Crop yield and quality depend on effective application of agricultural chemicals. Proper selection, use and maintenance of sprayers can save you money, improve the performance of the agrichemicals you use, and protect the environment.
By Bill Johnson, Department of Agronomy, Bill Casady, Department of Agricltural Engineering, University of Missouri, Dallas Peterson, Department of Agronomy and Dennis Kuhlman, College of Technology and Avitiation, Kansas State University
With the increased emphasis on custom application of herbicides, postemergence weed control, and use of herbicides that are active at low application rates, proper cleaning and maintenance of sprayers will be increasingly necessary to avoid injury to nontarget crop species. The issue will take on added importance as more producers use broad-spectrum herbicides such as Roundup and Liberty on their herbicide-tolerant crops. Postemergence applications sprayed directly on the crop foliage will generally have greater potential for crop injury than will soil applications. Serious crop injury can result from small amounts of herbicides remaining in the sprayer system.
In recent years there have been numerous occurrences of soybean crop damage with symptoms resembling injury from growth regulator herbicides (Figure 1). The injuries were attributed to various causes, including the use of other soybean herbicides and herbicide additives, but in many cases the spray tanks had not been cleaned properly before applying soybean herbicides. Crop injury from sprayer contamination can occur up to several months after using the sprayer if it has not been cleaned properly. Injury from sprayer contamination can affect crop growth and development for several weeks after application and in severe cases can reduce crop yields. Herbicide residues in the sprayer can be redissolved through later contact with herbicides, their solvents or spray adjuvants. The objective of this publication is to present the appropriate cleanup procedures for sprayer equipment following the use of various herbicides in corn, soybean, wheat and cotton production.
General sprayer cleanup procedures
Leaf cupping is a sign of sprayer contamination injury from growth regulator herbicides.
A crop with moderate damage will suffer both delayed maturity and reduced yield
Pesticides can settle to the bottom or cause rapid corrosion in the spraying system and thus should be washed from the whole system immediately after use. One should always try to end the workday with an empty tank. If you will be using the same agrichemical the next day, thoroughly flushing the sprayer tank and sprayer with clean water is sufficient and will help prevent drying and hardening of pesticide residues. If a different agrichemical will be used, then a more comprehensive procedure is recommended immediately after use.
When cleaning a sprayer, select a location where any spilled rinsate will not contaminate water supplies, streams, crops or other plants and where puddles will not be accessible to children, pets, livestock or wildlife. Preferably the area should be impervious to water and have a wash rack or cement apron with a sump to catch contaminated wash water and pesticides. If such a facility is not available, catch or contain the rinsate and spray the rinse water or the cleaning solution on a field in a manner consistent with the intended use of the agrichemical. Avoid discharging all the cleaning solution in a small area.
The quickest and easiest way to rinse a tank and spraying equipment and dispose of waste safely is to carry a 50- to 100-gallon drum of fresh water with the spraying equipment. When spraying is finished, flush the system in the field and spray the rinsate on the field in a manner consistent with the products intended use.
If spray material is spilled on the sprayer during loading or mixing, wash the outside of the sprayer immediately. As a general rule, plastic or polyethylene tanks and hoses tend to require more extensive cleaning than stainless steel tanks. Screens and strainers should also be cleaned or replaced frequently as they can be a major source of contamination. Residues can also accumulate in checked or cracked hoses. Inspect the inside of hoses and replace if necessary. Pay special attention to the following areas that may be missed or difficult to clean:
- Sprayer surfaces or components where buildup might occur due to repeated coats of spray followed by drying
- Sprayer sumps and pumps
- Inside the top of the spray tank and around baffles
- Irregular surfaces inside tanks caused by baffles, plumbing fixtures, agitation units, etc.
When switching between crops, such as applying soybean herbicides after corn spraying is complete, follow the procedure described in the box below to clean out sprayers.
Sprayer cleaning agents
Cleaning agents should be selected based on the herbicide and formulation to be cleaned (Table 1). Cleaning agents should penetrate and dissolve pesticide residues and allow them to be removed when the rinsate is removed from the sprayer. The functions of cleaning agents are dilution, solubilization and deactivation. Commercial tank cleaning agents and detergents help remove both water- and oil-soluble herbicides and are recommended on many pesticide labels. The commercial tank cleaning agents usually perform better than household detergents and can deactivate some herbicides in addition to solubilizing them.
Some tank cleaning agents and ammonia solutions also raise the pH of the rinsate solution, making some products such as sulfonylurea herbicides more water soluble and thus easier to remove from internal sprayer parts. Chlorine bleach solutions will accelerate decomposition of sulfonylurea and some other herbicides into inactive compounds. However, chlorine is less effective at dissolving and removing sulfonylurea herbicide residues from spray tanks than ammonia solutions. Chlorine bleach should never be added to ammonia or liquid fertilizers containing ammonia because the two materials react to form toxic chlorine gas, which can cause eye, nose, throat and lung irritation. Fuel oil or kerosene is effective for removing oil-soluble herbicides such as esters and emulsifiable concentrates. The fuel oil or kerosene should be followed by a detergent rinse to remove the oily residue.
All sprayer components, including the tank, pump, hoses and nozzles, must be thoroughly cleaned to avoid contamination. The lowest point of the spray system should have a drain, and all sprayer plumbing should gravity drain to that point. If the system does not allow all of the solution to drain out, the effectiveness of cleaning agents is greatly reduced and may be useless. Any contaminated solution remaining trapped in the sprayer system must be diluted and flushed out of the system with repeated rinses. Once the tank and all circulation lines have pure water, the spray valve to the nozzles should be opened and remain activated until all nozzles are spraying pure water. The sprayer must be thoroughly cleaned and flushed before the new herbicide mixture is added to the tank, or contamination will occur.