and long term, ageing, susceptible coffee trees will have to be replaced with existing resistant varieties,” he said.
“Questions have to be asked about the possible effects of climate change on the disease,” he concluded. “Creating planting material with long-lasting resistance is a major line of research. It is still possible to improve the resistance of cultivated material. However, the genetic resources we could use for crop improvement are not infinite, and we mustn’t underestimate the capacity of pathogens to evolve.” As Dr Peter Baker, a scientist at CABI in the UK and regular contributor to C&CI explained, despite occasional outbreaks, until now, the disease never quite lived up to its early notoriety and many farmers controlled it sufficiently with occasional ‘just-in-time’ sprays.
“This situation now seems to have changed,” he told C&CI. “Colombia suffered a serious outbreak in 2009- 2010, which coincided with a severe and enduring La Niña weather event. And whereas previously the rust was never problematic above 1,600m above sea level, these high-quality Arabica zones now came under attack.
Dr Baker said the outbreak in Central America (and now possibly Peru as well) appears to be a similar event, with anecdotal reports of heavier rainfall across the region. Currently however, hard data from the region is lacking and until this is available, the exact trigger for the event remains uncertain. Dr Baker said a meeting was due to be convened in April in Guatemala by World Coffee Research (WCR) which hopefully will throw more light on the causes. “Until we know what specific conditions are conducive to an upsurge, we will be quite unable to forecast a similar event in the future,” he said.
“The best available data comes from Colombia,” he told C&CI, “where we know that average Andean minimum temperatures at coffee-growing altitudes have increased by 0.1 to 0.3°C/decade and the diurnal temperature range has decreased by 0.2 to 0.3°C. At the same time, hours of sunshine have declined rapidly, in the range of 65 to 120 hours/year/decade.
The rust epidemic can therefore be interpreted as a consequence of more globally chaotic weather patterns which create unusual conditions that are difficult to predict and interpret in real time
“Previous laboratory studies have shown that optimum rust germination temperatures are high, at 21 to 25°C with a minimum of 15°C. Cool night-time temperatures (common on mountain sides) inhibit the process. The presence of water droplets and low light intensity are also critical for spore germination.” Dr Baker noted that the ideal conditions for rust germination are therefore very specific, and presumably hitherto rarely present in Latin America. However, gradually increasing temperatures (especially minimum temperature rise,
a signature of climate change) have expanded the zone of susceptibility. When specific weather patterns then occur, including long periods of rain and heavy cloud (whose frequency may also be linked to climate change), these create the ideal conditions for an outbreak. “The rust epidemic can therefore be interpreted as a consequence of more globally chaotic weather patterns which create unusual conditions that are difficult to predict and interpret in real time,” he said. “We can expect such events to become more common in the future. This could be regarded as a ‘canary in the mine’ moment; a time for the coffee industry to rethink its attitude to sustainable production. There is no evidence that the large amount of time and effort spent on sustainable coffee schemes in recent years has led to more sustainable coffee.”
New strain unlikely Dr Baker said the only alternative
explanation for the event is the emergence of a new virulent strain of the disease. However, there are problems with this theory, he explained, including the fact that there is no evidence for it and good evidence against it (from Cenicafé in Colombia). Also, it would be very unlikely that a new strain would arise widely across the region at the same time.
CABI is currently working with the Hanns R Neumann Stiftung in the Trifinio zone of Central America where it is helping farmers to devise coping strategies. A principal challenge will be how to manage the desire of farmers to switch to catimors (which are more resistant to rust). Which is the best variety to choose? How much price differential might there be compared to a susceptible variety? Are there other specific problems with catimors? – interestingly, they are often said to be more susceptible to American Leaf Spot (Mycena citricolor).
Dr Baker said that other problems that need to be addressed include whether
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