Subsurface applications drop pests in their tracks
For many years, turf managers have relied on broadcast applications of pesticides to control soil insect pests. Typically, this involves a surface application of an insecticide.
This approach generally provides acceptable control, but it may result in inconsistent or unacceptable performance, particularly where the turf has a thick thatch layer that prevents much of the active ingredient from reaching the root zone. Further, post-application irrigation often is necessary to move the active ingredient down to the feeding zone of the target pest.
A new application alternative Recently, equipment manufacturers, chemical companies and university researchers have cooperated in developing application equipment that places pesticides directly into the feeding zone of soil-inhabiting insects. Subsurface placement involves injecting liquid insecticides under high pressure into the soil or depositing granules into punctures or slits cut in the turf. Both approaches provide the advantage of placing a high percentage of the active ingredient directly into the root zone where the pest is active.
Compared with traditional application techniques, subsurface applications can be more effective, especially when a thick thatch layer is present. Because more active ingredient actually reaches the pest, you often can reduce application rates. This good news for turf managers. If you can reduce rates without sacrificing efficacy, you lower the cost of the application.
In addition to increasing effectiveness, subsurface application can improve safety and reduce environmental risks. Because soil-injected products do not sit on the surface, you avoid exposing non-target organisms to the pesticide. For the same reason, applicators and bystanders are less likely to come into contact with the chemical. Volatilization, photodegradation, drift and runoff are less likely with subsurface applications.
Subsurface applications do not, however, totally eliminate environmental concerns. Highly soluble pesticides tend to move in the soil profile. Injecting them below layers of thatch or organic matter could actually increase the risk of leaching. More research is needed to determine the leaching potential of specific pesticides and assess the suitability of subsurface applications on a case-by-case basis.
In addition to efficiently controlling insects, subsurface application lends itself to other uses. With this kind of equipment, you also can apply other products such as fungicides, herbicides, fertilizers, wetting agents and, with certain equipment, even seeds (see "Seeding with high-pressure injection," below).
You also can use high-pressure liquid-injection equipment for aerification. The high-pressure jets can inject streams of water 4 to 10 inches deep into the turf and loosen soil. This technique is especially useful ion golf and sports turfs, where soil cores from traditional aerification interfere with play.
How subsurface placement works There are two ways to place insecticides into the feeding zone of subsurface insects: slicing or puncturing; and high-pressure liquid injection (HPLI).
* Slicing is much like overseeding (see photo, top left). The subsurface applicator cuts a slice or groove in the turf. It then delivers the insecticide into the groove through a gravity-feed tube. Then a plate or roller "pats" the turf back into place. With puncturing-type equipment, the insecticide is delivered into a series of holes cut in the turf.
Slicing or puncturing has pros and cons. On the pro side, you can accurately set the depth of application-usually to within 0.125 inch. Therefore, the unit readily can adapt to the unique conditions of individual turf areas. Also, this method permits delivery of a wide range of pesticide products, including most granular formulations and, in some cases, liquid insecticides and even biological products.
The major downside to slicing or puncturing is that the application can inflict considerable damage to turf, which is especially serious when treating areas heavily infested with grubs. When heavy thatch is present, slicing or puncturing can leave debris on the turf surface that may interfere with the insecticide application. Plus, you may need to periodically remove debris from the machine to prevent clogging.
* High-pressure liquid injection (HPLI), also referred to as root-zone injection (RZI), involves injecting a liquid insecticide at high pressure (up to 5,000 psi) into the turf. HPLI or RZI consistently delivers the insecticide without disrupting the turf surface. This is important both aesthetically and functionally. The surface remains playable for soccer, football or golf immediately after the HPLI application.
Of course, HPLI only works for liquid formulations, and as with slicing or puncturing operations, insecticide leaching potential is increased in comparison to surface application.
Mechanical insect control An exciting aspect of HPLI is that it has the potential to mechanically control turfgrass pests without using any pesticides. High-pressure jets of water kill the target insects (both surface and subsurface pests). This could be especially valuable in landscapes such as schoolyards, athletic fields, zoos and turfgrasses near water, where pesticide applications may be restricted or forbidden.
The keys to effective mechanical control are injection coverage and penetration. To kill the target pest, a high-pressure stream of water must actually strike the insect. There are several ways to increase the likelihood of this.
First, decrease the distance between nozzles. This will increase the number of injection sites perpendicular to the direction of travel. Multiple-orifice nozzles produce angled streams (30 to 60o off vertical) that pass through more of the feeding zone, hitting more insects and providing better control (see photo, page Golf 18). You can also angle injections by repositioning the nozzles on the machine.
In certain cases, you can improve the effectiveness of mechanical control simply by increasing the injection pressure. This increases the depth of penetration and allows the streams to reach target pests deeper in the soil profile. However, this approach may not significantly improve control-most turf insects normally reside within the top 1 or 2 inches of the turf surface. Excessive pressure may also disrupt the turf surface more severely.
Reducing the ground speed of the applicator or making additional passes over the same area will increase the number of "hits." The slower the applicator travels or the more times it passes over the same area, the greater the number of injection sites and the better the control.
At the University of Nebraska, we used a John Deere RZI 700 to conduct several studies of RZI. We evaluated the effectiveness of both chemical and mechanical (water injection only) control of Southern masked chafer grubs (Cyclocephala lurida) and black cutworms (Agrotis ipsilon) in turf.
In a 1998 study, our subsurface applications of halofenozide (Mach 2) and isofenphos (Oftanol) provided better than 97 percent control of masked-chafer grubs. Mechanical (water injection) applications provided up to 74 percent control of white grubs and 57 percent control of black cutworms, depending on the injection pulse rate and number of passes.
So, what does all this mean for grounds managers? Subsurface application technology has the potential to provide control as good as or better than traditional surface-application methods, but without many of the drawbacks. For turf areas where pesticide use is forbidden, grounds managers now have a viable alternative method to control pests. While RZI is not as effective as pesticides, it can significantly reduce pest populations.
Several companies manufacture equipment suitable for subsurface applications. Some subsurface units are large tractor-mounted or tractor-pulled units. They are suitable only for larger, relatively level turf areas such as golf courses, athletic fields, cemeteries, parks and recreation areas. Others are walk-behind units that you can use in small or confined areas, such as home lawns or commercial properties, and on moderate slopes. Visit with industry representatives and get a close look at various models when attending industry trade shows (see product listing, at left).
As with any pesticide applications, be sure to read the label thoroughly. Application restrictions for pesticides vary from state to state. In most states, subsurface injection is legal unless specifically prohibited on the pesticide label. Always refer to the label for specific application instructions and never exceed the maximum labeled rate. Additional pesticide information is available on the internet, such as at the University of Nebraska's Pesticide Education Resources web page (www.unl.edu/ianr/pat/ephome.htm).
John Fech is an extension educator and Dr. Fred Baxendale is professor of entomology, both at the University of Nebraska (Lincoln, Neb.).
Dr. Milt. Engelke of Texas A&M University has been studying high-pressure injection (HPI) as a method of sowing bentgrass seed into existing turf stands. A non-surface-disruptive method of converting existing stands to new varieties is not currently available, so this would be a significant development, especially for courses converting greens to newer varieties.
Bentgrass seed, at 6 to 10 million seeds per pound, is small enough to pass through an HPI unit (Engelke used a Cushman Envirojet with the filter screen removed). By intercepting seeds ejected from the HPI nozzles and then germinating them, Engelke found that more than 70 percent were undamaged and viable. This is an acceptable rate of loss.
Depth of seed placement is a critical factor for seed survival and establishment. HPI can inject seeds to a range of depths. However, excavations by Engleke showed that most seeds that actually germinated were at a depth of 1/8 inch or less.
HPI may have little potential for seeding uses besides interseeding bentgrass greens. Most other turfgrass species' seeds are too large, and using HPI for new stand establishment (bare soil) is too surface-disruptive. However, Engelke's results show that this method of interseeding bentgrass can be successful. Thus, superintendents may have a valuable new tool for seeding bentgrass greens without disrupting play.
* Subsurface Injector, The Toro Co. This machine's stationary blades cut slits in the turf. Its nozzles spray a stream of liquid into the slits at 100 to 200 psi. The nozzles use stainless-steel tips in the a range of diameters in brass nozzle bodies.
* Envirojet 160, Cushman/Textron Turf Care And Specialty Products. The Envirojet can deliver pesticides, liquid fertilizers, wetting agents or polymers. It uses high-pressure pulses of water to create small, elongated holes, followed by subsurface fracturing to a depth of up to 6 inches.
* RZI 700, John Deere. This unit is controlled by a tractor-mounted controller that starts and stops the machine and adjusts the rate at which it injects liquids. The system can deliver pressures up to 5,000 psi and inject liquids to a depth of up to 6 inches. Multiple-orifice nozzles are available.
* DryJect 2200, Advanced Agro Technologies/Landpride. This machine injects both liquid and dry materials with high-pressure water at about 2,000 psi. It can inject material up to 8 inches deep, depending on soil type.
* TG 20, TG 70 granular slit applicators, Canaan Industries. Forty-four sets of steel Coulter discs are independently suspended and adjustable to provide penetration up to 3.5 inches.
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