From Benjamin L. Legendre, Ph.D., Sugarcane Specialist/Professor
LSU Ag Center, Sugar Research Station, St. Gabriel, LA 70776
Email Address: blegendre@agctr.lsu.edu
Website: www.lsuagcenter.com
In 2008, the following glyphosate formulations will be marketed for use as chemical ripeners in stubble sugarcane: Touchdown Total®, Roundup WeatherMAX®, and Roundup PowerMAX®; there may also be a limited supply of Polado L®. NOTE: THESE PRODUCTS ARE NOT LABELED FOR USE IN THE PLANT-CANE CROP. When used according to the label and the following recommendations, these products should increase recoverable sugar per ton of cane and yield of sugar per acre, although results may vary, especially under conditions favoring good natural ripening. These products will reduce vegetative growth and may reduce cane yields. However, cane yield losses are generally offset by the increase in recoverable sugar, resulting in equal or greater sugar yields when harvested during the suggested treatment-to-harvest interval.
RATES: Application rates of ripeners vary due to differences in glyphosate concentrations. Polado L was the standard ripener in Louisiana sugarcane for many years; however it is no longer being manufactured. With Polado L, best results were obtained when aerially applied at 4 to 10 oz. per acre in 5 or more gallons of water per acre. Equivalent rates are recommended for glyphosate ripeners currently being sold in Louisiana (Table 1). Label recommendations for all glyphosate-based ripeners are generally similar to the Polado L label. However, Polado L requires the addition of a surfactant; whereas, the newer formulations already contain surfactants, and no additional surfactants are needed (additional surfactants may actually hinder ripening), although drift-control agents may be used to avoid injury to nearby sensitive crops. Rainfall occurring in less than 6 hours after application may reduce efficacy.
Table 1. Equivalent rates for Polado L®, Touchdown Total®, Roundup WeatherMAX®, and Roundup PowerMAX®.
|
Glyphosate Formulation |
|
Ounces (by weight) of glyphosate acid per acre |
|
|
2 |
2.5 |
3 |
3.5 |
4 |
4.5 |
5 |
|
ae1 |
Ounces of product per acre |
|
Polado L® |
4 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
Touchdown Total® |
4.17 |
3.8 |
4.8 |
5.7 |
6.7 |
7.7 |
8.6 |
9.6 |
|
Roundup WeatherMAX® |
4.5 |
3.6 |
4.4 |
5.3 |
6.2 |
7.1 |
8 |
8.9 |
|
Roundup PowerMAX® |
4.5 |
3.6 |
4.4 |
5.3 |
6.2 |
7.1 |
8 |
8.9 |
1 Abbreviations: ae, acid equivalent (pounds of glyphosate acid per gallon).
RATES RECOMMENDED FOR LOUISIANA VARIETIES: As sugarcane varieties respond differently to glyphosate ripener applications, different rates are recommended for the different varieties grown in Louisiana (Table 2). Higher glyphosate rates should generally be used only for the last stubble crop; use lower rates on stubble cane you plan to keep for another year. There are four additional varieties recommended for commercial planting in 2008: L 99-226, L 99-233, HoCP 00-950, and L01-283. Preliminary results indicate that L 99-226 responds well to the 6 oz Polado L equivalent rate; whereas, L 99-233 does not. There is no information on the response of HoCP 00-950 or L01-283 to ripener application. Further testing is needed to determine appropriate application. Until this has been determined, rates recommended for the newer varieties will be similar to that of LCP 85-384.
Table 2. Rates of glyphosate-based ripener suggested for use in Louisiana sugarcane varieties.1:
|
Glyphosate Formulation |
|
LCP
85-384 |
HoCP
85-845 |
HoCP
91-555 |
HoCP
96-540 |
L
97-128 |
Ho
95-988 |
|
ae1 |
Ounces of product per acre2 |
|
Polado L® |
4 |
4-8 |
8-10 |
6-10 |
4-8 |
4-8 |
4-8 |
|
Touchdown Total® |
4.17 |
3.8-7.7 |
7.7-9.6 |
5.7-9.6 |
3.8-7.7 |
3.8-7.7 |
3.8-7.7 |
|
Roundup WeatherMAX® |
4.5 |
3.6-7.1 |
7.1-8.9 |
5.3-8.9 |
3.6-7.1 |
3.6-7.1 |
3.6-7.1 |
|
Roundup PowerMAX® |
4.5 |
3.6-7.1 |
7.1-8.9 |
5.3-8.9 |
3.6-7.1 |
3.6-7.1 |
3.6-7.1 |
1 ae; acid equivalent (pounds of glyphosate acid per gallon).
2 DO NOT round off rates from the decimal equivalent rates shown in the table.
TREATMENT TO HARVEST INTERVALS: Recommended treatment-to-harvest intervals for the new glyphosate formulations have been reduced due to the highly effective surfactants included in these formulations which enhance sugarcane’s response to glyphosate. Research has shown that repeated use of glyphosate ripeners on the same fields of LCP 85-384 at the Polado L equivalent rate of 6-oz or more may reduce the yield of cane per acre in following stubble crops. Even so, sugar yields for the entire crop cycle may still be slightly higher due to increases in recoverable sugar if harvested at the proper treatment-to-harvest interval.
APPLICATION SCHEDULE: With sugarcane harvest commencing in mid- to late-September, sugarcane will still be actively growing at rates of nearly one inch per day in mid- to late-August when a chemical ripener would be applied. Although maximum response from the use of a chemical ripener generally occurs at 5 to 6 weeks after treatment, it is recommended that the first applications be made no earlier than 4 weeks (28 days) before scheduled harvest to minimize the loss of cane tonnage. This will also allow for delays in scheduled factory openings without greatly impacting the current and subsequent sugarcane crops.
The following application schedule should be considered to maximize the expected response to these ripeners: For early harvest, September 15 to October 15, consider a treatment-to-harvest interval of 21 to 35 days; for harvesting from October 15 to November 15, consider a treatment-to-harvest interval of 28 to 42 days; and for harvesting from November 15 to December 1, consider a treatment-to-harvest interval of 35 to 49 days. Treatment to harvest intervals greater than 49 days is not recommended, especially if additional stubble crops are planned from that field. Sugarcane harvested after December 1 should not need to be treated with a ripener, as sugarcane will have matured naturally and no increase in recoverable sugar should be expected.
REGROWTH: Research has shown that reductions in spring shoot and harvestable stalk populations in subsequent stubble crops can occur if the rates of glyphosate exceed the 6-ounce Polado L equivalent rate and/or treated fields are harvested beyond the recommended treatment-to-harvest intervals, especially for LCP 85-384. Ultimately, this can result in a compounding effect on total cane and sugar yields for the crop cycle when both the reductions associated with the previous application(s) and the reductions associated with the current application are considered. Research has also shown that early harvesting, i.e. mid-September to early-October, has a greater negative impact on the subsequent stubble crop than application of glyphosate ripener, regardless of formulation used. Therefore, early-harvested sugarcane should be from fields that are scheduled to be destroyed and replanted.
Louisiana’s sugarcane varieties endure many stresses including: early harvesting, mulch (harvest residue), common brown rust and other diseases, herbicide injury, drought, and flooding. When combined with the additional stress of glyphosate ripener application(s), it may be too much for a weakened variety to overcome and disappointing yields may result. For example, leaving the mulch on ripener-treated LCP 85-384, L 97-128, Ho 95-988, and HoCP 96-540, reduced sugar yields 30% the following year. Therefore, it is recommended that the mulch be removed, especially from ripener treated sugarcane.
POINTS TO CONSIDER WHEN APPLYING A GLYPHOSATE-BASED RIPENER:
1.Follow product labels and use rate recommendations based on research.
2.Do not apply to seed-cane or plant-cane.
3.Apply the higher recommended rate for each variety only to the last stubble crop.
4.Do not exceed the maximum recommended treatment-to-harvest intervals (49 days).
5.Do not apply glyphosate ripeners to sugarcane after November 1st.
6.Remove mulch (harvest residue) as early after harvest as possible.
7.For best results, apply glyphosate to erect cane (If recently lodged, allow sufficient time, i.e. 7-10 days, for the cane to erect itself).
8.Response to glyphosate is based on sugar levels at the time of ripener application; therefore, it is recommended that a hand refractometer be used to test for Brix as an indicator of the cane’s sucrose content prior to application. Fields with the highest Brix should be treated first, and the fields with the highest Brix at the recommended treatment-to-harvest interval should be harvested first (Please refer to Brixing to Improve Sugarcane Quality, online Publication No. 2888: http://www.lsuagcenter.com/en/crops_livestock/crops/sugarcane/
publications/Brixing+to+Improve+Sugarcane+Quality.htm)
9.Use a drift control agent to avoid affecting nearby fields.
The use of chemical ripeners is an excellent management tool to increase recoverable sugar levels in cane. Remember to use these products wisely (DON’T abuse) for best results.
*Research data included in these recommendations were made available by Dr. Benjamin L. Legendre, LSU Ag Center, Sugar Research Station, St. Gabriel, LA and Dr. Edward Richard, Jr., Dr. Caleb Dalley, and Dr. Ryan Viator, USDA-ARS, SRRC, Sugarcane Research Laboratory, Houma, LA.