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Texas Plains: Rains Cause Runaway Cotton, Hardly Hamper Field Pests

Ernst Undesser
By Blayne Reed, Texas AgriLife Extension Agent for Hale, Swisher, and Floyd Counties August 23, 2017

Texas Plains: Rains Cause Runaway Cotton, Hardly Hamper Field Pests

General Status

Perfectly timed rains are rare in West Texas, especially during peak water use, but when they do come it seems we get too much of a good thing, or at least all at once. Cotton fields that were cut-out stage have set fruit incredibly well, but now threaten to enter regrow mode.

Fields that were not cut-out but less than 5 NAWF are staking more nodes and growth on. Fields that were not at the critical 5 NAWF before the rains started a few weeks ago have built up access levels of ‘steam’ and show no signs of slowing. Much like the proverbial end of the line, the average last effective bloom date looms just 6 days away and these growthy fields are a steam locomotive ready to bust the boiler.

Plant growth regulators (PGRs) were already common this season, and became more so over the past few weeks on known trouble fields or those that could be seen as troublesome from pavement. Now that we are starting to dry out and finally scouting hard and heavy on fields we have not been able to see during the storms and mud, we are finding many, many more runaway cotton fields.

While corn of all stages have enjoyed the rains (unless they were ready for harvest) it has also kicked off a massive surge in rust and other fungal diseases.

Meanwhile, the rains did not really slow the pest populations as much as should have been expected. Sugarcane aphid populations in sorghum continued booming through the moisture while banks grass mites in corn have surprisingly not faded much and remain a threat too.

Bollworms spreading from corn and fresh migrant worms moving in from the south are now increasing activity in cotton and late grain fields as we just started picking up serious egg lay today in our program.

Cotton

We are still running behind in our Plains Pest Management scouting program but running hard now that we should not be swimming to reach fields. So far this week our program cotton has ranged in stage from absolute cut-out of 3.5 NAWF or less up to 7 NAWF. Stage wise, fields have not progressed much in the past few weeks.

While we have accumulated some heat units with high temperatures being over 80⁰F most days, and were setting bolls, fruit development was slow and vegetative growth was off the chart, unless already at cut-out. Fruit set remains good with few pests of note so far.

Lygus could still be an issue but are only finding 1 Lygus / 9 row feet as the highest population. In most fields we are finding 1 / 18 row feet or less. We did find the odd stink bug but nothing higher than 1 / 25 row feet.

We are and need to remain on high alert for bollworms in all cotton fields. Non-Bt fields should be a threat priority but all fields are at risk. We have been finding a few eggs and bollworms over the past few weeks but no worm population larger than 1,200 worms per acre. Starting today, we began finding fresh eggs in almost every lush cotton field with the highest field being at 27,125 eggs per acre.

Most of the fields to-day were significantly less, coming in around 9,000 eggs. However, these eggs were all very freshly lain. More should be on the way soon. The Hale adult bollworm moth traps show another heavy increase in moth activity this week while the worms also appear to be moving out of the older corn fields.

Herbicide Resistance Info


The ET for bollworms remains at 8,000 – 10,000 worms per acre or 6% harvestable fruit damage, whichever is easiest to scout or calculate for you, and we should never spray for eggs. Predation from beneficials on eggs will often drop the actual hatching worm population to sub-ET levels on the Texas High Plains.

Corn

Our scouting program corn ranged in stage from silk to early dough to early dent. We were surprised again this week to note that the banks grass mites (BGM) had not dropped in population on our older field in the moist and humid conditions, usually very conducive to fungal diseases that can and often do clean BGM populations quickly.

Our older field remains at risk for mites with a damage rating of 2.2 on the 0-10 damage rating scale with 3.5-4 being ET. We should continue to monitor mite populations until starch lines begin to form on the grain. Until then, mite populations can damage yield, quality, and in the heavier cases, cause the weakening of the stalk and eventually lodging under high pressure. The bollworm population were leaving this field, plainly heading for younger corn fields, sorghum, or cotton.

With no other Lepidopteran pest noted in the older field, attacks directly to the ear become less likely but not impossible as the field dries. We have not found any FAW or Western bean cut-worms for the season in this older field. These two species can feed on much tougher and drier grain than the corn earworm / bollworm but would normally move into the field at an earlier stage.

Our late planted corn field is now very attractive to all moth pests and should endure a very heavy egg lay over the next few weeks from multiple species.

Diseases increased in our corn drastically this week with the moisture. The most noted was common rust which multiplied by a factor of 10 from our previous checks in both fields. Our fields were covered with 10-35% leaf coverage up to -1 leaf. With much more progression up the plant to zero leaf and above, a fungicide treatment might be required. It is very likely some longer fields are already at ET with these diseases.

Sorghum

Our fields ranged from boot to black line development. Bollworms and a few FAW were noted in our heads but were not near economic yet. This may change as moth egg lay continues. Sorghum is a more preferred host than cotton and will likely receive more moth interest over the next few weeks. All blooming fields are at risk for sorghum midge, and a few were found in our fields again this week. Sugarcane aphids continue to be the largest issue in sorghum.

It has been well recorded in many locations with lower altitude and higher humidity that SCA will often crash in and following heavy rains. This does not appear to be the case here this season. The population is doing quite well. We were able to place many SCA research trials this week on very healthy populations.

In most untreated plots and in pre-treatment counts, our SCA were running at 100% plants infested with 200-300 aphids per leaf. With ET being at 20-30% infested plants, stage depending, our plots, and likely many area fields, were already in rescue situations. There are a few exceptions with good IPM implementation.

In a seed treatment trial we are currently running, all commercially available insecticide treatments were giving still good control at boot stage, 59 days after planting. SCA ‘tolerant’ lines were still supporting fewer aphids this week. While both of these control measures will likely need to be treated for SCA eventually, the damage accumulated so far is much better.

Especially if pair together. Early planted sorghum, while heavy with aphids, is already at black line stage and only needs to wor-ry with the aphids if they look to be in the way of harvest or if field will be left standing until a freeze before harvest.

Ernst Undesser
By Blayne Reed, Texas AgriLife Extension Agent for Hale, Swisher, and Floyd Counties August 23, 2017