UGA Cotton Newsletter

May 31, 2000

Crop Situation 1 Managing a Late Crop
To Water or Not to Water
Fertilizing During a Drought
Rhizoctonia Seedling Blight Update
Dry Weather Can Reduce Nematicide Efficacy
Dual Magnum and Its Use in Georgia Cotton
Staple Plus Herbicide For Use In Roundup Ready Cotton
Tobacco Budworm and Plant Bug Management in Dryland Cotton

Crop Situation. (Brown) Just over 80 percent of our anticipated 1.5 million acres are planted as of May 30. No doubt, the lack of rainfall has slowed or even halted planting. Will we reach (and keep) the predicted acreage? Aquifer, river, and well levels are reported to be at 100-year lows. Parching drought continues to have a profound effect on stand establishment, weed management, and thrips control.

The prospect of "dusting in" additional or replant acres at this stage seems quite risky. As dry as most areas are, anything short of a good, soaking rain (maybe less than 1 inch) may germinate the seed but be insufficient for stand establishment. Both growers and crop insurers are forced to do some sober calculations to evaluate the financial possibilities of planting versus not planting.

Managing a Late Crop. (Brown) Considerable acreage is or will be struggling to a late start. Obviously, timely water is critical for the success of a crop compressed in time. Early varieties are strongly preferred now and care should be taken to avoid thick stands. Attention should also be given to proper pest management to avoid fruiting delays caused by insect damage, herbicide injury, or weed competition. To minimize the risk of excess vegetative growth, N rates should be on the conservative side.

To Water or Not to Water? (Brown) Traditional thinking is that once a stand is established, seedling cotton requires little water and that irrigation is generally not needed on young cotton. We normally don't water pre-bloom cotton unless wilting occurs.

Unquestionably, present conditions are extreme. Growers must consider not only the current water needs of a young crop but also the overall water content of the soil profile as well as the supply of irrigation water. In most areas falling too far behind may prevent recovery of soil moisture. Limited moisture stress may encourage root development and fruiting. We believe we are unable to make a good crop solely with irrigation.

These factors and common sense suggest that where possible, occasional watering should be employed, perhaps every 10 to14 days. Ideally, irrigation should thoroughly soak the ground rather than lightly wet it. Because of the differences in plant water requirements, early season irrigation should not approach the volume and frequency of watering during bloom. We hope there is relief soon.

Fertilizing During A Drought. (Harris) Unfortunately, questions on how to fertilize drought-stressed cotton have been all too common the last three growing seasons. In fact, it has gotten to the point that some farmers are saying, "I'm not putting any fertilizer on my dryland cotton until after I get a stand. And I might just wait until sidedress time." This is not good!

# 1 - Drought-stressed cotton has a hard time obtaining nutrients from the soil because water is limited. Poor soil fertility compounds the problem and adds another limitation.

#2 - Good soil fertility actually improves water use efficiency. Better root systems make better use of a limited water supply.

#3 - We (UGA) suggest applying 1/4 to 1/3 of the recommended nitrogen rate PREPLANT! This usually translates to about 20 to 30 lb N/A depending on yield goal. Waiting until after stand establishment or until sidedressing can limit yields. Nitrogen fertilization also improves the uptake of other fertilizer and soil nutrients.

#4 - We (UGA) recommend applying most, if not all, of the recommended potassium fertilizer at planting. Recent research shows that holding back half of the recommended K rate until sidedressing can also limit yields.

So where do we go from here?

If you have not fertilized and just now have a stand, apply the 20 to 30 lb N/A and most or all of the recommended K. You can go with a more conservative K rate if you plan to foliar feed K during the peak bloom period (first 4 weeks of bloom) when you decide you have some yield potential. Plan to come back with 40 to 60 lb N/A sidedress between first square and first bloom. As with K, you can go on the more conservative side with sidedress N if you plan to foliar feed N during peak bloom.

If you did not fertilize preplant and if the crop is approaching sidedress, apply N and K as early as you can in the sidedress window (first square to first bloom). These recommendations pertain to dryland cotton. Hopefully, irrigated cotton has been fertilized more aggressively. Remember that total N rates recommended by our UGA lab are based on yield goal, in which the 90 and 105 lb N/A rates correspond to 1250 and 1500 lb lint/A yield goals and assume irrigation. A recent popular press article explained that a neighboring state recommends 90 lb N/A regardless of yield goal. They also pointed out that 1250 was basically their peak yield goal, which happens to be the yield level at which we recommend 90 lb N/A. They do not have an N recommendation for 1500 lb lint/A cotton - maybe because they do not have any.

Finally, dry weather always raises questions about volatility losses of N fertilizers. These concerns are often exaggerated and mostly unwarranted. Basically, N applications during extremely dry periods simply remain on the soil surface "waiting for rain." Even with minimal rain (at least 0.25 inch), N is moved into the soil with little volatilization. Very little N is lost.

Problems occur when light showers (less than 0.25 inch) follow surface applications of N. Limited amounts of moisture initiate volatilization but fail to move the material into the soil. Granular urea is the N material most subject to losses through volatilization and losses are probably greatest following surface applications in strip-till situations with significant residue. Obviously, moisture conditions in irrigated cotton are much more favorable and afford the opportunity to water in N shortly after application.

Rhizoctonia Seedling Blight Update. (Kemerait) There have only been a few diseased cotton seedlings submitted to the diagnostic clinic in Tifton for evaluation this year. Most of the seedlings were infected with Rhizoctonia solani, a causal agent of seedling blight. The low volume of diseased samples is likely the result of warmer soil temperatures at planting time and identification of the disease in the field by the grower or county agent without the need for further assistance.

There has been some confusion as to the causal agent when a number of sequential seedlings in a row are diseased. Rhizoctonia solani, like many soilborne pathogens, may be unequally distributed in a field and cause greater disease severity in one spot than another. When one seedling is diseased, it is very common to observe that other seedlings in the near proximity will be diseased as well. This is especially true when the seeds are planted using the "hill drop" method. If one seedling in a hill-dropped group becomes diseased, it is very likely that the rest of the seedlings in the group will also. There has also been some concern that the soil clinging to diseased seedlings may indicate the presence of lesser corn stalk borer, whose web is seen attached to peanut seedlings. The soil clinging to the diseased cotton seedlings seems to be the result of the thread-like hyphae of Rhizoctonia solani and not the insect webbing.

Dry Weather Can Reduce Nematicide Efficacy. (Davis) Very dry conditions have prevailed in most cotton producing areas of the state during and after planting. The effects of drought on cotton emergence and early seedling development are obvious, but a less obvious result is the potential reduction in the effectiveness of nematicides.

Many farmers know that if conditions are too dry when Telone II is applied or immediately following application, then the gas escapes from the soil too rapidly and efficacy can be reduced significantly. Most farmers don't know that if conditions are too dry at or following Temik application, then Temik efficacy on nematodes can also be reduced. If soil conditions stay dry for 2 to 3 weeks following in-furrow application of Temik, a significant reduction in nematode control can occur. That happens because the active ingredient in Temik begins to degrade slowly as soon as it is comes in contact with the soil. If there is sufficient moisture in the soil, the chemical dissolves into the water where it can contact and kill nematodes. Under dry conditions, too little Temik contacts nematodes to provide adequate control, and by the time sufficient moisture is available much of the Temik may already be degraded. The longer Temik has been in the ground before sufficient moisture is available, the less nematode control you will get.

In fields where you would expect to see nematode damage if you didn't use a nematicide, a post-emergence, supplemental nematicide application may reduce nematode damage following a weather-related reduction in nematicide efficacy. The most effective supplemental nematicide application is to side-dress the rows with 5 to 7 pounds of Temik per acre when the cotton reaches pinhead square. Applications made more than a few weeks after pinhead square will probably not be as effective. Because of the significant expense of this treatment, it may be appropriate to target side-dress applications only to areas of fields where past experience demonstrates that nematode damage is significant (consider this a low-tech approach to precision agriculture). Side-dress applications of Temik will be most effective if they are followed by rain or irrigation.

Another option is to apply Vydate C-LV at 17 fl. oz./A to cotton around the 5 to 6 true leaf stage. Vydate is less expensive than Temik, but the potential return on investment and the likelihood of yield increases is lower. The best success with Vydate has been achieved on reniform nematodes in Mississippi when 3.5 lbs Temik is used in-furrow.

Testing of side-dress applications in southeastern states has achieved positive, though inconsistent, results. We do not have threshold levels to provide guidance for side-dress applications, but fields which have suffered significant damage in the past despite an at-plant nematicide application are likely candidates. Also, fields that were very dry following pre-plant/at-plant nematicide application may benefit from side-dress applications of Temik.

Dual Magnum and Its Use in Georgia Cotton. (Culpepper) Dual is being phased from the market place and is being replaced by Dual Magnum. Although both products are similar, Dual Magnum contains more of the active isomer of metolachlor (the active ingredient) than Dual; therefore, rates of Dual Magnum are less than those used with Dual.

Although Dual Magnum can be applied preemergence at planting in some states, it should not be used preemergence on Georgia soils. Severe plant stunting and sometimes stand loss can result from the use of Dual or Dual Magnum preemergence in Georgia.

However, Dual Magnum can be applied postemergence overtop or directed to cotton in Georgia and other states. The rate is 1.0 to 1.33 pt/acre and cotton should be 3 to 12 inches tall. The label clearly states to not use this product on sand or loamy sand soil. It also states to not apply postemergence overtop with any adjuvant or with fluid fertilizer.

The following mixtures for postemergence applications are mentioned on the Dual Magnum label: Dual Magnum + Cotoran DF can be applied overtop or directed (strongly suggests not applying overtop). Dual Magnum + MSMA, Dual Magnum + Caparol + MSMA, and Dual Magnum + Cotoran + MSMA can be postemergence-directed to 3- to 12-inch cotton in Georgia. Again, the label suggests avoiding sand or loamy sand soil.

Although mixing Roundup Ultra with Dual Magnum does not appear on the label, many questions have been asked regarding this combination. Research in North Carolina over the past several years has indicated only minor cosmetic injury. Observed injury symptoms include purple, pinhead-sized specks on the cotton foliage when applied directed or postemergence over-the-top of cotton.

Dual Magnum applied postemergence will not control existing weeds. However, residual pigweed and annual grass control by Dual Magnum when mixed with Roundup Ultra has been observed in experiments where Roundup Ultra and Roundup Ultra + Dual Magnum were compared. Although the residual control from Dual Magnum may be beneficial in some instances, it was of little benefit if timely late postemergence-directed applications (Caparol + MSMA in our experiment) were made. To reiterate, the label referenced for this article made no mention of mixing Roundup Ultra and Dual Magnum.

Results for controlling yellow nutsedge with Dual Magnum mixtures are inconsistent. In some of the North Carolina experiments, MSMA plus Dual Magnum looks better than MSMA applied alone in mid-season due to the residual control supplied by Dual Magnum (we would also assume similar results with Dual Magnum plus Roundup). However, in other tests with the same treatments, there were no differences. Do not apply Dual Magnum plus Staple overtop of cotton.

As Dual Magnum will replace Dual, Dual II Magnum will replace Dual II in the market place. Dual II and Dual II Magnum are different in that they contain a safener or antidote that is not included in Dual or Dual Magnum. The safener reduces the risk of injury to corn but does not work for cotton.

Staple Plus Herbicide For Use In Roundup Ready Cotton. (Culpepper). Both Roundup and Staple are effective in controlling a wide range of weed species often found in cotton. Staple Plus is a prepackaged mixture of Roundup and Staple. This combination herbicide package contains a water soluble powder packet (the Staple portion) and a bottled liquid (the Roundup portion). One container of this prepackaged herbicide will treat 10 acres of Roundup Ready (RR) cotton. Staple Plus may be applied postemergence or postemergence-directed to RR cotton.

Compared to weed control by Roundup alone, Staple Plus may be more effective controlling morningglories, dayflower species, and hemp sesbania. Additionally, residual weed control from Staple Plus may be noted on weeds such as pigweeds, spotted spurge, velvetleaf, and spurred anoda. Residual activity is dependent on rainfall and herbicide contact with the soil. Consult label for rotational restrictions to following crops.

Staple Plus applications should be made postemergence (over-the-top) to RR cotton from the first true leaf stage until the four leaf (node) stage of development (until the fifth true leaf reaches the size of a quarter). This product may also be applied using precision postemergence-directed or hooded sprayers to RR cotton through layby minimizing contact of spray with cotton. No more than two broadcast applications may be made from the first true leaf through the four leaf stage of development. No more than two postemergence-directed applications may be made from the fifth leaf stage through layby. All applications of this product must be at least 10 days apart and cotton must have at least two nodes of incremental growth between applications.

Although we did not note any cotton injury by Staple/Roundup mixtures in Georgia trials in 1999, Staple Plus may cause temporary leaf yellowing, bronzing, and/or leaf crinkling when applied as a postemergence application. Plant stresses from seedling diseases, insects, and other adverse conditions just prior to or soon after treatment increase the sensitivity of cotton to injury from Staple Plus. Allow cotton plants to recover from stress prior to treatment with this herbicide combination.

General Notes:

Tobacco Budworm and Plant Bug Management in Dryland Cotton. (Roberts) It has already been said, but to state the obvious: IT IS DRY. The ongoing drought will influence near term insect pest management decisions. As cotton begins to square, scouts should begin monitoring square retention and scouting for tobacco budworm. Both of these pests may potentially reduce square retention and decisions to control each or both will be difficult to make in drought stressed fields.

Cotton has the potential to compensate from early season square loss. Recent research indicates that 50 percent square removal for 2 to 3 weeks did not significantly reduce yield in irrigated experiments. Compensation occurred through greater boll retention higher on the plant and increased fruit on vegetative branches. Keep in mind that this research was conducted with ideal irrigation, underscoring the fact that late season moisture is critical for compensation.

Potentially, early fruit losses and subsequent compensation may result in a delay in maturity. Maybe more importantly is that high early fruit retention puts increased demands on the plant and may push the crop toward premature cutout. Lower retention (within reason) may even be a benefit by reducing demand on the plant and sustaining plant growth.

We still have ample time to set a crop. Tobacco budworm may potentially destroy terminals. Severe damage to cotton terminals will result in crazy cotton. On dryland fields we should consider using at least 10 percent damaged terminals as a threshold. Decision to treat dryland fields should be made on a field by field basis. A crystal ball would help here.


Scout Schools

June 3 RDC, Tifton

June 6-7 Jeff Davis County

June 8-9 Evans County

June 12 RDC, Tifton

June 12-13 Midville

Deep South Weed Tour, June 27-29, 2000

9:00 a.m. (CST) Tuesday, June 27 @ Jay, FL

8:00 a.m. (CST) Wednesday, June 28 @ Headland, AL

10:00 a.m. (EST) Thursday, June 29 @ Plains, GA

Sunbelt Expo Field Day, July 18, 2000, Moultrie, GA

CSRA Reduced Tillage Field Day, July 20, 2000, Waynesboro, GA (Contact Richard McDaniel)

Midville All Crops Field Day, August 17, 2000, Midville

Prepared by:

Steven M. Brown, Extension Agronomist-Cotton
A. Stanley Culpepper, Extension Agronomist-Weed Science
Glendon H. Harris, Jr., Extension Agronomist-Soils & Fertilizer
Richard F. Davis, Extension Nematologist
Bob Kemerait, Extension Plant Pathologist-Cotton
Phillip Roberts, Extension Entomologist-Cotton