Insecticides through your drip irrigation system

Above, a pepper field trial set-up for 2004- 2009.

Irrigation systems are critical for a successful vegetable production season, and drip, or trickle irrigation, systems are the method of choice due to their efficiency and compatibility with plastic mulch. These systems deliver water directly to the rootzone, reducing the total amount of water required to irrigate, as well as placing the water more precisely under plastic mulch. Evaporative losses are much less than other irrigation systems, and drip systems operate at low pressure, reducing fuel requirements. And, the foliage does not become wet as it does with overhead sprinklers, reducing potential washoff of protective fungicide and other management sprays.

Many growers already successfully apply fertilizers through drip irrigation systems (fertigation) at various times throughout the year. Recently, scientific tests have shown that insecticides can also be applied via drip irrigation systems (insectigation), resulting in effective control of certain insect pests of vegetable crops. Insectigation allows growers to apply pest control materials through a system they already have in place and saves significant time and money over ground-applied application. Spray drift, sunlight degradation and coverage of the foliage are not an important concern with insectigation as it is with foliar sprays.

The first insectigation trials using insecticides and drip irrigation injections were conducted at the Rutgers Agricultural Research and Extension Center (RAREC), Bridgeton, N.J., on bell peppers and pole lima beans in 1980-1981, although results were not encouraging. Plastic mulches and drip irrigation were just beginning to become popular with vegetable growers, and there were virtually no labeled insecticides available at that time for drip irrigation injection-and, almost none that were highly soluble, root systemic, safe to the crop and effective against insect pests. In 1986, researchers at Washington State University showed that disulfoton (Di-Syston 8) effectively controlled aphids on asparagus when applied through a drip system. In the early 1990s, research at RAREC showed that oxamyl (Vydate L) could be successfully applied through a drip system to peppers, although the level of control of the European corn borer was still, Inc.onsistent.

With the recent development of many new-chemistry insecticides (imidacloprid, thiamethoxam, chlorantraniliprole, dinotefuran, etc.) that are effective against certain insect pests at low rates, are highly soluble and systemic in action and safe to the crop and the environment, growers have new options. Successful insectigation trials have recently been conducted at the University of Arizona using Admire or Platinum for aphid control on lettuce; at the University of Florida and Virginia Tech University using Coragen for the control of worm pests on tomatoes; and at RAREC, N.J., using Coragen for the control of European corn borer in bell peppers. Researchers found that fewer applications were necessary, less insecticide was used and the level of control was equal to, or better than, multiple foliar sprays. As a result of these successful trials and others, many insecticide labels for vegetables now have specific drip application instructions,, Inc.luding Admire and Admire PRO, Aza-Direct, Coragen, Durivo, Lannate (Special Local Needs label for some states), Platinum, Venom and Vydate L.

European corn borer in pepper (above and right).

Vegetable growers considering drip irrigation can get information from many sources, such as county agricultural agents, agricultural industry specialists and drip equipment suppliers such as Lee Rain in N.J., Robert Marvel Plastics in Pa., and more. A good source of information for beginners is the article "Thinking of Using Drip Irrigation This Season", by William Lamont, published in the March 2008 issue of The Pennsylvania Vegetable Growers News (pg. 14-16), or the book "Production of Vegetables, Strawberries and Cut Flowers Using Plasticulture," edited by William Lamone (Natural Resource, Agriculture and Engineering Service Publication 133, Cooperative Extension Service, Cornell University, Ithaca, N.Y.).

Special equipment considerations

The injection manifold and mixing tank/pump.

Most of the equipment necessary for insectigation is already, Inc.luded in a standard drip irrigation system,, Inc.luding back-flow prevention check valves, pressure regulators and a sand filter, and growers need little additional equipment. Such equipment might, Inc.lude a quick-closing check valve to prevent the flow of fluid back toward the point of injection, and a functional, solenoid-operated valve located on the intake side of the injection pump and connected to the system interlock to prevent fluid from being withdrawn from the supply tank when the irrigation system is not operating. The system must also have a control to automatically shut off the insecticide injection pump when the water pump motor stops, or when the drip line pressure suddenly decreases to the point where pesticide distribution is adversely affected (such as a hole in the drip tube, a leak or drip line break, etc). Most labels that have drip application instructions list the required equipment needed for insectigation.

The goal of insectigation is to deliver a consistent and uniform application of an insecticide to the crop roots for uptake and distribution of the material throughout the plant. Systems must use a positive displacement injection pump (such as an electric diaphragm pump) or similar devise to ensure a uniform and measureable application. Uniformity of application is important. It is desirable to have the same amount of insecticide drip equally from every emitter in the drip line system. It is best to prime the system before injecting an insecticide so dry soils have a normal moisture range before initiating insectigation. Also, remember that underwatering will prevent the insecticide from reaching the entire rootzone of all the plants, and overwatering will leach the insecticide from the rootzone.

Beet armyworm on tomato. Beet armyworm on pepper foliage.

Don’t rush injection time. Extending the length of injection will improve the uniformity of delivery and ensure that the insecticide is well distributed for uptake by the plants. The minimum injection time is the time it takes water to move from the injection pump to the furthest emitter in the field. This time can be determined by injecting a soluble, nontoxic dye, or even a soap solution, through the system and recording the time it takes to reach the furthest emitter. Likewise, the minimum time for flushing the system with clean water after injection is the same. It is important to flush the system of all insecticide material after injection.

Only insecticides that specify "For trickle or drip irrigation systems" on the label can be applied in this manner. The use of any material that is 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 the emitters), the crop (phytotoxicity, illegal residues, etc.) and the soil.

More detailed information concerning drip injection requirements and information is available on most chemigation labels (such as "Chemigation Bulletin" on the Neemix label, available from Certis USA, L.L.C., or the "Chemigation" section located in the Dupont Coragen label, etc.). Another good source of information concerning chemigation is an eight-page bulletin from DuPont Crop Protection USA ("Drip Chemigation: Best Management Practices," DuPont Technical Update No. K-14954), which, Inc.ludes detailed information on how to calculate rates, times, amounts and recommendations for emitter distances, water management, pH and more.

The author is professor in the entomology department at Rutgers – the State University working at the Rutgers Agricultural Research and Extension Center in Bridgeton, N.J. He has worked since 1980 as an extension specialist in vegetable entomology.