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Lima Bean Fields Infested with ALS-resistant Pigweed in Delaware  

How Problems with ALS-Resistant Pigweeds Developed

Pigweed is one of the most wide-spread weed species in Delaware and the region, infesting vegetable crops as well as grain crops. Pigweed is capable of quickly becoming the dominant species in a field due to its high seed output, producing over 100,000 seeds per plant.

A number of herbicides are effective on pigweed species if applied in a timely fashion. However, there are pigweed biotypes that are resistant to some of the most commonly used herbicides in commercial agriculture. One such group of herbicides is Group 2 (ALS-inhibiting) herbicides. This group includes the SU and IMI herbicides. SU and IMI herbicides refer to the class of herbicides, sulfonylurea and imidazolinone herbicides, respectively. ALS stands for acetolactate synthase inhibiting herbicide, since these herbicides inhibit the function of this plant enzyme. Herbicides in this group include: Pursuit, Raptor, Sandea, Accent, Matrix (or Resolve), FirstRate, and others. In lima beans, Pursuit, Raptor, and Sandea are labeled and have been extensively used for broadleaf weed control. 

Preliminary surveys conducted by UD have found that many lima bean fields infested with pigweed at harvest often are infested with Group 2 resistant pigweed. 

Rinsate Disposal

Clean the sprayer in an area that will not contaminate water supplies, streams, or crops and in an area inaccessible to children, pets, and livestock. Pay particular attention to sensitive vegetation that is in the runoff area. The best method for rinsate disposal is in the field in a manner consistent with the product’s label. The easiest way to do this is to have rinse water available in the field, either on the sprayer or support vehicle.

Tank-Cleaning Agents

A tank-cleaning agent's function is to penetrate, loosen, and dissolve herbicide residues and then to remove them through dilution. In some cases, the agent will provide deactivation or decomposition of the herbicide. 

  • Commercial tank cleaners are recommended on many product labels and help remove water and oilsoluble herbicides.
  • Household ammonia, a commonly recommended cleaning agent, is effective at penetrating and loosening deposits and residues in the spraying system. Although ammonia does not decompose herbicides, it increases the solubility of some herbicides by raising the pH.
  • Chlorine bleach can decompose residues of most sulfonylurea and other herbicides into inactive compounds. However, some tank-mix partners may inhibit the decomposition. Care must be used with chlorine bleach. Chlorine bleach can combine with fertilizers containing ammonia to produce dangerous chlorine gas, which is irritating to the eyes, nose, throat, and lungs. Also, rinsate containing chlorine bleach is not labeled for application to cropland.
  • Kerosene or fuel oil should be used to remove oil-based herbicide formulations such as 2,4-D esters. Following the oil rinse, the system should be cleaned with detergent or ammonia. 

Removing precipitated pesticides

Tank-mixing more than one pesticide can sometimes result in the chemicals forming a “gunky mess” in the bottom of the tank. The result is that the pesticides are not compatible with one another and the pesticides will settle out (form gunk). If your tank does end up with incompatible pesticides gunking up the bottom use a compatibility agent (usually at a pint/100 gallons, follow directions). 

Surfactants and fertilizer additives

When switching from a growth regulator herbicide (2,4-D, Banvel, or Stinger) to a postemergence application in soybeans, special care should be taken if the application involves surfactants or fertilizer additives. Such materials are particularly adept at removing these herbicides from poly tanks, hoses, and strainers. It is recommended that a small amount of fertilizer or crop oil be flushed through the system before the application. 

General cleaning guidelines

To avoid drying and hardening of pesticide residues, and potential corrosion and damage to equipment, clean the sprayer immediately following an application. If you are continuing with the same pesticide the next day, flushing with water is sufficient. However, if you are switching products or crops, a more thorough cleaning is required.

Be sure to clean the entire sprayer system, not just the tank. Operate the pump and flush the cleaning solution through all hoses, strainers, screens, nozzles, and the boom. Small amounts of residue left in these areas can be sufficient to cause serious damage to a sensitive crop.

Most injury occurs when switching between crops. The following procedure is recommended when there are no specific cleaning requirements given on the label. 

1. Drain the sprayer tank and lines and rinse tank, boom, and lines with water for a minimum of 5 minutes.

2. Fill the tank with clean water and one of the following cleaning solutions per 100 gallons of water:

  • 1 gallon household ammonia, or
  • 8 lbs trisodium phosphate cleaner detergent, or
  • commercial tank cleaner (follow instructions).

Flush the solutions through the entire sprayer system. For growth regulator herbicides (2,4-D, Banvel, Clarity, Distinct, Stinger, etc.), let the solution stand overnight. Add more water to fill tank and agitate solution for at least 15 minutes and flush through the nozzles. Drain the tank.

3. Remove the nozzles, screens, and strainers and clean them separately in a bucket of cleaning agent and water.

4. Rinse the entire system with clean water. 

Consult the label

This publication provides general guidelines for cleaning your sprayer, but it is important to remember that the best source of information is the pesticide label. Some product labels require specific cleaning agents at specified concentrations, and/or provide stepwise procedures for cleaning the tank. Consult labels for the products that were previously in the tank, and for the products that will be used for the next application.

The following table indicates what cleaning agent is required for various herbicides. 

Herbicide Water only or not specified on label  Ammonia Commercial Tank Cleaner or Detergent 
2,4-Db      
Accent   either or
Aim     X
Atrazine     X
Authority First    either or
Authority MTZ    X X
Banvel   X X
Basagran     X
Basis   either or
Beacon   either or
Bicep II Magnum  X    
Bicep Lite II Magnum  X    
Blazer     X
Boundary   either or
Breakfree X    
Breakfree ATZ  X    
Buctril X    
Bullet X    
Callisto   X  
Canopy   either  or
Canopy EX   either or
Celebrity Plus      X
Cinch X    
Cinch ATZ  X    
Clarity     X
Classic   either or
Cobra X    
Command   either or
Define X    
Degree X    
Degree Xtra  X    
Distinct     X
Dual II Magnum X    
Enlight   either or
Envive   either or
Equip   X  
Evik     X
Exceed   either or
Expert   either or
Extreme X    
FieldMaster X    
Firstrate   X  
Flexstar     X
FulTime X    
Fusilade DX      X
Fusion     X
Gangster   either or 
Gramoxone Inteon  X    
Guardsman Max     X
G-Max Lite      X
Halex GT   either or
Harmony Extra    either or
Harmony GT   either  or
Harness X    
Harness Xtra X    
Hornet WDG    either or
Impact     X
Keystone X    
Keystone LA X    
Lasso X    
Laudis   either or
Lexar   either  or
Liberty     X
Liberty ATZ      X
Lightning X    
Lumax   either or
Marksman     X
MicroTech X    
Northstar   X  
Option   X  
Osprey   X  
Outlook     X
Peak   X  
Poast / Poast Plus      X
Princep     X
Prefix   either or
Prowl X    
Prowl H2O     X
Pursuit X    
Pursuit Plus X    
Python X    
Rage D-Tech    X X
Raptor X    
ReadyMaster ATZ      X
Reflex     X
Resolve   either or
Resource X    
Roundup products X    
Sandea   X  
Scepter X    
Select / Select Max X    
Sencor     X
Sequence X    
Sonic   either  or
Spirit   either or
Squadron X    
Status     X
Steadfast   either or
Steadfast ATZ    either or
Stellar X    
Stinger   X  
Storm     X
Stout   either  or
SureStart   either  or
Synchrony XP    either  or
Targa   either or
TopNotch X    
Touchdown products      X
Treflan X    
Ultra Blazer      X
Valor SX    X  
Valor XLT    either  or
Unity WDG   either or
Yukon   X X

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