North African knapweed (Centaurea diluta Aiton), cornflower (Centaurea cyanus L.), corn marigold [Glebionis segetum (L.) Fourr.], rigid ryegrass (Lolium rigidum Gaudin), and corn poppy (Papaver rhoeas L.) are weeds of economic importance in the Iberian Peninsula, particularly due to the limited herbicide options for effective control. For this reason, information about their seedling emergence has become critical to develop effective integrated management strategies and better time control actions. The aims of this study were to evaluate the effect of seed burial depth and soil disturbance on the emergence of the aforementioned weed species. Two pot experiments were carried out to 1) quantify seedling emergence at three burial depths (2, 5 and 9 cm), and 2) characterize seedling emergence in response to different frequencies and timings of soil disturbance. Burial depth limited the emergence of G. segetum and P. rhoeas at 5 and 9 cm, respectively; while seedling emergence of C. diluta, C. cyanus, and L. rigidum were reduced by 92, 90 and 67 % at 9 cm compared to 2 cm, respectively. Two or more sequential soil disturbance events increased total seedling emergence of C. diluta, P. rhoeas, and G. segetum compared with single events, while L. rigidum did not respond to repeated soil disturbance. These results suggest that turning the soil to bury weed seeds down to 5 cm or deeper would be a very effective method to control G. segetum and P. rhoeas, and moderately effective to control C. cyanus. Also, the use of stale seedbed would have some efficacy to reduce P. rhoeas and C. diluta weed pressure within the crop. This study illustrates how differences among species in seedling emergence in response to soil depth and disturbance can determine distinct emergence patterns ultimately influencing the selection of weed control tools and timing.

Field studies were conducted in 2021 in Kibler and Augusta, AR, to determine the effect of winter cover crops and cultivar selection on weed suppression and sweetpotato [Ipomoea batatas (L.) Lam.] yield. The split-split plot studies evaluated three cover crops [cereal rye (Secale cereale L.) + crimson clover (Trifolium incarnatum L.)], [winter wheat (Triticum aestivum L.) + crimson clover], and fallow; weeding (with or without); and four sweetpotato cultivars (‘Heartogold’, ‘Bayou-Belle-6’, ‘Beauregard-14’, and ‘Orleans’). ‘Heartogold’ had the tallest canopy, while ‘Beauregard-14’ and ‘Bayou Belle-6’ had the longest vines at 5 and 8 wk after sweetpotato transplanting. Sweetpotato canopy was about 20% taller in weedy plots compared to the hand-weeded treatment and vines were shorter under weed interference. Canopy height and vine length of sweetpotato cultivars were not related to weed biomass suppression. However, vine length was positively correlated to all yield grades (r >0.5). Weed biomass decreased one-fold in plots with cover crops compared to bare soil at Augusta. Cover crop biomass was positively correlated with jumbo (r=0.29), no.1 (r=0.33), and total sweetpotato yield (r=0.34). Jumbo yield was affected the most by weed pressure. On average, sweetpotato total yield was reduced by 80 and 60% with weed interference in Augusta and Kibler, respectively. ‘Bayou Belle-6’ was the high-yielding cultivar without weed interference in both locations. ‘Bayou Belle-6’ and ‘Heartogold’ were less affected by weed interference than ‘Beauregard-14’ and ‘Orleans’.

Cowvine (Ipomoea lonchophylla J.M.Black) is a native and widely spread summer broadleaf weed in Australia. It contains glycoresins which are toxic to livestock. However, limited information is available on seed germination ecology and growth phenology of this species. A series of experiments were conducted to determine the response of I. lonchophylla to different environmental conditions. Results showed that the primary dormancy exhibited by I. lonchophylla is due to the physical impediment of the hard seed coat. The seed germination percentage was the highest at the constant temperature of 27 oC and alternating temperatures of 35/25 oC. Germination of I. lonchophylla was not stimulated by light, suggesting that this species is non-photoblastic. I. lonchophylla germination was intolerant of a medium to high level of salt stress and germination was completely inhibited at 250 mM NaCl. The emergence of I. lonchophylla was not restricted by seeding depth up to 8 cm and only 5% emergence was recorded when seeds were planted at a 16 cm depth. The germination percentage was also drastically reduced by 90-100% after exposure to either three months in silage, 48-hour digestion in steers, or silage plus digestion treatments. The growth and reproductive phenology of I. lonchophylla was affected by emergence time. Plants that emerged in late spring (15 November) were able to produce more berries per plant than those that emerged in mid-summer (15 January) in southern NSW. Information gained in our study including high soil salinity, ensiling and digestion will help to develop more sustainable and effective integrated weed management strategies for the control and reduce the spread of this weed.

Palmer amaranth (Amaranthus palmeri S. Watson) is a troublesome weed in several cropping systems in the US. The evolution of resistance to multiple herbicides is a challenge for the management of this weed. Recently, we reported metabolic resistance to 2,4-D mediated by cytochrome P450 activity in a 6-way-resistant A. palmeri population (KCTR). Plant growth temperature can influence the herbicide efficacy and level of resistance. The effect of temperature on 2,4-D resistance in A. palmeri is unknown. In this research, we investigated the response of KCTR and a known susceptible (MSS) A. palmeri response to 2,4-D grown at low- (LT, 24/14°C, d/n) or high (HT, 34/24°C, d/n) temperature regimes. When MSS and KCTR plants were 8-10 cm tall, they were treated with 0, 140, 280, 560 (field recommended dose), 1120, and 2,240 g ai ha-1 of 2,4-D. Further, 8-10 cm tall MSS and KCTR plants grown at LT and HT, were also treated with [14C] 2,4-D to assess the metabolism of 2,4-D at LT and HT. The results of dose-response experiments suggest that KCTR A. palmeri exhibits 23 times more resistance to 2,4-D at HT than MSS. Nonetheless, at LT, the resistance to 2,4-D in KCTR was only 2-fold higher than MSS. Importantly, at HT there was enhanced metabolism of 2,4-D in both KCTR and MSS A. palmeri, than at LT. Further, treatment with cytochrome P450- inhibitor, malathion followed by 2,4-D increased the susceptibility of KCTR at HT. Overall, rapid metabolism of 2,4-D increased KCTR resistance to 2,4-D at HT compared to LT. Therefore, the application of 2,4-D when temperatures are cooler can improve control of 2,4-D-resistant A. palmeri.

Weeds are a fundamental component of agroecosystems and, if not appropriately managed, can cause severe crop yield losses. New perspectives on weed management are required because current approaches, such as herbicide application or soil tillage, have significant environmental and agronomic drawbacks. We propose the concept of “neutral weed communities,” which are weed communities that coexist with crops and do not negatively affect their yield and quality compared with weed-free conditions. Management practices that promote neutral weed communities can enable reduced use of herbicides and soil tillage while enhancing ecosystem services and biodiversity. We report scientific evidence of neutral weed communities and survey ecological explanations for why different weed communities have different effects on crop production. We also propose two weed management approaches for obtaining neutral weed communities. The first approach aims to maximize weed biodiversity using traditional approaches such as cropping system diversification and integrated weed management. Higher weed biodiversity is associated with lower dominance of competitive weed species that reduce crop yield. The second approach relies on modern tools such as robots and biotechnology to manipulate the density of specific weed species. This approach can remove highly problematic species and minimize niche overlap between the weeds and crops. Given the complexity of interactions between crops, weeds, and other components of the agroecosystem, we highlight the need for multidisciplinary research to illuminate mechanisms that determine the neutrality of weed communities.