Scientists will explore using drone-mounted lasers to blast weeds causing a billion-dollar headache for farmers in a new "map-and-zap" project.

With recent research putting the annual cost of weeds to productive land at $1.6 billion or higher, the agriculture sector urgently needed environmentally-friendly tools to get them under control.

Now, a new AgResearch-led, million-dollar programme may find the answer in drones.

"The idea is to mount specialist cameras on the drone or UAV (Unmanned Aerial Vehicle) that can first identify the weeds based on their unique chemical signatures and how they reflect light, and precisely map their locations using GPS," explained programme leader Dr Kioumars Ghamkhar, of AgResearch.

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"From there, we think smart spraying, or the right kind of laser mounted on the drone could hone in and damage the weed.

"We know there are lasers now available that could be suitable, and that they are extremely accurate, so if lasers are used, it would also avoid damaging the useful plants around the weed."

Current methods for tackling weeds could be very expensive and time-consuming, and often involve chemicals which can impact on crops, soil quality or water sources, Ghamkhar said.

"We want to develop something that could be an efficient option for users such as farmers, regional councils and the Department of Conservation.

"We've already spoken with our collaborators in the universities about the lasers that are available that might be suitable."

The effectiveness of lasers against plants had been tested overseas before, but only in the lab.

"We'll be starting with testing of different types of laser with plants at three different stages of growth in the lab, and from there we will select the best form of laser to see its impacts on the weeds out on a farm."

"There are issues we would have to consider such as heat generated by the lasers, and the risk of starting fire, and we'll be very conscious of this particularly where there are dry days or drought conditions.

"We'll also be looking at using a group of small lasers to direct at the weed, as opposed to one large and powerful laser that might generate more heat."

Ghamkhar said the method of identifying different plants by chemical signature had already been shown to be workable in other AgResearch projects, and the challenge now was to accurately identify weeds in the same way so use of the drone-mounted laser could be effective, or at a minimum targeted spraying from equipment mounted on the drone.

If successful, the Government-funded programme - also involving experts from the University of Auckland, University of Michigan and Kiwi tech firm Redfern Solutions Limited - could lead to commercial development.

Drones and science

• A Surf Life Saving New Zealand and Emsisoft collaboration used drones to help map currents and rips at beaches around the country last summer.
• An Otago University-led expedition to the cold and stormy subantarctic islands used drones to drop in on southern right whales last year.
• GNS Science has used drones to map and monitor volcanic White Island, and also dispatched one to survey damage along the South Island's Kekerengu Fault in the wake of November's Kaikoura Earthquake.
• AUT scientists have used drones to make ecological stocktakes of New Zealand's forests and wetlands, as well as ecosystems in Africa and Antarctica.