A Comparison of Visual and Photographic Estimates of Weed Biomass and Weed Control¹

Abstract

The objective of this study was to compare the consistency and accuracy of visually estimated weed biomass and weed control data to data obtained through image analysis. Weed biomass and weed control were evaluated in soybean herbicide efficacy trials conducted at the University of Nebraska–Lincoln during 1992 and 1993. Measurements were based on visual estimates and on aerial photographs taken at a height of 3.5 m above the soil surface. Photographs were digitized and classified, producing pixel values for broadleaf weeds, grass weeds, soybean, and soil. Percent weed cover was calculated in relation to the crop canopy, based on the respective number of pixels per image. Visual and photographic ratings of weed biomass and of weed control were not closely correlated. In the first year the visual method discriminated between more treatments than the photographic method, but the opposite occurred in the second year. The photographic method predicted yield more closely than the visual estimates. We concluded that visual estimates were less consistent and more subject to observer bias than measurements obtained with the photographic method.

Ground Cover Assessment of Perennial Ryegrass Using Digital Imaging

“…Imaging systems are commonly thought to provide a more reliable assessment of vegetation cover than visual methods because they remove observer bias (Neeser et al, 2000; Milberg et al, 2008; Liu et al, 2012). Ground‐cover assessment has benefited from advances in remote sensing systems (Neeser et al, 2000; Alberdi et al, 2010), and cheap, high‐quality digital images combined with free software, such as ImageJ, have reduced the cost of digital image analyses (Bauer and Strauss, 2014). Here we suggest that proximal digital imaging combined with ImageJ analysis may offer benefits over “traditionally” used visual scoring of ground cover, particularly where ground cover is low.…”

Image Processing Methods for Measurement of Lettuce Fresh Weight

“…Similar to the cameras, the image analysis software systems included both commercially available and projectspecific programs (Bumgarner et al, 2012). Digital images are commonly used in ecology to monitor plant-or landscapelevel changes; as a result, the image analysis method has proven useful in describing and identifying green leaves (Ide and Oguma, 2010;Casadesus et al, 2007;Neeser et al, 2009). Image assessment and other remote sensing-based methods have been used in horticultural crop applications, although further investment in techniques and applications were necessary (Lee et al, 2010).…”

Efficacy and environmental fate of imazapyr from directed helicopter applications targeting Tamarix species infestations in Colorado

“…Additionally, with the exception of several studies from New Mexico, much of the existing research on the chemical control of tamarisk and similar woody invaders has relied on qualitative metrics of plant mortality such as percentage foliar cover or defoliation. Visual estimates such as these metrics are known to be prone to high variability and observer bias for low‐lying plants and taller shrubs and trees alike . Therefore, in this study we employed a suite of objectively quantifiable metrics of tamarisk morphology to assess mortality more reliably and relevantly.…”