The Berry DisPatch

Newsletter of the Wisconsin Berry Growers Association

Chemigation

February, 2003

By Teryl Roper

UW-Madison, Extension Horticulturist

Recently questions have arisen about the feasibility of chemigation for applying pesticides to strawberries. Some pesticides that are labeled for strawberries do have chemigation requirements on their labels. Thus, if these requirements were met, these materials could be applied through the irrigation system. This article will attempt to outline in a general way what the requirements are for chemigation.

Chemigation is regulated under Wisconsin state law (ATCP 29.45 administrative code). These requirements can be found on the State of Wisconsin web site. The requirements are slightly different if you are chemigating from a municipal water system or from a private well. Specific requirements are listed on product labels.

Preventing backflow is a primary concern for chemigation. State law requires that specific backflow prevention devices be installed. In general these could be 1) a reduced pressure principle backflow preventer, 2) a barometric loop (35 feet in height), 3) two check valves in series, or 4) a check valve followed by a gooseneck.

The injector pump and the water pump must be connected electrically so that if either pump should fail the other pump will shut down automatically. The chemigation supply line must have a flow interrupter that will stop the flow if the injector pump stops. Further this line must have a flow sensor and a check valve to prevent siphoning. Obviously, each system is going to need to be approved by WDATCP before use.

While chemigation is possible, I don’t think it is a particularly good idea. The cost of the injection and backflow prevention devices is high. The cost goes up as the pipe diameter increases. Even if you are able to chemigate some pesticides, not all have a chemigation label so you will still need a boom or air-assist sprayer for the remaining materials. This is a double expense.

My biggest concern about chemigation is the inherent non-uniform application. Sprinkler systems simply do not apply water (or pesticides) evenly. A boom sprayer is always more uniform. Checking the uniformity of your sprinkler system is relatively easy. Place shallow cans (coffee cans work well) at even intervals through a field. A 20 to 30 foot grid would be ideal. Turn on your sprinkler system and allow it to run for 30 to 60 minutes. Collect the cans and measure the water that is in each can. This will show you the variation in application across a field. The variation can be as much as two-fold. Given this lack of uniformity, some areas will receive too much pesticide and others will receive too little.

Another requirement of chemigation is that lines must be cleared with clean water after the injector pump is shut off. It can take several minutes to have clean water to the furthermost sprinkler heads. Thus, the areas closest to the pumps may have much of the material washed off before the heads are clean at the end of the lines.
Wisconsin offers a chemigation certification that is in addition to your private pesticide applicator license. While this certification may not be required to chemigate, I highly recommend that you obtain this license before pursuing chemigation on your farm.