Lessons learned from a project aiming to revitalise integrated pest management in greenhouse tomatoes are helping growers shift from spray-based pest control to using biological controls.
The A Lighter Touch-Tomatoes New Zealand project is now in its third year, and results from demonstration sites in commercial greenhouses have shown greater suppression of greenhouse whitefly (GHW) and tomato-potato psyllid (TPP) populations can be achieved using biological control agents (BCAs) than with a full chemical approach.
However, moving from conventional chemical control to using the pests’ natural predators as the main method of pest control requires a different set of skills and knowledge, and lessons learned from the project to date are being shared with tomato growers.
Project grower lead Lex Dillon says understanding the pests you are trying to control is a key element of any integrated pest management crop protection programme.
“You need to understand the life cycle of the pests – from eggs, to nymphs to larvae or adults and what the different life cycle stages look like. The life cycle stage at which the pest causes damage in the crop can differ depending on the pest. Some BCAs only impact on certain stages of the pest’s life cycle so will be ineffective if introduced at the wrong time
“Knowing where on the plant each pest lives is also a key element, so its presence can be detected early and growers can act quickly and target appropriately. Understanding how a pest damages your crop means growers can use the appropriate intervention.”
Adult stage tomato-potato psyllid on a tomato leaf. Credit: Plant and Food Research.
It’s important for growers to advise their nursery that they plan to use BCAs so nurseries know they need to discuss with the grower the use of any chemical treatments upon the plants, prior to the grower receiving them. Some chemicals used at the nursery can still be active after the plants are planted in a grower’s greenhouse.
“The nursery needs to know you plan to use BCAs so they can advise you what impact those chemical treatments might have on your programme. It’s not just the natural predators that need to be considered – care also needs to be taken to ensure chemical treatments don’t impact on your bumblebees.”
Learnings from the project have shown the earlier BCAs are introduced into the crop, the more effective they will be at reducing the impact of pest incursions. Supplementary feeding will help maintain the BCA population before pests arrive.
“Some growers have questioned spending money on BCAs when they haven’t got pests in their crop, saying it seems like a waste. I’d suggest growers consider this cost as an ‘insurance policy’ in crop protection – the cost of a crop loss due to a severe pest infestation can be much greater.
“By building a population of BCAs from the time that crops are planted, growers are creating an immediate defence that will act as soon as the pests arrive.”
BCA suppliers will help advise growers about the quantities, location and timing of applications of the predators. The quantity and frequency of additional BCA introductions will be determined by both beneficial and pest insect populations.
Regular and accurate scouting is needed to understand the population and distribution of both pests and BCAs in the crop. Training staff for what to look for provides extra sets of eyes in the crop.
T&G Fresh grower Andrew Hutchinson scouts the crop for both pests and BCAs.
Using BCAs for crop protection does require a change of mindset for growers, as unlike chemical control, they are not a “knockdown” form of pest control, Lex says.
“BCAs will not 100% eliminate pests. The pest is the food source for the BCAs so you need some pests to allow the BCAs to survive. What BCAs do is suppress the pest population to minimize the economic impact of the crop damage.”
Other tools in the grower’s toolbox can support use of BCAs. Surfactants such as soaps and oils will help act as barriers with pest incursions, and mechanical interventions such as sticky traps and vacuum systems will also reduce pest numbers.
“From time to time growers may also need some chemical interventions. ‘Soft’ sprays can target specific pests and cause little or no harm to your BCAs – but before using any sprays discuss this with your crop advisors or BCA supplier to ensure they are not harmful to your predator population.”
Growers need to be very careful when using “hard” or non-selective sprays as use of these can result in not being able to use BCA’s for a significant period of time.
Lex says it is important to have some patience when growers begin using BCAs. “Remember you are dealing with a natural process and not everything may go as planned.”
The biological control agent Engytatus nicotianae. Credit: Francis Ferrada-Hartley.
It can sometimes take weeks or even months for the BCAs to gain control. If growers have concerns, they should discuss these with their crop and BCA advisors in order to come up with the best solutions.
“Every grower has a different environment, different outside influences and different tolerance levels. There will be some situations where conventional pest control may be the most effective option.”
Glasshouses that have high levels of technology have more tools to help manage the environment, but this has not stopped some low-tech growers having BCA success, Lex says.
Grower resources such as decision-trees, pest action cards and ‘how to’ video guides have been developed from the project and shared with the industry. These can be found on the Tomatoes NZ website.
