• Switching from crop to crop becomes risky in terms of crop response and often requires a thorough cleanout.
• Try to always spray out the full load before finishing for the day.
• Switching from pre-emergence products to post-emergence products may result in crop response if precautions are not taken to clean or flush out equipment properly.
• Always read and follow labels for products that are being used.

Crop injury from sprayer tank contamination continues to be one of the most common Crop Protection application concerns in agriculture.  Most tank contamination issues can be avoided with a minimal investment of time and effort.  It's also important to recognize the circumstances that increase both the risk of tank contamination and the potential for crop response.

Switching Crops
This poses the highest risk for tank contamination problems and for crop response.  Solution: As far as possible, dedicate sprayers to use on a specific crop.  When you must switch crops, be prepared for the necessary down-time involved with proper tank cleanout.

Changing to Post-Emergence Applications
A number of soil-applied products may cause spotting, speckling, burning, or distorted growth if applied to foliage.  Solution: Recognize which products may cause adverse effects to crop foliage.  Take the time for a thorough system flush or for a complete tank and system cleanout.

Highly Active or Persistent Products
Certain products are active at low concentrations, or are particularly prone to sticking to insides of tanks and boom lines.  Solution: Create a list of products you handle, and which are likely to cause problems.  Note when those products are being used.  Take extra care when prior spray loads have included those products.  With the persistent products, crop response may be noted even when multiple loads have been sprayed since those products were first used.

Accidental Tank Cleaners
Some products or tank mixes are surprisingly good at cleaning tanks and booms of residue from previous loads.  Problems of this kind normally show up with post-emergence applications.  Solution: A simple rinse or water flush ahead of these products and mixes may not be enough.  Be prepared for a complete tank and boom cleaning.

GENERAL RECOMMENDATIONS:

Frequent, Thorough Rinsing
There is no substitute for frequent rinsing of the sprayer system.  This keeps residue from building up.  As a minimum, sprayers should be thoroughly rinsed and booms flushed before parking equipment at night or when equipment will be inactive.

Spray Out the Loads
Sprayer and boom contamination can be partially caused when product sits in the tank and booms for extended time periods, even overnight.  Completely spray out the load, especially with the last load of the day.  If you are interrupted by sudden rain or other problems, arrange to agitate the partial load frequently to avoid product settling and sticking to tanks and in booms.

Special Nozzles / Rinse Systems
If your sprayer is equipped with rinse and flush systems, make use of this equipment.  It is always best to spray out rinsates on the field where the application took place.  If you don't have this equipment, arrange for someone to bring rinse water to you and use special nozzles designed to help rinse insides of spray tanks.

Straighten Hoses
Hose bends and end caps are places where product can settle out in the spray boom.  To the best of your ability, straighten these hoses and eliminate other "dead zones" where product can accumulate.

Chemical Inductors 

Chemical Inductors are prone to product and product solution sitting in the bottom near the valve. This becomes an issue when switching from one crop to another without through cleanout. To best minimize: always clean with fresh water after all products are added into the tank, and do a complete and thorough cleaning when doing a whole system cleanout, this will help to alleviate crop response due to contamination. 

Image: Soybean leaf speckling from tank contamination