By Georgina Hall
13 February 2002

A long term partnership between vegetable growers and researchers has borne fruit in the "excellent" brassica IPM programme, says Mike Parker, of Vegfed's fresh sector research committee.

Mr Parker, a vegetable grower and researcher with Pioneer Seed, has been closely involved in the programme's development over the last five years as a former chair of the committee.

Although development costs were significant, even with TBG funding assistance, Mr Parker says the programme saves growers' money and is very good for the consumer.

He believes it is imperative for the continued sustainability of all brassica production - including for organic and forage systems.

Furthermore the growers like it. Crop & Food Research entomologist, Graham Walker, says at Pukekohe 29 out of 30 leading brassica growers are using IPM. Nor has any grower dropped the system.

Success has not come over night - ten years of research were needed to develop the complete IPM package.

As well as research into biological controls, scouting systems, and chemical resistance in pest insects, Crop & Food Research have written an IPM manual and run seminars for growers (both funded by VegFed) and intensively trained crop scouts in three regions. Former Institute staff Peter Cameron, Nadine Berry and Nancy Beck were heavily involved in all this work.

Concerns remain over how long the efficacy of the new generation selective insecticides can be maintained.

In New Zealand, VegFed, Crop & Food Research and agrichemical companies have co-operated together and worked out rotations to maximise the life of the new sprays. "A number of the agrichemical companies have been very supportive of our work and the rotation strategy and without them we would have been stumped," Mr Walker says.

Still, he says its only a question of when diamondback moth gains resistance. "This has already happened in both Hawaii and Thailand after only a couple of years of use."

"To develop any other new generation chemicals may take another 10 to 15 years."

Mr Parker says its important all growers, nationwide, follow the insecticide rotation strategy, including organic producers and farmers growing brassicas for stock feed.

Although battling a 'Super Bug', New Zealand cabbage, cauliflower and broccoli growers have been able to drastically cut spray use, while maintaining product quality.

The 'Bug' - diamondback moth, aka DBM - is being kept in check with an Integrated Pest Management programme developed by Crop & Food Research with support from VegFed. This aims to cut down spraying and preserve the efficacy of new, far 'softer' and often naturally-based insecticides for as long as possible.

"The IPM system is excellent - its the only way to go," says Mike Arnold, agronomist with multi-million dollar vegetable grower, Leaderbrand of Gisborne.

"It delivers on control, management of the pesticide, cost and quality of produce."

Mr Arnold estimates IPM has cut costs by at least a third over Leaderbrand's 650 to 700 ha of broccoli and other brassica crops.

"There's less spraying - we like that idea - as well as less chemicals in the environment. Also they're lower toxicity chemicals and much more user-friendly."

Yet five to six years ago DBM had the vegetable industry in crisis worldwide as it had become resistant to every insecticide.

A serious pest of the brassica crops, such as cabbage, cauliflower and broccoli, some DBM-infested crops had to be drenched in insecticide but control was still slipping out of the growers' grasp. In New Zealand, badly affected crops were dug in.

Crop & Food Research entomologist, Graham Walker, says there was only one possible solution to this - Integrated Pest Management or IPM.

This involves using a "compatible combination of controls" on crop pests.

The Institute had already introduced biological control agents, such as insects that parasitise caterpillars of DBM and the other main brassica pest, white butterfly, and had developed straightforward scouting systems to monitor the levels of pests in crops.

However, the IPM system really fell into place with the release of new groups of insecticide sprays (including organic Bt sprays), which are mostly selective. That is, they kill off pest caterpillars - but not the other insects which parasitise or prey on them (such as spiders) and are an important part of the control strategy.

Mr Walker says with IPM, instead of spraying by the calendar, growers or scouts (two commercial scouting companies are operating) check out what insects are actually in each crop.

"There are a number of pests involved and also a number of beneficial insects, and of course plant diseases and weeds that can also be checked while scouting. The main pests are DBM, white butterfly and looper caterpillars and cabbage aphid.

"We have developed and proven thresholds, so we know it is not cost- effective to spray if the pest levels are below these thresholds. Growers only need to spray if the threshold is exceeded and then the sprays are used in rotation to help keep insecticide resistance at bay."

"With the new IPM we're using all possible controls - beneficial insects, not leaving old crops where pests can breed up, and crop rotation.

"But mainly it involves scouting and using the new selective "soft" sprays which maximise the other controls."

Scouting has proved no problem at Leaderbrand, says Mike Arnold, who recently took over chairmanship of VegFed's fresh sector research committee. "Now I can sleep at night. You know exactly what you've got in your crop if you're scouting properly."

"Before that you'd see a bug and spray. And before that again you'd just spray every 7 to 10 days."

"In a 70-day crop that's a maximum of five to seven sprays. With some of the crops we do now there's not a single spray. The absolute maximum we'd do now is three sprays - and that's on a very small area. Mostly its zero to two sprays."

Mr Arnold says that while the broccoli heads will be fine, sometimes the leaves look like they've taken a shotgun blast. "Initially you do take a bit more crop damage. You also take some criticism."

"You have to able to take that and be confident you have control."

Leaderbrand produce some organic crops and Mr Arnold says IPM has been a step between the two systems.

"In many ways IPM is nicer than organics - plants produce their own toxins if they have pests or diseases and these can be a lot worse than what we spray on."

"We won't consider any other option than IPM."