JBiopest 7(2):199-204(2014) Greenhouse evaluation of botanical extracts. © 461 In vitro and greenhouse evaluation of botanical extracts for antifungal activity against Phythopthora infestans Ngadze, E ABSTRACT The aim of this study was to evaluate plant extracts for antifungal activities against Phythopthora infestans (Mont.) de Bary, an important pathogen of potato which causes late blight disease. Acetone, ethyl acetate and water extracts of garlic (Allium sativum L.), Pawpaw (Carica papaya), Neem (Azadirachta indica), Mexican marigold (Tagetes minuta) and peri –winkle (Vinca rosea) were screened in vitro for their antifungal activities against Phythopthora infestans using the disc agar infusion and microtitre double-dilution techniques. The same extracts were then tested for antifungal activity in vivo in the greenhouse on inoculated potato plants. The water extracts of Allium sativum and Azadirachta indica were active against Phythopthora infestans and had a minimum inhibitory concentration (MICs) of 1.65 mg/ml. MICs of Allium sativum, Azadirachta indica and Tagetes minuta acetone extracts were 0.78, 3.13 and 6.5 mg/ml respectively against Phytophthora infestans. Allium sativum and Azadirachta indica water and acetone extracts performed well and they effectively reduced potato late blight in the greenhouse. These extracts compared well with the reductions due to application of Ridomil, a synthetic fungicide applied at 42.5g/l (active ingredient) and also with levels in the non-inoculated control. Allium sativum and Azadirachta indica were effective both in vitro and in vivo in controlling late blight have a potential to be used as fungicides against the disease. The plants are readily available and the extraction method is also simple and could lead to high adoption as fungicides by resource poor farmers. MS History: 20.09.2014 (Received)-09.10.2014 (Revised)-20.10.2014 (Accepted) Citation: Ngadze, E. 2014. In vitro and greenhouse evaluation of botanical extracts for antifungal activity against Phythopthora infestans. Journal of Biopesticides, 7(2):198-203. Key words: fungicidal, Phytophthora infestans, Allium sativum, Azadirachta indica, Tagetes minuta, Vinca rosea, Carica papaya. INTRODUCTION The late blight disease of potatoes is the most devastating disease of potatoes in the world. The disease is caused by the pathogen Phytophthora infestans (Mont.) De Bary which may also infect other solanaceous plants. Late blight may kill the foliage and stems during the growing season. It also attacks potato tubers in the field, which may rot either in the field or in storage. Late blight may cause total destruction of all plants in the field within a week or two (Agrios, 2005). The use of chemicals or synthetic chemical fungicides are being used successfully but indiscriminate use of these chemicals led to have development of fungicides resistance and more important environmental pollution, posing a potential risk to animal and human health such as undesirable side effects due to their carcinogenic properties (Alkhail, 2005; Lyon et al., 1995).Considering the adverse and alarming effects of synthetic pesticides on environment and natural habitats and the promotion of environmentally sustainable and organic agriculture, fungicide alternatives such as the use of natural plant products is needed (Slusarenko et al., 2008; Rice et al., 1998). Plants contain antimicrobial compounds which can be toxic to pathogens and these natural plant products can be used to control plant diseases. Contrary to the problems associated with the use of synthetic chemicals, botanical extracts are environmentally non pollutive, renewable, inexhaustible, indigenously available, easily accessible, largely non phytotoxic, systemic ephemeral, thus readily biodegradable, relatively cost effective and hence constituted as suitable plant protecting agents in the strategy of disease management (Kuberan et al., 2012). The objective of this study was to screen botanical plant extracts