Wireworms Notable in the Area
After
being alerted to some potential heavy wireworm populations in the area by Dr.
Pat Porter, District Entomologist, I have been making rounds behind the planter
in some of the area’s earliest planted cotton fields. What I am finding is troubling. The population of wireworms, or rather the
amount of their resulting feeding damage on yet to emerge seedings, I am
finding indicates a very high threat level to cotton stand establishment. High enough that I feel wireworms could be
one more establishment issue we have to address with prevention in each and
every cotton field in the area.
Thus
far, cotton planting conditions here in West Texas are far from ideal. It is desperately dry, most days windy, the soil
temperatures are following the air temperature closely (with tantalizing highs
and seedling jolting lows) with scorching temperatures predicted and little to
no rain in the forecast, and irrigation equipment and capabilities that have
seen better days. Adding to these problems
look to be these wireworms.
Wireworms do not
like cotton and it is not a preferred host.
They will however attack cotton after germination and before emergence
as a survival method, often as a last resort to save off starvation. When we review the literature, we find a list
of circumstances where wireworms could be a problem for seedling cotton.
- Following a grain, forage, or hay crop.
- In a dry season
following a wet year.
- In a field
with a heavy cover crop or heavy fall or spring weed pressure.
The
damage from wireworms to cotton seedlings can be two-fold. First, is the direct damage from their
feeding. If the feeding occurs on the
cotyledons only the damage is usually minimal.
It takes an experienced eye to even spot this type of damage. If the feeding occurs along the tap root it
could be substantial causing developmental delays for that plant taking weeks
to recover from, and if heavy enough, eventually fatal. If the feeding occurs at the apical meristem
(growing point found between the two cotyledons) or the curve just below the
cotyledons, it is almost always fatal for that plant. There is a substantial amount of secondary damage
that is normally associated with wireworm feeding on the taproot of cotton
seedlings. The wounds caused by the
feeding open gapping wounds allowing seedling diseases to impact young plants
at a level I would estimate to be near ten-fold.
The conditions we
are experiencing today fall in line with a heavy wireworm “storm.” Last September, rain and cool temperatures
were widespread. The resulting weeds and/or
vegetative growth were abundant. And we
had something of an open fall, allowing plenty of time for that excess vegetation
to grow off, not wanting to stop for winter.
Wireworms, the larval form of click beetles and an array of false wireworm
species, flourish in high vegetative situations. Now we are much drier and wireworm food
sources are reduced. They become reduced
even more with field preparation and cleaning/clearing of green vegetation. Now, heavy wireworm population is hungry and
desperate for a food source. If this
population is high enough, it alone has enough potential to devastate cotton seedlings
before stand emergence. A moderate
population will reduce cotton stands. If
this moderate population of wireworms is aided by other factors (i.e. drought,
seedling disease, high winds, night or irrigation cooled soil temperatures,
etc.) we could also see failure to establish stands.
How do we address
this issue? First let me state that,
once wireworm problems are found at a level that are interfering with stand
establishment, the only control option is a replant. No over the top application has ever been
proven effective in controlling the problem.
While it is difficult and costly to move treatments below the soil
surface, the failures in achieving control are probably because the damage to
the seedlings are irreversible. It should
also be stated that, even at their worst, predicting which fields wireworms
will be an issue is impossible, and thus preventative over the top or
chemigation type treatments have never been justified for any particular field
and remain untried or unproven. Even the
best wireworm sampling methods only give a positive or negative indication of
presence and are not a population estimating tool.
So, we are left
with what we can do for field preparation and at planting. Research trials have shown that insecticidal
seed treatments such as Cruiser, Gaucho / Poncho / Honcho can offer 60%-75%
control of wireworms. Meanwhile, other insecticidal
seed treatments such as Orthene offer no or limited protection. If a higher level of control is justified in
any particular field, there are an assortment of labeled insecticidal seed box treatments
for wireworms that can offer 90%-99% control but come with difficulties in
dealing with vacuum planters. In
addition to chemical control options, fields with fewer hindrances to stand
establishment will establish cotton stands faster and leave a shorter window
for wireworm damage to accumulate. Once
cotton stand establishment is achieved, wireworms should no longer be an issue
for cotton.
I strongly suggest
digging in seedbeds and checking germinated cotton seedlings 4-10 days behind
planting for wireworm damage. If issues
exist in your field or fields, replant and actions are much better sooner rather
than later. If issues are indeed persistent
for the majority of your already planted fields, preventative actions should be
taken before any additional plantings are made.
Blayne
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