Published on 04/02/2021
Initially developed by AgResearch, and now supplied to the New Zealand market by BioStart, BioShield Grass Grub contains the active ingredient Serratia entomophila, a soil bacterium that occurs naturally in NZ which causes amber disease in grass grub.
The bacteria are ingested by grass grub larvae as they feed,and multiply in their gut to cause the disease. Within two to three days the larvae stop feeding and starve. When they die, the bacteria in their gut are released into the soil where they are then available to be ingested by other larvae.This sets up a cycle of infection for long-term grass grub control.
BioStart CEO Dr Jerome Demmer says while pasture is the first ‘crop’ most people usually think of when it comes to damage from this insect pest, it also has a big appetite for both the roots of grape vines (the larvae) and the leaves (adult beetles). Hence there’s been increasing interest in the liquid formulation of BioShield Grass Grub for vineyard application, not least because it is certified for use in organic vineyards.
Modelling undertaken with AgResearch has shown clear potential here, he says. “We looked at the simulated effect of adding liquid BioShield to the vineyard when grub numbers are relatively low, in other words before an outbreak and post an outbreak. “In both cases the ‘normal’ population curve was quite disrupted.”
Application timing in this context is early March to late April, when late second to mid third instar grass grub larvae are actively feeding on grapevine roots, and the population density is beween 100 and 300 larvae per square metre. As with all biopesticides, correct conditions are critical for success – soil temperature must be above 10 deg C, soil moisture above 15 per cent and the grass grub larvae must not have developed past the mid third instar stage.
Demmer says it’s also very important that growers and vineyard managers don’t use other grass grub control measures such as insecticides as well as BioShield, because these reduce its efficacy. Meantime, the company is also developing and trialling a new BioShield Grass Grub granule that is certified organic. The existing granule formulation must be drilled into pasture, but the one in development can be broadcast, and so offers potential to reduce application costs for end users because it would allow them to apply the product themselves.
Recommended timing for pasture applications of both the liquid and existing granules is from February to mid-April, with the same caveats regarding larvae development stage and population density as for vineyards. At higher populations (significantly over 300 larvae per square metre), BioShield may not be economic, he says. “It takes around six weeks to see initial effects. After that time, about 10-20 per cent ofthe grass grubs present should show signs of amber disease. One year later the grub population should be half what it was at the time of application. Dead grubs will not be visible – they quickly disappear by natural decay processes.”
Depending on environmental conditions, BioShield Grass Grub provides around three to five years’ pasture protection.
For more detail contact your BioStart territory manager.