Pests and marigolds

Greg Montez GregM at
Mon Mar 20 15:57:15 EST 1995

In article <"95-03-14-18:02:28.07*LWE"@NCCIBM1.BITNET>, 
>Actually, this post consists of two separate questions.  The first
>regarding a specific pest.  Can anybody identify for me the tiny, white,
>"hopping" creatures I find on the soil of certain of my houseplants.
>They are most noticeable during watering of the plants, as they them
>seem to be disgruntled.  I managed to drown most of them by continuously
>dousing my plants in the sink, though while stirring up the soil with a
>spoon while doing so, more appear.
>     My questions:
>1.  What are they?
>2.  Are they harmful to plants?  If so, what part (roots, stem)?
>3.  Is there a sure-fire method of getting rid of them, and keeping them
>from spreading to other plants?
>4.  Are they plant-specific?

They are most likely springtails, order Collembola.  They
thrive in moist organic matter, and they have been reported
to cause damage to roots when in very high numbers.  Probably,
they are not doing you any harm and in fact you are encouraging
them by overwatering.  Let the soil dry out and you may find
they will dissapear.
>Okay, on to the next question.  Regarding marigolds, is there a specific
>variety which I should use to "keep pests out of my vegetable garden"
>(as is commonly advertised) this year, or is there a certain species
>that has this repelling effect?  Also, how densely (how close to one
>another) should I plant them.  I tried planting seeds from a run-of-the-
>mill marigold I had - around the periphery of my garden last year; they
>grew well, but didn't flower until the fall, and were selectively dying,
>so I ended up with very few.  And if I need to get a special sort, where
>can I procure such?  Thanks!

Marigolds do have a significant impact on soil-dwelling nematodes
(tiny worms that feed on plant roots).  There has been a variety
developed called Nemagold that is used just for the purpose.
In my own experience, I feel that marigolds have very little
impact on above-ground pests like aphids or caterpillars.  You will
probably find someone who will say the opposite, but there are
many factors that affect pests in a garden.  Encouraging predators
and parasites is a far more effective means of controlling pests
than relying on marigolds.  That is, if you want to stay away from
Gregory Montez
Citrus Entomology Lab
University of California
Kearney Agricultural Center

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