MICROBIO: A NOVEL MICROEMULSION AS AN EFFICIENT
TANK-MIX ADJUVANT FOR HERBICIDE TREATMENTS
Alberto Colombo, Gianfranco Paganini and Peter Bohus
Agro-Chemistry Laboratory; Cesalpinia Chemicals (Lamberti Group);
Via Piave, 18 - 21041 Albizzate (VA), Italy
A new microemulsion adjuvant for tank mix application containing: fatty acid esters
from transesterification of vegetable oils, anionic ester of alkylpolyglucoside and
ethoxylated fatty alcohols was developed. Physico-chemical properties were optimized
to improve stability, synergism amongst components and compatibility with various
Surface tension and particle size were measured; rheological characterisation of the
adjuvant was carried out to verify microemulsion physical status and stability.
This adjuvant mixture was designed to quickly wet and spread droplets on the leaf in
order to get a uniform spray deposit over foliage surface. Wettability and spreading on
specific surfaces were also determined.
Biological efficacy in weed control of various tank-mix blends of the adjuvant with
commercial herbicide formulations was studied. Three herbicide/weed combinations of
Microbio as tank mix adjuvant were examined: one water soluble herbicide (Bentazone
Na salt) applied on black nightshade; two water insoluble actives (Nicosulfuron and
Quizalofop-P-ethyl) applied on wild oat.
Key words: microemulsion, alkylpolyglucoside, tank-mix.
Fatty acid esters from transesterification of vegetable oils, alkylpolyglucosides and
ethoxylated fatty alcohols have individually been widely used as tank-mix or built-in
adjuvants for herbicides. They are valuable because of the following properties:
improvement of biological efficacy of active ingredients, excellent versatility and ease
of use in combination with various formulations of actives, application technologies and
crop varieties. In addition, they can replace adjuvants which are harmful to the
environment, such as nonylphenol ethoxylates or fatty amine ethoxylates.
Recently, a new class of anionic esters of alkylpolyglucoside have been described as
novel tank-mix adjuvants (1,2), which appear to have good potential as adjuvants in
Microemulsion is a highly effective physical form of agrochemical delivery system,
which combines stability of complex formulations, performance and easy handling. We
have developed a stable microemulsion (Microbio®
from Cesalpinia Chemicals SpA,
Italy) containing a citric ester of alkylpolyglucoside, fatty acid esters from
transesterification of a vegetable oil and an ethoxylated fatty alcohol, which proved to
be a higly effective adjuvant with different herbicide actives.
METHODS AND MATERIALS
Wettability and Surface Tension
Analysis of static surface tension (EST) was performed using a Sigma 70 tensiometer
(KSV Instrument Ltd) on the adjuvant mix diluted in water at different concentrations at
25°C (ISO 304, ISO 4311).
Wetting power of aqueous spray was evaluated at 25°C by determining the sinking time
of a cotton diskette, using an internal method based on DIN 53901.
Dynamic contact angle, as a function of time, was studied using a Rycobel PG-X
goniometer at different concentrations of Microbio on a glass plate (ASTM D-724).
Particle Size Analysis
Was carried out using a N4 Plus Nanosizer (Coulter) at 20°C with the following
parameters: refractometric index (n=1.433), density (d=0.98 kg/dm3
) and viscosity
(η=40 mPa.s), which are characteristic of Microbio. Scanning was performed at
different angles with 360 sec run time.
Rheological profile was studied with Advanced Rheometer 2000 (TA Instruments),
using a double gap geometry. Viscosity of Microbio was measured as a function of
temperature (from 0° to 70°C) and shear rate (from 1 s-1
to 400 s-1
). Rheograms of shear
stress vs shear rate (under steady state flow) and of ln η vs T-1
Biological Efficacy Trials (carried out by SurfaPlus bv, Wageningen, NL)
Black nightshade (Solanum nigrum L.; Bayer code SOLNI) and wild oat (Avena fatua
L.; Bayer code AVEFA) were grown in a growth chamber under 14 hrs of light, at
18/12 (±0.5)°C (day/night) temperature, and in 70/80 (±5)% (day/night) relative
humidity. Light was provided by high-pressure mercury lamps and fluorescent tubes to
give 70 W/m2
(PAR) at leaf level. The plants were grown in 11 cm diameter plastic pots
filled with a mixture of sand and humic potting soil (3) (1:2 by volume). The pots were
placed on a sub-irrigation matting, which was wetted daily with a half-strength nutrient
solution. After emergence, the black nightshade and wild oat plants were thinned to one
and five plant(s) per pot, respectively. Black nightshade was treated at the four-leaf
stage and wild oat was treated at the 2-3 leaf stage.
Treatment solutions were applied with an air-pressured laboratory track sprayer having
1.2 mm nozzles fitted with a perforated (0.6 mm) whirling pin and delivering 200 L/ha
at 303 kPa. The adjuvants Microbio and Hasten®
(emulsifiable esterified rapeseed oil
from Victorian Chemicals) were added at 0.25% (v/v).
Herbicide formulations used were: Bentazone (Basagran®
from BASF); Nicosulfuron
from Syngenta); Quizalofop-p-ethyl (Targa Prestige®
Measurement of herbicide performance
The fresh weight of the aerial parts of black nightshade and wild oat was determined as
a parameter of herbicide performance.
Experimental design and data analysis
Experiments were conducted with four replicates per experiment, according to a
completely randomized design. The data of the adjuvant tests were subjected to analysis
of variance using the Genstat statistical package (Release 6.1; Rothamsted Experimental
Station). The means of each treatment were compared according to Fisher’s LSD (0.05).
LSD (0.05) is the Least Significant Difference between mean values at the 5% level.
RESULTS AND DISCUSSION
Wettability and Surface Tension
Aqueous spray of Microbio show better wetting properties than a corresponding
emulsifiable vegetable oil. A lower surface tension and sinking time with the
microemulsion system were obtained (Table 1 and 2).
Table 1: Static surface tension of aqueous solutions at 25°C
Surface tension (mN/m)
Surface tension (mN/m)
Microbio 31.1 29.3
Emulsifiable vegetable oil 33.5 31.5
Ethoxylated Alcohol 27.0 26.7
Alkylpoly Glucoside Ester 25.8 25.5
Table 2: Sinking time of a cotton diskette in 0.25% w/w of aqueous spray at 25°C
Water Microbio Ethoxylated
Time (sec) > 300 110 5 182 25 5
Spreading of aqueous dilutions of Microbio was determined in comparison to a solution
of ethoxylated fatty alcohol, as a function of time (Table 3).
Fig. 1: Contact angle determination vs time
In agreement with the effect of surfactants on surface tension and contact angle reported
in the literature (4), it can be seen in Fig. 1 that, within the range considered, the higher
the concentration of Microbio (curves group marked A), the lower the contact angle
measured. This finding is analogous to the behaviour typical spreading adjuvants
(curves group marked B).
Particle Size Analysis
Particle size analysis (Table 3) suggests a droplets distribution of Microbio (detected
only at high deviation angles) that falls within the microemulsion range (5).
Table 3: Particle size of Microbio measured at 25°C (expressed in nm)
Angle Medium diameter Standard deviation
21.3° Not detectable ---
64.6° 31.0 13.2
90.0° 25.7 11.7
The flow curve of Microbio (Fig. 2) indicates a Newtonian behaviour (a general feature
of low viscosity microemulsions) (6). From the linear curve of Fig. 2, viscosity was
found to be independent of shear rate and equal to 44.8 mPa.s.
Fig. 2: Flow curve of Microbio at 25°C
Thermodynamical parameters were calculated from a rheogram of ln η vs T-1
using equation 1 (6):
With eq. 1, values of ∆H and ∆S were calculated, from which ∆G was obtained, as
reported in Table 4. The thermodynamic parameters derived from rheological studies
suggest an intrinsic stability of Microbio, as reported in literature for similar system (6).
y = 0,0438x + 0,0113
y = -3E-06x + 0,0448
0,1 1 10 100 1000
Shear rate (1/s)
shear stress interpolation
( ) RT
Fig 3: rheogram of ln η vs T-1
Biological Efficacy Tests
As detailed in Methods (see above), Microbio was tested on Black nightshade (Solanum
nigrum L.) and Wild oat (Avena fatua) in combination with three herbicide active
ingredients: Bentazone (Basagran from BASF); Nicosulfuron (Milagro from Syngenta);
Quizalofop-P-ethyl (Targa Prestige from Bayer). Our new adjuvant was compared at the
same concentration of 0.25% (v/v) in water to a well known commercial adjuvant
(Hasten, from Victorian Chemicals, Australia).
Results are reported in Fig. 4 (A, B, C).
Fig. 4, A
Fig. 4, A shows the effect on Black nightshade at two dosages of Bentazone. (20
and 40 g/ha). Microbio and Hasten have a dramatic effect on herbicide efficacy at the
lower sub-optimal dosage of 20 g/ha.
Fig. 4, B shows the effect on Wild oat at two dosages of Quizalofop-P-ethyl (2
and 6 g/ha). Microbio shows a slight better effect on herbicide efficacy than Hasten at
the lower sub-optimal dosage of 2 g/ha.
Infuence of adjuvants on bentazone efficacy (SOLNI)
Sample controlled variable ∆∆∆∆H ∆∆∆∆ S ∆∆∆∆G (298K)
(kJ/mol) (J/K*mol) (kJ/mol)
Microbio Shear Stress 35.6 -61.5 53.9
Evaluation of ∆∆∆∆ H e ∆∆∆∆ S
y = 4281,1x - 17,414
0,00305 0,0031 0,00315 0,0032 0,00325 0,0033 0,00335 0,0034 0,00345 0,0035 0,00355
Fig. 4, B
Fig. 4, C
Fig. 4, C shows the effect on wild oat at two dosages of Nicosulfuron (5 and 15 g/ha).
Microbio shows a similar effect on herbicide efficacy as Hasten at the lower sub-
optimal dosage of 5 g/ha.
We have developed a mixture containing three components, each one displaying
individual adjuvant activity in combination with herbicides. Therefore, a carefully
balanced microemulsion of the three ingredients shows excellent stability, synergism
amongst components and compatibility with various pesticide formulations.
Rheological profile and thermodynamic parameters confirm the microemulsion physical
status of the mixture, which appears to also have good spreading and wetting properties.
These properties should translate in ease of use and effectiveness in actual field
Biological efficacy trials in weed control with various tank-mix combinations of the
adjuvant with different herbicide active ingredients applied on Black nightshade or Wild
oat, at a constant concentration of 0.25% (w/w) in water, showed that at all hebicide
dosages tested, Microbio showed either an equal or better efficacy than a reference
commercial adjuvant. Our novel microemulsion adjuvant combines the advantages of
eco-friendly components with long term storage stability, easy handling and good
Infuence of adjuvants on nicosulfuron efficacy (AVEFA)
Infuenceof adjuvantsonquizalofop-P-ethyl efficacy(AVEFA)
1. Bohus, P., Colombo, A.; 2004. Proceedings of 7th
International Symposium on
Adjuvants for Agrochemicals, Cape Town, SA pp 301 – 306
2. European Patents n° EP 510564
3. Soil no. 12, Colent b.v. , Lent, The Netherlands
4. Singh, M., Orsenigo, J.R., Shah, D.O.; 1984. JAOCS vol 61 n°3 pp 596 - 599
5. Tadros, T. F.; 2005. Applied Surfactants; Wiley-VCH; Weinheim pp 309 – 311
6. Acharya, A., Ghosal, S.K., Moulik, S.P., Subramanian, N. et al.; 2005. Chem.
Pharm. Bull. vol 53(12) pp 1530 –1535.
We wish to thank Dr. Hans de Ruiter for very helpful suggestions and collaboration.