By Cathy Peck
Beltrami County Master Gardener
'Right Plant, Right Place' is a book that illustrates a horticultural
truth: plants will thrive if they are appropriate for where they are
planted. If a plant’s cultural needs are met (soil pH, fertility,
light, air circulation, moisture, drainage, etc.) and are appropriate
for the growing zone, plants can withstand and even thrive when
confronted with insect threats. Many of us are not so skilled at
providing those conditions consistently and none of us can control
the weather. There are tools that can help us when insects threaten
that will have low impact on us and on the environment.
Bacillus thuringiensis is a naturally occurring disease of insects
and forms of it are specific to different insects. There are
different product brands but the active ingredient is Bt. Check the
label which will indicate whether it is for caterpillars (butterfly
and moth larvae) that affect cole crops, gypsy moths, or forest tent
caterpillars, for Colorado potato beetles or mosquito, black fly or
fungus gnat larvae. Bt will also kill desirable butterfly and moth
larvae.
Another low impact insecticide category includes horticultural oils.
They work by suffocating insect and mite eggs as well as some
immature and adult insects such as aphids and scale crawlers.
A third category of insect control is insecticidal soap. The active
ingredient is potassium salts of fatty acids that penetrate and
disrupt the cell membranes of soft bodied insects like aphids.
A fourth category, neem and neem derivatives, comes from the neem
tree of the tropical part of our world. Neem products deter insects
by interfering with their feeding, by repelling them, or by
disrupting their life cycle. These products work against aphids,
caterpillars, beetles. leaf miners, and thrips.
A derivative of ground flower blossoms of the chrysanthemum plant
called pyrethrin is a fast-acting insecticide that affects the nervous system and
paralyzes the insect. A synergist is sometimes added to the
pyrethrin to make it more effective. Pyrethrins work on a wide array
of insects. They are also very toxic to aquatic life.
The fifth category is another product that attacks the nervous
system of insects. It is called spinosad and is produced by the
fermentation of a soil-dwelling bacterium. Speedy, it works best on
caterpillars, flies (leaf miners), and thrips but also works on leaf
beetles and grasshoppers, insects that eat a lot of foliage.
Spinosad is toxic to bees, those important pollinators as well as
mollusks.
Whatever product we use must be appropriate and targeted at the
problem taking place. Understanding how a plant grows and whether it
is an insect causing the problem or could be the result of another
cause is crucial to remedying it. General overall spraying should
never be done. Observing plants so that treatment can be done at an
early stage is most effective with low impact products. Some of
these can even be used preventively.
Spectacular ads for synthetic products often promise immediate
solutions to insect problems. In our zeal to have perfect plants and
instant results, we forget or perhaps don’t know that these products
can also be destructive of beneficial insects that pollinate our
crops, flowers, and trees, can destroy creatures in the soil that
keep our soil healthy or be part of web of creatures that has kept
our ecosystem in balance for eons. They can also cause human health
problems and persist in our groundwater. Which direction is most
important?
Jeff Hahn, entomologist with the University of Minnesota Extension
Service, provided this information.
