Those indices are sensitive to moisture content in plant leaves suggesting leaf succulence was important in crop weed separation and weed to weed separation. The SWIR band serves as a measure of water content, leaf internal structure, and dry matter; whereas, the NIR band serves as measurement of only leaf internal structure and dry matter . When combined into an index, SIWSI provides a measurement of leaf water content expressed as equivalent water thickness. Also, GRNDVI was ranked within the top three indices for each date supporting the role that plant pigment played in separating the plant species. Other pigment indices having relevant variable importance values on both dates were GNDVI and NPCI. NDVI, the most wildly used vegetation index throughout the literature was ranked eighth and eleventh according to the variable importance tabulated for the June 30, 2014 and September 17, 2014 datasets respectively, indicating its weak relevance for discriminating between the plant species.
Thus, the variable importance rankings of the former were easily understood by evaluating the variable importance rankings of the latter. Therefore, vegetation indices derived with one those bands would be ranked higher on the variable importance scale than a vegetation index excluding SWIR bands . The findings of this study are similar to those of , which indicated shortwave-infrared data were important for soybean weed discrimination. Their study focused on the following weeds discrimination from soybean: hemp sesbania , palm leaf morning glory , pitted morning glory , prickly sida , sicklepod , and small flower morning glory . Overall,vertical grow systems for sale this study demonstrated that vegetation indices derived from leaf reflectance data can be used as input into cforest for differentiating soybean, velvetleaf, and two pigweeds. It is important to note that the data were collected using pure leaf spectra and not canopy spectra. For canopy spectra, some differences will occur due to in-canopy shadowing, leaf orientation, and differences in leaf area. One of the strengths of vegetation indices is that they are influenced less by shadowing and sensor viewing angle than multispectral bands, indicating the benefit of using them at the canopy level.
Conyza bonariensis Cronq. Walker is a weed annual broad-leaved species in the Asteraceae family native to South America , present in fallow in autumn and spring in Argentina. Previous to the widespread adoption of no-till systems, this species was confined to pastures and undisturbed areas . No-till favours germination and emergence of small-seeded weed species including Conyza spp which typically emerges during the whole fallow period. In the last years, applications of glyphosate in no-till fallow have increased significantly achieving initially very good control of Conyza spp. in the region of the study . At present, control of some populations is difficult in many sites of the Argentine soybean region, although no glyphosate resistant Conyza spp. biotypes have been reported. The selection of these tolerant biotypes may be due to suboptimal growth stage at application,overreliance on glyphosate and long-term use of sublethal doses . Resistance to glyphosate of C. bonariensis was observed for the first time in 2003 in South Africa . At present, resistance to five modes of action with Conyza canadensis Cronq. and four modes of action C. bonariensis have been reported . Resistance biotypes were identified in Europe -, Brazil and USA . In Argentina, a better understanding of the differences in control between biotypes is essential for developing effective long-term management strategies.
The small size of weed plants at herbicide application is relevant for achieving an acceptable control as at this stage, weeds are more susceptible.Glyphosate efficacy is particularly influenced by weed size In some biotypes of Conyza spp., glyphosate control fails due to an inappropriate dose when there is a delay in application that allows plants to reach sizes that are difficult to kill consistently . In no-tillage fallow, control of annual weeds increases by applying residual herbicides combined with glyphosate Many of the residual herbicides for Conyza spp. control are acetolactate synthase – inhibiting herbicides, particularly chlorimuron-ethyl, metsulfuron-methyl and diclosulam Mixtures of such herbicides with glyphosate may control biotypes resistant to glyphosate . Other herbicides included in this group consist of mixtures containing sulfometuron or chlorsulfuron and are less studied, so the dose for adequate control is not clear.