Agricultural products certified as organic and free of pesticides cannot use synthetic chemicals in the production process. In this context, the search for new natural products appears as an alternative to the use of conventional pesticides, aiming to combat agricultural diseases. Menthol is a natural product obtained from plants that has importance in different branches of industry, mainly due to the feeling of freshness it provides in contact with skin and mucous. Menthol (70%-90%) is the main compound of the menthol mint essential oil, followed by menthyl acetate (7%-12%), which is an indicator of maturation. There are references to the period of maturation of menthol mint essential oil corresponds the period of flowering, on the other hand, are also presented evidence that the maturation of menthol mint essential oil is controlled by leaf expansion, namely with the physiological age of each leaf. Besides evaluating the essential oil production and quality extracted by hydrodistillation of young leaves (3rd to 5th node) and adult (6th to 8th node), was also proposed in this work to study the effect of menthol mint essential oil on the development of fungi of agricultural significance and commercial seeds of lettuce and tomato. After the extraction of the essential oil, was noted that adult leaves presented a higher content of essential oil, combined with the best commercial quality, showing higher levels of menthyl acetate and menthol. The menthol mint essential oil exhibited average fungitoxicity and antigerminative activity on Fusarium oxysporum, Rhizoctonia solani and Sclerotium rolfsii. On the other hand, menthol and terpineol, two essential oil components, showed the maximum fungitoxicity activity under this species and no inhibitory effect on the germination of lettuce and tomato.

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The purpose of this work was to evaluate the effects of different phosphorus levels (0.05, 0.5, 1 and 2 mM) under nitrogen metabolism and the essential oil profile of menthol mint (Mentha arvensis L.). The relationship between the leaf maturity and the essential oil profile was also explored. The experiment was conducted in a hydroponic system located in a grow chamber during 41 days and after the harvest, nitrate reductase activity, and the NO− -N, amino-N, and soluble sugars levels of each plant part were evaluated. Also the essential oil from young leaves (6th to 8th node) and adult leaves (3rd to the 5th node) was analyzed. An uptake mechanism related to the increase in fresh weight of the roots was promoted with the use of low P levels (0.05 and 0.50 mmol•L −1 ). With 1 mmol•L −1 P plants showed in all parts an increased nitrate reductase activity and high levels of nitrate and amino-N in leaves. Plants submitted to the lowest P level (0.05 mmol•L −1 ) presented high levels of menthol. In leaves from 6th to 8th node (mature leaves) menthol level was approximately 87% of the essential oil however leaves from the 3rd to the 5th node (young leaves) showed high levels of pulegone, that can be toxic for humans. The results indicate that the essential oil quality in menthol mint is influenced by the leaf maturity and the P levels. Also it was showed that the oil extracted from mature leaves of plants under low P levels has the best commercial profile.