Pest Control Methods for the Organic Garden

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PHOTO: FOTOLIA/FOTOSENMEER.NL
There are only two sprays that I will use: Bacillus thuringiensis (Bt) and Bacillus thuringiensis var. san diego—the former for cabbage loopers, cabbage worms, and tomato hornworms; and the latter for the Colorado potato beetle. I use them because they are non-toxic and because they only kill the target insects, and even then only if they eat a leaf that has BT on it.

The best pest control methods for the organic garden is to keep your garden healthy, pests don’t become a problem until there is a weakness in the health of the garden.

The best method of controlling insects that damage crops is
to keep your garden a secret. Don’t invite them to the
party. Think of insects like germs. There are always plenty
of them around, but they don’t become a problem until there
is a weakness. What pest control methods for the organic garden work? Who cares if the sphinx moths fly around
your garden, as long as they don’t lay eggs on your tomato
plants that will hatch into tomato hornworms? If we assume
they are only going to lay eggs on weak plants, we can be
assured they will leave alone our happy and healthy plants
growing in humus rich soil. It is clearly better to avoid
an insect problem than to have to deal with it. A nutrient
balanced soil is the best way to get insects to avoid your
garden.

Garden Pest Barriers

Another way to keep insects from getting to your plants is
to create a barrier they cannot surmount. You need to know
a little bit about the insect to erect the most effective
barrier. Someone might have the image of a garden enclosed
in mosquito netting. That might work but it is not very
cost-effective. I say might, because there are a lot of
different insects and if their motivation is strong enough,
they are likely to find a way in. Netting can be a
cost-effective barrier in some circumstances. Root maggots
are the larval form of a fly that lays eggs on the stems of
young plants. The flies may lay eggs on more mature plants,
but if they do the plants are growing fast enough to
survive. Young plants can be protected by a netting barrier
laid right over the seedling or even over the seed bed
before the seedlings emerge. A square foot of netting will
protect a hill of cucumbers. Clearly there is not much work
or material involved in this and the hill will produce a
lot of cucumbers if helped through the tender stage.

Unhappy radishes will also attract root maggots. Since you
would have to cover the whole row with netting to protect
them, and considering that radishes reach maturity in a
little over three weeks, a barrier hardly seems worth the
effort. Radishes also attract flea beetles–usually
radishes planted too early in the spring in my garden.
While the radishes are shivering in the cold, growing
slowly while they wait for the air and ground to warm up a
bit more, the flea beetles are feasting, sometimes setting
the plants back so severely I lose the crop. No problem: I
just throw in some more seeds. Flea beetles will do the
same number on broccoli directly seeded in the garden.
Since I am going to transplant this crop later, the
seedlings can all be grown in a foot-long row which can be
covered easily. When the plants are four or five inches
tall and ready for transplanting, there is enough when they
cut down the leaf surface of transplants. After all, we
prune larger plants when we transplant them so the damage
to the roots is balanced with a decrease in the above
ground portion of the plant.

While on transplants, we must not forget the insect most
often combated with barriers: the cutworm. Cutworms also
get around on wing but generally the grub is already in the
ground when we have to deal with it. A collar of tar paper,
cardboard, or some similar material that can be formed into
a circle about three inches in diameter and a couple of
inches tall and pushed into the soil an inch to make a wall
around each transplant.

Diatomaceous earth can also be used as a barrier. This is a
powder made up of calcified one-celled plants. To
soft-bodied insects it is a sea of razor-sharp edges. What
insects crawl on the surface of the ground to reach plants?
None, actually, but slugs do. Slugs are mollusks, not
insects, but gardeners can find little reason to make this
distinction. A band of diatomaceous earth around the
cabbage and/or lettuce if these are the crops being
plagued, or around the whole garden, will keep slugs at bay
if they are coming “from away” as we say in Maine. The
diatomaceous earth cuts the bodies of slugs and soft-bodied
insects that come in contact with it.

Garden Pest Traps

Slugs suit my purpose as an example of how traps can be
used. They do most of their work at night when it is damp
and cool. On a hot day, they can be found in cool, moist
places. If you put some boards down in the garden, you may
find lots of slugs under them in the heat of day. They also
are attracted to malt. Dishes of beer will attract them
…and they’ll drown happily.

Electric insect zappers will attract night-flying moths
which lay eggs that turn into hungry worms. A light placed
in juxtaposition to a sticky surface is a good combination
for attracting and killing night-flying insects. It is
preferable to the zapper because you can see the insects
you are trapping and identify them. You will likely find
that the majority are, at worst, benign.

Yellow cards covered with sticky stuff attract many
insects. Sticky red balls hung in apple trees get covered
with insects landing on them, also. These can be used as
traps to decrease populations but they are more often used
to monitor the number of insects present at any given
time.

Integrated Pest Management (IPM)

IPM uses the sticky traps just described to time the
spraying of pesticides. IPM is a giant step forward for
commercial growers who used to spray large quantities of
contact poisons as a matter of routine. If you were selling
stuff for farmers to spray on their crops, wouldn’t you
want them to spray lots and spray often? Most, if not all,
good farmers use IPM methods now. It has cut the use of
pesticides in this country dramatically. If you are a gardener and you are spraying a contact poison like Sevin at
the first sign of an insect, you are the last of a dying
breed. Think about it.

Pests and the Timing of Garden Planting

Some people have reported success in avoiding insects by
timing plantings so insects are avoided. For example, corn
earworms generally do not survive winter much north of New
Jersey. If you can figure out when they hatch and how long
it is likely to take them to get out of your garden, you
can time your planting so the ears form after the first
flight and before the second. This won’t always work
because of variations in winter weather. However, if you
have several plantings of corn and some have big problems
and other don’t, make a note of it. While you may not want
to cut out any of the succession crops, you may decide one
planting will be better for the bulk of the storage crop
than another.

Timing can also be helpful in disrupting an insect’s life
cycle. Tilling the garden in the fall, for example, puts
the cutworm larva up on the surface where birds can find
them. I wouldn’t recommend this unless I had a major insect
problem that couldn’t be reasonably dealt with in any other
way. The disruption in the problem insect’s life cycle is
likely to be a disruption to a lot more friendly and benign
insects as well.

Garden Pest Sprays

There are only two sprays that I will use: Bacillus
thuringiensis (Bt) and Bacillus thuringiensis var. san
diego–the former for cabbage loopers, cabbage worms,
and tomato hornworms; and the latter for the Colorado
potato beetle. I use them because they are non-toxic and
because they only kill the target insects, and even then
only if they eat a leaf that has BT on it.

Predator Insects

The two most famous of these are ladybugs and praying
mantis. Several kinds of wasps and lacewings are also
helpful. You can buy some of these beneficial insects for
release in your garden. I won’t go into the gruesome
details of how many aphids a hungry ladybug can eat in an
hour. Consider what that hungry bug is going to do when the
food runs out. “Fly away, fly away” to someplace where the
food supply is better. I have got some of all of these
insects in my garden or close by, I think, though I don’t
see them often. I’m glad not to, since that means there
isn’t much for them to eat.

If I come across a tomato hornworm carrying a load of white
oval packages on its back, I leave it alone. The packages
are eggs of a parasitic wasp. I want them to hatch so there
will be more wasps around to seek out hornworms. The wasps
are much better at finding them than I am.

Companion Planting

I have been planting rows of beans next to rows of potatoes
for over 20 years, because I read somewhere that the beans
would discourage Colorado beetles and potatoes would
discourage Mexican bean beetles. I am seldom bothered with
Mexican bean beetles, but if the beans have had an effect
on the potato beetles it has been very inconsistent. It
says in Organic Plant Protection, by the editors of
Organic Gardening and Farming magazine (Rodale Press,
Inc., Emmaus, PA, 18049) that nasturtiums will repel
aphids. In my experience I would be more likely to believe
that nasturtiums are a catch plant for aphids.

It seems to me that companion planting is a nice idea but
that the information available may be more anecdotal than
scientific. Tansy is suppose to repel lots of insects, but
who wants bales of tansy in the fall even if it would be
great on the compost pile?

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