Performance and physical property evaluation of palm oil-based adjuvant formulated in glyphosate isopropylamine and glyphosate monoammonium for weed control

In all glyphosate herbicide formulations, an adjuvant is usually added or incorporated to enhance the wetting, spreading and penetration of the active ingredient on the leaf surface. However, conventional adjuvants have side effects such as aquatic toxicity and irritation to skin and eyes. Palm oil-based adjuvants being renewable, environmental friendly, less flammable (due to higher flash points) and cause fewer medical problems and allergies as to end-users or spraying operators provides the alternative solution to the problems. The general objective of the experiment is to evaluate the performance and physical properties of palm oil-based adjuvant or blended adjuvant formulated in the glyphosate isopropylamine and glyphosate monoammonium herbicides from the number of adjuvants developed by the Advanced Oleochemical Technology Division of Malaysian Palm Oil Board (AOTD,MPOB). Four experiments were conducted which includes bioefficacy evaluation of seven type of palm oil based adjuvants formulated in glyphosate isopropylamine and glyphosate monoammonium herbicides, physical properties evaluation of the selected formulations, influences of different adjuvant concentrations on the performance of the selected glyphosate formulations and rainfastness evaluation. The results showed that MAGIPAS3 and MAGIPAS4 with 10% adjuvant concentration were the most effective glyphosate isopropylamine formulation as it has given visual weed mortality of 95.00% and 95.55% on Paspalum conjugatum, 93.90 % and 96.00% on Asystasia gangetica and 95.10% and 98.07% on Ottochloa nodosa respectively at 14 Days After Treatment (DAT) which is significantly higher than other formulation and comparable with the standard product Roundup and Asset. For glyphosate monoammonium formulations, MAGMAS6 and MAGMAS7 with 10% adjuvant concentrations were the most effective formulation with the visual weed mortality of 85.00% and 95.24% on Paspalum conjugatum, 85.00 % and 95.00% on Asystasia gangetica, 95.02% and 98.00% on Ottochloa nodosa respectively. In the physical properties evaluation, all the glyphosate isopropylamine and glyphosate monoammonium samples formulated with palm oil based adjuvant showed surface tension below 40 mN/m for all the three adjuvant concentrations of 7.5%, 10% and 12.5%. Surface tension for MAGIPAS4 with 7.5% (35.25 mN/m), 10% (34.86 mN/m) and 12.5% (34.98 mN/m) was significantly lower than the standard product Asset (45.03 mN/m) but no significant different with Roundup (40.05 mN/m). As for glyphosate monoammonium, MAGMAS6 and MAGMAS7 at all adjuvant concentrations showed significantly lower surface tension (39.55 mN/m and 34.20 mN/m respectively) than the standard product of Ammo Supre (50.57 mN/m) and water (control) (72.24 mN/m). MAGIPAS4 at 10% concentration showed lower mean contact angle at 32.6° on Paspalum conjugatum and 27.7° on Asystasia gangetica indicating good wetting properties on the leaf surface. MAGMAS7 at 10% adjuvant concentration recorded lower mean contact angle on all weed leaf surface (74.6° on Paspalum conjugatum, 52.7° on Asystasia gangetica, 58.2° on Ottochloa nodosa and 37.5° on Clidemia hirta) compared to MAGMAS6. MAGIPAS4 and MAGMAS7 at 10% adjuvant concentration is the optimum formulation that consistently provide the largest droplet spread area and higher droplet spread coefficient on leaf surfaces. In the influence of adjuvant concentration study,MAGIPAS4 has edged over MAGIPAS3 significantly in term of visual weed mortality for adjuvant concentrations of 10.0 and 12.5% on P. conjugatum and A. gangetica but were equal to the standard product of Roundup and Asset. While MAGMAS7 at all concentration has shown superiority over MAGMAS6 in term of visual weed mortality, fresh and dry weight reduction and chlorophyll content degradation for P. conjugatum and A. gangetica resulting from better droplet spread area and spread coefficient. In the rainfastness experiment, none of the glyphosate isoropylamine or glyphosate monoammonium formulations with palm oil based adjuvant formulated samples were capable of providing rainfastness effect 30 minutes post-spraying on P. conjugatum and A. gangetica. However, MAGIPAS4 with 10% concentration proved to be a rainfast formulation on P. conjugatum 90 minutes post-spraying. For glyphosate monoammonium, none of the formulations were rainfast 90 minutes post-spraying. The increase of adjuvant concentrations did not increase the level of rainfastness of the glyphosate formulations.

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