When plants are grown outdoors, pests and insects are ever-present but
most of the time they are kept in check by the forces of nature. The wind,
rain, changes in temperature, predators and diseases work as a system of
checks and balances to keep the populations down despite a phenomenally high
theoretical reproductive capacity.
Indoors, invading plant pests discover an ideal environment, with few of
the hazards they would find outdoors and with an abundance of food. Within
a few weeks of invasion the implications of the pests' theoretical
multiplication rate are evident and the plants may suffer the ravages of the
attack. For this reason, any pest invasion is treated very seriously and
quickly.
Every insect invasion to the garden has a cause. Most of the time, the
pests were carried into the garden by the gardener. Less frequently, pests
enter through the windows, cracks, or through the ventilation system.
Cautious growers never go into the indoor garden after working outdoors or
being in an outdoor garden. They never work on healthy plants after being
around or working on infected ones. In some commercial greenhouses, workers
change clothing in a dressing room before entering from outside.
One grower keeps a plastic dishpan filled with salt water at the entrance
to his grow room. As he enters the room he dips the soles of each shoe in
the water. This kills any pests which might be riding on the undersides of
his shoes.
To get a close look at insects, it is a good idea to get a photographer's
loop magnifying glass or a portable low-power microscope. Even the most
inexpensive ones are adequate.
There are six pests that are most likely to attack marijuana indoors:
aphids, mealybugs, mites, whiteflies, scale, and caterpillars. A few others
sometimes invade greenhouses. These include caterpillars, cutworms,
grasshoppers and leafhoppers.
APHIDS
Aphids are usually found on the undersides of leaves and on stems, though
they are sometimes found on the leaf tops. The adults are about 1/32 to
1/16 of an inch long and are oval, almost egg shaped. They have two
protrusions from their rear which look like pipes and may or may not have
wings. They are usually found in dense colonies with an adult surrounded by
a cluster of young. They are usually pale green or yellow, but sometimes
are brown, black or red. They molt leaving a white shell. They secrete
"honeydew" which is shiny and sticky and is found on infested foliage.
Honeydew isa concentrate of the sugars the animal has sucked out of the
plant and discarded in its search for protein. Aphids are frequently found
together with ants which farm them for their honeydew by carrying them from
plant to plant.
Infested plants weaken from the insects' constant sucking of sap which
they eat by penetrating the deep tissue. Older leaves curl and younger ones
grow deformed. Mold sometimes forms on the honeydew. Within weeks the
plant may wither. Aphids are carriers of molds and viruses.
Indoors, aphids reproduce parthenogenetically; that is, all the insects
are females and they can reproduce without being fertilized. They bear live
young, which may actually carry embryos of their own before they are born.
They can reproduce when they are 6 days old.
Luckily, aphids are not difficult to control. Action is taken at the
first sign of infection. First, the garden is checked for ants. Any
colonies are eliminated using ant bait, ant stakes or boric acid.
Then all visible aphids are wiped off the plants using a sponge and soapy
water, a soapy water spray or insecticide. A soapy water spray is made by
mixing 1.5 tablespoons Ivory Snow Flakes or any other soap without detergent
in a gallon of water. Some growers reported success using Dr. Bronner's
Eucalyptus or Mint liquid soaps (these are often found in health food
stores) at the rate of 1 tablespoon per gallon. This will eliminate most of
the pests so that the grower has some breathing space. However, even the
most thorough spraying or sponging does not eliminate all of the pests, and
since they reproduce parthenogenetically, even one remaining insect can
restart the colony.
If the plants are not flowering, then spray can be used every 2 or 3 days
for several weeks. Thorough sprayings may eventually destroy the colony.
They certainly keep it in check.
Another convenient spray is available commercially. Pyrethrum is a
natural insecticide found in chrysanthemum-family plants. It has not been
found harmful to warm-blooded animals but is toxic to aphids, among other
insects. Pyrethrum may be purchased as a powder, a liquid concentrate, in a
pump or aerosal spray. Usually growers with small gardens choose the
aerosols for convenience, while those with large gardens find the
concentrates or powders much less expensive. [pH:I wonder what, if
anything, adding this to the water for the plant would do to the aphids? If
it kills them, this would be a good way to kill them if the plants are
flowering.]
Some benign insects like to eat aphids and are convenient to use in a
greenhouse or grow-room situation. Ladybugs and green lacewings are
predators which eat aphids. They can be purchased commercially from
insectiaries. These insects also go through a rapid lifecycle and may eat
hundreds of aphids as they grow to adults. The insects come with
instructions for their use.
People are sometimes a little queasy about bringing beneficial insects
indoors because they are afraid they will escape into unwanted areas.
However, for the most part these insects stay where they belong as long as
there is food for them to eat. Adult beneficials sometimes fly directly
into metal halide lamps and die instantly. One grower placed a glass
reflector around his lamps. The trick is to get the adult beneficials to
lay eggs because the predators are most voracious during their immature
stages. Given enough food (aphids) this presents no problem. Once the
predators become established they keep the pest population at a negligible
level, but never eliminate their source of food.
MEALYBUGS
Mealybugs are light-colored insects which exude a white, waxy
cotton-looking substance in which they nestle or which covers their body.
They are usually found on the undersides of the leaves and in the joints
between the leaves and stems. The adults are from 1/16 to 1/8 inch long.
They suck juices from the plant and exude honeydew. Their breeding rate is
much slower than many other pests; a generation takes a month or more.
A small mealybug infection may be eliminated by using a sponge to wipe
the creatures off the plants. They can also be destroyed using a cotton
swab dabbed in alcohol, which kills them instantly. More serious
infestations may be controlled using a soapy water solution or pyrethrum.
As well as eating aphids, green lacewings also eat mealybugs.
MITES
Mites are the most dangerous pest that can enter a garden. They are not
insects, but an arachnid, which is the class of animals that include
spiders. Mites are tiny and may not be noticed until they have developed
into a serious infestation. There are many species of mites. However the
one most likely to attack the garden is the 2 spotted mite, which has two
spots on its back which can be seen under a magnifying glass.
The first indication that a grower may have mites is seeing pinpoint
yellow spots on fan leaves. These spots are located above the points where
the mites have pierced the tissue to suck out the plant juices. Mites are
very small, measuring only 3-6 thousandths of an inch. They look like small
dots colored black, red or brown. Mites' maturity and reproductive rates
are affected by temperature. A female lays about 100 eggs during her
lifetime, but at 60 degrees she produces 20 offspring, at 70 degrees she and
her offspring number 13,000 and at 80 degrees she represents a potential
13,000,000 individuals over a single month. Under ideal conditions mites
reproduce a week after hatching. [pH:I have friends who have lost entire
plants to these things.]
As the mite population rises, the plants weaken. Infested leaves curl
under and spider-like webbing is spun which covers the plants and is used by
the pests to move from plant to plant. Mites also walk down stems, across
medium and across dry space in search of new plants to colonize. [pH:To
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