09 February, 2004
___The Cotton CRC has published an update on the pattern of insecticide resistance in the cotton industry._
The review was prompted by changes in chemical use triggered by the introduction of transgenic varieties, and the implementation of integrated pest management techniques involving greater reliance on friendlier insecticides.
Cotton CRC spokesman, Dr Lewis Wilson, said ongoing resistance monitoring was a coordinated effort between researchers, consultants, growers and extension personnel in both NSW and Queensland.
He said the different life cycles and ecology of different pests has led to the development of resistance strategies that vary between important insect species involved in cotton production systems.
__A joint author of the review, Dr Louise Rossiter, research entomologist with NSW Agriculture, said that of the two Helicoverpa species in cotton, H.armigera has developed the greatest resistance, while H.punctigera has the biological capacity to become resistant, although it has not done so.
“Helicoverpa armigera are also mobile pests that, given favourable weather conditions, can move between cropping regions. This makes it necessary to have an industry wide strategy that coordinates resistance management,” she said.
She noted that with the introduction of Bt cotton and industry-wide acceptance of IPM for pest control, secondary pests that once would have been managed inadvertently through Helicoverpa control, are increasing in importance, thus a strategy must also be implemented to manage resistance in secondary pests.
The most important of these at present are aphids, mites and whitefly, which have very short life cycles (5, 8 and 16 days respectively), allowing them to develop resistance to insecticides very quickly.
Dr Wilson said it is important not to consecutively apply insecticides from the same group for control of these species, or when selecting chemistry for other pests.
“This avoids selection of multiple generations with the same insecticide group and applies even if short life cycle pests are below thresholds in pest checks.
“Rotation between insecticide groups is especially critical with pests that reproduce by cloning, such as aphids. Any resistant survivors will pass their resistance trait directly to their offspring,” he said.
He said aphids, mite and whitefly all use a wide range of hosts, so management of these through winter to reduce the size of over-wintering populations is critical.
For aphids, he said it is important to use softer chemistry earlier in the season, better utilising beneficial insects to reduce surviving aphids. It is also important to avoid early season use of carbamate and organophosphates.
“The use of pyrethroids against Helicoverpa can also exacerbate resistance problems by selecting resistant aphids,” he said.
Dr Wilson said mites are also currently widely resistant to organophosphate insecticides, bifenthrin, and increasingly to chlorfenapyr.
He said silverleaf whitefly is resistant to most insecticides, hence control strategies hinge on an integrated approach incorporating biological, cultural and insecticidal management practices.
“This includes the avoidance of broad spectrum sprays and the strategic early use of insect growth regulators, to slow the growth of whitefly populations while allowing the build-up of beneficial insects.
“Sucking pests such as mirids and vegetable bugs, previously controlled by broad spectrum sprays for Helicoverpa, are becoming more common, particularly as greater areas of Bt cotton are planted, with an associated reduction in sprays.
“Over-reliance on any one insecticide or insecticide group, increases the risk of selecting for resistance in sucking pests,” Dr Wilson said.
A comprehensive review of insecticide resistance in the cotton industry is available in leaflet form from David Larsen at the Technology Resource Centre at the Cotton CRC, Locked Bag 59, Narrabri 2390, or on the Cotton CRC website at www.cotton.crc.org.au.
Joint authors of the review are Lewis Wilson, Louise Rossiter, Bruce Pyke, Robyn Gunning, Grant Herron and David Kelly.
_Further Information: _Dr Lewis Wilson 02 6799 1550, Robert Eveleigh, John Marshall, or Craig McDonald
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