Modifying greenhouses helps slash pesticide use

Research trials with a Sydney cucumber grower have found that pesticide use can be significantly reduced by making modifications to standard greenhouses.

Many of the insects which have developed resistance to pesticides are winged, and with standard greenhouse design they simply fly in - and settle on the produce.

NSW Department of Primary Industries entomologist, Dr Leigh Pilkington, says "some of the worst insect pests can move around easily because they have wings.

"By having greenhouses with open ends all we are doing is inviting them to fly straight in."

Trials conducted by Dr Pilkington more than halved the numbers of thrips and whitefly found in a Sydney cucumber grower’s greenhouses.

Dr Pilkington advocates an integrated pest management strategy, an approach combining good farm hygiene with a monitoring program for pests and diseases, optimal growing conditions, use of soft chemicals and biological controls.

In recent research trials, Dr Pilkington used a high grade mesh to screen all openings in the greenhouse, improved the ventilation by maximising the size of air vents and put fans in for better air circulation.

The aim was to gain greater control over the environment inside the greenhouse.

One of the biggest impacts was to drop the average temperature inside the modified greenhouses by an average 11.6 degrees C in the middle of the day, compared with the unmodified greenhouses.

"Pests generally like high temperatures, whereas ‘beneficial’ insects used as biological control agents struggle to survive when it gets too warm", Dr Pilkington said.

"By reducing the temperature, the growing environment is more conducive to using biological control options and generally far better for the plants."

The biggest impact was on containing the pest insects, western flower thrips, which are already resistant to a wide range of chemicals, and greenhouse whitefly. This is expected to become more resistant to pesticides in the near future.

In the Sydney trial, the greenhouse modifications reduced numbers of pest insects to the point that chemical use could be restricted to reduced-risk chemicals.

Yields were also up, because the cooler environment inside the greenhouses was better for the plants.

Another big advantage was that the modified greenhouses were safer and more comfortable for people to work in.

One of the next phases in the project is to cost different modifications and work out viable options for growers.

Results of this research were recently presented at the Australian Entomological Society 38th annual scientific meeting.