Browsing by Person "Roeb, Johannes"

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Untersuchungen zum Herbizidstress in Zuckerrüben mit drei feldtauglichen optischen Sensoren und Methoden der Bildanalyse
(2014) Roeb, Johannes
Weed management in sugar beets is based on the repeated use of herbicide mixtures after crop emergence. Due to the limited selectivity of active ingredients, herbicide treatments not only control the weeds but will reduce the growth of sugar beets also. Yield losses due to herbicide stress are expected to range between 5-15%. Using optical sensors is a nondestructive method to assess changes in reflection, leaf fluorescence or chlorophyll fluorescence kinetics induced by herbicides. To evaluate the applicability of three optical sensors for assessing herbicide stress and to measure the influence of herbicides and herbicide mixtures on sugar beets, a pot experiment was performed at the University of Hohenheim, Germany. Sugar beets were grown under natural light and temperature conditions and treated with the active ingredients metamitron, phenmedipham, desmedipham, ethofumesate, triflusulfuron-methyl and dimethenamid-P in their commercially available formulation and practical dosage. In total five single herbicides as well as five different herbicide mixtures were applied in the cotyledon stage (EC 10), the two-leaf stage (EC 12) or the four- to six-leaf stage (EC 14/16) of sugar beets. Stress reactions were monitored with three optical sensors: Images of a digital camera (Canon EOS 1000D) were used to determine leaf coverage area, plant shape and leaf color. Measurements were performed about every second day and a growth index had been calculated. A multispectral fluorometer (FORCE-A MULTIPLEX®) was used to detect the blue-green fluorescence, red fluorescence and far-red fluorescence and to calculate fluorescence indices. A portable imaging sensor of chlorophyll fluorescence kinetics (WALZ IMAGING PAM) was used on a daily basis to determine changes in the maximum quantum efficacy (Fv/Fm) induced by herbicide treatments. Four respectively two weeks after the treatment sugar beets were harvested for dry matter analysis. For each of the herbicide treatments and for each of the three application dates five Mitscherlich pots were used for replication. Each pot had about four sugar beet plants. Based on digital imaging it was possible to measure leaf coverage area and determine growth depressions induced by herbicide treatments containing mixtures of the active ingredients phenmedipham, desmedipham and ethofumesate. Herbicide mixtures with more active ingredients increased the stress reaction of sugar beets. Differentiation between untreated plants and sugar beets treated with different herbicides or mixtures was possible a few days after application. Results were correlated with dry matter. Changes in plant shape parameters indicated a delayed development of herbicide treated plants. Higher red content of leaf color was attributed to a relative loss of chlorophyll. Measurements with the FORCE-A MULTIPLEX® fluorometer detected an increase in red and far-red fluorescence but not blue-green fluorescence within 1-2 days after treatments with the aforementioned mixture of active ingredients. About the same trends were found at all application dates. Most fluorescence values were affected by growth stage and leaf area of sugar beets. Thus, although differences between treated and untreated plants were strong, it was not possible to discriminate between stress reactions on different herbicide treatments. Based on the maximum quantum efficacy (Fv/Fm) measured with the WALZ IMAGING-PAM chlorophyll fluorescence sensor previous studies, describing the time course of stress reaction on application of PSII-inhibitors in sugar beets were confirmed. After a strong decrease of Fv/Fm within one day, recovery to the initial value was observed within ten days. Quantification of herbicide stress induced by PSII-inhibitors was possible due to different intensities and durations of the stress reaction. Photochemical stress response to treatments with metamitron or chloridazon was lower than with products containing phenmedipham or desmedipham. Stress reaction on herbicide mixtures not only depended on content of PSII-inhibitors but also on formulation. Weather conditions were more important than the sugar beet development stage considering the stress reaction. Observations from previous studies, indicating an increase in herbicide stress after precipitation and at low temperatures, were also confirmed in this study. Differences in stress reactions of cotyledons and first true leaves can be explained by a higher uptake of herbicides in young tissues. The influence of other herbicides, mixtures, dosages and formulations on herbicide stress in sugar beets has to be further investigated. Moreover the complex interrelations between sugar beet development stage, weather conditions and stress reaction could only be investigated in systematic field trials. For the measurement of stress reactions on herbicides the described optical sensors and methods can be used, each having different advantages and disadvantages.