Brian Jervis: Ask a Master Gardener
Sunday, July 19, 2020
Q: I have bagworms all over my arborvitae. What
can I do to get rid of them? JG
A: Bagworms
seem to be everywhere this year. Getting rid of them can be a challenge, but it
is possible if you are up to the task. First, let us talk about the bagworm
life cycle because understanding their life cycle is key to controlling them.
To
begin, let’s go back a couple of months. Bagworm larvae overwinter in the bag
and begin to emerge in late April or early May. Once emerged, these larvae
begin to feed and construct the bags with which we are familiar. Initially,
these bags may be only ¼ of an inch in length. But, as the larvae feed and
begin to grow, they increase the size of the bag. This feeding is what can
cause damage to the host plant. You mentioned arborvitae, but they also like
eastern red cedars and junipers. However, in peak seasons, they can make their
homes on pines, spruce, bald cypress and others.
For
the female bagworms, the bag is their forever home. They do not develop wings,
legs, eyes, or antennae and are almost maggot-like in appearance. Adult females
can grow to about 1 inch in length. Males on the other hand grow to become
small black moths that have a wingspan of about 1 inch.
Pupation
occurs within the bag, and in the late summer or early fall, the males emerge
from their bags in search of females. Adult males and females have a short
lifespan — the female, a couple of weeks; the male, only a couple of days so
the search is on. Neither the adult female nor male feeds. After mating, the
adult female lays several hundred eggs within her bag and then dies. The eggs
overwinter within the bag only to start the cycle all over again the following
year.
So
back to your question of what to do about them. With bagworms, timing is
everything. When they are in their bags, about the only thing you can do is to
remove them by hand, and you can do this any time of year. If your shrub is of
an appropriate size, this is a good strategy, one the kids might enjoy helping
with as well. Once the bags are collected, they need to be destroyed or placed
in a sealed bag in the trash.
About
the only other time you have a shot at control is in April and May when the
larvae are feeding. During this time, you can spray with an organic pesticide
called Bacillus thuringiensis or Bt for short. This organic pesticide only
affects feeding caterpillars. You spray the pesticide on the infested plant,
they ingest the pesticide while eating and die. Spraying this time of year
while the bagworms are in their bags will not be an effective strategy as the
bag does a great job of protecting them from harm.
Typically,
damage is minimal from bagworms. However, infestations that build up over time
can be detrimental to the health of your plant. So taking appropriate action at
the appropriate time is key to bagworm control.
Get answers to all your gardening questions by calling the Tulsa
Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center
at 4116 E. 15th St., or by emailing mg@tulsamastergardeners.org.
Garden tips
·
When
watering your lawn, ornamentals, or vegetables, always do so in the morning if
possible. If watered in the evening, plants will go into the night still being
moist. Most disease-causing organisms need moisture, and because they grow best
at night, leaving leaves wet in the evening will promote many plant diseases.
·
Bulb
onions are ready to harvest when the tops fall over. They should be removed and
allowed to dry in a well-ventilated, shaded area. After the tops are completely
dry, they may be stored in a cool, dry area.
·
Tall,
spindly tomato plants with scarce fruit are usually due to either too much
nitrogen fertilizer or too much shade.
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