Whitefly and Pyrethrum spray?

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  • #14797

    Stefan Olson


    Unfortunately, despite my best efforts I still have thousands of whitefly in my conservatory. I was wondering if one of those Pyrethrum sprayers that spray out every few minutes in order to rid your house of pests would work on the whitefly in the conservatory?


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    I’m as thick as a whale omelette when it comes to plants, but according to wikipedia:

    Apparently the common name in English, “marigold”, is derived from “Mary’s Gold”.

    The French marigold refers to Tagetes patula. It is used in companion planting for many vegetable crops. Its root secretions kill nematodes in the soil and it is said to repel harmful insects, such as white fly amongst tomatoes. In spite of its name, it is native to South America.

    African marigold usually refers to cultivars and hybrids of Tagetes erecta, although this species is not native to Africa.

    English marigold refers to Calendula officinalis, also known as pot marigold. Plant pharmacological studies have suggested that Calendula extracts have anti-viral, anti-genotoxic and anti-inflammatory properties.

    I am interested in testing all of them for their Aphis nerii repelling properties, but I suspect from what I have read so far that it is the marigolds from the Tagetes family, and in particular Tagetes patula that are the right kind of marigolds to repel whitefly and aphids.



    Yes Tatia, it is never a waste of time to plant marigolds for their many good properties, not the least of which is that they are high in nectar as well. They are great in pots too, easy to grow anywhere in fact! : )



    Do the marigolds help with thrips as well? I have all my milkweed in pots (tropical), so would interspersing the marigolds in pots be useful?



    That is so true about the marigolds. I grow hundreds of them here in the vege garden and no sign of a whitefly anywhere, but one or two won’t do – plants lots! French or african – I think they are the same thing (opposite side of the mediteranean)

    I can’t speak highly enough of them as a suppressor of weeds, deterant to sucking insects, soil builder, eliminator of soil nematodes, nectar plant for butterflies. In the vege garden every spare bit of soil is covered in them and they are chopped into the soil to break down when they are finished. BEST PLANT!!! and so easy for new gardeners who think they can’t grow anything too : ) Jane



    That’s right Jacqui.African marigolds



    And that’s African Marigolds, isn’t it, Bernie? Or English ones… I always get confused. Jane wrote about them in a recent newsletter.



    I have mentioned this before on some link some time ago.Years ago,,I read somewhere about “companion plants” which can provide a sort of protection from pests.If you grow marigolds,it deters whitely from infesting other plants nearbye.I have been using these for over 20 years,not only as a source of nectar for the butterflies but also to deter whitefly.I don’t even give the whitefly a thought now as I just don’t have a problem with them.Before I used marigolds in my flight area,I always had lots of whitefly



    Pyrethrum is an extract from the pyrethrum daisy and as such is sold as a ‘natural’ alternative to chemical spray methods which it is, however, make no mistake that Pyrethrum is a knock down ‘contact’ spray which does not descriminate between one bug and another, and is very effective in killing all caterpillars and eggs included.

    ‘Contact’ means it must make contact with the insect it is intended to kill, and you are very likely to miss all the whitefly that are underneath the leaves. And don’t let the ‘natural’ tag fool you either. There are many natural sprays that are still deadly to most critters, and in the case of Pyrethrum – it WILL affect your caterpillars. I’m not knocking pyrethrum as a control method and have and do use it myself selectively in some situations. It’s advantage is that although it will kill ALL on contact, it does not have a considerable residual effect and will be biodegraded in a few days. The best control for whitefly is cultural IE COLD – put the plants outdoors where the plants will harden up to the elements, and the whitefly won’t be able to cope. This should work in your case Stefan as the Manawatu is very cold in winter, but it may not be effective for those of you living in the balmy north.

    Once the plants are ourdoors, THEN, use a knockdown insecticide in the conservatory on all your hard surfaces, walls, floors windowsills, mats, and shelves to get rid of the sheltering whitefly adults and eggs that will otherwise happily overwinter in your protected conditions ready for a vigorous onslaught as soon as spring arrives.

    The whitefly are treating your conservatory as a tropical holiday in Tonga!! Even outdoors in sheltered conditions there will be a few that will survive under leaves, but at least your plants will be effectively hardened off to the attack so that the spring juveniles aren’t having a feast on overly lush soft foliage.

    Good luck though Stefan. I hear your frustration loud and clear and have suffered from it myself when running glass houses for commercial production. There is no EASY answer I’m afraid.

    Another method is to use a natural predator which is a tiny wasp called Encarsia formosa which will knock the population under controlled conditions, BUT, will never kill them all. With this method it is all about population dynamics and a tricky non-stop system of monitoring and counting is required, with renewed introductions of Encarsia at regular intervals. There has been a bit of talk on the forum about sticky yellow traps in the past. The traps only catch as small percentage of the whitefly, and must be hung in amongst the plants at the same level to get a true indication. Each day new flies on the yellow cards are circled with a pen so that you can get a daily reading on the population dynamic, and when the population of your pest begins to rise, a new Encarsia introduction is made. (So often I see the sticky monitoring cards hanging from a ceiling no-where near the plants!! These will do nothing except make you feel better. The sticky cards are not a method for killing whitefly as they will only get a small percentage, and are to be used purely as a population monitoring tool)

    The predator Encarsia formosa is purchased as eggs on a small card, which is clipped to your plants. I used to purchase them from Fruitfed. This method is a professional control method requiring constant and ongoing management and will also never give you 100% control as it is not intended to.

    The only tried and true method of killing ALL your whitefly is to use a chemical control method for a clean slate approach. I am not recommending this method but it WILL work. Such chems as Orthene will kill everything in sight. I don’t use it myself, but have worked with many people who choose to because they can’t be bothered, or do not know how to use less environmentally damaging population dynamic methods.




    good luck..those white fly…I had to end up killing my plants in order to get rid of mine..at least aphids can be squished. Hope the Pyrethrum wouldn’t have a negative affect on any future caterpillars or butterflies. I certainly hope this is a solution.

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