  The cotton boll weevil, Anthonomus grandis Boheman is a serious pest to the
U.S. cotton industry that has cost more than 16 billion USD in damages since it
entered the United States from Mexico in the late 1800s. This pest has been
nearly eradicated; however, southern part of Texas still faces this issue and
is always prone to the pest reinfestation each year due to its sub-tropical
climate where cotton plants can grow year-round. Volunteer cotton (VC) plants
growing in the fields of inter-seasonal crops, like corn, can serve as hosts to
these pests once they reach pin-head square stage (5-6 leaf stage) and
therefore need to be detected, located, and destroyed or sprayed . In this
paper, we present a study to detect VC plants in a corn field using YOLOv3 on
three band aerial images collected by unmanned aircraft system (UAS). The
two-fold objectives of this paper were : (i) to determine whether YOLOv3 can be
used for VC detection in a corn field using RGB (red, green, and blue) aerial
images collected by UAS and (ii) to investigate the behavior of YOLOv3 on
images at three different scales (320 x 320, S1; 416 x 416, S2; and 512 x 512,
S3 pixels) based on average precision (AP), mean average precision (mAP) and
F1-score at 95% confidence level. No significant differences existed for mAP
among the three scales, while a significant difference was found for AP between
S1 and S3 (p = 0.04) and S2 and S3 (p = 0.02). A significant difference was
also found for F1-score between S2 and S3 (p = 0.02). The lack of significant
differences of mAP at all the three scales indicated that the trained YOLOv3
model can be used on a computer vision-based remotely piloted aerial
application system (RPAAS) for VC detection and spray application in near
real-time.
