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La Nina Causes Pest Outbreaks in Australia

14 February 2011

AUSTRALIA - The recent floods brought about by the La Nina weather pattern have created headaches for farmers battling insect pests. according to the Queensalnd Government.

Crop pest researcher Hugh Brier, from the Department of Employment, Economic Development and Innovation (DEEDI), said the extra rain presented many challenges for farmers.

"Without doubt these conditions can allow for an explosion in numbers of certain types of pests, including helicoverpa (caterpillar) and podsucking bug populations in summer pulse crops," said Brier. "The cooler conditions are also likely to favour soybean aphids, which were present in damaging numbers in the cool wet summer of 2007.

"The problem arises not only because some pest insects like the cooler conditions and the increased moisture favours the development of early season crop and weed hosts, but also because farmers cannot ´sample´ their crops for bugs as often as they need to."

But the good news is that some bugs don´t like the wet.

"In contrast, the wet conditions are very unfavourable for etiella in peanuts, and damaging populations close to harvest will not threaten crops as they did in recent drought years," said Brier.

Despite the challenges, solutions are at hand for farmers facing bug outbreaks in their crops.

"Opportunistic sampling - that is the answer," said Brier.

"Every opportunity must be taken to sample crops when the opportunity arises between rain events. If you know what the likely pests and their damage symptoms look like in advance you will be better placed to manage them effectively.

"This allows for faster decision making, so the appropriate control measures can be applied before the next wet weather event.

Brier said farmers should also try to sample crops when the crops are at greatest risk.

"For summer pulse crops, the most critical time is from flowering onwards, through pod set and fill and, for some pests, well into pod ripening," he said.

"However if your crop experiences significant pest activity at critical crop stages because you are unable to enter, let alone sample the crop, don´t despair. In many instances the crop will be able to compensate for significant early damage, especially as soil moisture is unlikely to be limiting in a wet summer.

"The proviso is that subsequent pest activity is minimised. La Nina also presents challenges to normal spraying routines.

While farmers feel under greater pressure to spray before wet weather sets in, it is important wherever possible not to use sprays that kill natural pest predators or parasites, as these will help counter pest activity when you cannot get near your crop to sample or control pests.

"Farmers should also avoid panic spraying, for example spraying pests if the crop has a long way to go until the at-risk period for the pest in question."

Mr Brier also recommended ensuring correct pest identification, as some pests were not very harmful to crops and could be left alone, and some pests were easily confused with predatory insects.

TheCropSite News Desk

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