New option for Psa control in kiwifruit

Nufarm’s biological fungicide Botector now has a label extension for Psa control in kiwifruit, giving growers a valuable new tool for managing the industry’s most significant disease.

Business development manager Katie Morrison says the new claim builds on Botector’s existing activity against Sclerotinia, providing one product that targets two major kiwifruit diseases.

“Botector is a protective fungicide that fills micro-scratches on the kiwifruit plant surface through competitive exclusion,” Morrison explains.

“A key benefit is its excellent compatibility, offering flexible application windows.”

Early users have welcomed the new label extension.

Morrison says reps and packhouses have described it as ‘game changing’ because of the flexibility, ease of use, and convenience of having one biological that works effectively against both Sclerotinia and Psa.

Nufarm received the label extension late last year and acted quickly to import further product so it could be utilised during the 202/26 cropping season.

This enabled early use through reps and packhouses even though they received the label extension once the season had started.

The 2026 season represents the first full commercial launch.

As Morrison puts it: ‘Botector is a biological that works for your programme, not against it.’

The product contains two live strains of the naturally occurring yeast-like fungus Aureobasidium pullulans (DSM 14940 and DSM 14941).

It works by rapidly colonising wounds and micro-scratches on plant surfaces, outcompeting pathogens for space and nutrients so they cannot establish.

This creates a physical barrier that reduces the number of open sites available for Psa infection.

Psa remains the most economically damaging bacterial disease affecting kiwifruit in New Zealand.

It enters the plant through natural openings or wounds and is spread by wind, rain splash, and contaminated tools or people.

Once established, it can cause leaf spotting, shoot dieback, flower drop, cane collapse, and in severe cases overall vine decline or death.

Botector, while not a bactericide, plays a valuable supporting role in integrated disease management by colonising potential entry points and limiting infection sites, Morrison says.

The product can be applied from bud burst through to six weeks post-flowering.

Applications are made at seven to 10 day intervals as required, with the shorter interval under high disease pressure when vines are growing rapidly.

Thorough coverage is essential for good control.

The addition of a compatible wetting agent may be used to improve coverage but is not required.

Water rates per hectare should be adjusted to suit canopy growth stage and density.

Botector is BioGro approved, has no withhold period when used according to label directions and supports resistance management as an alternative mode of action with very low resistance risk.

Because it acts through competitive exclusion rather than directly attacking the pathogen, the risk of resistance developing is minimal.

Morrison says the benefit of two strains is significant.

Different Aureobasidium pullulans strains thrive under varying environmental conditions. Having both DSM 14940 and DSM 14941 in Botector provides broader protection and adaptability across a wider range of temperatures.

This allows the product to establish and remain active in conditions where single-strain products may struggle.

Data shows the strains maintain growth and viability effectively between 4°C and 30°C, with accelerated growth rates around 15–30°C.

Once applied, Botector works quickly to colonise wounds - think of it as applying a dressing or forming a scab.

“We often get queried on a rainfast period,” Morrison says.

“Growers should always endeavour to get product on in front of the rain and with enough time for the product to colonise, humidity and temperature will influence how quickly the product can colonise.”

As a general rule of thumb, it has a 24-hour rainfast period, with best results if it can dry for at least four hours before rain.

The organism produces an extracellular polysaccharide (pullulan gum) that helps it stick to surfaces and seal micro-scratches.

Botector can be safely mixed with copper-based products when needed, a major advantage over many other biologicals, she adds.

This compatibility stems from the strains’ origins in orchards where copper was regularly used.

When using incompatible products, allow a three day interval before or after applying Botector.