Plant infections caused by plant are difficult to prevent or cure. Recently, however, tests by researchers in India and the United States have shown neem extracts can prvent many types of viral infection and reduce the severity of any damage once there is an outbreak ( Saxena, et al,1985) ; ( Simon, 1981). The effect is probably a combination of neem's pest control properties and it recognized anti-viral compounds. Pests flying from an infected plant can carry viruses to uninfected plants, thereby spreading the disease. Reducing the number of disease - carrying insects can therefore help reduce the spread of the virus. Neem also actively inhibits viral diseases . Just as it does with viruses that attack humans and animals, neem prevents the virus from being able to survive outside an infected cell and many also strengthen a plant's ability to fight the infection.
Crop can be protected from viral diseases and their vectors in two ways. First, the field the crops are to be planted in is covered with neem cake and then plowed to work it into the soil. This provides crops long term and systemic protection for seedlings. Second, the plants are sprayed with neem extracts whenever problems begin to appear. This directly attacks any disease organisms or vectors ( insects) and allows the leaves to quickly absorb the effective compounds.