Potential of two cover crops, signal grass and ruzi grass: suggested allelopathic effect on some important weeds

Abstract

There is evidence that signal (SG) and ruzi (RG) grass have an allelopathic effect on weeds. This study aim to evaluate this effects on difficult-to-control weeds: hairy beggarticks (HB), benghal dayflower (BD), horseweed (H), sourgrass (S) and tall windmill grass (TWG). The first experiment was installed in a completely randomized design with 2 donor species (SG and RG) × 4 extract concentrations (0, 75, 150 and 225 mg ml−1) in factorial scheme with four replicates. Weed germination percentage was evaluated in three-day intervals. In the second experiment, the weeds emerged in substrates previously cultivated with SG and RG, in completely randomised block design with four replicates. The emergence, shoot growth and root growth were evaluated. The results were as follows: (i) on horseweed (H), 84% germination inhibition by RG leaf extracts and 38% emergence inhibition by SG root exudates were observed; (ii) on benghal dayflower (BD), 84% germination inhibition by RG leaf extracts and 37% emergence inhibition and 4.3 times the SRL values than control by RG root exudates; (iii) on hairy beggarticks (HB) 52% germination inhibition by RG leaf extracts scored, while SG root exudates reduced 43% of the emergence, 24% shoots biomass accumulation and 11.3% root length; (iv) on sourgrass (S) 71% germination inhibition by both donor plants and 75% germination inhibition by RG leaf extracts were measured. Finally, on tall windmill grass (TWG) 69% germination inhibition was observed upon using both donor plants. It can be concluded that foliar allelochemicals inhibit the germination of: BD > S > TWG > H > HB, while root exudate allelochemicals, inhibit the emergence and root development of all weeds

The impacts of ecological mowing combined with conventional mechanical or herbicide management on weeds in orange orchards

“…This mulch has a suppressive effect on weeds, which may be physical, chemical and biological, depending on cover crop species and the amount of biomass previously produced and subsequently deposited on the soil by the ecological mower (Martinelli et al, 2017). In addition, U. ruziziensis leaf extracts and root exudates were reported to have allelochemical effects on difficult‐to‐control and high‐frequency weeds in Brazilian citrus orchards, such as B. pilosa , C. benghalensis , C. canadensis , D. insularis and C. elata (Villela et al, 2021).…”

“…About the pressure of selection of species adapted to the plant residues management by ECO‐mowing, some of the dominant weeds in the present study, such as R. raphanistrum , need shading to start their germination process (negative photoblastic species, Górski et al, 2013) and A. tenella , which may have been influenced by the lack of luminosity caused by mulch, as the absence of light is responsible for higher levels of total germination and speed of germination of this species (Vivian et al, 2008); and B. pilosa , which demonstrated signs of tolerance to the allelopathic effects of U. ruziziensis and U. decumbens (Villela et al, 2021).…”

“…For residues of U. ruziziensis , studies show an increase in the density of Amaranthus viridis at the level of 3.0 t ha −1 of mulch compared to its absence (Oliveira Jr et al, 2014) and an increase in emergence speed by 3.6 times for Ageratum conyzoides and almost twice for L. virginicum at the level of 1.5 t ha −1 of mulch compared to its absence (Martinelli et al, 2017). Moreover, leaf extracts of U. ruziziensis decreased the germination speed in 19 days of C. canadensis compared with U. decumbens and the absence of both, whilst root exudations of these Urochloa species delayed the emergence of C. benghalensis by up to 8 days (Villela et al, 2021).…”

“…Moreover, leaf extracts of U. ruziziensis decreased the germination speed in 19 days of C. canadensis compared with U. decumbens and the absence of both, whilst root exudations of these Urochloa species delayed the emergence of C. benghalensis by up to 8 days (Villela et al, 2021).…”

“…Therefore, the weed seed bank dominance for U. decumbens, R. raphanistrum and G. parviflora in CONV treatments, such as control (CTRL), MECH and P/P, can be explained: (i) by mulch absence on the tree-row area, which can be an impediment to U. decumbens and For B. pilosa, this weed has a certain tolerance of the allelopathic effects from Urochloa foliar and roots allelochemicals (Villela et al, 2021), which can explain its seed bank increase over time on ECO w/ POST treatments, as this treatment has no residual effect, there may be a selection of this weed, as a short-cycle species that develops in the application intervals, predominating in the weed seed bank (Monquero & Christoffoleti, 2005). This species also has high fecundity and can produce up to 6000 seeds per individual, with soil longevity of ≈80% germination by five years old seeds (Reddy & Singh, 1992).…”