Texas Plains IPM: Lygus Numbers Rise, Drought Stress Continues

Tarnished plant bug, aka lygus bug. Photo: Lisa Ames, University of Georgia, bugwood.org.

General Status

A few more rain showers visited most of our fields this last week, but again the real beneficial amounts were very isolated. In the area of Tulia, some flooding even occurred with 3.5” falling in a short time. The rest of us received much less, only ranging from a trace up to about 0.6” with most getting around 0.2”.

While we are thankful for any moisture, few acres could be described as having adequate soil moisture and most fields can still be described as being in a drought, if not severe drought. Irrigation systems are ensuring a pretty decent boll set and pollination, so far as we can tell, but are still falling farther behind as most plants are smaller in stature than we would like.

I have noted a growing number of area grain fields plainly abandoned before crop maturity over the past month. Without a widespread quick change in the moisture situation, I would expect to see more of the same, but in a wider range of crops.

Despite the droughty situations, several pest populations were on the increase again this week for most production fields. Just a few required treatment, but we are watching just as many that were borderline ET (economic threshold) for close inspection next week.

Despite all the adverse situations, there remain some pretty good fields out there today. As we enter peak water use stages with pest populations on the rise, more adverse situations are ensured.

Cotton

This week our scouting program cotton ranged from 1/3 grown squared wildcat cotton up to 4.6 NAWF (nodes above white flower). Most fields were averaging just over 5 NAWF with outliers on either extreme.

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Boll set / fruit set still looks really good from a percentage standpoint, unless plant bugs were an issue. Our plants are coming into these stages early and are generally smaller statured and thus, have a below “average” number of fruiting sites to set fruit on.

This could put some emphasis on protecting our percent fruit retention/drop today, as there might not be much more additional fruit set if an early absolute cut-out occurs soon.

Lygus populations did increase again this week. Still, we only had one field reach ET requiring treatment. Most fields held fewer than 1 Lygus per 5 row feet with fruit drop being under 15%.

In our ET field, we found 1 Lygus per 1.9 row feet with drop increasing to 23%. The bulk of our Lygus noted this week were still adults. In many cases when adult Lygus increase in population to steadily notable populations, we see nymphs hatching out soon.

This is how most of our Lygus ET situations become problematic with the less mobile nymphs joining the adults in causing damage.

Fleahoppers have been in most cotton field’s past for some time now. However, our wildcat cotton, still not in bloom yet, reached ET for the pest with a fruit drop increase of 19%. We did note some bollworm eggs in our program again this week, however most were located in our bollworm/Bt efficacy trial where we are taking an inordinate amount of data.

With 400 whole plant inspections in a fairly small area, we only found 68 bollworm eggs per acre. With our ET being 8,000-10,000 bollworms per acre (or 6% harvestable fruit), we are far below ET. While our moth traps are still running very low, this trend should continue. On an average year, the peak bollworm egg lay occurs about mid-August in the Plainview area.

We also started finding a few plants showing symptoms of verticillium wilt this week. This too is a touch early as symptoms usually do not start until the first week of August. During the 2019 season, verticillium was very light, and it is not known how heavy 2020 will be.

Conditions can play a large roll in vert expression and infection. It is known that once a cotton field is verified with vert, there will be 20 years of spores available from that 1 year, so the potential for disease issues remain if a field has a history of at least some vert.

Once symptoms start to show, there is little that can be done to alleviate the situation. All vert control options are prophylactic and involve rotation and variety selection. The next few weeks to month should be a great time to evaluate where your fields stand with vert.

Corn

Our program corn ranges in stage from VX up to early dent with the majority being in early to mid-dough stages. After being almost impossible for us to find all season, Banks grass mites have arrived and increased in population rapidly.

Our highest program population rated a 0.8 with pockets of 2s on our 0-10 Texas A&M AgriLife Extension mite rating scale. This remains well below our ET of 3.5 to 4 in the Plainview area, but the mites look to be catching up quickly in the race to determine what will happen first, the mites reaching ET or fields developing past mite damage.

For many nearby areas, the mites have already won with several fields treated not so far away.

Diseases, most notably just common rust, in-creased some this week also, but remain very light. Bollworms/corn earworms made a larger impression in corn this week. This too seems lighter than an “average” year.

So far the few bollworms in the area remain more attracted to the corn as we are not finding very many outside of corn. Here they can sink into the crop without many economic impacts. That cannot be said for cotton or sorghum.

Southwestern or European corn borers have not been found in our program so far.

Sorghum

Our sorghum ranged in stage from V5 up to soft dough and several stages in between. Sugarcane aphids (SCA) were much easier to find this week and were confirmed to be in all but one of our older fields, but could not be found in any of our younger fields.

Much like last season, the SCA are behaving slower than in previous seasons. The reasons could have a couple of causes. One, we are managing the aphid better with proven thresholds in a timely manner. Two, nature is finding a balance and predators are attacking the aphid in a more assertive way.

For whatever reason, the aphid is not infesting and increasing at the high rate we have seen before. Do not let this fool you. This aphid can still out reproduce expectations and deserves to the monitored closely.

Our highest field population held 5.76% plants infested with thumb sized colonies. This could easily reach our High Plains ET of 30% for post boot sorghum quickly.

We are still not seeing any sorghum midge in our blooming sorghum. We did find Banks grass mites in about ½ of our older sorghum fields at sub-ET levels and even found 1 headworm (bollworm) on soft dough stage sorghum. This was the only actual worm found outside of corn.

If needed, a great sorghum headworm ET calculator can be found here.




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