Ability of eleven Thailand herbs to prevent silkworm fungal infections

Thai silk, mainly produced in north and northeast of Thailand, is one of the natural textiles of the world most famous for its quality and beauty. Usually, microbial infection of the silkworm in rainy and summer seasons causes its lower productivity. Formaldehyde used by the farmers in its eradication is toxic to human and animals, as the contaminated fried pupa is a delicacy of some citizens. Hence, this research into alternative plant fungicides using soxhlet and maceration extracts (16 – 500 ppm) of eleven herb species of Thailand; Ocimum tenuiflorum L., Mental cordifolia Opiz., Zingiber officinale Ros., Alpinia galanga Swart, Curcuma longa L., Cymbopogon citratus (DC.) Staph., Citrus hystrix DC., Zingiber montanum Dietr., Piper samentosum Roxb., Ocimum basilicum Linn. and Piper betle Linn., three Aspergillus species; A. flavus, A. oryzae and A. niger, paper disc diffusion and microplate assays. Extracts of C. hystrix, Z. montanum and C. longa inhibited spore germination and growth of fungi, with MIC values of 6.25 – 125 ppm., while positive controls; toxic formaldehyde and ketoconazole showed MIC values of 3.12 – 6.25 ppm, suggesting their use as alternative to toxic formaldehyde. Thus, plant active compounds were investigated, other silkworm pathogenic microorganisms were also tested and field experiments are future study.