Detecting Squarrose Knapweed (Centaurea virgata Lam. Ssp. squarrosa Gugl.) Using a Remotely Piloted Vehicle: A Utah Case Study

Abstract

Determining the location of founding weed populations is critical to minimizing the diffusion of weedy species. Remote sensing is a promising tool for early detection of these small weed patches. The objective of this study was to determine the capability of a small remotely piloted vehicle (RPV) (carrying a digital camera and GPS) to acquire aerial photography from which small infestations of squarrose knapweed (Centaurea virgata Lam. Ssp. squarrosa Gugl.) could be detected and mapped. Two Utah rangeland sites were studied. The location of squarrose knapweed found on the digital air aerial photography (true color) was compared to a complete census of knapweed conducted on the ground. Although the two study sites had different vegetation species mixes, site histories, and soil conditions, the results were comparable. Despite the large scale of the aerial photography, the knapweed detection rate on the spring photography was only 5%. In contrast, knapweed detection rates on late summer imagery were about 50%. False alarm rates at all seasons were extremely low. Despite the capability shown for weed detection with the RPV and digital camera system, the practical difficulties of using a small RPV in the field requires more research before the system can be operationalized for weed management tasks.