Spider Mites Explained
By:
Advanced Nutrients
Two-spotted spider mites
Contrary to popular opinion, two-spotted spider mites (tetranychus
urticae) are not insects-they are very small, almost
microscopic arachnids, closely related to spiders. They suck
plant juices from the leaves of your crop, causing a
discolouration of leaves due to the loss of chlorophyll.
Leaves of infested plants have distinct pale-yellowish
blotches. The spider mite's life cycle depends on the
temperature of the grow room-anywhere from 40 days at 55
degrees F or 5-7 days at 75 degrees F. As they grow from egg
to larva to protonymph, deutonymph and adult, their legs
increase from six to eight. As they increase in numbers, they
form a very fine web on the underside of the leaves, often
growing into a large web over the plant, resulting in not only
the leaves dying, but eventually the plant, as well.
The absolute best way to test for spider
mites at the early stage is to use a hand held magnifying
glass known as an 8x film loop, which can be bought for four
or five dollars. Turn the leaves over and check on the
undersides. Provided there is a spider mite infestation, you
should be able to see either some clear eggs, round and
translucent, or some larvae or nymphs crawling around. You may
also hold a clean, white sheet of paper underneath the
suspected branch, and shake the plant slightly. Little specks
should fall off and start crawling across the paper. If you
look at them under the 8x film loop, you will confirm that the
larvae have only 3 pairs of legs, while the nymphs and adults
have eight legs. The adults are very small (1/60 to 1/80th of
an inch, or 0.5mm in length), are oval in shape, and range in
colour from clear to light yellow or green, to brownish
orange. Two dark spots can be seen on the sides of the adult.
Spider mite species seem to be warm
weather or cool weather active pests. The two-spotted,
European red, honeylocust, and oak spider mites do best in
dry, hot summer weather. The spruce and southern red spider
mites do best in cool spring and fall weather.
David J. Shetlar, of Ohio State University, explains it all
this way: "All spider mites go through the same stages of
development. Adult females usually lay eggs on their host
plants. The eggs hatch in days to weeks into the first stage,
called a larva. Larvae are round bodied and have only three
pairs of legs. The larvae feed for a few days, seek a
sheltered spot to rest and then molt into the first nymphal
stage. The first nymph now has four pairs of legs. The first
nymphs feed a few days, rest and molt into the second nymph.
The second nymphs feed, rest and molt into the adult stage.
The males are usually the size of the second nymph and have
pointed abdomens. The females have rounded abdomens and are
the largest mites present."
The two-spotted spider mite is an example of a 'warm season'
mite. This pest has been reported from over 180 host plants
including field crops, ornamental plants, house plants and
weeds. Not to forget cannabis sativa or indica or the hybrids.
Outdoors, the females over-winter in the soil or on host
plants. The females become active in April and May when they
seek out the undersides of leaves on suitable hosts. Each
female may lay over 100 eggs. A single generation may require
as much as 20 to as few as five days, depending on the
temperature. These mites prefer hot, dry weather and often do
not reach damaging populations in cool, rainy periods.
In the summer, the adults and nymphs are
white with two greenish spots. However, over-wintering females
usually turn reddish-orange and can be mistaken for other mite
species.
Article Courtesy of
Advanced Nutrients |
