Antifungal activity of neem

Parthasarathy Seethapathy.

Department of Plant Pathology, Tamil Nadu Agricultural University, 

Coimbatore – 641 003. Email:spsarathyagri@gmail.com.

Neem has demonstrated antifungal activity and is very successful against fungi that cause certain plant diseases viz., rots, smuts, wilts, mildews, diebacks and other plant diseases. Field and laboratory experiments have indicated considerable results against several diseases. Neem products are very useful against diseases of field crops, vegetable crops and fruit trees.

Field crops

Neem oil can protect the seeds of chickpeas against the serious fungal diseases Rhizoctonia solani,  Sclerotium rolfsii, and Sclerotinia sclerotiorum. It also slows down growth of Fusarium oxysporum, but does not kill it. In addition, neem cake incorporated into the soil completely blocks the development of the resting forms of R. solani there by interfering with the long-term survival of this devastating fungus.

In another test, neem seed extracts showed beneficial effects against leaf fungi. Spraying crude neem oil on lilac bushes, when done before any sign of outbreak, prevented powdery mildew from breaking out for the rest of season. This protect ant also gave essentially 100% controls on hydrangeas in greenhouses better than benlate (benomyl), the standard mildew treatment in much of the world. In addition to affecting root-knot nematodes, treating soil with neem can reduce the populations of pathogenic fungi in the rhizosphere that attack and feed on plant roots.

Pulses

In the case of bean rust, neem extract gave 90% control when applied before the plants were exposed to the fungus.  However, it worked poorly once rust was established. Neem cake (1.5%) proved very effective product in reducing the ashy gray stem blight of cowpea. NSKE was evaluated in poison food technique against root rot; wilt, blight and color root pathogens of chickpea, and reported it as a best fungicide.

Oilseeds

Three sprays of 1% neem leaf extract have been recommended for effective and economical management of tikka disease of groundnut and three sprays of 2% neem leaf extract for effective control of the mustard powdery mildew. Nimin and neem cake were also found best against severity of club root disease of yellow sarson. Alternaria blight and white rust infection in mustard can be controlled by two applications of ethanol extract of neem. The treatment checked the stag head formation and percent severity on leaves. Neem extract can also be included in soil treatment for the management of soil borne pathogens. Leaf extract of neem was tested for control of stem rot of mustard as application. The treatment was found superior in controlling the disease and increasing percent plant stand over the control. The treatment has also exhibited increased germination of seeds.

Other field crops

Among the neem-based compounds, repelin was significantly superior over control to reduce rice blast disease. Picnidial formation was not observed in treated condition. The neem leaf extract and neem seed extract were found most effective in checking mycelia growth of fungus Sclerotinia sclerotiorum and Phomopsis vexans

Vegetable and spices crops

To manage disease of vegetable crops, usage of neem products may prove safe and eco-friendly. Extracts of neem provided sufficient protection against clump rot of small cardamom. Application of neem cake in soil may act as useful amendment in soil. In addition to that, soil application of neem cake @ 1 tons per hectare was effective as drenching of carbendazim against Rhizoctonia root rot disease of fenugreek. The derivatives of neem including aqueous extract of neem leaf and neem oil 3% provided suitable protection against powdery mildew disease and die-back or fruit rot disease of chili. The extract was also found effective for inhibiting sporulation of the pathogen. Neem leaf extract can be used as fungicide against brinjal stem and branch blight caused by Sclerotium rolfsii and collar rot disease caused by Phomopsis vexans.

The extract inhibits mycelia growth and fungal development. Damping off of tomato seedling caused by p .aphanidermatum can be managed by the application of aqueous extract of neem leaves. The results of laboratory experiment revealed maximum inhibition of mycelium.

 Fruit trees

Neem leaf extract 10% was found effective against basal stem rot of coconut. The treatment was effective against basal stem rot of coconut. The treatment was effective in suppressing the mycelial growth of G. lucidum in vitro by recording 67% reduction of mycelial growth over control. In field condition, the treatment was effective in control disease. Mango wilt caused by Fusarium solani can be managed by adding organic amendment like neem cake in the soil. The population of wilt pathogen was reduced in pot culture and resulted in maximum control of wilt.