Intercropping corn with soybean, lupin and forages: weed control by intercrops combined with interrow cultivation

Intercropping corn with legumes is an alternative to corn monocropping and is a possible way to reduce the use of inputs, such as herbicides, while maintaining current weed control levels. Two experiments were carried out at each of two sites in both 1993 and 1994. The first experiment investigated the effects of seeding soybean or lupin alone or in combination with one of three forages (annual ryegrass, Lolium multiflorum Lam.; perennial ryegrass, Lolium perenne L.; and red clover, Trifolium pratense L.) on weed control. The second experiment examined the effects of seeding date (simultaneous with corn or 3 weeks later) and number of rows of large-seeded legumes (one or two) seeded between the corn rows, on weed control. Whenever seeding of legumes/forages was delayed, weekly interrow tillage operations were used to control weeds until legume/forage seeding. The density and biomasses of monocot weeds, either on or between the corn rows, were not affected by cultivation or intercropping. The density and biomass of dicot weeds on corn rows were reduced by some intercrop systems. For the various cropping systems tested, the dicot weed biomass and density between corn rows were most affected (in some cases reduced by 73-100% of the weedy control). A more effective dicot weed control was observed in delay seeded treatments, which allowed extra interrow cultivations. Intercrops that included soybean were also more successful at reducing weed populations than those containing lupin. Underseeded forages did not reduce weed biomass or density.     

Spectral and time-resolved fluorescence signature of four weed species as affected by selected herbicides

In the present study we show for the first time the suitability of the laser-induced fluorescence technique to evaluate in vivo herbicide-induced damages as revealed by changes of fluorescence spectra and lifetime. Four herbicides of different modes of action (glyphosate, bromoxynil, mesotrione, and amitrole) were selected and applied to four weed species (Stellaria media, Setaria viridis, Chenopodium album, and Viola arvensis). Modifications of the fluorescence signature depended on the agrochemical – plant species interaction as well as on the time after application. Measurements in the red and far-red spectral region reveal disturbances in the functionality of the photosynthetic apparatus and chlorophyll concentration, e.g. after application of bromoxynil or mesotrione. Recordings in the blue and green spectral regions indicate changes of both amount and composition of specific fluorophores, i.e. after application of glyphosate and amitrole. In all spectral measurements, the position of peak maxima was not affected by herbicide application. The fluorescence lifetime, expressed as LTmean or as lifetime 1 (LT1, short-duration) and LT2 (long-duration) fractions, provided additional information to the spectrally resolved data. Thereby, significant alterations of the lifetime duration and fractional characteristics were observed at specific wavelengths, e.g. after application of bromoxynil, mesotrione, or amitrole.