Effect of Adjuvants on Herbicidal Activity and Selectivity of Three Phytotoxins Produced by the Fungus, Stagonospora cirsii

Abstract

The use of many fungal phytotoxins as natural herbicides is still limited because they cannot penetrate leaf cuticle without injury and a little is known on their selectivity. In order to assess the herbicidal potential of phytotoxic 10-membered lactones (stagonolide A, stagonolide K, and herbarumin I), the selection of adjuvants, the evaluation of selectivity of the toxins and the efficacy of their formulations were performed. Among four adjuvants tested, Hasten™ (0.1%, v/v) increased phytotoxic activity of all the toxins assayed on non-punctured leaf discs of Sonchus arvensis. When assayed on intact leaf fragments of 18 plants species, 10 species were low to moderately sensitive to stagonolide A, while just five and three species were sensitive to stagonolide K and herbarumin I, respectively. Both leaf damage or addition of Hasten™ (0.1%) to the formulations of the compounds considerably increased or altered the sensitivity of plants to the toxins. Stagonolide A was shown to be non-selective phytotoxin. The selectivity profile of stagonolide K and herbarumin I depended on the leaf wounding or the adjuvant addition. Stagonolide A and herbarumin I formulated in 0.5% Hasten™ showed considerable herbicidal effect on S. arvensis aerial shoots. This study supported the potential of the oil-based adjuvant Hasten™ to increase the herbicidal efficacy of natural phytotoxins.

Mechanistic Aspects and Effects of Selected Tank-Mix Partners on Herbicidal Activity of a Novel Fatty Acid Ester

“…The situation was completely different with the adjuvant Hasten. This product is very safe according to safety data sheet information and also possesses no herbicidal activity at typical use concentration up to 1% [ 31 , 49 , 52 , 53 ]. When sprayed on plants, no phytotoxicity symptoms were observed up to the highest tested concentration (5%), which also indicates no own herbicidal activity.…”

Structure–Activity Relationship of Phytotoxic Natural 10-Membered Lactones and Their Semisynthetic Derivatives

“…Herbarumin I (4) inhibited the growth of Amaranthus hypochondriacus seedlings [4] and caused necrotic lesions on sowthistle punctured leaves [10]. In our previous studies stagonolide A (1) and herbarumin I (4) demonstrated the potent post-emergent herbicidal activity against perennial sowthistle aerial shoots, the treatment of plants with these toxins supplemented with Hasten™ led to the development of wide necrotic lesions on the leaf surface [19]. For adequate assessment of future perspectives of most phytotoxic compounds it is important to compare their target activity with that of chemical herbicides.…”

“…The final concentration of ethanol was 5% (v/v), the concentration of the tested toxins was 2 mg/mL, 5% EtOH was used as control treatment. Punctured leaf discs of perennial sowthistle (Sonchus arvensis) were placed in a wet chamber and treated with 10 µL of test solutions [19,23]. The diameter of the necrotic lesions was measured 48 and 120 h after treatment.…”

“…Strain G-51 S. cirsii, a specialized pathogen of perennial sowthistle (Sonchus arvensis), was patented as a producer of stagonolide A and herbarumin I at a preindustrial level (over 100 mg/L and 450 mg/kg, respectively) [18]. Among S. cirsii secondary metabolites, stagonolides A, J, K, and herbarumin I displayed promising phytotoxic activity that can be used for the development of a natural herbicide [10,19]. In the framework of our ongoing research on phytotoxic ten-membered lactones, we report here the results of SAR analysis for these compounds.…”

Efficacy of Metribuzin Doses on Physiological, Growth, and Yield Characteristics of Wheat and Its Associated Weeds

“…Adjuvants help to reduce herbicide dose and improve its biological activity by altering the surface tension of spray solution, increasing absorption, translocation rate, effect on atomization, and enhanced penetration ( Hamouda et al, 2021 ). Some adjuvants completely alter the chemical composition of herbicide or even cover the plant surface by keeping the herbicide in contact with plant tissue and hence increase the herbicide penetration and binding ability to kill the target plant without damaging the actual crop ( Dubovik et al, 2020 ). Several studies have demonstrated that adjuvant’s efficacy is dependent on the herbicide being used and the characteristics of the target weed ( Javaid and Tanveer, 2013 ).…”