Fungus gnats

Mix 1/4 cup neem meal with 3 cups vermicompost and top-dress your plants. Water in and unless you're plants are suffering from acute angina you won't have fungus gnats to deal with.
 
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 Yes and yes...pure worm castings do not exist unless you're running a serious worm bin set-up and have a few years of experience to draw from.
 
It certainly does not exist with bagged retail products - not even close.
 
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Seaweed and Plant Growth
10-15
 
The Answer
    Eichmeir reported that two-spotted spider mites raised on snap beans showed that treatment with gibberellic acid resulted in significant reductions in mite populations. Rodriguez reported similar effects on gibberellin treated bean and apple trees.
    Hormones are reported to keep certain insects sexually immature so they can't reproduce. Hormones have also been reported to prevent female insects from producing sex attractants they need in order to mate.
    Booth sums the situation up by saying:
   
    Taking the situation as a whole, there is experimental evidence to show that liquid seaweed products, trace elements, and growth retardants have an adverse effect on the reproduction of insects. There are also practical experiences with seaweed products and suggestions, from spraying contractors that a mixture of liquified seaweed and an insecticide is more efficacious than the insecticide alone.

 

Seaweed in Agriculture and Horticulture - William A. Stephenson
Chapter 7
 
Mr. Stephenson was the founder of Maxicrop which began operations in the early1950's - the first powdered seaweed extract produced for commercial farmers. During that period he and his staff worked closely with Dr. T.L. Senn from Clemson University who was in the iddle of his 55-year career studying brown kelp in agriculture and horticulture.
 
Cite:
 
It is known that plants treated with seaweed products develop a resistance to pests and diseases, not only to sap-seeking insects such as red spider mite and aphides, but also to scab, mildew and fungi. Such a possibility may seem novel, but it is in keeping with the results of research in related fields. The control of plant disease by compounds which reduce or nullify the effect of a pathogen after it has entered the plant is an accepted technique. It is in this way that streptomycin given as a foliar spray combats fireblight in apples and pears, and antimycin and malonic acid combat mosaic virus in tobacco. The subject of controlling plant disease by introducing substances into the plant itself is known as chemotherapy, and is dealt with in a useful round-up article in the Annual Review of Plant Physiology, 1959, by A. E. Dimond and James G. Horsfall of the Connecticut Agricultural Experiment Station, New Haven, United States.

 

I've never seen neem oil not work for gnats. I put some nematodes in mine and it seems to help. I was thinking I may need more or perhaps a different brand. Then they just live in the soil so no more additions of bits or scheduled drenches of neem. I think it would've worked better if applied at the start rather than when you have a decent population. Any one have success using a certain brand? I got mine from planet natural.