Abstract
Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] is one of the most challenging weeds for winter wheat (Triticum aestivum L.) growers to manage. Italian ryegrass has evolved resistance to the majority of the herbicides labeled for use in wheat and the competitive ability of the species makes it a significant factor driving winter wheat production practices around the world. Previous research has utilized remotely sensed spectral imagery to detect Italian ryegrass in winter wheat to aid weed control decisions. Two studies from 2016 to 2017 were initiated with the intent of identifying the spectral reflectance properties of Italian ryegrass and winter wheat using an unmanned aerial vehicle (UAV) equipped with a 5-band multispectral sensor. Image analysis was conducted to determine the potential for species discrimination throughout the growing season. Supervised classification of the imagery was used to evaluate the ability of the UAV platform for further discrimination between Italian ryegrass and winter wheat. Species differentiation proved to be possible, however the data was not able to be referenced across dates. Due to light variability, the reflectance values changed to such a degree that unsupervised classifications were not possible using a database of values from previous flights. Supervised classification of the multispectral image resulted in >70% classification accuracy between the species. However, near infrared light consistently differed enough for accurate classification between Italian ryegrass and winter wheat across different weed densities, flight altitudes, and imaging dates. On a single field basis, species differentiation was successful and resulted in classified maps of Italian ryegrass and winter wheat. This study also analyzed the exact accuracy of the species differentiation based on the quality and uniformity of light conditions and growth stage of plants.
Highlights
Wheat (Triticum aestivum L.) is a staple crop grown worldwide (Gupta et al, 2008)
Further research on the yield implications of Italian ryegrass infestations found that every 10 plants meter2−1 can decrease yield by 4.2% in the Southeast United States (Liebl and Worsham, 1987); if not controlled, Italian ryegrass can decimate a wheat crop yield (Hashem et al, 1998)
The objectives of this research were to determine the accuracy of supervised classification and spectral reflectance for Italian ryegrass and winter wheat detection, if the spectral reflectance of Italian ryegrass was influenced by its density and if those densities could be accurately identified through time and across different flight altitudes
Summary
Farmers around the globe produce over 708 million tons of wheat per year (United States Department of Agriculture, 2014). Appleby et al (1976) found that yield losses due to Italian ryegrass infestations can reduce wheat yield up to 60% relative to weed density in the Pacific Northwest United States. Further research on the yield implications of Italian ryegrass infestations found that every 10 plants meter− can decrease yield by 4.2% in the Southeast United States (Liebl and Worsham, 1987); if not controlled, Italian ryegrass can decimate a wheat crop yield (Hashem et al, 1998). Italian ryegrass is becoming increasingly difficult to manage due to the evolution of herbicide resistance This species has evolved resistance to all herbicides labeled in winter wheat (Grey and Bridges, 2003; Hoskins et al, 2005; Grey et al, 2012; Heap, 2021)
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