Comparison of crop and weed height, for potential differentiation of weed patches at harvest

Abstract

Weeds and weed control are major production costs in global agriculture, with increasing challenges associated with herbicide‐based management because of concerns with chemical residue and herbicide resistance. Non‐chemical weed management may address these challenges but requires the ability to differentiate weeds from crops. Harvest is an ideal opportunity for the differentiation of weeds that grow taller than the crop, however, the ability to differentiate late‐season weeds from the crop is unknown. Weed mapping enables farmers to locate weed patches, evaluate the success of previous weed management strategies, and assist with planning for future herbicide applications. The aim of this study was to determine whether weed patches could be differentiated from the crop plants, based on height differences. Field surveys were carried out before crop harvest in 2018 and 2019, where a total of 86 and 105 weedy patches were manually assessed respectively. The results of this study demonstrated that across the 191 assessed weedy patches, in 97% of patches with Avena fatua (wild oat) plants, 86% with Raphanus raphanistrum (wild radish) plants and 92% with Sonchus oleraceus L. (sow thistles) plants it was possible to distinguish the weeds taller than the 95% of the crop plants. Future work should be dedicated to the assessment of the ability of remote sensing methods such as Light Detection and Ranging to detect and map late‐season weed species based on the results from this study on crop and weed height differences.

Assessing the Capability and Potential of LiDAR for Weed Detection

“…This study demonstrates that LiDAR sensors can be considered as a potential valuable technique for automated weed detection and location, based on their height difference from the crop canopy. Persistent weed species such as Avena fatua and Sonchus oleraceus which tends to persist in the field until harvest, grow taller than the crop and shed their seeds before harvest [ 28 ] could be the potential targets of this method.…”

“…A plot of wheat (cultivar Magenta) (45 m × 2 m) was sown in May 2019 with a row spacing of 0.20 m and a standard seed rate for Australia of 80 kg/ha ( Figure 3 a). Seeds of Avena fatua and Sonchus oleraceus , which were reported as the common weeds growing taller than crops in Western Australia [ 28 ], were grown in plastic pots. Seeds were placed in Petri dishes on agar and cold treated for germination.…”

“…3a). Seeds of Avena fatua and Sonchus oleraceus, which were reported as the common weeds growing taller than crops in Western Australia [28], were grown in plastic pots. Seeds were placed in Petri dishes on agar and cold treated for germination.…”

“…However, the effectiveness of the LiDAR systems for detecting and mapping weeds that grow taller than the crop canopy and persist in the crop until harvest is still unknown. Using manual height measurements, Shahbazi et al [ 28 ] reported that a number of common weeds grow taller than crops, so could potentially be differentiated based on their height. Weeds mapped at late phenological stages indicate where the weeds were not controlled, due to ineffectiveness of the herbicide, herbicide resistance or not being sprayed [ 29 ].…”

“…Weeds mapped at late phenological stages indicate where the weeds were not controlled, due to ineffectiveness of the herbicide, herbicide resistance or not being sprayed [ 29 ]. Some of the persistent weed species that grow taller than the surrounding crops include cannabis ( Cannabis sativa ) and brown mustard ( Brassica juncea (L.) Czern ) weeds in spring wheat in Western Canada [ 30 ], annual sow thistle ( Sonchus oleraceus L.) in wheat crops in Eastern Australia [ 31 ] and wild oat ( Avena fatua L.), wild radish ( Raphanus raphanistrum L.) and sow thistle in wheat, barley ( Hordeum vulgare L.), lupin ( Lupinus angustifolius L.) and chickpea ( Cicer arietinum L.) crops in the central wheat-belt region of Western Australia [ 28 ].…”