Instead of using copper, sulphur, or even systemic treatments, biological neem oil is used on
fruits, nuts, vegetables, herbs, spices, roses, houseplants,
flowers, trees, and shrubs. And it is specially indicated on
vineyards against mildew, who attacks grapes plants, not
only as a prevention, but also as an effective curative treatment.
Neem Oil is an effective fungicide for the prevention and control of
various fungal diseases including powdery mildew, black spot, downy
mildew, anthracnose, rust, leaf spot, botrytis, needle rust, scab
and flower, twig and tip blight, and alternaria.
Agricultural Research, June, 1994 by Hank Becker
"...in numerous tests, a spray of 1-percent neem oil in water
"stopped 95 to 100 percent of the powdery mildew on hydrangeas,
lilacs, and phlox."
A single spray application was sufficient to protect these
ornamentals from infection. Repeated applications at 7- to 14-day
intervals as the plants grew provided disease protection without any
plant damage. On plants where mildew had begun to develop, "it was
arrested, providing control comparable to each of three chemical
Powdery mildew, which also attacks crepe myrtles and roses, causes
leaves to turn white. Preliminary results indicate the oil will
arrest and control the fungus that plagues these popular
ornamentals, especially in humid zones.
This research, begun in cooperation with former ARS entomologist
Hiram Larew, also demonstrated that neem oil can reduce damage
caused by various pests, including spider mites.
"In preliminary tests, a 2-percent spray of neem seed oil applied
directly to spider mite eggs resulted in an 87-percent mortality".
Research at USDA on plant-derived natural pesticides, such as
nicotine, dates back to the 1920's. Beginning in 1975, extraction
products from neem seeds were evaluated for their insect-killing
properties. Many insect pests may be affected by Azadirachtin
including aphids, beetles, caterpillars, lace bugs, leafhoppers,
leafminers, mealybugs, psyllids, thrips and whiteflies.
Neem seeds and leaves contain many compounds which are useful for
pest control. Unlike chemical insecticides, neem compounds work on
the insect’s hormonal system, not on the digestive or nervous system
and therefore doe not lead to development of resistance in future
generations. These compounds belong to a general class of natural
products called ‘limonoids’.
The liminoids present in neem make it a harmless and effective
insecticides, pesticide, nematicide, fungicide etc. The most
significant liminoids found in neem with proven ability to block
insect growth are: azadirachtin, salanin, meliantriol and nimbin.
Azadirachtin is currently considered as neem’s main agent for
controlling insects. ‘It appears to cause 90% of the effect on most
pests. It does not kill insects – at least not immediately – instead
it both repels and disrupts their growth and reproduction. Research
over the past years has shown that it is the most potent growth
regulator and feeding deterrent ever assayed. It will repel or
reduce the feeding of many species of pest insects as well as some
nematodes. In fact, it is so potent that a mere trace of its
presence prevents some insects from even touching plants.’
Certain hormones are necessary for growth and development of
insects. These hormones control the process of metamorphosis as the
insects pass from larva to pupa to adult. Azadirachtin blocks those
parts of the insect’s brain that produce these vital hormones. As a
result, insects are unable to molt. It is through these subtle
hormonal effects that this important compound of neem breaks the
life cycle of insects. The insect populations decline drastically as
they become unable to reproduce.
Meliantriol and salannin act as powerful antifeedants. Nimbin as
well as nimbidin (another neem component) have antiviral property.
Blocking the larvae from molting is considered to be neem’s most
important quality which can be used to eliminate many pest species.
Neem products are harmless to most insect eaters, humans and other
mammals, except certain marine life like crabs, lobsters, fishes and
In spite of high selectivity, neem derivatives affect ca. 400 to 500
species of insects belonging to Blattodea, Caelifers, Dermaptera,
Diptera, Ensifera, Hetroptera, Hymenoptera, Isoptera, Lepidoptera,
Phasmida, Phthiraptera, Siphonoptera and Thysanoptera, one species
of ostracad, several species of mites, and nematodes and even
noxious snails and fungi, including aflatoxin-producing Aspergillus