Targeted Weed Control in Rice
The Goal
A rice grower in northern NSW hired us for spot weed control after finding patches of Caldwell's club-rush (Bolboschoenus caldwellii) on a routine check. This weed cuts yields, taints the harvest, and is building herbicide resistance. We mapped the locations to stop spread, cut chemical use to save money and slow resistance, shielded the rice from excess exposure, hit the prime spray window, and kept drift off the neighboring tomatoes.
The Approach
To scientifically address this weed management challenge, we deployed a comprehensive detection-to-application workflow. Using high-precision imaging and green-on-green detection technology, we identified and mapped Club-rush patches across the entire paddock, then generated prescription maps for targeted spray application.
Hardware Selection
The mission utilized an RTK-equipped mapping drone for high-precision aerial survey, capturing imagery at 2cm/pixel resolution across the 141.3-hectare paddock. For targeted application, DJI spray drones were selected for their ability to load prescription maps directly and execute precise, drift-controlled herbicide application near sensitive crops.
Data Collection
Our certified pilot completed the paddock mapping flight in 2 hours, conducting the mission during early morning to minimize wind and ensure clear imagery. The RTK system provided centimeter-level accuracy for precise georeferencing, critical for subsequent spray operations.
Analysis
Multiple detection and mapping techniques were employed to ensure accurate weed identification and safe, effective treatment:
Green-on-Green Detection
Our advanced computer vision algorithms analyzed high-resolution imagery to distinguish Club-rush from rice plants based on spectral signatures and morphological features, identifying 0.9 hectares of actual weed infestation.
Buffer Zone Calculation
1.5-meter buffer zones were automatically generated around each detected weed patch to account for GPS accuracy and boom width, ensuring complete control while still maintaining a 97% reduction in treatment area compared to blanket application.
Prescription Mapping
Treatment zones (4.3 hectares total including buffers) were exported as standard shapefile format, enabling direct loading into DJI spray drone controllers.
Targeted Application
Spray drones completed the targeted application in 3.5 hours, treating only the mapped weed zones with precision herbicide delivery.
The Results
Massive Herbicide Savings and Crop Protection
We reduced spray area by 97% from 141.3 ha to 4.3 ha, saving 87 liters of herbicide, enough for another paddock. This cut input costs by $3,088 on one application, paying for the service three times over. It lowered resistance risks, protected 137 ha of rice from unneeded chemicals to keep yield and quality high, and avoided any drift to nearby tomatoes. These outcomes are impossible with blanket methods.
Prescription map showing 4.3 ha treatment area vs 141.3 ha total paddock (97% reduction)
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