March 2024 - 26

HEMP PRODUCTION
Twospotted
spider mites
(Tetranychus urticae) are one
pest that both indoor and outdoor
producers have struggled with at
some point in their operation.
- Marguerite Bolt
Twospotted spider mite
Twospotted spider mites (Tetranychus urticae) are
one pest that both indoor and outdoor producers
have struggled with at some point in their operation,
mentioned Bolt.
" They're pretty common, they have a wide host range,
but they can cause some pretty significant losses if
they're unchecked, " she said.
You want to look for stippling and webbing on the
plant, which is a good indication of a twospotted spider
mite problem. Some level of chlorosis can occur; whitelooking
dots on the leaves early on is a good indication
that you really need to look for spider mites. " You can
shake those leaves onto white paper or a paper plate
and see the spider mites crawling, " Bolt said.
For control in hemp, growers can implement biocontrol
programs - there are predatory mites available
from biocontrol companies. " There are different
organic products that are under the OMRI label that
are available, but there is research on conventional
miticides, specifically abamectin for mites, " she said.
Broad mite
" Broad mites (Polyphagotarsonemus latus) are
another one that I've seen get pretty out of control, "
said Bolt. They are very small and can do a lot of
damage. You will see cupping and curling of the leaves
as the first signs of a broad mite infestation, so you're
going to want a hand lens to look for the mites and
eggs especially on new growth, she said.
" We see broad mites very often congregating on
new growth, so looking at the tops of plants, the areas
where you're having active growth, for the mites
themselves, " said Bolt.
Broad mites have pretty distinct eggs, those are like
little white tufts on them, so they're actually pretty
easy to ID in that regard. And again, there are biocontrol
options for this particular species that are available
26 | MARCH 2024 * HEMP PRODUCTION
Broad mites have distinctive eggs that show white tuft-like
protrusions on the exterior.
Hemp russet mites are very small so higher magnification than a
hand lens can provide may be necessary for identification.
through these commercial insectaries. Miticides are an
option just like with spider mites.
Hemp russet mite
The Hemp russet mite is an eriophyid mite. It
does not produce webbing and is much smaller than
broad mites, most likely requiring a dissecting scope
to identify.
" You may see bronzing or chlorosis [on the leaves]
that have this sort of upward leaf curl - lots of
growers call it 'taco leaf' - and then leaves can
become quite brittle, " said Bolt.
But you see leaf curling caused by other stressors,
like plants infected with viruses that have an upward
leaf curl. You may have a nutrient issue where you have
some leaf curling, so it's good to pull out that hand lens
and actually inspect the leaves for pests, she said.
Proper sanitation is key for this one. I often see hemp
russet mites come into facilities on propagules, so going
through quarantine, inspecting plants and making sure
March 2024

Table of Contents for the Digital Edition of March 2024
