Management Considerations for Blooming Cotton (Collins, Edmisten, & Reisig)
Several fields of early planted cotton began blooming this week or will be blooming soon. Normally we would expect to see the first blooms at 58-60 days after planting, however our heat unit accumulation over the past few weeks has accelerated growth in many fields, some of which have started blooming in 52-54 days after planting. First Bloom is an important stage in cotton growth, when certain management considerations come into play.
PGRs: Some areas received badly needed rainfall late last week and over the weekend. These rains will do this crop a lot of good. Other areas (mainly some of the western counties) are still in bad need of rain. Now that most top-dressed fertilizer has been applied, the recent rains (in areas that received rain) will spur terminal growth for the time being. Terminal growth rates are generally the highest in cotton that is at or approaching the blooming stage, which will likely trigger some PGR applications. Evaluate and consider the following when making these decisions:
- PGRs may be justified at First Bloom if plant height is 25 inches or greater, NAWF is 7 or greater, and internodes between the 4th and 5th true leaf from the terminal are 2.5-3 inches or greater. A field history of rank growth, especially when later maturing varieties with greater growth potential are planted, increase the likelihood of positive responses to mepiquat applications.
- Reddening mainstems and large squares in the terminal could indicate that the plant is under some sort of stress. This should be accompanied by NAWF less than 7 and/or internodes less than 2.5 inches. In these scenarios, a PGR application may not be justified. This is especially the case in sandier soils and earlier maturing varieties.
- As always, soil moisture should be sufficient for continued vigorous growth with a strong chance of rain in the near forecast. If soil moisture is marginal or rain is unlikely, you may want to hold off for a few days to see if the soil moisture status changes.
- See our previous article regarding other considerations for PGR management at http://cotton.ces.ncsu.edu/2015/06/pgr-management-considerations-collins-edmisten/
Irrigation: See our previous article for irrigation management approaches for high-yield cotton at http://cotton.ces.ncsu.edu/2015/06/considerations-for-irrigating-cotton-collins-edmisten/. First Bloom marks the point in time in which weekly irrigation rates begin to increase, as a boll load develops. It’s very important to accurately document when fields reach First Bloom….at this stage, blooms should be fairly difficult to find as they are near the very bottom of the plant with only one bloom every five feet of row or so. If you can ride by a field and see blooms with little effort, then chances are that the field is already 7-10 days into the bloom period. If you document this as First Bloom, then you will likely be behind on irrigation by at least a week for the remainder of the season. It is very difficult to catch up on irrigation if hot or dry conditions prevail, therefore thorough scouting is necessary to document when the field reaches First Bloom so that optimal weekly irrigation rates can be used.
Insect Management: Continued scouting for plant bugs will be necessary to determine if bloom treatments need to be made. As a boll load develops, you may want to consider changing from a sweep net to a drop cloth to evaluate and document when thresholds are reached. Keep in mind that while some of the neonicitinoid products may be preferred in squaring cotton (Admire Pro, Belay, Centric, Trimax Pro), we may need to transition to pyrethroid products (bifenthrin, Karate, etc.) or premix products (Endigo, Hero, Tempest, Swagger, etc.) or possibly Belay (only if you have not used a neonicitinoid prior to bloom). As we approach mid to late bloom, and additional applications for plant bugs are necessary, you would need to transition to an organophosphate product at that point (Bidrin, Bidrin XPII, Orthene, etc). This article could help you with product selection for plant bugs: http://cotton.ces.ncsu.edu/2014/06/insecticides-for-plant-bugs/.
As other crops such as corn begin to mature, other insect pests such as corn earworm, may appear during the bloom period, which necessitates the need for thorough scouting. There is a plethora of pyrethroid products available to control these pests which can be found in the NC Ag Chem Manual: http://content.ces.ncsu.edu/publication/north-carolina-agricultural-chemicals-manual/ but make sure you can properly identify these insects and where they are likely to be found on the plant (http://cotton.ces.ncsu.edu/insect-scouting-guide/)
Now that we are in entering the bloom period, keep in mind the weekly thresholds for stinkbugs and how the dynamic thresholds change as the bloom period progresses. Again, if you can ride by a field and easily see blooms, you may already be entering week 2 of bloom, in which the thresholds decrease. Weeks 3, 4, and 5 of the bloom period mark the time in which the largest proportion of stinkbug susceptible bolls are present on the plant and the thresholds are the lowest. If stinkbugs are present (accompanied by scouting of quarter-sized bolls which indicates external and internal damage to these bolls), treatments may be necessary. As the thresholds are the lowest during weeks 3, 4, and 5 of bloom, targeting treatments at this time will likely have the greatest impact on yield in managing this insect pest. Identifying the type of stinkbug (green, southern green, brown, and potentially brown marmorated) that is present in above-threshold numbers could help in product selection. Pyrethriods are often effective on brown marmorated, green, and southern green stinkbugs; however, these may be somewhat weaker on brown stink bugs (the exception being a full rate of bifenthrin, which can be effective against brown stink bugs). In many cases, Bidrin (dicrotophos) or Bidrin XPII (dicrotophos plus bifenthrin) may be necessary for control of Brown Stinkbugs. See the following link for more information on stinkbug management: (http://cotton.ces.ncsu.edu/insect-scouting-guide/)