**3. Results and discussion**

*Legume Crops – Characterization and Breeding for Improved Food Security*

**Herbicide appl.**

lactofen

fluazifop

**Dew RH (%)**

6/30/2011 10:30 am All No 35 32 26 G 10–36 6/02/2012 2:30 pm All No 51 29 31 D 25–43

7/13/2013 6:30 am Imazapic Yes 90 24 27 G 15–25(A)

7/14/2013 6:30 am Lactofen Yes 94 24 27 G 15–25(A)

7/23/2013 7:00 am Clethodim Yes 96 26 26 E 20–46(U) 7/24/2013 7:00 am Fluazifop Yes 96 24 26 E 20–46(U)

**AT (°C)**

**ST (°C)**

Yes 90 31 27 E 15–36(A)

Yes 98 25 27 E 20–46(U)

**SMa WSa, <sup>b</sup>**

**(cm)**

15–38(C)

15–30(C)

15–30(C)

infestations of *A. palmeri* at the High Plains location were present at a population

*A, A. palmeri; AT, air temperature; C, C. melo; D, dry; E, excellent; G, good; RH, relative humidity; ST, soil* 

At the High Plains location, OLin [24] was planted in both years at the rate of 100 kg/ha. Planting date in 2011 was April 27, while in 2012, the planting date was May 1. Tamrun OL07 [25] and Georgia 09B [26] peanut were planted at the rate of 110 kg/ha in South Texas on June 14, 2012 and June 6, 2013, respectively. At neither

Weed control or peanut injury was estimated visually using a scale of 0 (no weed

Data from the High Plains were analyzed using a five by a two-by-three factorial analysis (POST herbicide by dose by adjuvant), while the data from South Texas were analyzed using a two-by-two-by-six factorial analysis (POST herbicides by dose by adjuvant). Significant differences among treatments were determined using analysis of variance and means were separated by protected Fisher's LSD test at P < 0.05 [28]. Visual estimates of weed control and peanut injury were transformed to the arcsine square root prior to analysis of variance, but are expressed in their original form for clarity because the transformation did not alter interpretation. The untreated check was not included in the weed control or peanut injury analysis.

control or peanut injury) to 100 (complete weed control or plant death) relative to the untreated control [27]. Weed control ratings and peanut injury consisting of chlorosis and/or stunting (where applicable) were taken 2 and 4 weeks after

. *A. palmeri*, *C. melo*, and *U. texana* were present in South

in both years.

**84**

range of 6–8 plants/m2

*Only A. palmeri was present at Halfway.*

**Date Time of** 

High Plains

South Texas

*a*

*b*

**Table 2.**

**day**

7/19/2012 7:45 am Imazapic

7/23/2012 8:00 am Clethodim

**2.4 Peanuts and planting**

herbicide application.

Texas at a population density of 6–10 plants/m2

*temperature; SM, soil moisture; U, U. texana; and WS, weed size.*

*Environmental conditions at time of herbicide application at each location.*

location was peanut harvested for yield.

**2.5 Weed efficacy ratings and data analysis**

#### **3.1** *Amaranthus palmeri* **control**

#### *3.1.1 High Plains of Texas*

No attempt was made to consolidate data over years since there was a treatment by year interaction and environmental conditions (relative humidity, soil temperature, and soil moisture) at time of herbicide application varied between years (**Table 2**). Also, extremely hot, dry weather conditions were observed in 2011 (data not shown). Although the test area was irrigated, the record high temperatures and low rainfall [29] made it difficult to maintain adequate soil moisture for plant growth.

In 2011, only the high dose of acifluorfen and 2,4-DB showed no response to the addition of an adjuvant, while the addition of either Agridex or Induce to the low dose of acifluorfen and 2,4-DB improved *A. palmeri* control over those herbicides with no adjuvant (**Table 3**). The addition of Induce to either imazapic or imazethapyr at 0.035 kg/ha or lactofen at 0.11 kg/ha improved control over those herbicides without any adjuvant, while the addition of Agridex to the high dose of these herbicides improved control over Induce or the use of the herbicide with no adjuvant. Other research has reported that herbicide rates can be reduced up to 75% with the use of adjuvants, usually when applications are made during early growth stages [30–32]. However, successful control using reduced herbicide rates depends on weed growth stage sensitivity [33, 34] and current environmental conditions [35, 36].

In 2012, the low dose of either imazapic or lactofen showed no response to *A. palmeri* control with the addition of an adjuvant, while acifluorfen, imazapic, imazethapyr, or lactofen at the high dose and 2,4-DB at both doses resulted in greater control with the addition of either Agridex or Induce over the use of no adjuvant (**Table 3**). *A. palmeri* control with acifluorfen, imazapic, or lactofen herbicides was similar with either adjuvant. Imazethapyr, at either dose, provided better control with the addition of Agridex than the addition of Induce. Since soil moisture was low in 2011 and weed size at time of herbicide application was greater in 2012 than 2011 (**Table 2**), the use of an adjuvant proved beneficial. Adjuvants have been reported to increase absorption of bentazon in *Abutilon theophrasti* Medic. [37] although plants were water-stressed [38]. Bellinder et al. [39] reported that there was no benefit in using a crop oil concentrate (COC) with either bentazon or fomesafen at the 0–2 or 2–4-leaf stage of *A. theophrasti*; however, control was inconsistent at the 4–6-leaf stage even when a COC was used.

#### *3.1.2 South Texas*

In 2012, only the addition of ETA to imazapic at the low dose improved *A. palmeri* control over the use of either imazapic or lactofen without an adjuvant (**Table 4**). In 2013, the addition of either Induce or Cide-Kick II to the low dose of imazapic or Cide-Kick II and 90–10 to the high dose of imazapic improved control over both doses of imazapic without an adjuvant. No other adjuvants improved *A*. *palmeri* control over either dose of imazapic or lactofen without an adjuvant.

In both years, *A. palmeri* amaranth control when using lactofen with or without an adjuvant was at least 88% with the exception of the addition of ETA to the high dose of lactofen in 2012, which resulted in 78% control. Grichar and Dotray [40]

reported that lactofen control of *A. palmeri* was greater when applied to 2–5 cm tall compared with either 15–20 or 25–30 cm tall plants.

Mayo et al. [41] concluded that *A. palmeri* control generally decreased as application timing was delayed for acifluorfen, imazethapyr, and lactofen.


*a Adjuvant doses: Agridex, 1.0% v/v; Induce, 0.25% v/v.*

*b No injury was noted in 2011.*

*c Acifluorfen and lactofen leaf injury consisted of leaf burn, interveinal chlorosis, and marginal necrosis while 2,4-DB injury consisted of leaf curling and irregular leaf growth.*

#### **Table 3.**

*Peanut injury and* Amaranthus palmeri *control in the High Plains 1 month after herbicide application when using different adjuvants.*

**87**

*a*

*b*

*c*

**Table 4.**

*C-K II, Cide-Kick II.*

**3.2** *Cucumis melo* **L. control**

*lactofen application when using different adjuvants.*

with imazapic POST applications.

In neither 2012 nor 2013 did the use of any adjuvant with either dose of imazapic or lactofen improve *C. melo* control over the use of no adjuvant (**Table 4**). In 2013, using Induce with the low dose of imazapic did reduce *C. melo* control compared to the use of no adjuvant or ETA. Imazapic at 0.04–0.07 kg/ha controlled greater than 90% *C. melo* in corn (*Zea mays* L.) regardless whether applied either preemergence, early POST or late POST [42], while Grichar [43] has seen similar results in peanut

*Influence of Adjuvants on Efficacy of Postemergence Herbicides Commonly Used in Peanut…*

**Herbicide/dose Adjuvanta,b Peanut injuryc A. palmeri C. melo**

**2012 (%)**

Imazapic/0.035 kg/ha None 0 0 66 70 82 97

Imazapic /0.07 kg/ha None 0 0 75 64 99 95

Lactofen/0.11 kg/ha None 23 2 94 96 82 97

Lactofen/0.22 kg/ha None 22 6 97 98 99 100

LSD (0.05) 11 5 22 12 14 9

*Adjuvant dose: Agridex, 1.0% v/v; Induce, 0.25% v/v; Cide-Kick II, 1.0% v/v; 90–10, 1.0% v/v; and ETA, 1.0% v/v.*

*Peanut injury ratings taken 4 days after herbicide application in 2012 and 7 days after herbicide application in 2013.*

*Peanut injury,* Amaranthus palmeri*, and* Cucumis melo *control in South Texas 1 month after imazapic and* 

**2013 (%)**

**2012 (%)**

Agridex 0 0 82 75 89 89 Induce 0 0 72 86 91 82 C-K II 0 0 66 82 85 93 90–10 0 0 53 66 91 90 ETA 0 0 88 80 94 97

Agridex 0 0 73 71 97 91 Induce 0 0 83 66 97 97 C-K II 0 0 80 83 95 98 90–10 0 0 88 79 99 99 ETA 0 0 83 57 98 99

Agridex 38 18 99 97 89 99 Induce 27 4 91 92 91 95 C-K II 33 18 99 100 85 94 90–10 18 10 88 98 91 89 ETA 33 19 93 96 94 99

Agridex 38 20 97 89 97 100 Induce 19 7 91 99 97 100 C-K II 33 17 99 92 95 99 90–10 23 10 99 95 99 99 ETA 38 22 78 97 98 100

**2013 (%)**

**2012 (%)**

**2013 (%)**

*DOI: http://dx.doi.org/10.5772/intechopen.82708*


*Influence of Adjuvants on Efficacy of Postemergence Herbicides Commonly Used in Peanut… DOI: http://dx.doi.org/10.5772/intechopen.82708*

*a Adjuvant dose: Agridex, 1.0% v/v; Induce, 0.25% v/v; Cide-Kick II, 1.0% v/v; 90–10, 1.0% v/v; and ETA, 1.0% v/v. b C-K II, Cide-Kick II.*

*c Peanut injury ratings taken 4 days after herbicide application in 2012 and 7 days after herbicide application in 2013.*

#### **Table 4.**

*Legume Crops – Characterization and Breeding for Improved Food Security*

cation timing was delayed for acifluorfen, imazethapyr, and lactofen.

**Herbicide/dose Adjuvanta Peanut injuryb,c**

compared with either 15–20 or 25–30 cm tall plants.

reported that lactofen control of *A. palmeri* was greater when applied to 2–5 cm tall

Mayo et al. [41] concluded that *A. palmeri* control generally decreased as appli-

Acifluorfen/0.28 kg/ha None 3 7 22

Acifluorfen/0.56 kg/ha None 5 27 32

Imazapic /0.035 kg/ha None 0 33 70

Imazapic /0.07 kg/ha None 0 58 78

Imazethapyr/0.035 kg/ha None 0 27 10

Imazethapyr/0.07 kg/ha None 0 42 47

Lactofen/0.11 kg/ha None 4 8 15

Lactofen/0.22 kg/ha None 6 40 22

2,4-DB/0.23 kg/ha None 2 12 37

2,4-DB/0.46 kg/ha None 5 68 73

LSD (0.05) 2 18 8

*Acifluorfen and lactofen leaf injury consisted of leaf burn, interveinal chlorosis, and marginal necrosis while 2,4-DB* 

*Peanut injury and* Amaranthus palmeri *control in the High Plains 1 month after herbicide application when* 

 **(%) A. palmeri (%)**

**2012 2011 2012**

Agridex 7 30 30 Induce 5 30 25

Agridex 6 43 47 Induce 6 43 47

Agridex 0 22 67 Induce 0 53 70

Agridex 0 80 93 Induce 0 58 93

Agridex 0 27 27 Induce 0 50 12

Agridex 0 65 82 Induce 0 27 67

Agridex 4 18 22 Induce 4 33 20

Agridex 5 73 35 Induce 6 38 37

Agridex 3 52 63 Induce 3 65 60

Agridex 5 77 87 Induce 5 78 83

**86**

*a*

*b*

*c*

**Table 3.**

*Adjuvant doses: Agridex, 1.0% v/v; Induce, 0.25% v/v.*

*injury consisted of leaf curling and irregular leaf growth.*

*No injury was noted in 2011.*

*using different adjuvants.*

*Peanut injury,* Amaranthus palmeri*, and* Cucumis melo *control in South Texas 1 month after imazapic and lactofen application when using different adjuvants.*

#### **3.2** *Cucumis melo* **L. control**

In neither 2012 nor 2013 did the use of any adjuvant with either dose of imazapic or lactofen improve *C. melo* control over the use of no adjuvant (**Table 4**). In 2013, using Induce with the low dose of imazapic did reduce *C. melo* control compared to the use of no adjuvant or ETA. Imazapic at 0.04–0.07 kg/ha controlled greater than 90% *C. melo* in corn (*Zea mays* L.) regardless whether applied either preemergence, early POST or late POST [42], while Grichar [43] has seen similar results in peanut with imazapic POST applications.

The high humidities at application timing may have been a factor in the excellent control [44]. Wichert et al. [44] reported that relative humidity appeared to be a more important environmental factor than temperature on the activity of lactofen and other diphenylether herbicides on *Sida spinosa* L. Control of *Xanthium strumarium* L. and *Ambrosia artemisiifolia* L. with acifluorfen at 85% relative humidity was 10–30% greater than control with treatments applied at 50% relative humidity [45].

#### **3.3** *Urochloa texana* **control**

The use of an adjuvant with either dose of clethodim did not improve *U. texana* control over clethodim alone at either evaluation timing or in either year (**Table 5**). Trends in 2013, when evaluated 2 weeks after herbicide application, did indicate that the addition of either Agridex or Cide-Kick II hastened the kill of *U. texana.* Jordan et al. [46] reported that the most consistent grass control with clethodim was obtained when applied with adjuvants containing a crop oil constituent or with the adjuvant Dash. They stated that although clethodim applied with a conventional nonionic adjuvant or silicone-based adjuvant controlled grasses in some instances, especially when applied at the higher dose of 0.14 kg/ha, control was inconsistent. They concluded that differences in efficacy among experiments could not be explained by differences in visible plant stress or extremes in temperature or relative humidity.

As seen with clethodim, the addition of an adjuvant to fluazifop-P-butyl did not improve *U. texana* control over the use of fluazifop alone at either dose (**Table 5**). At the time of herbicide application, relative humidity was at least 96% and soil moisture was excellent in both years (**Table 2**). These conditions can greatly influence herbicide activity [47, 48]. The effect of one climatic factor, such as humidity, will be greatest when other factors such as temperature or soil moisture are optimal [48].

#### **3.4 Peanut injury**

No injury was noted at the High Plains location in 2011 (data not shown). In some instances, imazapic can cause a yellowing of peanut plant for approximately 7–10 days after application; however, no injury was noted when rated 1 month after herbicide application (**Table 3**) in the High Plains or 4–7 days after application in South Texas (**Table 4**). Acifluorfen did cause a leaf burn, which was still noticeable 1 month after herbicide application (**Table 3**). The use of either Agridex or Induce with the lower dose of acifluorfen resulted in greater leaf burn than acifluorfen alone; however, this was not seen with the higher dose as there was no difference in leaf burn with/without the use of an adjuvant. The use of 2,4-DB did result in leaf curling and some irregular leaf growth, but no differences were noted with or without adjuvant with either dose (**Table 3**). Lactofen can also result in peanut leaf burn. Peanut injury ratings with lactofen were less in the High Plains (**Table 3**) than South Texas (**Table 4**), and this was due in part to the time interval between herbicide application ratings. In South Texas, ratings were taken 7 days or less after herbicide application, while in the High Plains, ratings were taken 30 days after application. Also, delaying the rating in 2013 by 3 days resulted in less injury than the 4 days evaluation (**Table 4**). At the High Plains location, no differences in leaf burn were noted with any adjuvant with either dose of lactofen (**Table 3**). At the South Texas location in 2012, leaf burn was greatest with Agridex when using the lower dose of lactofen (**Table 5**). At the higher dose of lactofen, Agridex, Cide-Kick II, and ETA resulted in greater injury than lactofen alone or lactofen plus Induce. In 2013, leaf burn with lactofen was greater when Agridex, Cide-Kick II, or ETA was used with either dose of lactofen. The addition of Induce or 90–10 resulted in 10% or less injury when added to either dose of lactofen (**Table 4**).

**89**

*a*

*b*

**Table 5.**

**4. Conclusion**

*C-K II, Cide-Kick II.*

*Influence of Adjuvants on Efficacy of Postemergence Herbicides Commonly Used in Peanut…*

Clethodim/0.05 kg/ha None 73 74 98 80

Clethodim/0.1 kg/ha None 84 90 98 95

Fluazifop-P/0.11 kg/ha None 65 81 92 96

Fluazifop-P/0.22 kg/ha None 67 88 92 95

LSD (0.05) 15 24 19 15

*Adjuvant dose: Agridex, 1.0% v/v; Induce, 0.25% v/v; C-K II, 1.0% v/v; 90–10, 1.0% v/v; and ETA, 1.0% v/v.*

U. texana *control with clethodim and fluazifop-P when using different adjuvants.*

**2 weeks after 4 weeks after 2012 (%) 2013 (%) 2012 (%) 2013 (%)**

Agridex 68 92 89 87 Induce 75 77 97 88 C-K II 60 82 84 83 90–10 65 77 98 91 ETA 77 81 98 70

Agridex 91 90 99 94 Induce 81 64 97 95 C-K II 77 81 85 97 90–10 76 77 93 94 ETA 77 87 95 96

Agridex 62 85 65 93 Induce 63 81 87 88 C-K II 62 72 73 88 90–10 63 95 78 97 ETA 65 86 85 90

Agridex 58 62 91 93 Induce 65 79 94 93 C-K II 57 99 83 93 90–10 62 96 95 97 ETA 63 90 84 96

**Herbicide/dose Adjuvanta,b** *U. texana*

The use of an adjuvant in South Texas did not always improve weed efficacy, while in the High Plains of Texas, the use of an adjuvant did improve weed efficacy in most instances. The herbicide-adjuvant-plant interaction is a complex system. An adjuvant can impose its impact at several stages of the herbicide application including tank mixing, deposition and retention on the plants, absorption by the plants, and translocation from the applied area to the site of action [15, 18, 20, 23]. Understanding the different roles of adjuvants in enhancing herbicide efficacy is essential for the optimum use of adjuvants in herbicide application. Reducing the

*DOI: http://dx.doi.org/10.5772/intechopen.82708*


*Influence of Adjuvants on Efficacy of Postemergence Herbicides Commonly Used in Peanut… DOI: http://dx.doi.org/10.5772/intechopen.82708*

#### **Table 5.**

*Legume Crops – Characterization and Breeding for Improved Food Security*

**3.3** *Urochloa texana* **control**

**3.4 Peanut injury**

The high humidities at application timing may have been a factor in the excellent control [44]. Wichert et al. [44] reported that relative humidity appeared to be a more important environmental factor than temperature on the activity of lactofen and other diphenylether herbicides on *Sida spinosa* L. Control of *Xanthium strumarium* L. and *Ambrosia artemisiifolia* L. with acifluorfen at 85% relative humidity was 10–30% greater than control with treatments applied at 50% relative humidity [45].

The use of an adjuvant with either dose of clethodim did not improve *U. texana* control over clethodim alone at either evaluation timing or in either year (**Table 5**). Trends in 2013, when evaluated 2 weeks after herbicide application, did indicate that the addition of either Agridex or Cide-Kick II hastened the kill of *U. texana.* Jordan et al. [46] reported that the most consistent grass control with clethodim was obtained when applied with adjuvants containing a crop oil constituent or with the adjuvant Dash. They stated that although clethodim applied with a conventional nonionic adjuvant or silicone-based adjuvant controlled grasses in some instances, especially when applied at the higher dose of 0.14 kg/ha, control was inconsistent. They concluded that differences in efficacy among experiments could not be explained by differences in visible plant stress or extremes in temperature or relative humidity. As seen with clethodim, the addition of an adjuvant to fluazifop-P-butyl did not improve *U. texana* control over the use of fluazifop alone at either dose (**Table 5**). At the time of herbicide application, relative humidity was at least 96% and soil moisture was excellent in both years (**Table 2**). These conditions can greatly influence herbicide activity [47, 48]. The effect of one climatic factor, such as humidity, will be greatest when other factors such as temperature or soil moisture are optimal [48].

No injury was noted at the High Plains location in 2011 (data not shown). In some instances, imazapic can cause a yellowing of peanut plant for approximately 7–10 days after application; however, no injury was noted when rated 1 month after herbicide application (**Table 3**) in the High Plains or 4–7 days after application in South Texas (**Table 4**). Acifluorfen did cause a leaf burn, which was still noticeable 1 month after herbicide application (**Table 3**). The use of either Agridex or Induce with the lower dose of acifluorfen resulted in greater leaf burn than acifluorfen alone; however, this was not seen with the higher dose as there was no difference in leaf burn with/without the use of an adjuvant. The use of 2,4-DB did result in leaf curling and some irregular leaf growth, but no differences were noted with or without adjuvant with either dose (**Table 3**). Lactofen can also result in peanut leaf burn. Peanut injury ratings with lactofen were less in the High Plains (**Table 3**) than South Texas (**Table 4**), and this was due in part to the time interval between herbicide application ratings. In South Texas, ratings were taken 7 days or less after herbicide application, while in the High Plains, ratings were taken 30 days after application. Also, delaying the rating in 2013 by 3 days resulted in less injury than the 4 days evaluation (**Table 4**). At the High Plains location, no differences in leaf burn were noted with any adjuvant with either dose of lactofen (**Table 3**). At the South Texas location in 2012, leaf burn was greatest with Agridex when using the lower dose of lactofen (**Table 5**). At the higher dose of lactofen, Agridex, Cide-Kick II, and ETA resulted in greater injury than lactofen alone or lactofen plus Induce. In 2013, leaf burn with lactofen was greater when Agridex, Cide-Kick II, or ETA was used with either dose of lactofen. The addition of Induce or 90–10 resulted in 10%

or less injury when added to either dose of lactofen (**Table 4**).

**88**

U. texana *control with clethodim and fluazifop-P when using different adjuvants.*

### **4. Conclusion**

The use of an adjuvant in South Texas did not always improve weed efficacy, while in the High Plains of Texas, the use of an adjuvant did improve weed efficacy in most instances. The herbicide-adjuvant-plant interaction is a complex system. An adjuvant can impose its impact at several stages of the herbicide application including tank mixing, deposition and retention on the plants, absorption by the plants, and translocation from the applied area to the site of action [15, 18, 20, 23]. Understanding the different roles of adjuvants in enhancing herbicide efficacy is essential for the optimum use of adjuvants in herbicide application. Reducing the

herbicide rate proved to be effective in South Texas but not so in the High Plains due to several factors including a higher relative humidity, the time of herbicide application in the early morning hours, and excellent moisture conditions at time of herbicide application in South Texas. Postemergence herbicide efficacy may be affected by environmental factors including light duration and intensity, air temperature, relative humidity, and dew or precipitation [47–51]. These environmental conditions may influence processes such as herbicide absorption, translocation, or plant metabolism, which influence herbicide efficacy [52]. Air temperature in South Texas varied from 25 to 31°C, while air temperature varied from 29 to 32°C in the High Plains region (**Table 2**). As temperature increased, glyphosate efficacy on *Avena fatua* L., *Urochloa panicoides* Beauv. [53], and *Echinochloa colona* (L.) Link [54] increased. Temperature also influenced 14C-glyphosate absorption by cultured velvetleaf cells [55]. Nearly twice as much glyphosate was absorbed at 28°C than at 4 or 16°C. Similar temperature effects were observed with *Cynodon dactylon* (L.) Pers. [56] and *Sorghum halepense* L. [57]. Herbicide activity or absorption increased with increasing relative humidity for *Elytrigia repens* (L.) Nevski [58], *C. dactylon* [56], *U. panicoides* [53], *E. colona* [54], and *S. halepense* [57]. Generally, high relative humidity and high temperatures, as well as low light intensity before treatment, increased plant susceptibility to POST herbicides [49]. Plant stress may also reduce systemic herbicide activity and account for relatively poor performance. Buhler and Burnside [58] noted that glyphosate was less effective on drought-stressed annual grass species than actively growing plants. Contact herbicides such as lactofen are not as dependent on translocation for activity, and their activity is not as adversely affected by drought-stressed plants. The above-mentioned factors all contributed to the lack of difference of the postemergence herbicides alone or with an adjuvant as well as the effectiveness of the 1/2X herbicide doses specifically in the South Texas studies. Many field applications of herbicides in South Texas start early in the morning to avoid windy conditions that may develop late in the day when coastal sea breezes may start up. Under the early morning conditions, with high humidity, dew can be found on weeds as well as on the crop at the time of application. Dew, defined as the presence of free water on plant foliage [59], could affect the foliar uptake and therefore efficacy of foliar-applied herbicides, mainly those of high water solubility. The presence of dew at application is believed to increase or decrease foliar herbicide efficacy [60]. Herbicide runoff and herbicide dilution could explain the negative effect of dew [61]. By contrast, dew can increase the total area of herbicide interception and reduce the impact of large drops on foliage surfaces, avoiding their loss from the leaves [62]. At the same time, the presence of dew results in hydration of the cuticle and may play an important role favoring foliar uptake [59]. The effect of dew on herbicide activity is not thoroughly understood, due to limited research where dew has not been quantified [63]. Another factor which may explain the lack of a response to a surfactant in South Texas may be the effects of higher spray volumes used in South Texas (190 L/ha) compared to the High Plains (94 L/ha). In order to obtain acceptable control with lactofen, a contact herbicide, a large portion of the leaf, must receive a spray solution [64] and with higher spray volumes in South Texas more of the leaflet received spray coverage. The drift guard (DG) nozzles used in South Texas contained larger droplets [65]. A larger droplet size causes localized injury to the weed leaf resulting in better control with contact herbicides such as acifluorfen and lactofen. Several researchers have investigated the effects of carrier volumes on the efficacy of herbicides [66–69] and results have been variable. At a constant spray droplet size, glyphosate [66, 67] and paraquat efficacy increased as application volume decreased. However, clopyralid activity decreased as application volume decreased [68]. Results from these trials suggest that not all adjuvants perform the same for individual herbicides. It is

**91**

provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Texas A&M AgriLife Research and Texas A&M AgriLife Extension Service,

and Mark A. Matocha3

*Influence of Adjuvants on Efficacy of Postemergence Herbicides Commonly Used in Peanut…*

critical that a quality adjuvant be used when the label suggests that one is needed for maximum herbicidal activity. Since adjuvants may also increase herbicidal toxicity to crops, it is also critical to omit the surfactant if the label suggests to do so for

The Texas Peanut Producers Board and the National Peanut Board provided financial support for this research. Dwayne Drozd provided technical assistance.

The authors have declared that no competing interests exist.

\*, Peter A. Dotray2

3 Texas A&M AgriLife Extension Service, College Station, TX, USA

1 Texas A&M AgriLife Research, Corpus Christi, TX, USA

\*Address all correspondence to: w-grichar@tamu.edu

*DOI: http://dx.doi.org/10.5772/intechopen.82708*

individual herbicides.

**Acknowledgements**

**Conflict of interest**

**Author details**

William James Grichar1

Lubbock, TX, USA

*Influence of Adjuvants on Efficacy of Postemergence Herbicides Commonly Used in Peanut… DOI: http://dx.doi.org/10.5772/intechopen.82708*

critical that a quality adjuvant be used when the label suggests that one is needed for maximum herbicidal activity. Since adjuvants may also increase herbicidal toxicity to crops, it is also critical to omit the surfactant if the label suggests to do so for individual herbicides.
