Original article by Growing Magazine (Dr. Gerald M. Ghidiu)
Chemigation, in general, can be defined as the application of an agricultural chemical through any irrigation system, using the irrigation water to distribute the chemical. Chemicals include pesticides (insecticides, fungicides, herbicides, nematicides), fertilizers, plant growth regulators and other materials. Chemigation can be applied only if the product label allows such application, and only according to the label directions and restrictions.
The three basic crop irrigation systems include overhead/sprinkler, drip/trickle, and surface/gravity flow systems. The proper equipment, depending on the irrigation system, is essential for successful (as well as legal) chemigation. Although overhead irrigation and surface flow systems may be suitable for some vegetable crops, drip irrigation is widely used in vegetable production.
Why consider drip chemigation?
Many growers throughout the vegetable-growing regions of the U.S. are already using drip, or trickle, irrigation as a water management tactic. Chemigation via drip irrigation allows growers to apply pest control materials through a distribution system they already have in place (the drip system), thus saving significant time and money over ground-applied chemicals. Over the past 10 to 12 years, many field tests throughout the U.S. have demonstrated that application of insecticides via the drip system results in highly effective control of specific insect pests of vegetable crops using low rates of labeled insecticides.
Drip chemigation has many advantages over the traditional row-crop sprayer in vegetable production:
1. The total insecticide input for control of targeted pests in most vegetable crops is significantly reduced when compared with ground applications, because the amount of insecticide used is based on the actual wetting zone, not on the total field size. For example, plants set on 60-inch centers on plastic mulch likely have only a 36-inch wetting zone, so application calibrations would be based on a 36-inch row.
Furthermore, because the insecticides used in drip systems are root systemic, they quickly translocate throughout the plant, resulting in essentially 100 percent protection of the plant for an extended period of time. Many research trials have demonstrated that one or two applications via a drip system are just as effective as multiple ground applications for controlling insect pests such as beetles, caterpillars, aphids and others.
2. Weather is generally not a factor during application, as injection of an insecticide via a drip system can be made in wind or rain, or when fields are too muddy or soft to operate ground equipment without getting stuck. If plastic mulch is used, the insecticide is not lost to wind drift or to rainwater runoff, but remains in the root zone for the plant to utilize.
3. Less energy is required to distribute insecticide solutions to the crop because of the low pressures and velocities in drip systems as compared with other irrigation systems or ground application equipment; a 1/3 to 1/2 hp injection pump often suffices in drip systems. Since a ground sprayer is not needed, the soil compaction that normally results from heavy tractors or spray equipment being operated over the field does not occur. Further problems caused by tractor or sprayer operation within the crop include physical plant damage as well as the spread of some plant diseases, such as Phytophthora.
4. With drip chemigation, applicator exposure to insecticides, both in terms of physical contact and length of exposure, is significantly reduced compared to exposure from ground sprayer application. Also, since many of the new-chemistry insecticides now labeled for use in drip systems are selective to specific insect pests, they are generally less disruptive to nontarget species and beneficial organisms such as predators. Thus, drip chemigation fits well into an efficient and effective insect pest and soil management program.
However, there are some special considerations to using drip chemigation:
1. Drip irrigation and chemigation require consistent maintenance and monitoring of all equipment for pressure drops, leaks in the system, plugged emitters, etc. A high level of management is required for the irrigation system, and for the safe use of insecticides and skill in calibration.
2. Additional equipment increases the capital expenditures. However, the extra equipment needed for chemigation (injection pumps, safety equipment, valves, etc.) is reusable, and the cost per hour of operation decreases the more the system is used.
3. Only certain pesticides are labeled for chemigation. The use of any material not specified for drip systems on the label is not only illegal, it can cause serious damage to the pump (corrosion), the drip lines (plugging emitters) and the crop (phytotoxicity, residues, etc.). Remember, the label is a legal contract between the manufacturer and the user that must be followed.
Most of the equipment necessary for drip chemigation is already included in a standard drip irrigation system: backflow prevention check valves, sand filter, shutoff switches and pressure regulators. Additional equipment includes an insecticide mix tank, an injection pump, and additional safety equipment such as a solenoid-operated valve on the intake side of the injection pump to prevent fluid from being sucked out of the supply tank when the system is not operating. An automatic sensor and shutoff switch to shut down the insecticide injection pump when the water pump stops, or when the drip line pressure suddenly drops, is also required.
Pesticide labels that permit drip chemigation list specific equipment and safety requirements under the “Chemigation” section of each label. For example, Certis USA LLC, offered a “Chemigation Bulletin” on the Neemix label, which contains general chemigation information as well as safety equipment and injection directions specific to each chemigation system.
Other helpful sources of information for drip chemigation equipment and injection are manufacturer bulletins such as “Drip Chemigation: Best Management Practices,” a 2008 technical update from DuPont Crop Protection, and “Best Use Guidelines for Drip Application of Crop Protection Products,” a 2009 technical bulletin from Syngenta Crop Protection. Both include detailed information on the equipment necessary for injection into a drip system, calculation of rates, timing of applications, etc. Another source of information may be your state crop production guidelines or chemigation fact sheets, often available online.
Chemigation via the drip system is a sound and economical option in place of traditional foliar sprays of insecticides for control of specific vegetable insect pests. It enables growers to precisely apply an insecticide under virtually any weather condition for control of many insect pests, including aphids, whiteflies, leafhoppers, beetles and caterpillars, while at the same time reducing the total insecticide, labor and energy inputs as compared with foliar sprays. It enhances your pest management program because many of the new-chemistry insecticides labeled for drip chemigation are selective to specific pests, and because they are applied to the root zone, they are generally less toxic to beneficial and nontarget organisms. Over a dozen labels currently allow chemigation via the drip system for a wide range of insect pests, and several new-chemistry insecticides are being added to this list every year.