ISSUE 1 May 7, 1998
MICRO RATE FOR SUGARBEET
The EPA has approved the supplemental label that makes legal the micro rate of Betanex or Betamix in combination with methylated seed oil in North Dakota and Minnesota. AgrEvo should be given credit and thanks for preparing and submitting the supplemental label. Also, the EPA deserves credit for reviewing and approving the label in a timely manner.
Some of the provisions on the supplemental label and additional information follow.
1. Betanex or Betamix rate must not exceed 0.5 pt/A when used in combination with a methylated seed oil adjuvant. Higher herbicide rates plus oil adjuvants may cause excessive sugarbeet injury especially to small sugarbeet plants. Betanex or Betamix at 0.5 pt/A may be mixed with UpBeet and/or Stinger and methylated seed oil. The rates of UpBeet, Stinger and oil are not specified on the supplemental label and the label does not specify the addition of a herbicide for grass control.
Research in North Dakota and Minnesota supports the following rates for the micro rate system. All rates are given in product amounts per acre. Betanex or Betamix at 0.5 pt/A + UpBeet at 1/8 oz/A + Stinger at 1.3 fl oz/A + methylated seed oil adjuvant at 1.5% v/v. The 1.5% v/v means 1.5 gallons of adjuvant per 100 gallons of spray solution. The spray volume per acre affects the total amount of oil adjuvant applied per acre when oil is added at 1.5% v/v. The minimum amount of oil applied per acre should be 1.0 pt/A and the maximum should be 2.0 pt/A. Too little oil can reduce weed control. Too much oil will not be harmful but more than 2.0 pt/A is not needed. Methylated seed oil adjuvants were equal or superior to other tested adjuvant types for weed control and gave similar or less sugarbeet injury. However, only a few examples of adjuvant types were tested. Many adjuvant brands have not been tested with the micro rate.Research has demonstrated that a reduced rate of a grass herbicide can be added to the micro rate for improved grass control. Suggested rates of the grass herbicides are:
Select at 2 fl oz
Prism at 4 fl oz
Poast at 5.5 fl oz
Assure II at 4 fl oz
Valent has obtained a supplemental label for Select at 2 to 3 fl oz/A plus the micro rate as of April 30, 1998.
2. Micro rate treatments should be applied a minimum of three times. The grass herbicides at the rates given above should be included three times for best grass control. Betanex should be used if pigweed are present. Betamix should be used if pigweed are not present.
3. Micro rates should be broadcast applied starting when weeds are only a few days past emergence. The supplemental label specifies a 5-day interval between treatments. Aerial and ground application are listed on the supplemental label. Precise application of herbicides in a band is more difficult than precise broadcast application. A larger percentage of spray droplets are lost from the target area with a band sprayer than with a broadcast sprayer. The micro rate must be applied precisely and accurately since the rate is at a minimum and all of the spray must reach the target.
Weed control with sugarbeet herbicides is best when weeds are actively growing in a soil with adequate moisture. Weed control from both micro and regular rates will be reduced if weeds go into drought stress. Spraying small weeds will help reduce the effect of drought since weeds that have been emerged only a few days will be less likely to be drought stressed than larger weeds. Proper timing of the micro rates is very important in obtaining good weed control.
4. The supplemental label obtained by AgrEvo has made the micro rates plus oil adjuvant legal. However, the sugarbeet grower who uses the micro rates must assume all risks for lack of weed control, sugarbeet injury or other problems. AgrEvo and the companies who make the other herbicides can not be expected to warranty rates of herbicides that are 66 to 75% lower than the normal labeled rates. Also, dealers and distributors of herbicides should not be expected to service complaints on micro rates.
5. Sprayer nozzle and screen plugging has been a problem with micro rates. The rates are so low that the herbicides apparently do not stay in suspension in the water and a precipitate forms in the spray solution. This precipitate can plug screens and nozzles. The precipitation problem was studied using a small roller pump and a single 8002 nozzle with a 100 mesh screen at the nozzle. Six quarts of spray solution was prepared and allowed to set in a bucket for six hours after mixing. The precipitate was then stirred with a spatula to loosen the precipitate that had settled to the bottom of the bucket and the roller pump was used to agitate the solution for 1 to 2 minutes. About 4 quarts of the solution was sprayed through the screen and nozzle and the amount of precipitate that collected on the screen was evaluated. The discussion that follows is based on the evaluations of screen plugging, sugarbeet grower observations and earlier laboratory research where small amounts of spray solution were centrifuged in test tubes. Please note that the single nozzle test system and laboratory work do not duplicate what may happen in a commercial field sprayer.Time Between Mixing and Spraying.
The research with micro rates was done with 8001 nozzles, 100 mesh screens and 8.5 gpa. The screens and nozzles used in research did not plug but we mix and spray in a few minutes. The precipitate forms over time and that is why the spray solution was allowed to set for six hours in the test system in order to maximize the precipitate.
To minimize precipitate, spray out the load as soon as possible after mixing. Spray until the tank is dry. Do not let left over spray set in the sprayer. Flush out the tank and lines as needed to prevent a build up of precipitate. Clean screens regularly. Acetone was found to be very effective at dissolving precipitate from screens and the buckets used in the test system.Warm Water.
Less precipitate formed in warm water than in cold water. Several growers reported more nozzle plugging when they mixed into cold water just pumped from a well and less plugging when they allowed the water to warm before mixing.
UpBeet has a solubility of 100 ppm at pH 7 and a solubility of 11,000 ppm at pH 9. Raising the pH of the water will help dissolve the UpBeet so raising the pH of the water used for slurrying UpBeet will be beneficial. Also, less precipitate collected on the 100 mesh screen of the test system when pH was increased. The pH was increased by adding household ammonia (2% concentration) at 1 gallon per 100 gallons of water or 1.3 fl oz per 1 gallon of water. Do not add too much ammonia and raise the pH too high. The target pH after adding the herbicides should be about pH 9.0 to 9.5. Raising the pH too high can cause insoluble salt formation and even more problems.Table 1. Precipitate collected in the single nozzle test system with micro rates alone and micro rate plus household ammonia at 1 gal per 100 gal of water.
100 mesh screen
100% of screen thickly covered
5% of screen thinly covered
Please notice that the tap water started at pH 8.4 but the herbicides reduced the pH to 6.5. The water did not have enough buffering capacity to keep the pH high. The ammonia was needed even though the water pH was high.
A new adjuvant from Agsco, Quad 7, increases the pH of the spray solution and it also reduced the amount of precipitate collected on the 100 mesh screen as compared to no additive. Weed control from Quad 7 plus the micro rate only has been evaluated in one experiment. Weed control with Quad 7 in that experiment was similar to weed control with methylated seed oil but more research is needed with Quad 7.Grass Herbicides.
The use of grass herbicides with the micro rate reduced the amount of precipitate some of the time in testing. The results in the laboratory were different than the results with the single nozzle test system. Also, the results with the test system were inconsistent, sometimes no benefit from grass herbicides was observed.
In the laboratory, micro rates plus Poast or Prism gave the least precipitate, Select was in the middle and Assure II gave the most precipitate but all combinations that included a grass herbicide has less precipitate than solutions without a grass herbicide. With the single nozzle test system, the grass herbicides often, but not always, reduced the precipitate on the 100 mesh screen. Precipitate on the screen often was less with Assure II than with the other grass herbicides.
Increasing the pH of the water with ammonia was more effective in reducing precipitate than the grass herbicides. Ammonia plus grass herbicides plus micro rate sometimes resulted in more precipitate on the 100 mesh screen than ammonia plus the micro rate or the gras herbicide plus the micro rate. Assure II plus ammonia gave less precipitate than the other grass herbicides plus ammonia plus the micro rate.
Increasing the pH of the water with ammonia was more effective in reducing precipitate than the grass herbicides. Ammonia plus grass herbicides plus micro rate sometimes resulted in more precipitate on the 100 mesh screen than ammonia plus the micro rate or the grass herbicide plus the micro rate. Assure II plus ammonia gave less precipitate than the other grass herbicides plus ammonia plus the micro rate.
Volumes of 4, 8 and 12 gpa were compared for precipitate using the single nozzle test system and the micro rate with no ammonia or grass herbicide.
Table 2. Micro rate mixed as if applied at three spray volumes and then sprayed through a single 8002 nozzle with a 100 mesh screen.
|Solution||Volume||Precipitate on 100
|screen covered thickly|
|screen covered thickly|
These results suggest that precipitate is less at low water volumes. This may partially explain why aerial applicators do not have plugging problems. Use of low spray volumes with a ground sprayer would require the use of small nozzles and fine mesh screens which will plug easier than larger nozzles and screens. Also, all the weed control research with micro rates has been done at 8.5 gpa spray volume so no data is available on the influence of very low volumes on weed control from a ground sprayer.
In 1997, one experiment was conducted where 40 psi spray pressure and 8.5 gpa spray volume through 8001 flat fan nozzles was compared to 100 psi and 11.7 gpa through a D1.5 disc - #23 core nozzle. In this experiment, the micro rate gave less control of redroot pigweed and green foxtail when applied at 100 psi than at 40 psi. Increasing spray pressure produces smaller spray droplets which increases the risk of damaging drift. The micro rate will injure most other crops grown around sugarbeet so drift control techniques such as low spray pressure should be used with micro rates.
In the test system and in the laboratory, mixing order had only a small effect on precipitate. Mark Haugland with AgrEvo has observed situations where less precipitate was formed when the Betanex/Betamix was put in the tank first. DuPont generally recommends that the sulfonylurea herbicides like UpBeet be placed in the tank first. In any case, the UpBeet should be slurried before it is added to the tank. Use ammonia in the slurry water or use warm water to speed the process. Never allow the granules of UpBeet to become coated with Betanex, Betamix or oil since that can greatly reduce the solubility of the granule.
At this time we believe that either UpBeet first or Betanex/Betamix first will work. The Stinger grass herbicide and oil can come later. The ammonia can be added first but do not put all the ammonia for the full tank in a partial tank of water. Raising the pH too high can cause problems. If you fill the tank 1/3 full and then add herbicides, only use 1/3 of the ammonia in the 1/3 tank of water. Add the rest of the ammonia after the tank is nearly full.
Less precipitate was observed with gentle agitation than with severe agitation using the single nozzle test system. This suggests that agitation should be only vigorous enough to keep the solution mixed.
The oil adjuvants Moract, Sun-It II, MethOil, Scoil and Dash were used in combination with the micro rate in the laboratory. All adjuvant combinations produced similar amounts of precipitate. The micro rate plus Destiny oil adjuvant was compared to the micro rate plus MethOil in the single nozzle test system. The amount of precipitate on the 100 mesh screen was similar with the two adjuvants.
A comparability agent, Combine, reduced the pH of the micro rate spray solution to pH 2.9 and did not reduce the amount of precipitate collected on the 100 mesh screen in the test system as compared to the micro rate without Combine. Quad 7 reduced the amount of precipitate on the 100 mesh screen probably because Quad 7 increased the pH of the micro rate spray solution.
If nozzle and screen plugging persist, clean the sprayer and use normal herbicide rates.
6. The micro rate system is not for everyone. Management requirements are greater for micro rates than for conventional rates. Timing is critical. Broadcasting the micro rate will have a similar cost compared to banding conventional rates. The advantages of the micro rate include: a) the micro rate can be applied throughout the day, b) broadcasting is faster, easier and more accurate than band spraying, c) the micro rate makes aerial application affordable and d) the oil adjuvant in the micro rate reduces the antagonism between the grass herbicides and the other herbicides so grass herbicides mixed with the micro rate will be more effective than grass herbicides mixed with conventional rates without the soil adjuvant.
NDSU/U of MN Extension
Sugarbeet Weed Specialist
John L. Luecke
NDSU/U of MN Extension Sugarbeet
Weed Research Specialist