Crop protection - Good coverage beats timing
Research has shown that good coverage rather than application timing for the Helicoverpa nucleopolyhedrovirus (NPV) biopesticide (commercialised as Gemstar® and Vivus®), is the key to achieving high levels of pest control in sorghum.
Queensland Department of Primary Industries researcher Dr Dave Murray explains: “Helicoverpa NPV is a virus that affects only larvae of the Helicoverpa/ Heliothis complex. It affects nothing else and leaves no residues or toxins, and has no impact on non-target organisms.”
When first released it was thought that evening application would be best to avoid degradation of the virus by sunlight. Additional research by Dr Murray and his colleagues on grain sorghum has now shown that the larvae take up the virus so rapidly that UV degradation is not a concern. Rather, the most important issue when applying NPV is to ensure good crop coverage.
Good coverage has been achieved with both aerial and ground applications. Aerial applications use high-volume application at 30 litres of water per hectare, or ultralow volume (ULV) application using total spray volumes of 3L/ha with petroleum oil as a carrier. Ground rig applications use up to 100L water/ha with appropriate nozzles and pressure parameters.
Contributing to the good kill rates achieved when using the NPV, is the increased predation and parasitism; these organisms are killed with conventional insecticides.
Dr Murray says that NPV should be applied to sorghum plants three days after 50 percent of the heads have completed flowering, and that it is not effective against Helicoverpa larvae greater than 13mm. The ideal larvae size is 7mm or less.
These results are relevant to other crops attacked by Helicoverpa, but growers must check registrations or permits before application of Helicoverpa NPV.
For more information:
Dr Dave Murray, DPI Toowoomba, Qld, 07 4688 1326, Dave.Murray@dpi.qld.gov.au
GRDC RESEARCH CODE DAQ539, program 3