**5. Benefits of integrated weed management**

Effective weed management is very important to maintain agricultural productivity. By competing for light, water and nutrients, weeds can reduce crop yield and quality and can lead to billions of dollars in global crop losses annually. Because of their ability to persist and spread through the production and dispersal of dormant seeds or vegetative propagules, weeds are virtually impossible to eliminate from any given field. The importance of weed management to successful farming systems is demonstrated by the fact that herbicides account for the large majority of pesticides used in agriculture, eclipsing inputs for all other major pest groups. To no small extent, the success and sustainability of our weed management systems shapes the success and sustainability of agriculture as a whole [86].

technology. No tillage systems became widely used and weed control costs were lowered. Total applied herbicides and labor inputs declined initially and narrow-row on soybean became the standard. In 1995 the GR soybean areas treated with glyphosate were only 20%, but they took over 96% in 2006 [84]. Currently, the GR soybean represents over 94% of the soybeans grown in

The initial advice for GR soybean system was only one spray and its late application would not undermine crop yield. In extremely wet sites with late sowing — Iowa, for example —, weeds emerged early and single POST glyphosate spray was enough for effective control till the end of the cycle [85]. But for the midwest region, the sowing scheduled occurred earlier, thus only one application was unsuitable for weed control, usually requiring additional sprays.

Concerns about the definition of better periods of spraying, along with the appearance of the first glyphosate resistance case, registered for *Lolium rigidum* in 1998, have collaborated with gradual increase in herbicide use. For the period 2003-2009, herbicides applied to GR soybean increased 30%, whereas consumption remained stable for conventional soybeans [83]. Among changes observed in the global agricultural production, there is the search for socioeconomic and environmental efficiency. Farmers want new tools for weed management. New GM crops have allowed simple and effective solutions, but if producers keep outdated manners when using new tools with GR soybean and glyphosate, these tools will soon become obsolete [25].

As a result, a second generation of GR soybean was launched recently in the US in 2009. Although this technology offers the same soybean resistance to glyphosate as the first gener‐ ation (RR1), it has a higher yield potential, between 7% and 11%. Some farmers reported no increasing yield in relation to first GR soybean generation; perhaps others found positive yield effect. In 2010, soybean farmers pointed that second GR soybean generation has, on average,

Many soybean farmers currently use glyphosate mixed with residual herbicides employed previously. The increase of these mixtures permits earlier glyphosate sprays promoting weed management for a larger period. Using conventional herbicides into new GM soybeans are also essential to ensure its resilience, since new traits will be released to use with former herbicides. New technologies include GM soybeans resistant to glufosinate "Liberty Link", to 2,4-D "Optimum GAT", to dicamba and also to glyphosate plus ALS inhibitors. Despite the creation of technologies for landing efficiency and easy management on weed control, good practices at all soybean crop system are rather necessary. Also, weaknesses and difficulties on weed management in many regions of the US have attracted the interest for non-GM soybeans. Differentiated prices in the international market have also stimulated this substitution, yet it

Effective weed management is very important to maintain agricultural productivity. By competing for light, water and nutrients, weeds can reduce crop yield and quality and can lead

about 5% of yield improvement.

72 Soybean - Pest Resistance

is constrained to small and middle producers.

**5. Benefits of integrated weed management**

the US, and more than 90% of soybeans produced worldwide are considered GR.

Integrated pest management (IPM) concept was introduced in the 60s comprising many definitions from then. The primary goals of IPM programs are to reduce pesticide use and the subsequent environmental impact and to rely more on alternative strategies to control pests [87]. Integrated weed management (IWM) comes as a secondary effect of IPM, but it has similar proposal of using multiple management tactics and incorporating the knowledge of weed biology and crop physiology into the weed management system. The goals of IWM range from maximizing profit margins to safeguarding natural resources and minimizing the negative impact of weed control practices on the environment [88].

Integrated Weed Management combines multiple management tools (biological, chemical, mechanical and others) to reduce a pest population to an acceptable level while preserving the quality of existing habitat, water, and other natural resources. The integrated management provides connection of all the involved organisms, whether weeds, pests or diseases, and should focus on decision-making with case studies. There are many practices set out in the integrated management systems, whose benefits have been extensively studied by several authors (Table 8). These studies demonstrate many benefits and the efficiency of integrated tools in crop management systems.


**Table 8.** Practices evaluated in previous studies as part of an Integrated Weed Management (IWM).

However, there are no more ready-made and generalized solutions without risk of errors. IWM is characterized by reliance on multiple weed management approaches that are firmly underpinned by ecological principles [89]. As its name implies, IWM integrates tactics, such as crop rotation, cover crops, competitive crop cultivars, the judicious use of tillage, and targeted herbicide application, to reduce weed populations and selection pressures that drive the evolution of resistant weeds. Under an IWM approach, a grain farmer, instead of relying exclusively on glyphosate year after year, might use mechanical practices such as rotary hoeing and interrow cultivation, along with banded PRE and POST herbicide applications in a soybean crop one year, which would then be rotated to a different crop, integrating different weed management approaches.

a 20-year period and found that differences between scenarios are not due to weed densities

Weed Management in Soybean — Issues and Practices

http://dx.doi.org/10.5772/54595

75

In fact, despite all the benefits, the implementation of IWM is extremely challenging for researchers and especially for farmers. In a recent paper — *True integrated weed management* was highlighted in glowing way the need for a single platform development, including sensors and decision-support software, that has multiple application technologies for weed manage‐ ment [103]. According to the actor, "*Ideally, a self-guided machine is needed that could comb the field in a systematic way to identify weeds and then apply the necessary control tool (eg spray, mow, cultivate) at the individual plant or patch scale*". The illustration of a machine model (Figure 6), which allows the required operations case by case is utopian, although it is believed that efforts to achieve

but differences in total cost on weed control.

**Figure 6.** Illustration of a robotic weed control using multiple tools designed [103].

Weed management has always been inserted into the soybean crop system, contributing decisively to the success of this crop in major producing countries nowadays. The evolution of weed management practices in Argentina, Brazil and the US has been developed similarly, by means of mechanical growers and massive use of GM soybean. However, weeds also have

Despite the persistent search for weed control in the soybean areas, it is observed that man‐ agement of those has increased considerably in the last 10 years. There are numerous cases of

evolved and as new tools were used, new species or new biotypes appeared.

this goal are unlimited.

**6. Conclusions**

Earlier studies have also demonstrated that IWM strategies are effective in managing herbi‐ cide-resistant weeds. For example, glyphosate-resistant horseweed in no tillage soybean can be controlled by integrating cover crops and soil-applied residual herbicides [100]. In a recent experiment in which the integration of tillage and cover crops was evaluated for controlling glyphosate-resistant *Amaranthus palmeri* in Georgia, the combination of tillage and rye cover crops reduced *A. palmeri* emergence by 75% [101]. In addition to cultivation and cover crops, other practices can be used to manage resistant-weed populations.

In another experiment, it was experienced biological and chemical control to *Sesbania exaltata* [Raf.] Rydb. ex A.W. Hill in soybean field. Different concentrations of *Colletotrichum trunca‐ tum* (Schwein.) Andrus & Moore were tested alone and in combination with glyphosate. Positive results suggest that it might be possible to utilize additive or synergistic herbicide and pathogen interactions to enhance *S. exaltata* control [94]

Despite many results, researchers suggest that implementation has been slow, and that farmers rarely move beyond incorporating cost-effective, targeted pesticides application [102]. Many growers are not adopting integrated management because current assessment methods are inadequate [99]. In their study, evaluating data from eastern North Carolina, US, they considered four components of the integrated management: weed, pest, environmental and general management of the properties. The component weed had the highest percentage (79%), indicating that growers were undertaking its management.

In [97] it was evaluated a cropping system, including various combinations of seeding rate and date, herbicide timing and rate, and tillage operations, by measuring weed response to six IWM systems, in a wheat–oilseed rape–barley–pea rotation. Changes in weed communities assessed over 4 years indicated a gradual increase of *Thlaspi arvense*, *Chenopodium album*, *Amaranthus retroflexus* and *Fallopia convolvulus* in the no herbicide ⁄high tillage system. Winter and early spring annuals and perennials increased in most systems, but particularly in the low herbicide ⁄zero tillage and medium herbicide⁄zero tillage systems. This study confirms the potential of contrasting IWM systems under the challenging environmental conditions.

Some mathematical models are also used into IWM. It allows to model scenarios and to compare long-term economic and weed population outcomes of various integrated manage‐ ment tools. In southern Australia, species like *Lolium rigidum* and *Raphanus raphanistrum* were managed for many years with selective herbicides. But these species became resistant and are widespread now. In [93] it was tested an integrated model to compare the management over a 20-year period and found that differences between scenarios are not due to weed densities but differences in total cost on weed control.

In fact, despite all the benefits, the implementation of IWM is extremely challenging for researchers and especially for farmers. In a recent paper — *True integrated weed management* was highlighted in glowing way the need for a single platform development, including sensors and decision-support software, that has multiple application technologies for weed manage‐ ment [103]. According to the actor, "*Ideally, a self-guided machine is needed that could comb the field in a systematic way to identify weeds and then apply the necessary control tool (eg spray, mow, cultivate) at the individual plant or patch scale*". The illustration of a machine model (Figure 6), which allows the required operations case by case is utopian, although it is believed that efforts to achieve this goal are unlimited.

**Figure 6.** Illustration of a robotic weed control using multiple tools designed [103].
