A field experiment was carried out at Ismailia Agricultural Research Station, Ismailia Governorate,
Egypt, during the two successive seasons of 2017 and 2018 to study the impact of beneficial microorganisms
Trichoderma harzianum (fungi), Streptomyces griseus (bacteria) and two common chemical fungicides (copper
sulphate and difenoconazole) to controlling spearmint rust disease. The vegetative growth, chemical constituents,
essential oil production and its components in spearmint (Mentha viridis L.) plants were evaluated. The obtained
results concluded that the use of copper sulfate as a chemical fungicide and the two bioagents [Streptomyces
griseus and Trichoderma harzianum] reduced the incidence and percentage of rust disease severity in compared
to untreated plants (control). Similarly, the level of vegetative growth, essential oil percentage and yield and the
percentage of minerals and total carbohydrates in herb as well as carvone content in essential oil were noticeably
more in compared to the chemical fungicide (difenoconazole) and untreated plants (control). Thus, reduce the
using of chemical fungicides means reducing environmental risks.