Effect of reduced doses of a post-emergence graminicidal mixture to control Lolium rigidum G. in winter wheat under direct seeding in a Mediterranean environment (2023)

Plant protection

Part 24, Number 10,

October 2005

, side 880-887

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A study was carried out for 2 years (2002/2003 and 2003/2004) on a private farm in Alentejo (Évora), in southern Portugal, where wheat was sown with rain after the start of the winter rainy season. A no-tillage wheat crop was used, as this technology provides the necessary soil capacity for post-emergence at different stages of weed development. A mixture of diclofop-methyl+fenoxaprop-p-ethyl+mefenepir-diethyl was used in three doses at two times with three different application volumes.

The results indicate that lower herbicide concentrations with higher water application volumes reduced weed control efficiency at both weed developmental stages. In each treatment, the first weed development stage (starter shoot) resulted in a higherharvest grainyield. At this stage, both the weed and the crop are more sensitive to the herbicide, and as a result, the higher weed control efficiency was not reflected in higher grain yield due to some crop toxicity caused by the herbicide as the concentration increased.

Weed recurrence was low for both application times, suggesting that lower than recommended herbicide rates (2.5-31 ha)−1) or usually used by Portuguese farmers (21ha−1) can be used for satisfactory control ofA stiff lollipopG. In winter wheat, postemergence treatments can reduce rates when combined with adequate application volumes and early application times. When herbicide application was delayed (complete seeding), higher herbicide rates were required to achieve the highest crop yield.


Economic aspects, negative effects of pesticides on the environment and risk of food contamination have led to a reduction in the use of agricultural chemicals, including herbicides, in recent years. Widespread concern about the environmental side effects of herbicides, combined with public health fears, has led to several herbicides being banned in some countries and increased pressure on farmers to reduce herbicide use (Matteson, 1995). However, herbicides have been the predominant means of weed control in the developed world for over 40 years (Gill and Holmes, 1997).

Recent studies strongly advocate two directions for developing cropping systems with a reduced reliance on herbicides (Sterrenberg and Brandt, 1996; Lotz et al., 1997). One, called chemical refinement, focuses on reducing the use of herbicides through the development and improvement of curative tactics based on technological solutions, such as improved application technology, improved application time, factor-adjusted dosages and the development of herbicides with low environmental impact. effect (Bastiaans et al., 2000).

Today, the goal of weed control is to keep the weed community at acceptable levels rather than keeping the crop completely weed free. Satisfactory weed control can often be achieved when herbicides are used at doses lower than those normally recommended (Zhang et al., 2000; Boström and Fogelfors, 2002) and thus maintain satisfactory crop yields (Steckel et al., 1990; Hamill and Zhang, 1995b). Lower dose herbicides are often sufficient to control weed densities at or below threshold levels, and sublabeled herbicide doses combined with some mechanical weed control have been shown to be an effective way to reduce herbicide inputs in agricultural systems (Hamill and Zhang, 1995a).

To facilitate the decision of what is an appropriate dose in a particular field, the farmer needs support (Boström and Fogelfors, 2002) and a number of different types of decision support systems are currently available to help crop advisors and farmers to choose optimal herbicide. . dose (Forcella et al., 1996; Stigliane et al., 1996; Buhler et al., 1997; Shaw et al., 1998).

To ensure satisfactory weed control even under unfavorable field conditions, producers often recommend higher doses than necessary. Knowledge of the effects of various factors that influence herbicide effectiveness, e.g. weed species present, growth stage (Bruce et al., 1996), crop competitiveness, variety and weather conditions (Xie et al., 1997; Skuterud et al., 1998; Tottman et al. al., 1998), increases the possibility of using a herbicide dose that is lower than the recommended dose, while achieving sufficient weed control and an acceptable crop yield (Fogelfors, 1990; Salonen, 1992a, Salonen, 1992b). Zhang et al. (2000), based on several studies in different crops and under different environmental conditions, found considerable variations in weed control efficiency with different herbicide doses. In a few studies at the recommended rate, they achieved a weed control efficiency of only 20-40%, while a weed control efficiency of 70% or higher was achieved in 50% of the studies with herbicide doses as low as 20% of the recommended rate. . . The same authors found that weed control efficiency was usually lower and varied more at lower doses than at the recommended dose, but remained within the 60-100% range in over 90% of cases. For cereals, greater than 70% weed control was maintained in over 90% of cases with rates between 30% and 60% of recommended rates.

Currently, the majority of Portuguese farmers still rely on the conventional tillage system based on the body plough, disc harrow and/or tooth harrow to establish crops with the main purpose of seed bed preparation and initial weed control. However, due to the reversal of soil layers, weed seeds are buried, mixed and carried back to soil layers, from which they emerge and become established in the next crop. The need for additional chemical weed control with other economic and environmental disadvantages of conventional tillage is leading more and more farmers to use alternative tillage systems such as shallow tillage and direct seeding. The use of these tillage systems changes the distribution of weed seeds in the surface layer of the soil and the timing of weed emergence. In Mediterranean conditions, high initial weed growth can be expected after the first rainfall, as most weed seeds remain at or near the soil surface. For example, spraying before sowing removes a significant proportion of potential weeds and subsequently reduces weed pressure in the established crop.

Both the reduced weed pressure and the benefit of much better tillering capacity, which allows better timing of application, especially in direct seeding, should allow adequate weed control at lower herbicide rates. Earlier application dates will not only bring the weed to a more sensitive stage, but may also allow the use of lower application rates to ensure adequate crop penetration and contact with the weed leaves. In addition, as shown by O'Donovan et al. (1985), early weed removal is important to prevent crop yield reduction.

The increasing interest of Portuguese farmers in the application of conservation tillage systems was a goal to investigate the possibility of reducing the use of herbicides in winter wheat grown without tillage. In addition, it enabled the verification of the effect of different application volumes and times on the weed control efficiency of lower herbicide doses.

Fragments section

Materials and methods

In 2002/2003, a trial was carried out to investigate the effect of three doses of a post-emergence herbicide to control Lolium rigidum G. in winter wheat (Triticum aestivum L.) in interaction with three different application volumes and two weed development stages. and 2003/2004, on a private farm near Évora/southern Portugal. The herbicide used was a commercial mixture of 250 µl−1of 22.73% (w/w) diclofop-methyl+20 gl−1of 1.82% (w/w) fenoxaprop-p-ethyl+40 gl−1of 3.64% mefenpyr-diethyl. Your


Lolium control showed no significant differences between the different herbicide doses and application volumes or for their interaction. However, there was a trend toward a decrease in Lolium control as application volume was increased (Table 5) for all herbicide rates and weed developmental stages. In the first weed development phase (the beginning of the run), the effectiveness of all herbicide doses was higher for the lowest application volume (V1). In second weed development phase


Other authors (Zhang et al., 2000; Boström and Fogelfors, 2002) reported that satisfactory weed control can be achieved with lower doses than normally recommended. The results obtained in these trials show that the success of lower doses of herbicides depends on the early time of application when the weeds are more sensitive (O'Donovan et al., 1985).

The tillage system (direct seeding) used in this study seems to contribute in two different ways to the possibility of reducing the amount


The control of Lolium rigidum G. as the main grass weed problem in winter wheat under Mediterranean conditions is a major contributor to the total cost of weed control.

The results of this study show that it is possible to reduce the dose from 2.5 to 31 ha−1of the diclofop-methyl+fenoxaprop-p-ethyl+mefenepir-diethyl herbicide mixture recommended by the manufacturer and even the dose normally used by the Portuguese farmers (21ha−1) to achieve sufficient Lolium control efficiency for


The authors would like to thank the University of Évora, which supported these experiments.

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      Quote excerpt:

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