How to Make Reduced Herbicide Rates Work

All users of herbicides want to apply the lowest herbicide rate that will control the target weeds. Or, from a different viewpoint, all users of herbicides want to apply the rate of herbicide that will provide the greatest return over the cost of the herbicide plus application. This "best" herbicide rate will be different for every combination of herbicide-environment-weed species-crop-weed growth state-crop growth stage-adjuvant-weed density-tolerance for risk by user. Sometimes, the "best" herbicide rate will be lower than the lowest rate on the herbicide label. To understand why this is true, we need to understand some of the assumptions and considerations of the companies when they write a label.

Weed Size and Crop Size. Companies must make an assumption about the normal size of weeds and crops when the herbicide will be applied. Generally, small weeds are more susceptible to herbicides than large weeds, but small crop plants also may be more susceptible. Herbicide rate reduction may be possible if the herbicide is applied to weeds that are smaller than the weed size on the herbicide label. The crop also may be smaller than the suggested crop stage at application, so knowledge of safety to the crop would be needed. So, herbicide rates can sometimes be reduced by early application but special knowledge is needed.

Environment. Companies can not write a label that anticipates all environments in which a herbicide may be used. Environment has a large influence on the efficacy of herbicides. So, herbicide rate reduction may be possible if the specific environment will favor high phytotoxicity from the herbicide but special knowledge is needed on the environment-herbicide interaction.

Adjuvants. The efficacy of some postemergence herbicides is enhanced by adjuvants such as surfactants, crop oils, methylated seed oils or fertilizer. Adjuvants vary considerably in ability to enhance herbicide efficacy even among a class of adjuvants. For example, some surfactants may double percent weed control from a herbicide while other surfactants may have little effect. The number of adjuvants presently sold is so large that testing all adjuvants with all herbicides is not possible. Companies must set label rates for herbicides by assuming that adjuvants will or will not be used and that adjuvants used will be similar to those tested with the herbicides. Herbicide rates can sometimes be reduced by using an adjuvant that is highly effective with the specific herbicide but special knowledge is needed. The herbicide-adjuvant combination must be safe on the crop as well as provide good weed control.

Method of Application. Sprayer pressure-volume-speed-nozzle type=delivery system will influence herbicide efficacy. Companies must assume an average or common application method when writing a herbicide label. Special knowledge of the best application method for a specific herbicide and situation may allow a reduction in herbicide rate.

Weed Species. Weeds may vary considerably in susceptibility to a herbicide. Companies sometimes list weed species separately on the label with different rate for different weeds. Some labels do not vary rates by weed species. Herbicide rates can often be reduced if the field is infested only with weed species that are highly susceptible to the herbicide. Special knowledge of weed response to the herbicides is needed.

Performance Complaints. Chemical companies recommend product use to obtain adequate performance across most all conditions and uses. However, product complaints are seldom avoided. Herbicide rates on labels are often set to reduce the risk of less than adequate weed control and to reduce numbers of complaints. A herbicide user who is willing to accept a higher risk of poor weed control can reduce herbicide rates below the labeled rate. This should only be done when conditions favor high efficacy from the herbicide and susceptible weeds are present.

Production Cost of the Product. Companies rarely consider the production cost of the product when they set the labeled rate of a herbicide. Companies that sell herbicides are not selling a product, they are selling a service. The companies would prefer to recommend the least amount of herbicide to control the weeds because the value of the service (the weed control) would be the same regardless of rate of herbicide. So, companies do not deliberately set rates higher than necessary but refinements in rates are possible with special knowledge about specific situation.

Are Low Rates Legal? A herbicide user can legally choose a rate lower than listed on the herbicide label. However, the company has no obligation to support herbicides when the application rate was less than labeled rates. Herbicide users should not expect a company representative to provide any comfort or assistance if weed control is less than expected from a low rate of herbicide.

American Cyanamid has received registration of Raptor (1 lb ai/gal), a postemergence soybean herbicide. The active ingredient is imazamox, an ALS-inhibitor in the imidazolinone chemical family as is Pursuit herbicide. Raptor is similar to Pursuit, except it is more active on grass and broadleaf weeds. Raptor has much shorter residual than Pursuit and allows rotation to most crops the following year after application. However, with rainfall after application, Raptor may provide a short period of residual weed control. Raptor provides equal or greater weed control than Pursuit with the addition of better common lambsquarters control. Weed species which may not be adequately controlled by Raptor applied alone are common ragweed, wild buckwheat, Venice mallow, and ALS resistant kochia. The maximum growth stage of weeds on Raptor label is larger for most weeds compared to Pursuit. All Raptor produced has been already placed by company representatives for the 1997 season.

Raptor should be applied after soybean emergence but before bloom and when weeds are at the correct growth stage (see table below and label). The 4 fl oz/A rate may be used if a soil applied grass control foundation treatment was applied. The 5 fl oz/A rate may be used as a total postemergence treatment. Raptor requires a use of an adjuvant and a nitrogen additive. Apply with either a nonionic surfactant at 1 qt/100 gallons water or petroleum oil at 2 pt/A or and methylated seed oil (MSO type) adjuvant. Add a nitrogen additive at 1 to 2 qt/A of 28%N or 2.5 lb/A of ammonium sulfate. NDSU studies have shown that MSO type (Sun-It II) adjuvants are superior to petroleum oil and nonionic surfactant adjuvants.

Raptor should be applied to weeds before they exceed a height of 5 inches.

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			Recommended ht 
Weed			   (inches)
--------------------------------------
Barnyardgrass		    2 to 5
Woolly cupgrass		    2 to 4
Foxtail species		    2 to 6
Wild proso millet*	    2 to 4
Wild oat		    2 to 4
Field sandbur*		    2 to 4
Volunteer wheat		    2 to 4
Quackgrass*		    4 to 8
Common cocklebur	    2 to 8
Kochia			    1 to 4
Common lambsquarters   	    2 to 5
Nightshade species	    2 to 5
Mustard species		    2 to 8
Pigweed species		    2 to 8
Giant ragweed		    2 to 5
Common ragweed*		    2 to 5
Annual smartweed	    2 to 5
Sunflower		    2 to 8
Velvetleaf 		    2 to 8
Venice mallow*		    1 to 4
Field bindweed (seedling)*  2 to 4
Canada thistle*		    2 to 5
Annual sowthistle*	    2 to 4
--------------------------------------
*For suppression of light or moderate 
populations at the 5 fl oz/A rate in a 
total POST program. All weeds listed 
are labeled for control when a soil-
applied foundation treatment is applied.

Tankmixing Raptor with postemergence grass herbicides may result in reduced grass control. Tankmixing broadleaf herbicides with Raptor may reduce grass control from Raptor. A tankmix of Raptor with diphenylether herbicides (Blazer, Cobra, Reflex) is recommended for improved common ragweed and waterhemp control. Raptor requires a 1 hr rainfree period. Raptor can be applied through aerial application. There is an 85 day preharvest interval between application and soybean harvest. Do not feed or graze.

Rotation Crop Restrictions
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				 Months After 
Crop			         Application
---------------------------------------------
Soybean	 			      0
Wheat	 			      3
Barley and rye	
Alfalfa, corn, dry beans, oat,
   onion, pea, potato, sunflower      4 
Sugarbeet and canola (soil pH >6.5)  18
Sugarbeet and canola (soil pH <6.5)  26
Crops not listed on label	     18
---------------------------------------------

The Herbicide Selection Guide Weed Management Computer Program

The Herbicide Selection Guide is a DOS based computer program developed for herbicide use in North Dakota and contains information specific for North Dakota agriculture. The program was developed through a cooperative effort between Whetstone Software and NDSU Extension Service to aid in herbicide selection and weed control. The Herbicide Selection Guide displays possible herbicides based on selection from one 27 crops at various growth stages and over 40 weeds species. The program simulates field conditions by allowing the user to select a crop and one or more weeds after which the program displays herbicides, herbicide pre-mix, and herbicide tank-mix options listed in order of weed control efficacy from greatest to least. The program also displays cost per acre of each treatment listing.

Herbicide performance of each product on each individual weed can be evaluated by scrolling through all labeled herbicides and herbicide combinations. As a result, the most effective and economical treatments can be selected. F keys allow the user to access information on weeds controlled, herbicide rates, carryover potential, other labeled crops, and crop growth stages, grazing restrictions, rainfall intervals after herbicide application, herbicide residues, and adjuvant selection. Word search capability allows the user to type in any word and is then forwarded to text files where the word is found. The program allows full editing to regionalize the program for other areas. For example, herbicide prices can be changed, and individual state supplemental and emergency labels can be added.

Weed-Pro is a DOS-based computer program developed by NDSU Extension Service and is a computerized version of the North Dakota Weed Control Guide. Weed-Pro is included in The Herbicide Selection Guide or is available as a separate program. Weed-Pro used alone or within The Herbicide Selection Guide provides an extensive amount of weed control and herbicide use information presented in a rapid-information-access and easy-to-use format.

Weed-Pro contains herbicide label information specific for North Dakota. A distinguishing feature of Weed-Pro are several data bases containing summaries of North Dakota State University weed control research over several years.

Telemarketers are out in full force selling high priced herbicides that contain very little active ingredient and claiming these herbicides can do unbelievable things. We need your help to shut these people down. The North Dakota Department of Agriculture has indicated that with proper documentation of phone call conversations they can take action against companies that use this approach.

For example, reports have been made of a chemical company selling a product containing 2,4-D and bromacil (Hyvar) at a total concentration of 2% ai for $90/gal + $21 freight. By my calculations, the grower is spending the equivalent of: $,961.76 for a gallon of 2,4-D LV4 and $2,610.33 for a gallon of Hyvar X-L.

In North Dakota, an average price for 2,4D LV4 is $14 per gallon and $55 per gallon for Hyvar X-L (2 lb/gal). They are selling this herbicide for 47 times and 283 times the cost than if the grower were to buy the 2,4-D LV4 and Hyvar X-L from his dealer.

Absurd claims are made with these products. For instance, one application of a product called Triple Threat (three phenoxy herbicides at a total of 1 lb/gal) was reported by the telemarketer to control leafy spurge for 5 years. Do you think the telemarketer would give its name to guaranty that claim -- NOT!

We need your help to rid our state of this pillage. Please document each call to you or your growers and report the information to me of Bob Vandal of the ND Dept of Ag (701) 328-1501. Get the following information if you can:

1. Date
2. Time of call.
3. Name, EPA registration number of product.
4. Name, formulation and concentration of active ingredients.
5. Name, address, and phone no. of company.
6. Full name of telemarketer and origin of call. (Good luck!)
7. Any claims made by telemarketer.
8. Any other information that would be useful.

Stay Out Of The "Kom-Bat" Zone

Indiana has banned the herbicide Kom-Bat offered for sale by Stockade, Inc. KOM-BAT is sold through aggressive telemarketing to farmers with the product being represented as either a selective herbicide suitable for use in the production of agronomic crops or as a non-selective herbicide with long (up to seven years) residual soil activity.

Reflex has received supplemental labeling for use in certain areas of Minnesota, North Dakota, and South Dakota.

Minnesota: All areas north of U.S. Hwy 212 and south of Interstate 94

North Dakota: All areas east of Interstate 29 from Fargo south to the South Dakota state border.

South Dakota: All areas east of Interstate 29 from North Dakota State border to Watertown, all areas east of U.S. Hwy 81 from Watertown to Madison and all areas east and south of State Road 34 and U.S. Hwy 281 to the Nebraska state line.

A maximum of 0.75 pt/A of Reflex herbicide (or a maximum of 0.1875 lb ai/A of fomesafen from any product containing fomesafen) may be applied per acre in alternate years. Weeds controlled are common cocklebur (a,b), annual smartweed, common lambsquarters (c), wild mustard, black nightshade (2-leaf max), pigweed species (2-leaf max), common ragweed (2-leaf max), sunflower, Venice mallow (2-leaf max).

1. Do not apply in cotyledon stage.
2. It is necessary to use 1% MSO type adjuvant and 2.5% v/v 28%UAN.
3. Suppression only

Rotational Crop Restrictions
--------------------------------------------
				Months After 
Crop			        Application
--------------------------------------------
Wheat, barley, oat	 	     4
Alfalfa, dry beans, corn, peas	    10
Sunflower, sugarbeet		    18
--------------------------------------------

Common milkweed has become a problem weed in cultivated cropland due to an extensive root system, insulating winter snow, moist to wet summer conditions, tolerance to many commonly used herbicides, and lack of persistence in chemical, mechanical, and cultural control measures. Common milkweed is not controlled with one herbicide application (except possibly patch spray with Tordon at 1 to 2 gallons/A) -- it takes continuous effort to control milkweed.

Seeds readily germinate and new plants readily become established from seed in fields. Common milkweed becomes perennial (capable of reproducing from underground roots) approximately three weeks after seedling emergence. New shoots developing from established roots begin emerging in late April and grow more rapidly than spring seeded crops.

Some reasons why herbicides are ineffective in controlling common milkweed are: large underground roots that can penetrate to more than 13 feet below the soil surface, shoots arising from as deep as 3 feet below the soil surface, waxy leaves which hinder herbicide uptake, and root buds near plant stems that are most tolerant to systemic herbicides. Increased control results from fall application of systemic herbicides due to greater movement to large buds that are closest to plant stems as they begin to develop. Greatest herbicide translocation extends out to the outer buds because they act as "sinks" as the buds develop. Ammonium sulfate stimulates root bud growth.

Control recommendations in small grains: In 1990, researchers from University of Minnesota applied several small grain herbicides at the highest labeled rate. Herbicides included: 2,4-D ester, MCPA + Banvel, Bronate, Curtail, Stinger, Harmony Extra, and Starane (to be released in 1998). Most herbicides did not reduce milkweed plant mass, height, or stand. However, the best treatments were Harmony Extra at 0.5 oz 75DF/A, and Starane at 1.5 lb ai/A. None of the treatments decreased milkweed populations the year following application.

Reports from the Minot area have indicated that season-long control and reduced plant populations have been achieved by a 3-way tankmix of Express + 2,4-D + Banvel at 0.33 oz 75DF + 0.75 pt/A + 2 fl oz/A.

NDSU Research Data --
applied June of 1988
------------------------------------------
Herbicide	 Rate   Fall 88  Spring 89
------------------------------------------
		 pt/A	 --% control--
2,4-D		  4	  36	    48
Banvel		  2	   7	    61
Banvel + 2,4-D  0.5+2	  26	    15
Curtail		  4	  13	     6
Tordon		  2	  86	    83
Roundup		  6	  56	    99
------------------------------------------

General recommendations:

Apply when milkweed is in the late-bud to flowering stage and actively growing.

CAUTION: The following treatments may cause significant crop injury and death if applied on cropland. Growers must determine the benefit from control against crop loss from excessive herbicide rates applied. In addition, Tordon will leave a residue for several years and may injure crops grown in successive years. However, applications made to small patches of milkweed may be justified because only a small percentage of the field will be applied.

Roundup Ultra: (No residue)
Patches: 3 to 4 qt/A
Rope or Sponge Wick: 33% solution

Tordon at 2 to 4 qt/A (Many years of residue)

(Submitted by Dr. Richard Zollinger, Extension Weed Specialist)