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Monday, May 7, 2018

Wireworms Notable in the Area and a Threat to Cotton Establishment


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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