Drechslera gigantea, a potential mycoherbicide of grass weeds, was isolated in Florida from naturally infected large crabgrass (Digitaria sanguinalis); it produces phytotoxic metabolites in liquid culture. The main metabolite was identified by spectroscopic methods and optical properties as ophiobolin A (1), a well-known phytotoxic sesterterpene produced by several phytopathogenic fungi of important crops and already extensively studied for its interesting biological activities. The other three minor metabolites proved to be related to ophiobolin A and were identified using the same techniques as 6-epi-ophiobolin A and 3-anhydro-6-epi-ophiobolin A (2 and 3) and ophiobolin I (4). Assayed on punctured detached leaves of several grass and dicotyledon weeds, ophiobolin A proved to be on average more phytotoxic as compared to the other related compounds. Some structural features appear to be important for the phytoxicity, such as the hydroxy group at C-3, the stereochemistry at C-6, and the aldehyde group at C-7. Furthermore, grass weeds usually proved to be more sensitive to the phytotoxins than dicotyledons, on which ophiobolin A caused the appearance of large necrosis even at the lowest concentration assayed. This is the first report about the production of ophiobolins from D. gigantea and of the proposed use as potential natural herbicides against grass weeds.

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Silybum marianum Gaertner is spreading in many crops of Southern Italy, particularly in durum wheat, sugar beet and some vegetable crops. Information about its biology are useful to set up effective control strategies. Four experiments were carried out at the Crop Science Department of the University of Bari (Southern Italy). Two trials were conducted in Petri dishes and evaluated the effects of different light, temperature and osmotic stress conditions on the seed germination. Another trial evaluated the ability of seedlings to emerge from different depths. The effects of eight different sowing periods on the plant growth were assessed in the fourth experiment. The highest germination rate was found with constant temperatures of 25 °C or 30 °C and with alternating temperatures of 25- 15 °C for 8 and 16 hours respectively. Germination was affected by the light and was significantly decreased at 0.2 Mpa and completely inhibited at -0.8 Mpa. Plant emergence was strongly reduced from a depth of more than 3 cm. The plant size at the first bloom was reduced by postponing the sowing period from October to February. The same decreasing trend was observed in the number of flower heads and in the number of days required for the first bloom. Results can suggest some important strategies to manage this species. False sowing, followed by irrigation, can be recommended in summer, in order to obtain the highest seed germination. Since the emergence of this plant is very scarce from a depth of more than 3 cm, ploughing can be effective to bury seeds in case of strong disseminations in order to reduce the infestation in the following crop

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Widespread use of synthetic herbicides in weed control could result in negative impact on human health and on the environment. Natural compounds could be successfully used as bioherbicides because they are potentially more environmental friendly and safe. Plants are an important source of active compounds. In particular, many species belonging to the Labiate family produce essential oils containing compounds that could act as natural herbicides. In this paper we report on preliminary studies about the effects on seed germination and plant growth of an oregano hybrid (Origanum vulgare L. ssp. virilidum x O. vulgare L. ssp. hirtum (Link) Iestwart). Experiments were done both in pots and in the field. Increasing amounts of chopped leaves and stems of oregano were added to the soil. In the pots, several weed species were sown, whereas naturally occurring infestation was evaluated in the field. In comparison with the control, a reduced number of weeds was observed where oregano biomass was added. The above-mentioned trend was more visible in the pots than in the field. The results suggest that the hybrid of oregano used in the trial could be an interesting source of natural compounds effective against weeds. Hence, further studies with this plant are likely to be successful.

This paper reports a survey on the weed flora and seed bank in an almond orchard sited in Apulia region (Southern Italy), where the following soil management practices have been compared for over 30 yrs: no-tillage, keeping the soil totally weed-free throughout the year by using pre-emergence herbicides to prevent plant emergence or post-emergence herbicides in case of weeds already emerged; no-tillage, with post-emergence herbicides; no-tillage, with mowing of natural weed flora in spring; cover cropping, with faba bean sown in November and green manured in springtime; conventional soil tillage. The different management techniques influenced significantly the weed flora in experimental plots, both in terms of quantity and quality. The seed bank was clearly impoverished after the long-term applications of pre-emergence herbicides, both in terms of richness and of diversity. During the fall period, the plots of conventional tillage or pre-emergence herbicides had less natural ground-flora than the others. During springtime, prior to the sward control practices, the plots treated by foliar herbicides or mowing had the highest total weed cover. We conclude that post-emergence weed control by mowing or using chemical herbicides or the green manure of the cover crop may be proposed to reduce impact to the soil and to promote the growth of abundant and sufficiently diversified and balanced flora. If appropriately managed, this flora can provide potential ecological services, without competing with the orchard, as suggested by the literature. During the autumn, natural flora can uptake soil nitrogen thus preventing leaching in the rainy season. In springtime, after the sward has been destroyed, natural flora can supply a substantial amount of biomass to the soil. Indicator species analysis was also used to find the species characterizing each treatment and some of their combinations. Weeds belonging to the Poaceae botanical family were significantly associated with post-emergence herbicides and mowing treatments. These species produce a substantial amount of biomass and have bunched roots; consequently, they supply beneficial effects by improving porosity and structure of the soil and reducing erosion hazard

Conservative agriculture includes a range of management strategies with low energy inputs such as no-tillage, minimum tillage, and low application of fertilizers. Weed flora in arable fields is strictly affected by agronomic practices such as tillage and fertilization management. This study was conducted seven years after the beginning of a long-term—durum wheat–faba bean—rotation. It analyzes the combined effects on the soil seed bank of three different tillage systems (conservative, reduced, and conventional tillage) and two levels of nitrogen fertilization. The effects were investigated both using stepwise discriminant analysis and analysis of variance in order to find statistical differences among main factors and their interactions. The seed bank of Conyza canadensis, Papaver rhoeas, Solanum nigrum, Fallopia convolvulus, and Fumaria officinalis was higher in conservative or reduced tillage plots. The magnitude of the response to nitrogen supply varied among weed species. Conyza canadensis seemed to be favored by low nitrogen supply, whereas Sinapis arvensis by higher doses of nitrogen. Anagallis arvensis showed the lowest seed bank in conventionally tilled plots, without distinction of nitrogen supply. The results suggest that different tillage systems and, to a lesser extent, different nitrogen supply, produce changes in the seed bank size and composition, along the soil profile.