Source: American Society of Agronomy
Barnyardgrass is a summer annual grass weed with a global impact on corn production. Yield losses due to barnyardgrass competition have been estimated up to 45 percent or more for crops such as cotton and corn. Besides corn, it can also be a serious weed pest in rice, soybean, sugarbeet, cotton and corn. Integrated weed management techniques can be used for control of barnyardgrass in corn.
High populations of this weed can occur in fields of continuous corn. A high population of barnyardgrass may attract an infestation of armyworms, which moves from the weed to feed on corn leaves.
There are a variety of herbicide options for control of barnyardgrass in both preplant and postemergent situations. In a tolerant corn crop, glyphosate can be applied over-the-top until the V8 stage for grass control. Barnyardgrass can be difficult to control, however, if it is drought stressed.
Just published research from a team of scientists at the Laboratory of Agronomy, Faculty of Crop Science, Agricultural University of Athens in Greece has studied using integrated weed management (IWM) for the control of barnyardgrass in corn.
The results of this study offer some essential insights in the development of an integrated weed management strategy for corn. Findings suggest that despite the high competitiveness of barnyardgrass, careful selection of a competitive corn hybrid and control of barnyardgrass through at least the V2 to V4 growth stage could dramatically reduce grain yield loss and weed seed production.
IWM helps growers reduce the development of resistant weeds and mitigate the social, health, and environmental impacts of agriculture. Using competitive crops and cultivars are important components of IWM that are useful in both conventional and organic (and other low-input) farming systems.
The success of barnyardgrass as a weed pest is attributable to many factors including a long germination and emergence period, seed germination under a wide range of environmental conditions, rapid growth and development, and vast production of easily dispersed seeds.
To develop efficient herbicide use and provide a logical basis for the development of an IWM system, information on the critical period of weed control is essential. In quantitative studies on weed-crop competition studies, weed relative to crop growth has a large impact on weed losses and was more important than other parameters such as weed density, to determine the need for postemergence control.
Also, information regarding the critical period of weed control in corn may lead to less reliance on the use of residual herbicides and to more reliance on well-timed postemergence herbicides.
To date, and especially in Europe, there is little information on the critical period of weed control in grain corn. In Mexico, a weed-free period of 50 d from seeding was required to prevent corn grain yield loss. In the United States, a weed-free period of 4 wk was required to prevent corn yield losses resulting from johnsongrass. In Canada, similar studies determined weed- free requirements from 3- to 14-leaf stages of corn development.
Little information is also available on the effect of weed species and the timing of emergence that may result in minimal agronomic impact, that is, few or no weed seeds produced and little or no crop yield loss. Reproductive output of barnyardgrass is also highly variable, while information on seed return as influenced by time of emergence is required to predict future population changes.
No studies have evaluated the impact of time of barnyardgrass emergence on yield components of several corn hybrids and barnyardgrass growth and reproductive output.
The objectives of this research were to determine the effects of barnyardgrass emergence date on biomass and fecundity of barnyardgrass and corn yield components and evaluate the competitiveness of four corn hybrids under the field conditions of western Greece.
Field experiments were conducted in western Greece in 2008 and 2009 to determine the influence of barnyardgrass emergence time and corn hybrid on corn yield and barnyardgrass growth and fecundity.
The researchers found that barnyardgrass biomass, tillers, canopy area, and seed production were significantly affected by the date of barnyardgrass emergence. Barnyardgrass plants emerging with corn produced 1010 to 1305 seeds per plant compared to only 112 to 240 seeds from plants emerging after the V4 growth stage. Maximum corn grain yield loss ranged from 24 percent to 34 percent for early emerging barnyardgrass, and <9 percent yield loss occurred from barnyardgrass seedlings emerging later than the V4 growth stage. Corn hybrids with rapid initial growth rate were more competitive than the other hybrids.
The researchers state that the study results indicate that both corn hybrid and time of barnyardgrass emergence relative to corn growth stage were fundamental in determining the outcome of the competition between corn grain yield and barnyardgrass growth and fecundity.
In fields of Greece infested with barnyardgrass, a delay of about 7 to 12 d in barnyardgrass emergence, which could be accomplished by early herbicide application or mechanical weed control, could reduce grain yield loss by about 10 percent to 15 percent.
Another interesting finding of their study has to do with the fact that keeping the field weed-free through at least V2 seems crucial for the optimal corn growth, while the late barnyardgrass emergence (V6) does not reduce grain yield. On the contrary, another novel finding is that there is still many seed produced by the barnyardgrass plants, which can easily contaminate the field and preserve the seed bank for the next growing season.
In addition, their results confirm that corn hybrid competitive ability might have a substantial range. Consequently, selection of corn hybrid could be an important weed management tool for the corn growers, while further research is required to rank the competitiveness of more corn hybrids. Knowing which corn hybrid to select in weed-infested fields could offer a significant yield advantage.
Source: American Society of Agronomy