Texas Plains Cotton: Wireworms, Thrips, Drought Stress

Photo: Pat Porter, Texas AgriLife Extension

Welcome to the 2018 growing season and another round of the Plains Pest Management Newsletter here to serve and update Hale, Swisher, & Floyd County with pest and crop updates and IPM solution recommendations.

While we are excited about this season’s potential and look forward to another year of serving our growers, party favors and happy dances are few out and about the countryside at this time. Desperate rain dances are more the normal today.

There was a fleeting time in early to mid-May when about 2/3 of the area caught some relief and difficult environmental conditions were not the main focus of our concerns for some of us. This occurred when the northern portions of the Plains Pest Management service area received between 0.5-inches to 1.8 inches of rain.

The outrageously dry conditions prior to these rains that absorbed the moisture ridiculously fast and the return of heat with dry winds have reversed those events to a memory of nice but not enough, particularly for all dryland acres.

These limited rains were not without pockets of harsh weather that damaged hard fought early stands of some of our crops and we still have the other 1/3 of our production acres that did not receive these rains, only accumulating 0.25-inches down to a trace or even less.

The final stance of our dryland crops is yet to be seen. Most are being or have been planted so that with a decent rainfall, they would emerge in decent shape. Without a good rain these fields will remain dry seed or germinate, desiccate, and die.

Several dryland fields that did receive rains earlier are already in this situation need moisture quick before expiring.

AgFax Weed Solutions


Our producers have been able to wrestle most of our irrigated fields into acceptable stands with heavy irrigation inputs and excellent planter skills and some field management. That being stated, it is easy to spot fields struggling with irrigation capacity, antiquated irrigation systems, or other issues, which do include some of those rotten pests to be very mindful of.

Weeds

Weeds are not having the same difficulties establishing that our crops are in these dry conditions. Within very spot within our Plains Pest Management scouting program fields where water has pooled, set, or even been moist for any period of time are flushing with seedling summer weeds, Palmer primary among them.

The only difference being the density of the weed flush with the more aggressive residual herbicide treatments that were better incorporated having fewer emerging. I can find no that can be considered completely clean at this time with young weeds that will need to be dealt with soon.

Cotton

Our Plains Pest Management scouting program cotton ranges in stage from seed bouncing across fields in the planter box to 4th true leaf stage with most pushing (and sometimes drying) to 2nd leaf stage. The dry environment has been a major challenge in establishing viable stands, and have caused some replant issues, but this is not the only factor we are dealing with.

Wireworms have been the pest highlight for the past few weeks. All fields we have been in have some level of wireworm damage this season. This damage has ranged from so light that it takes an experienced eye to note it to destroying stand establishment. Most of our irrigated fields are experiencing a 5% to 15% stand reduction just to this subterranean larval pest.

The heaviest wireworm pressure fields this spring seem to be no or min-till fields that were planted before the rain events or where no rain event happened and heavy irrigation was a must for seed germination.

Not all of the fields that fit this description are so heavily impacted before stand establishment, but many were. Some to the point of failure while other fields treated with the best efficacious seed treatments still experienced a 40% reduction in stand establishment.

Wireworms, the general term for several larval forms of multiple beetle species including click beetles, false wireworms, and the High Plains false wireworm, 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 or wet fall.
  • 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 gaping wounds allowing seedling diseases to impact young plants at a level I would estimate to be near ten-fold.

How do we address this issue? Once wireworm problems are found at a level that are interfering with stand establishment, the only control option is a replant with the addition of an insecticidal seed treatment or a more effective seed treatment than was previously utilized.

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.

Not to be outshined, thrips have increased in pressure over the past week from above the ground to demand attention also. As per usual, our thrips pressure in out program fields are higher in the northern areas with more wheat fields nearby but the population in the southern areas of Hale and Floyd is notable too.

This week our thrips counts ranged in the north from from 2.25 thrips per true leaf in untreated 2nd true leaf stage cotton down to 0.5 thrips per plant in fields newly emerged. Even scouting fields behind over-the- top treatments made this week and with insecticidal seed treatments still active and showing at least some true leaf stage held around 0.8 thrips per plant in the northern areas.

To the south, our numbers were ranging between 0.61 thrips per true leaf up to 1.1 thrips per true leaf. Beneficial counts remained very low in our fields this week with most predators only consisting of crab spiders so far.

Corn & Sorghum

We do have just a few early planted seed milo fields and a few April planted corn field in our program this year. Both of our corn fields range in stage this week from V5 to V6. These are very important stages as ear size and a few other deciding traits are beginning to be determined now and consequently many herbicide labels require treatment at or before V5.

We found no pest of note in either corn field this week, but with high temperatures and moth flights in the region, we may begin seeing whorl damage soon and a few spider mites increasing on our lower leaves.

These few early planted sorghum field might be the only sorghum in our program this year, our research program’s test plots at Halfway that are yet to be planted aside.

These fields ranged in stage more across fields than between them, a testament to the difficult planting and environmental conditions this season. These stages ranged from V1 to V4. This could prove difficult to manage during pollination and for midge management, but today we consider them successfully established in a tough situation.

We have seen no pest of report in our sorghum either.


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