No abstract

In herbicide-selectivity experiments, response can be measured by visual inspection, stand counts, plant mortality, and biomass. Some response types are relative to nontreated control. We developed a nondestructive method by analyzing digital color images to quantify color changes in leaves caused by herbicides. The range of color components of green and nongreen parts of the plants and soil in Hue, Saturation, and Brightness (HSB) color space were used for segmentation. The canopy color changes of barley, winter wheat, red fescue, and brome fescue caused by doses of a glyphosate and diflufenican mixture, cycloxydim, diquat dibromide, and fluazifop-p-butyl were described with a log-logistic dose–response model, and the relationship between visual inspection and image analysis was calculated at the effective doses that cause 50% and 90% response (ED50 and ED90, respectively). The ranges of HSB components for the green and nongreen parts of the plants and soil were different. The relative potencies were not significantly different from one, indicating that visual and image analysis estimations were about the same. The comparison results suggest that image analysis can be used to assess color changes of plants in response to some herbicides and may have the potential to provide an objective measurement of symptoms.

Cotton productivity on a per-hectare basis is low in Pakistan. As boll is the basis for seed cotton yield, within-boll yield components can potentially serve as the most basic determinants of cotton productivity on a per unit land area basis. Before attempting the improvement of any trait, it is necessary to know the genetic mechanism lying behind its inheritance. The current study aimed to estimate the genetic basis of within-boll yield components in cotton. The research trials were conducted at the research area of the Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Pakistan. Epistasis was found to be involved in all traits such as average boll weight, seed number boll -1 , seed mass boll -1 , lint mass boll -1 , lint mass seed -1 , seed index, seed volume 100-seeds -1 , seed density, and surface area seed -1 . Additive variance was greater in magnitude than dominance variance for traits such as lint mass boll -1 and lint mass seed -1 in cross I and for seed number boll -1 , seed mass boll -1 , and lint mass seed -1 in cross II. The magnitude of both variances was nearly equal for seed density in cross I and seed number boll -1 in cross II. While dominance variance was found to be greater in magnitude than additive variance for all the remaining traits in both crosses, the degree of dominance √(H/D) in cross I was partial for lint mass boll -1 and lint mass seed -1 . We found complete dominance for seed density and overdominance for the remaining traits. While in cross II the degree of dominance was partial for seed mass boll -1 and lint mass seed -1 , complete dominance was found for seed number boll -1 and overdominance for the remaining traits.

Recent development of site-specific weed management strategies suggests patch application of herbicides to avoid their excessive use in crops. The estimation of infestation of weeds and control thresholds are important components for taking spray decisions. If weed pressure is below a certain level in some parts of the field and if late germinating weeds do not affect yield, it may not be necessary the spray such places from an economic point of view. Consequently, it makes sense to develop weed control thresholds for patch spraying, based on weed cover early in the growing season. In Danish maize field experiments conducted from 2010 to 2012, we estimated competitive ability parameters and control thresholds of naturally established weed populations in the context of decision-making for patch spraying. The most frequent weed was Chenopodium album, accompanied by Capsella bursa-pastoris, Cirsium arvense, Lamium amplexicaule, Tripleurospermum inodorum, Poa annua, Polygonum aviculare, Polygonum persicaria, Stellaria media and Veronica persica. Relative leaf cover of weeds was estimated using an image analysis method. The relation between relative weed leaf cover and yield loss was analysed by nonlinear regression models. The competitive ability parameters and economic thresholds were estimated from the regression models. The competitive ability of weed mixtures was influenced by the increasing proportion of large size weeds in the mixtures. There was no significant effect of weeds which survived or established after the first herbicide application, indicating that early image analysis was robust for use under these conditions. Keywords: weed management, economic threshold, yield loss prediction, herbicide application, patch spraying, relative weed cover. ALI A, STREIBIG JC, CHRISTENSEN S & ANDREASEN C (2015). Image-based thresholds for weeds in maize fields. Weed Research 55, 26-33.

To suppress weeds in an apple (Malus sp.) orchard, we placed spruce (Picea spp.) bark mulch and cocoa (Theobroma cacao) husk mulch for 3 months in thicknesses of 0, 2.5, 5, 10 and 15 cm. To assess the development of weed cover, an innovative use of log-logistic doseresponse models was applied, with mulch thickness as the independent variable. Weed cover was measured by non-destructive image analysis by estimating the relationship between the number of green pixels and the total number of pixels in each experimental plot. The thickness of mulch layer required to attain a 50 and 90% weed suppression (ED50 and ED90) differed significantly within and between mulch types. In all except one instance, the cocoa mulch was superior in suppressing weeds. This method was useful for the evaluation, but further research is needed to give a more general conclusion about the suppression ability of the two mulches under other climatic and growing conditions.