UGA Cotton Newsletter

June 23, 1999

Table of Contents

Crop Condition
Sidedress Fertilizer Questions and Concerns
One Last Chance for Nematode Control in Problem Fields
Herbicide Options in Roundup Ready Cotton
Harvade-5F Labeled for Post-Directed Applications to Cotton
Mid-Season Tropic Croton Control in Conventional Cotton

Crop Condition. (Brown) We=ve had a rugged start. Our crop has suffered severe crusting, wind, sand blasting, thrips, hail, and seedling disease. We=ve seen low vigor and Ano vigor@ seed. Most non-irrigated acres have faced serious moisture deficits. However, over the past 10 days much of the state has received RAIN, and it is remarkable how water and moderate temperatures have rallied the crop. Overall, our prospects have brightened considerably...except for price.

Growth stages range from cotyledon cotton to the third week of bloom. Whether or not Georgia producers planted 1.5 million acres remains to be confirmed. We=re close.

The fact that marginal stands exist in many fields puts additional pressure on weed control programs, increasing the importance of residual/layby herbicides. Residual herbicides will likely be even more critical in Roundup Ready cotton to prevent late season weed competition.

County agents in extreme southwest Georgia reported significant tobacco budworm activity beginning on June 22. Scouts have observed high egg numbers and small worms on non-Bt cotton. This may be an indication that the expected July 4th moth flight will be earlier than normal.

Sidedress Fertilizer Questions and Concerns. (Harris) Most of our crop is squaring right now and sidedressing is in full swing. A lot of cotton currently looks yellow which is possibly due to the lack of water or insufficient preplant nitrogen. Remember for next year, we recommend that 25 to 33 percent of the total N rate be applied at planting.

Some dryland acreage remains drought-stressed or at least on the edge of moisture stress. In these situations growers may want to be conservative with sidedress N rates. This is okay as long as additional N needs can be applied by foliar N if the weather improves. Growers with smaller acreage could cut back initially and then sidedress again if the rainfall situation improves. Irrigated land should be fertilized for target yield goals.

Dry conditions also bring questions concerning volatilization losses of N materials. These concerns are probably exaggerated and sometimes unwarranted. However, broadcast surface applications of granular urea are subject to rapid volatilization, especially in conservation-tillage. For other N sources including liquid N, volatilization losses are greatest if there is just enough soil moisture or a light shower (less than 0.25 inch) soon after application. Under totally dry conditions or with rain or irrigation in excess of 0.5 inch, losses should be minimal.

Concerns are therefore greater in dryland. Plowing in sidedress N may actually do more harm than good due to pruning and losing soil moisture. You can also slightly increase the sidedress N rate to compensate for loss, which may be better than pruning roots and losing soil moisture.

During the past 2 years, there have been isolated cases of volatilization burn when using

28-0-0-5 (S). This is thought to be from substituting ammonium bisulfite for ammonium thiosulfate as the S source. Ammonium bisulfite is apparently more volatile under hot (95+), dry conditions and will Ableach out@ lower leaves (mimicing contact herbicide injury) . These leaves can eventually burn up entirely and fall off the plant. In the reported cases, foliar injury has been temporary and yields were essentially unaffected.

Remember not to push late cotton (planted after June 1) with excessive N rates. Sidedress timing is also more important with late cotton to maximize nutrition during the shorter season.

Based on last year=s on-farm and experiment trials, ultra narrow row cotton can be fertilized similarly to wide row cotton. Research plots with reduced N rates in Tifton last year and Moultrie this year show obvious N deficiency. The need for split applications (sidedressing) vs. applying all fertilizer at planting is still being determined.

Since boron (B) applications need to be made sometime between first square and first bloom, B can be included with sidedress N. Complete sidedress materials such as 14-4-14 contain B and liquid micronutrient packages which include B can be added to N solutions. Foliar B materials include wettable powders and liquids. Some suppliers are recommending liquid B and N-B formulations at reduced rates compared to Solubor. The claim is that these specialty products are at least 3 times more efficient than Solubor in supplying B to the plant (which would be necessary since they usually cost about 3 times as much per pound of B as Solubor). However, given the cost of these alternatives and the lack of independent data to support these claims, it seems prudent to stay with standard B sources. The recommended rate of 0.5 lb B/A still applies for all B fertilizer sources.

Sidedress potassium (K) and foliar K sprays are encouraged on deep sandy soils and any fields with high yield potential. A study was conducted last year to evaluate sidedress K and foliar K sprays on Tifton-type soils under high yield conditions. Based on this first year data, split K rates (2 at planting and 2 at sidedress) may not provide enough K Aup front.@ Perhaps 3/4 at planting and 1/4 at sidedress would be more efficient. In addition, 3 applications of 10 lb/A of potassium nitrate (starting at first bloom and spaced 10 days apart) was as good as a sidedress application. In fact, highest yields were obtained with all the recommended K at planting followed by foliar K. The study is being repeated this year.

One Last Chance for Nematode Control in Problem Fields. (Davis) There may be one last opportunity to minimize losses in fields severely infested with nematodes. Rhône-Poulenc has amended the Temik label to allow a post-plant Asidedress@ application to cotton to supplement the traditional in-furrow treatments. Research on sidedress Temik is limited, but the current recommendation is to apply 5 to 7 lb/A of Temik along side the rows with light incorporation at the pinhead square stage. It seems probable that applications considerably later than pinhead square would be significantly less beneficial, so many fields are beyond the appropriate stage for treatment. The treatment is expensive and thus should be used in fields with high levels of damaging nematodes.

Results in southeastern states have been inconsistent. Many of the fields in which a yield increase was not observed with sidedress applications benefitted from at-plant but not follow-up treatments. The idea behind sidedress applications is to supplement at-planting control measures and further reduce early-season nematode populations to allow cotton to develop the largest, healthiest root system possible. As plants mature, good root health minimizes plant stress and leads to increased yield. Root health will only be increased by a Temik sidedress if plants are subject to significant nematode pressure following the at-plant nematicide application. We do not have threshold levels to provide guidance for sidedress applications, but fields which have suffered significant damage despite at-plant nematicide applications are likely candidates.

Temik, like all nematicides, is degraded to the point of no longer being toxic to nematodes within a few weeks of application. As a result, repeat application is necessary to kill surviving nematodes or those produced after the initial nematicide application. There is an ongoing debate about the best time to apply Temik sidedress because of the scarcity of research. One argument is that an application 2 or 3 weeks after planting is best because it provides a nearly continuous window during which Temik is at toxic levels in the soil. Another argument is that an application near pinhead square is best because it provides toxic levels of Temik just as nematode levels are starting to recover from the at-plant nematicide application. Hopefully, additional research and field experience will improve the consistency of results.

Rhône-Poulenc representatives are trying to increase awareness of, and interest in, sidedress treatments with Temik. They have application equipment and are working with farmers who wish to try it. If it is too late for this season, make notes and maps of nematode trouble spots in fields and consider sidedress applications next year.

Herbicide Options in Roundup Ready Cotton. (Culpepper, Brown) We estimate that over half of the 1999 Georgia cotton acreage is planted in Roundup Ready cotton. Roundup can be applied over-the-top of Roundup Ready cotton until the 5th true leaf reaches the size of a quarter. Thereafter, Roundup should be applied with precision post-directed equipment taking care to minimize contact with the cotton foliage. Roundup post-directed would most likely be more effective in controlling large grasses, bermudagrass, and some perennial weed species compared to other herbicide alternatives. Alternatives to applying Roundup post-directed include the following: fluometuron (Cotoran, Meturon), cyanazine (Bladex, Cy-Pro), prometryn (Caparol, Cotton-Pro), Cobra, Goal, and MSMA.

These alternatives, particularly the traditional directed combination of Bladex plus MSMA, may offer several advantages which include the following:

1) Traditional post-directed options offer a different spectrum of weed control compared to Roundup (including morningglory, dayflower, others).

2) Traditional post-directed options offer rotation of herbicide chemistry (reduction in the potential of weed shifts).

3) Most traditional post-directed options offer residual weed control.

4) Over the past several years there have been a few instances of unexplained fruit loss in Roundup Ready cotton; some have questioned the involvement of Roundup in these unexplained cases. Currently, extensive investigations are being conducted across the U. S. Cotton Belt on this issue. Concerns about this infrequent problem are another (though admittedly small) reason to consider traditional post-directed treatments on Roundup Ready cotton.

When spraying with Roundup in Roundup Ready cotton, growers may want to consider leaving a small untreated area for comparison.

Harvade-5F Labeled for Post-Directed Application to Cotton. (Culpepper) Harvade-5F may be applied as a precision post-directed treatment in cotton at least 10 inches tall. Target weeds include sicklepod, morningglory, and pigweeds. General recommendations include a combination of Harvade-5F at 6 oz/A plus MSMA at 2 lb AI/A plus 1 pt/A crop oil concentrate as a broadcast spray. At 6 oz/A broadcast, Harvade-5F costs around $4/A, which makes it an economical treatment. Other potential tankmix partners with Harvade-5F include Bladex, Caparol, Diuron, Cobra, and Roundup Ultra (Roundup Ready cotton only). Harvade-5F applications should not exceed a total of 14 fluid oz/A per year for post-directed and defoliation treatments. Limited research and weed control efficacy data are available and thus we suggest growers apply Harvade-5F to a limited number of acres until we gain more experience.

Mid-Season Tropic Croton Control in Conventional Cotton. (Culpepper) Tropic croton is becoming more troublesome in many of our cotton producing areas. Two experiments are underway to compare mid-season post-directed herbicide options for control of tropic croton Table 1). At 7 days after treatment, similar control was noted for combinations containing

Cy-Pro, Cobra, or Caparol. Generally, greater control was noted with all herbicide systems in Turner County because of the smaller size of croton and better coverage at the time of appli-cation, thus emphasizing the importance of a timely treatment.


Table 1. Percent tropic croton control by mid-season post-directed herbicides.


Tropic Croton Control

Post-directed Herbicides*

Turner County**

Dodge County**

MSMA + Induce



Cy-Pro + MSMA + Induce



Caparol + MSMA + Induce



Meturon + MSMA + Induce



Cobra + MSMA + Induce



Direx + MSMA + Induce



Harvade + MSMA + Induce



*Herbicides applied broadcast at the following rates: MSMA, 2 lb AI/A;

Cy-Pro, 2.0 pt/A; Caporal, 1.33 pt/A; Meturon, 2.0 pt/A; Cobra, 9.6 oz/A;

Direx, 0.8 pt/A; Harvade, 6.0 oz/A; and Induce at 0.25% V/V. Cy-Pro is

equivalent to Bladex, Meturon to Cotoran.

**Tropic croton was 3 to 6 inches in Turner County and 6 to 12 inches in Dodge County at the time of application.

PGRs. (Brown) Rains have typically been in the form of thunderstorms and thus rainfall amounts have varied widely. Subsoil moisture is limited and it will take frequent rains to sustain growth. Current vigorous growth in non-irrigated cotton does not necessarily call for aggressive use of PGRs (Pix, Mepex, etc.). Conservatism is still warranted in these fields, which means if favorable moisture continues, a single application of 6 to 8 oz/A of mepiquat chloride (MQ) may be useful. Follow-up applications should be made only with continued rain and rapid growth.

Generally, irrigated cotton is in good to excellent condition. Many fields are receiving 8 to 12 oz/A Pix prior to or at first bloom and additional treatments will follow.

Last year the new product MepPlus, which contains mepiquat chloride and a bacteria (Bacillus cereus), captured a significant portion of the PGR market. The same product is being marketed in 1999 under the name Pix Plus. It sells for a premium over Pix and other MQ products. To date, our research has failed to show a yield advantage of the new product versus traditional MQ.

Several commercial formulations of MQ are available. The following chart includes these formulations and provides a rate comparison with Pix which contains 4.2% active ingredient. Except where noted, measurements are fluid oz.





Active Ingredient, %

Formulation rate equivalent to traditional Pix

at 1 oz/A

at 8 oz/A

Pix (0.35 lb/gal)

4.2 %

1 oz

8 oz

Pix Concentrate

(2.0 lb/gal)

22.5 %

0.175 oz

1.4 oz

Pix DF

(in 2 oz packets)

35 %

0.125 oz (dry)

1 oz (dry)

Pix Plus (0.35 lb/gal)

4.2 % (plus Bc)

1 oz

8 oz

Mepex (0.35 lb/gal)

4.2 %

1 oz

8 oz

Mepichlor Liquid (0.35 lb/gal)

4.2 %

1 oz

8 oz

Topit (0.35 lb/gal)

4.2 %

1 oz

8 oz


Deep South Weed Tour, June 29-July 1 (contact SM Brown)

8:00 a.m. (CST) Wednesday, June 30 @ Headland, AL

10:00 a.m. (EST) Thursday, July 1 @ Plains, GA, Southwest Branch Station

1:00 p.m. (EST) Thursday, July 1 @ Tifton, GA, Ponder Farm

Southern Conservation Tillage Conference, Tifton, July 6-8 (contact John Baldwin)

CSRA Conservation Tillage Field Day, Waynesboro, July 15 (contact Richard McDaniel)

SunBelt Ag Expo Field Day, Moultrie, July 20 (contact Mike Bader)

Milan No-Till Field Day, July 22 in Milan, TN

The web address for the UGA Cotton Page is

Prepared by:

Steve M. Brown, Extension Agronomist-Cotton
A. Stanley Culpepper, Extension Agronomist-Weeds
Glen H. Harris, Extension Agronomist-Soils & Fertilizer
Richard F. Davis, Extension Nematologist