Some fields got a much needed rain with the scattered storms this week, and others either didn't get any or only got a tenth of an inch. I had a couple of locations in Matagorda county that got 4 and 5 inches of rain, and others just next door that didn't get any. This week I started seeing blooming cotton, so its time to start looking for stink bugs and bollworms in those fields. I haven't seen any bollworms or stink bugs in cotton yet, but I have heard from a consultant that started seeing stink bugs. In cotton that isn't as far along and still in peak squaring, fleahoppers are still a concern. I found fleahoppers in a field near El Toro with 40 fleahoppers on 100 plants this week. The threshold for fleahoppers is 15 to 25 per 100 plants, so treatment was necessary for that location.
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| Green Stink Bug Photo: Kate Harrell |
Stink bugs are difficult to scout, especially in tall, vigorous cotton. Adults tend to group together, and the distribution of stink bugs within a field may be highly concentrated, particularly along field margins. Use any of the sampling techniques such as visual inspection, drop cloth, and sweep net for scouting. Recent research by entomologists at the University of Georgia and Clemson University suggests that decisions to treat for stink bug infestations are best made based on the percentage of bolls with evidence of internal damage (warts or stained lint associated with feeding punctures). To use this technique, remove about 10 to 20 bolls, one inch in diameter (about the size of a quarter), from each of four parts of the field, avoiding field edges, and break open the bolls by hand or cut them with a knife. Look for internal warts on the boll walls and stained lint on the cotton locks.
Check bolls with visible external lesions first to determine if the internal damage threshold has been met, since bolls with external lesions are more likely to also be damaged internally.
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| H. zea Moth Photo: Kate Harrell |
I also want folks to be on the lookout for bollworms as cotton begins to bloom. I have not found any larvae yet, but I have seen moths moving around in cotton. To scout for bollworms in Bt cotton, search the entire plant for larvae and injury. A proper sample includes squares, white blooms, pink blooms, bloom tags, and bolls. Reduce the scouting intervals to 3 to 4 days during periods of increasing bollworm egg-laying, especially during peak bloom. The presence of eggs alone should not trigger treatment since hatching larvae must first feed on the cotton plant to receive a toxic dose.
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| H. zea eggs Photo: Kate Harrell |
To use the terminal and square inspection method, divide the cotton field into four or more manageable sections, depending on the field size. Examine 25 plant terminals (upper third of the plant), selected at random from each quadrant, for small larvae and eggs. Also, from each quadrant, examine 25 half-grown and larger green squares as well as small, medium, and large bolls for bollworms and bollworm damage. Keep track of the number of undamaged and damaged squares and bolls. Select fruit at random and do not include flared or yellow squares in the sample. Pay attention to bloom tags and petals stuck to small bolls; they will often hide larvae that burrow into the tip of the boll.
To use the whole plant inspection method, once again divide the cotton field into four or more manageable sections, depending on the field size. Make whole-plant inspections of five randomly chosen groups of three adjacent cotton plants in each section. Look in every square, bloom, and boll. Thoroughly inspect dried blooms or bloom tags attached to small bolls. Count the number of undamaged and damaged fruit and calculate the percentage of damaged fruit.
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| Managing Cotton Insects in Texas, pg 14 |
Thresholds in Bt cotton fields are based on how many worms survive to late first- or second-instar larval stage, not on newly hatched larvae or the presence of eggs. Since newly hatched larvae must feed on the plant for the Bt toxin to be effective, base treatment decisions on damaged fruit and the presence of larvae. Insecticides in the diamide, oxadiazine, and spinosyn classes are more selective than the pyrethroid and carbamate classes. See the tables below for suggested insecticide options.
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| Managing Cotton Insects in Texas, pg 31 |
Last week we put out 3 large moth traps in each county with Helicoverpa zea (bollworm) lure in each. Below I have included the number of bollworm moths caught this week at each location.
Wharton County:
7- Elm Grove
1- Near the Wharton Airport
1- Blue Creek Area
Jackson County:
26- El Toro
7- La Salle
5- Between Weedhaven and Palacios
Matagorda County:
4- Near Blessing
4- Near Tidehaven School
1- Tin Top
These moths are probably moving out of corn and sorghum and will be moving into cotton as our growing season progresses. I am still looking for earworm caterpillars out of non-bt or refuge corn. If you have high populations, please contact me. We are looking to conduct a Bt resistance study again and need caterpillars out of non- Bt sources to give a fuller idea of what the make up of our entire population is like.
Some of the larger cotton I looked at this week may be in need of a PGR application soon, especially in areas that received a good amount of rainfall, so I asked my intern Jared Schindler to provide some information on what PGRs are, how they work, and when applications should be considered. Check out his write up below:
Plant Growth Regulators
Cotton growth
modification has become a key part in the creation of a successful yield,
whether growth has been modified through means of adjusting the fertility,
saturation and/or using some harvest aids to get the crop in tip-top shape.
Applying plant growth regulators (PGRs) to early or midseason crop is
comparable to the tactics listed above.
Plant
growth regulators function as chemical messengers for intercellular
communication. There are currently five plant hormones these PGRs imitate.
These include auxins, which are responsible for directing plant leaves toward
sunlight, gibberellin, a hormone that lengthens the stems of plants,
cytokinins, which delay the natural aging process of plants, causing them to
have longer lifespans, ethylene, a hormone that requires oxygen to be produced,
initiates the ripening process in many plants, and abscisic acid, which that
detects the level of water stress in a plant and alerts other parts in times of
drought or “thirst”.
These
synthetic hormones do have varying application rates, however. Pix, also known
as Mepiquat Chloride, was the first PGR in cotton production to have a
noticeable impact on plant growth. Introduced in the 1980s, this
anti-gibberellin reduces the production of gibberellin, which would enlarge
plant cells, causing the plant to shift its energy from stems and leaves to the
boll itself, increasing boll retention and reducing boll rot caused by a
thicker canopy. Pix is most efficient when first used near the early bloom stage,
and then again within 4 weeks on cotton that is prone to rapid growth. Applications
should begin when 50% of the plants have one or more
matchhead squares. It is best to manage
high growth potential early if conditions favor excessive growth for an extended
period of time.
These
application rates and number of applications may be subject to differences,
depending on what sort of variety is being grown. For example, varieties with
high vegetative growth potential may require multiple applications at or near
blooming. Some of these varieties may be more responsive to PGRs, but most
still need multiple applications from squaring to 1st bloom. Depending
on which variety is planted, the crop may need multiple applications. See the
table below for more information.
Sources:
http://www.ugacotton.com/2018/01/relative-plant-growth-regulator-requirements-for-cotton-varieties-updated-for-2018/
http://www.untamedscience.com/biology/plants/plant-growth-hormones/
https://extension2.missouri.edu/g4258
Have a great Memorial Day weekend, everyone!
Sincerely,
Kate Harrell
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