A vision for Weed Science in the twenty-first century

Breen, John,Ogasawara, Masaru The Korean Society of Weed Science and The Turfgra 2011 Weed Biology and Management Vol.11 No.3

Weed Science, particularly in Japan, needs to return to a focus on "undesirable plants." In three major eras until the present, the discipline has shifted from an exclusive focus on agriculture to land uses with more complex weed management goals. The goals of Weed Science, once clearly understood and universally recognizable, in the present era appear to lack clarity. This is due to various factors including: a perceived lack of unmet technical needs in weed management, a lack of funding for research, a frequent lack of understanding and respect of our discipline from fellow scientists and academic administrators, and a bad reputation for herbicides among non-scientists. We present a future vision for the discipline that includes a return to the basics for Weed Biology, an integrated approach to Weed Management, and a need to educate both scientists and non-scientists about the importance of Weed Science.

Biological control of invasive plant species: A stochastic analysis

Chalak, Morteza,Ruijs, Arjan,Van Ierland, Ekko C. The Korean Society of Weed Science and The Turfgra 2011 Weed Biology and Management Vol.11 No.3

Biological control agents are regarded as a relatively safe method to control weeds. However, their impact on weeds can be relatively low and unpredictable. The aims of this article were to: (i) assess whether or not a weevil (Apion onopordi) and a mycoherbicide (Sclerotinia sclerotiorum) are desirable as biological agents for the control of Californian thistle (Cirsium arvense) in New Zealand despite their uncertain effectiveness; (ii) identify the combination of control options that is optimal to control the thistle; (iii) analyze the economic consequences of excluding chemicals from the weed control strategy; and (iv) assess the feasibility of the eradication of this weed. Two optimization models were developed and compared: one deterministic model and one stochastic model. The results showed that taking into account the stochastic effectiveness of biological agents can change the optimal integrated strategy, particularly if the biological control agent is relatively expensive. However, for a cheaper biological agent, the stochastic efficacy is less likely to change the optimal control strategy. On the basis of the modeling results, the authors argue that, in the context of the agri-environmental setting of this article's case study, chemicals can be replaced by more environmentally friendly control options at a relatively low cost. The authors also show that the eradication of the thistle is unlikely, at least given the efficacy of the existing control methods.

Weed control in irrigated corn by hairy vetch interseeded at different rates and times

Mohammadi, Gholam Reza The Korean Society of Weed Science and The Turfgra 2010 Weed Biology and Management Vol.10 No.1

In order to study the potential of interseeded hairy vetch as a living mulch to control weeds in corn, a field study was conducted at the Agricultural Research Farm, Razi University, Kermanshah, Iran. The experiment was carried out in a split-split plot arrangement with four replications. The main plots were two weed treatments (weedy and weed-free for all of the growing season), the subplots were two hairy vetch planting dates (simultaneous with corn planting and 10 days after corn emergence), and the sub-subplots were three hairy vetch planting rates (0, 25, and 50 $kg\;ha^{-1}$).The results indicated that the weedy condition for all of the growing season reduced corn plant traits, including the seed yield, number of ears per plant, number of seeds per ear, 100-seed weight, height, Leaf Area Index, and leaf chlorophyll content, as compared to the weed-free condition for the entire growing season. The hairy vetch dry weight also was reduced by the full-season weedy condition. The traits under study were not significantly influenced by the hairy vetch planting times, but increasing the hairy vetch planting rate from 0 to 50 $kg\;ha^{-1}$ improved the corn yield, number of seeds per ear, 100-seed weight, height, Leaf Area Index, and leaf chlorophyll content. However, the number of ears per plant was not significantly influenced and the weed dry weight was reduced by half. Overall, from the standpoint of corn seed production, an interseeding amount of 25 $kg\;ha^{-1}$ of hairy vetch is recommended; taking into consideration the legume forage yield, an interseeding amount of 50 $kg\;ha^{-1}$ of hairy vetch is more beneficial.

Effect of adjuvants on the rainfastness and performance of tribenuron-methyl on broad-leaved weeds

Pannacci, Euro,Mathiassen, Solvejg Kopp,Kudsk, Per The Korean Society of Weed Science and The Turfgra 2010 Weed Biology and Management Vol.10 No.2

The influence of a non-ionic surfactant (20% isodecyl alcohol ethoxylate plus 0.7% silicone surfactants), an anionic surfactant (25.5% alkylethersulfate sodium salt), and a vegetable oil (95% natural rapeseed oil with 5% compound emulsifiers) on the performance and rainfastness of a new commercial formulation of tribenuron-methyl was assessed on four broad-leaved weeds: wild mustard (Sinapis arvensis), scentless mayweed (Tripleurospermum inodorum), common poppy (Papaver rhoeas), and common lambsquarters (Chenopodium album). In one experiment, six doses of tribenuron-methyl alone or in a mixture with each of the three adjuvants were applied to each weed species at two different leaf stages. In another experiment, the plants of T. inodorum were sprayed and subsequently subjected to 3 mm of rain at 1, 2, and 4 h after treatment (HAT). The activity of tribenuron-methyl was significantly enhanced by all the adjuvants on all the weed species and only minor differences were observed among the tested adjuvants. The impact of the adjuvants varied among the weed species and growth stages.The highest response to the inclusion of adjuvants in the spray liquid was found at the late growth stage and on C. album, followed by P. rhoeas and T. inodorum, while S. arvensis was less responsive to the adjuvants. All the adjuvants significantly improved the rainfastness of tribenuron-methyl on T. inodorum, with differences among the adjuvants being more pronounced when rain occurred shortly after herbicide application. The effect of the vegetable oil on tribenuron-methyl's rainfastness was significantly lower than that of the surfactants with rain at 1 HAT, while no significant differences among the three adjuvants were observed when rain occurred at 2 and 4 HAT.

Allelopathic effect of itchgrass (Rottboellia cochinchinensis) on seed germination and plant growth

Meksawat, Sunyata,Pornprom, Tosapon The Korean Society of Weed Science and The Turfgra 2010 Weed Biology and Management Vol.10 No.1

Herbicides produce a wide range of toxic side-effects that pose a potential hazard to the environment. The development of natural allelochemicals is one method of addressing these issues. Here, we describe the allelopathic activity of itchgrass (Rottboellia cochinchinensis), which can inhibit the seed germination and growth of weeds. Farmers in Lampang, northern Thailand, have been cultivating itchgrass and using it as a mulching material to control other weeds in vegetable fields. It has long been observed that itchgrass interferes with the growth of other plants. This study showed that the density of weed species in the itchgrass-infested areas was lower than that in the itchgrass-uninfested areas.The shoot and root growth of Bidens pilosa, Mimosa pudica, Ageratum conyzoides, Echinochloa crus-galli, Oryza sativa var. RD 6, and Lactuca sativa var. OP were significantly reduced in soil previously planted with itchgrass. Water-soluble extracts from all parts of itchgrass had inhibitory effects on the growth of some test plants. Allelochemicals from itchgrass can inhibit seed germination and plant growth better at a 1 cm distance than at a 3 cm and 5 cm distance from itchgrass. Our results suggest that itchgrass has a strong competitive ability and possible allelopathic activity to other plant species. The allelopathic activity of itchgrass in the soil can influence the germination of adjacent species, causing reduced growth of seedlings.

Effects of some integrated management options on parthenium interference in sorghum

Tadesse, Besufekad,Das, Tapas K.,Yaduraju, Nanjapur T. The Korean Society of Weed Science and The Turfgra 2010 Weed Biology and Management Vol.10 No.3

Parthenium is widely distributed across the uncropped areas of the tropics. It has slowly encroached into many crops and causes considerable yield loss. It heavily infests sorghum, which is widely cultivated by the resource-poor farmers in Africa and Asia. Its interference and management in sorghum in these cropping systems is not well understood. Therefore, this experiment was undertaken to determine the appropriate parthenium management techniques to use in sorghum crops. All the studied weeds, in combination with parthenium, offered greater competition to sorghum than parthenium alone. Similarly, under a composite stand of weeds, parthenium was inferior in competitiveness to the other weeds until 60 days after sowing (DAS); by 90 DAS, it could accumulate a higher dry weight due to its consistent growth. A pre-emergence treatment of atrazine (0.75 $kg\;ha^{-1}$) with wheat straw mulch (5.0 $t\;ha^{-1}$) brought about a consistent and significant reduction in the parthenium growth and, consequently, increased the sorghum yield by 90.8%. Cowpea intercropping with and without pendimethalin (1.0 $kg\;ha^{-1}$) as a pre-emergence treatment could not control parthenium between 0 and 60 DAS, but could reduce the parthenium growth during the later period of 60.90 DAS, which resulted in a significant increase in sorghum growth.These intercropping treatments increased the sorghum grain yield by 156.2% and 142.4%, respectively, over the unweeded control and by 18.5% and 12.1%, respectively, over the weed-free control. These treatments also promoted a higher uptake of N, P, and K by the sorghum crop. Thus, cowpea intercropping was the most effective method for parthenium management vis-$\grave{a}$-vis sorghum yield improvement, followed by cowpea intercropping with pendimethalin and then by atrazine as a pre-emergence treatment with wheat straw mulch.

Competition of sorghum cultivars and densities with Japanese millet (Echinochloa esculenta)

Wu, Hanwen,Walker, Steven R.,Osten, Vikki A.,Robinson, Geoff The Korean Society of Weed Science and The Turfgra 2010 Weed Biology and Management Vol.10 No.3

Field studies were conducted at two locations in southern Queensland, Australia during the 2003-2004 and 2004-2005 growing seasons to determine the differential competitiveness of sorghum (Sorghum bicolor L. Moench) cultivars and crop densities against weeds and the sorghum yield loss due to weeds. Weed competition was investigated by growing sorghum in the presence or absence of a model grass weed, Japanese millet (Echinochloa esculenta). The correlation analyses showed that the early growth traits (height, shoot biomass, and daily growth rate of the shoot biomass) of sorghum adversely affected the height, biomass, and seed production of millet, as measured at maturity. "MR Goldrush" and "Bonus MR" were the most competitive cultivars, resulting in reduced weed biomass, weed density, and weed seed production. The density of sorghum also had a significant effect on the crop's ability to compete with millet. When compared to the density of 4.5 plants per $m^2$, sorghum that was planted at 7.5 plants per $m^2$ suppressed the density, biomass, and seed production of millet by 22%, 27% and 38%, respectively. Millet caused a significant yield loss in comparison with the weed-free plots. The combined weed-suppressive effects of the competitive cultivars, such as MR Goldrush, and high crop densities minimized the yield losses from the weeds. These results indicate that sorghum competition against grass weeds can be improved by choosing competitive cultivars and by using a high crop density of >7.5 plants per $m^2$. These non-chemical options should be included in an integrated weed management program for better weed management, particularly where the control options are limited by the evolution of herbicide resistance.

Effects of the relative time of emergence and the density of common lambsquarters (Chenopodium album) on corn (Zea mays) yield

Sarabi, Vahid,Mahallati, Mehdi Nassiri,Nezami, Ahmad,Mohassel, Mohammad Hasan Rashed The Korean Society of Weed Science and The Turfgra 2011 Weed Biology and Management Vol.11 No.3

Common lambsquarters (Chenopodium album) is one of the world's worst weeds. In order to study the competitive potential of single-cross 704 corn (Zea mays) in competition with common lambsquarters at different relative times of emergence and density levels of the weed, an experiment was conducted in 2006 at the farm of the Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran. This experiment was designed as a split plot based on a randomized complete block design with three replications. The emergence time of the weed was considered at three levels (7 days and 14 days earlier than corn and simultaneously with corn) as the main plot, while the density of the weed was considered at six levels (0, 4, 8, 12, 16, and 20 plants per $m^2$) as the subplot. The results showed a decrease in the grain yield and biomass of corn, as the emergence time of corn was delayed in comparison with the weed in a way that the maximum reduction was observed at the earlier emergence of the weed, compared to corn, and also at a high density of the weed. As the weed emerged earlier than corn, the rate of yield loss resulting from the first flush of weeds was not that high. However, with every few days that the weed emerged earlier than corn, the rate of yield loss became higher as the density of the weed increased to its maximum. The maximum reduction in the yield components was observed at 14 days earlier emergence of the weed, compared to corn, and at high densities, as the corn plants were overshadowed by the weed canopy and no ear was produced.

Overcompensation of seed production caused by clipping of Bidens pilosa var. radiata (Compositae): Implications for weed control on Iriomote-Jima Island, Japan

Shimamoto, Yuko,Nomura, Naofumi,Takaso, Tokushiro,Setoguchi, Andhiroaki The Korean Society of Weed Science and The Turfgra 2011 Weed Biology and Management Vol.11 No.3

The invasion of natural ecosystems by exotic species is a major threat to biodiversity on a local, regional, and global scale. Endemic island flora are particularly vulnerable to invasive species. Bidens pilosa var. radiata is a common invasive weed of roadsides, which are subject to clipping, on Japanese subtropical islands. To assess compensation by the weed to damage by clipping, a pot experiment was conducted under common garden conditions. The above-ground parts were clipped with pruning shears at various frequencies, ranging from no clipping (the control) to clipping at 4-16 week intervals for 32 weeks in summer. The clipped individuals regenerated new branches from the axillary buds and flowered for ${\leq}12$ weeks after the clipping. The regeneration after the clipping gave rise to secondary reproduction, whereas minimal regeneration occurred in the unclipped individuals after the maturation of the fruit. Consequently, the total flower head mass, represented by the dry weight of the inflorescences throughout the experiment, was higher on the individuals that were clipped at 12 and 16 week intervals than on the unclipped individuals, suggesting overcompensation in fecundity. At the higher frequencies of above-ground clipping, the flower head mass was suppressed at 8 week clipping intervals, while both the flower head mass and the productive biomass were suppressed at 4 week clipping intervals. This indicates that clipping at intervals of ${\leq}8$ weeks is required to prevent the reproduction of this weed.

Interference of redroot pigweed (Amaranthus retroflexus) in green bean (Phaseolus vulgaris)

Mirshekari, Bahram,Javanshir, Aziz,Arbat, Hamdollah Kazemi The Korean Society of Weed Science and The Turfgra 2010 Weed Biology and Management Vol.10 No.2

Weeds that emerge along with or immediately after crop plants usually can reduce the yield of those crops. Two randomized complete block design experiments were conducted during 2006 and 2007 in Tabriz, Iran to determine the critical period of redroot pigweed control in the green bean hybrid "Cantander". The treatments were weed-infested and weed-free plots at 2, 4, 6, 8, 10, and 14 weeks after bean emergence (WABE). The green bean biomass was affected by the early emergence of redroot pigweed, but it was not reduced when redroot pigweed emerged at 10 weeks after crop emergence, along with crop emergence, and grew with green bean until 4 WABE. The redroot pigweed biomass decreased by 2.7 $g\;m^{-2}$ per day when weed emergence was delayed. Each 100 $g\;m^{-2}$ of weed biomass that was produced resulted in a 1.4 $kg\;ha^{-1}$ loss in the green bean yield. When redroot pigweed interference lasted for ${\geq}4$ weeks after green bean emergence, the green bean yield was reduced significantly. Weeds, which emerged 2 weeks after green bean and thereafter were controlled, did not decrease crop productivity significantly. The highest crop yield was obtained when the weed emerged at 14 WABE. The critical period of redroot pigweed control, considering a 10% yield loss, was between 19 and 55 days after green bean emergence. Thus, weed control practises should be begun no later than 3 WABE and should continue until at least 8 WABE in order to obtain the maximum green bean yield.