Early warning system helps growers beat apple canker

Apple growers have a new weapon to help control the potentially devastating canker fungus thanks to an innovative early-warning system that has been added to Agrovista’s sector-leading pest and disease forecasting service, Growers Choice Interactive.

The new canker model informs growers whether their orchards are infected, and if so at what level, by monitoring factors that can cause outbreaks, including rainfall, leaf wetness, temperature and tree wounds, says Agrovista fruit agronomist Alex Radu.

“Accurate information is essential to produce reliable model outputs. This is provided by high-quality Plantsystems weather stations that GCI growers lease, similar to the existing scab and codling moth models they are familiar with.”

Information is forwarded every 15 minutes to a central server. The software model, based on RIMpro pest and disease prediction software, integrates this with information on canker’s lifecycle stored in the program.

The resulting graph shows spore germination, relative numbers of spores on wounds and a resulting infection value (see panel).

Canker infection occurs through fresh tree wounds, so the display includes a graph showing the amount of fresh and healing wounds caused by leaf drop, based on orchard information supplied by the grower as well as weather station information.

While pruning cuts, bud burst, petal fall and fruit drop are all risk periods, the biggest danger comes at leaf fall in the autumn.

“If there are few fresh wounds then treatment may not be needed, regardless of infection value,” says Mr Radu. “But if wound levels are significant and the trend is rising and coinciding with a high infection value, treatment should be considered.”

The level of residual fungicide from previous treatments will play a part in that decision, he adds. Growers who subscribe to GCI Premium have an additional function on the model, which calculates the amount of fungicide remaining in the orchard based on UV levels, rainfall, relative humidity and temperature.

GCI also includes a 10-day weather forecast, which indicates the likelihood of disease outbreaks over that period, says Mr Radu. “This allows growers to apply preventative sprays with confidence two to three days ahead, which is very useful if heavy rain or wet ground would otherwise have prevented travel.”

Overall, the new model ensures canker sprays are applied when needed, rather than as three or more prophylactic treatments in the autumn. “This is good for growers’ pockets, the environment and helps meet tightening supermarket protocols,” says Mr Radu.

GCI canker graph / 

GCI canker graph: What the grower sees


The canker graph is divided into three sections.

In the lower section, the dark blue areas represent rain events and light blue areas indicate leaf wetness.

The middle section includes timing and the level of spore dissemination, represented by yellow peaks, and the potential for germination of these spores, indicated by white peaks.

The model calculates the resulting potential for spore germination, producing an infection value (red line). When the magnitude of infection exceeds 3000, the risk is significant.

The need to spray can then be assessed against the amount and proportion of fresh and healing wounds using the top section.

The grey area in the middle section represents residual fungicide levels on trees (for growers with GCI Premium).

The vertical blue line indicates the current time.


08 April 2015

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