Surface drip (SD) irrigation of field crops has been gaining interest in the farming community. However, rodent damage is one of the major drawbacks for SD acceptance. This research documents the cost of repairing drip tubing and effectiveness of several rodent control methods. Four sites were used to identify cost of repairing tubing. Treatments included untreated drip tubing, tubing that was lightly buried, sprayed with an insecticide or animal repellent, and edible rodenticide placed next to the tubing. Once a leak was found, it took an average of 4 minutes to repair the hole. Each repair had an average cost of $0.67 for labor and repair materials. This repair cost does not include time or transportation cost to find the leak. Rodent damage was the same in the untreated versus any chemical treatment tested. At Site 4, the animal repellent, Ropel®, did have less rodent damage (2392 holes/ha) compared with the untreated (6049 holes/ha) however, the damage was extensive enough that it was more economical to replace than to repair the tubing. There was less rodent damage to the thin-walled tubing compared with the thicker-walled tubing. Drip tubing that was slightly buried had the best rodent control (5 holes/ha) compared with all other treatments (1771 holes/ha). One disadvantage of burying the drip tubing is removal. Strip tillage along with burying the drip tubing showed excellent resistance to rodent damage and appears to be a cost effective management tool for SD.
Almost one million ha are irrigated in Georgia, Florida, and Alabama, with 36% being irrigated by overhead irrigation systems (
Surface drip and SDI systems are typically installed to irrigate high value crops. In recent years, drip irrigation has expanded, with good success on field crops such as corn (
The conversion of non-irrigated land to SD or SDI can be challenging for land owners, especially with the day-to-day management of these systems concerning rodent damage. Both SD and SDI are subject to rodent or other animal damage especially in crops where there is maximum crop cover such as peanut. Wildlife that can cause damage to SD tubing include the Hisbid cotton rat (
The result of holes in the tubing are obvious but also include loss of pattern and irrigation efficiency, drought stress to areas that no longer receive water, water logging around the hole, nutrient leaching, and on undulating topography, possible soil erosion. In addition to the inefficiency of the irrigation water and possible loss of yield and resultant revenue, there is the added cost associated with tubing repair. This would include the cost of the repair materials, which can be minimal, and labor, which could be substantial, depending on the time it takes to find and repair the holes.
There is very little information on rodent damage and control in peanut (
Four sites were selected where SD irrigation was used to irrigate peanut. Site 1 was on a Greenville fine sandy loam (Fine, kaolinitic, thermic Rhodic Kandiudults) with 0 to 1% slope. A SD system was installed two years prior to irrigate cotton (2003), strip-till corn (2004), and strip-till peanut (2005). The area was clean tilled and cotton (DP 555 BG/RR) was planted. Drip tubing (Roberts Irrigation Products, 57 L/hr, 0.20 mm wall thickness, and 30 cm emitter spacing;
Site 2 was on a Faceville fine sandy loam (Fine, kaolinitic, thermic Typic Kandiudults) with 0 to 1% slope. This project was in cooperation with a long term cropping systems project described by
Sites 1 and 2 were primarily used to document the cost of finding and repairing leaks that occurred in SD. Management was such that the number of leaks, type of leak (mechanical or biological), and time it took to repair the leak could be documented. Documentation also included the type and quantity of materials needed to repair the leak. When repairing leaks, costs include labor, thick walled tubing (1.2 mm wall thickness), stainless steel wire ties, wire-tie tool, extra SD tubing, scissors, and rubber boots.
Site 3 was on a Faceville fine sandy loam with 2 to 3% slope (same as above). The area received full conventional tillage in the fall. Accepted best management practices were followed (see previous) to plant peanut (Georgia Green) in the spring of the year (2005). Tube wall thickness was an added variable to test rodent control. In randomized plots, rodent repellent and insecticides were applied to the drip tube surface. There were three tube thicknesses, five chemical treatments, four field positions, and three replications per treatment. Irrigation drip tubing was installed using the same equipment describe earlier (Roberts Ro-Drip with 0.20 mm, 0.25 mm, and 0.38 mm tube thickness). Sub-plots were 1.83 m wide and 60 m long. The chemical treatments were untreated, Contrac Blox® (Bromadiolone: [3-[3-(4′-Bromo-[1,1-biphenyl]-4-yl)-3-hydroxy-1-phenylpropyl]-4-hydroxy-2H-1-benzopyran-2-one]), Ropel® (Benzyidlethyl (2.6 xylyl carbamoyl) Methyl Ammonium Saccharide and Thymol), Lannate LV (Methomyl), and Orthene (Acephate). Just prior to peanut canopy closure, insecticides and animal repellent were banded over the SD tubing. Lannate was banded at a concentration of 12.5 ml/L and applied at 25 L/ha. Ropel® was diluted to 50% and banded at 25 L/ha. Orthene concentration was 24 g/L and applied at the same rate as Ropel® and Lannate. Ropel® manufactures suggest that this chemical does not wash off with precipitation, which was one of the major criteria for selecting this product. Contrac Blox® was placed in a grid next to the drip tubing at 185 Blox®/ha. Three Contrac Blox® were monitored to determine when to re-apply the Blox® if needed. Prior to harvest, the SD tubing was removed and holes were counted in 15 m sections (positions) for each tube thickness and treatment. Position 1 was adjacent a grass area while position 4 was adjacent a corn plot. Positions 2 and 3 were between positions 1 and 4.
Site 4 was adjacent to Site 3 with the same soil type and slope. This area received the same tillage and management practices as described for Site 3. This site had a non-irrigated and irrigation component such that only half the total plot was irrigated. Each irrigated plot had a non-irrigated plot on each side. Irrigation tubing was not installed until the middle of June to facilitate a tillage project. During tube installation all three laterals (designated outside east, middle, and outside west) were treated with Ropel®. As tubing (0.20 mm tube thickness) spooled off the roll, it passed through two rope wicks, top and bottom, which was attached to a chemical bath, thus, placing the repellent on both sides of the tubing. Ropel® was applied only at installation and not at row closure as with other sites. Both outside tubing locations (east and west) were adjacent a nonirrigated plot. There were three replications across the field. Sub-plots were 5.5 m by 60 m. No chemicals were applied to the other half of the irrigated treatment. Prior to harvest, the SD tubing was removed and holes were counted in 15 m sections (positions described earlier) in the field.
Data collected during the growing season at all four sites were: 1. Documentation of the number of holes that were fixed, 2) time it took for repair, and 3) equipment needed for each repair. In Sites 3 and 4 at the end of the growing season, all tubing was inspected in each treatment to identify total number of existing holes not repaired.
Site 1 will be used as a comparison since the tubing was covered and chemical treatment was not feasible. Site 2 was mainly used to determine cost to repair damaged tubing. Sites 3 and 4 were analyzed separately because of different treatments. The number of holes in each treatment was subjected to randomized block analysis of variance (ANOVA) procedures (
Precipitation recorded during the growing season (01 April to 01 October) totaled 727 mm as measured by an electronic weather station located onsite. Precipitation events were quite frequent such that only two time periods during the growing season had 15 days between events and four time periods with 9 days between events.
Visual inspection of drip tubing showed that most holes were started on the folded edge. It is most likely that if the drip tubing was full of water the mice and rats are unable to open their mouths wide enough to chew on the tubing edge. However, without frequent irrigations the drip tubing lays flat allowing the mice and rats to chew on the edges. Thus, less frequent irrigation events would give the rodents a longer opportunity time to gnaw on the tubing edge. These frequent precipitation events resulted in fewer irrigation events and possible washing off of the insecticide chemicals on the drip tubing thereby increasing the number of incidence of rodent damage.
Total number of leaks repaired at Sites 1, 2, 3, and 4 for various treatments of surface drip tubing with untreated, soil cover, animal repellent, insecticides, and a rodenticide. Site 1 had drip tubing in use for three years. Sites 2, 3, and 4 used tubing for one year. These values were used to identify time required per repair.
There was little or no biological damage to the drip tubing in corn or cotton in Site 1 (2003 and 2004) or Site 2 (2005). There was major tube damage in peanut (
The time required to find and repair a drip tube leak can be variable. It is possible for a leak to occur and water move off-site resulting in extensive time required in finding the hole. Time data collected from these four sites indicate that it takes about 4 minutes to repair any given leak (repair time data not shown). This repair time does not include the time it takes to find the leak. The best way to find or locate a leak was to check the flush end of the tubing. If the flush end had no pressure then a leak was in that row. By walking across the end of the field opposite the supply side, a manager could quickly identify which rows had leaks.
Site 3 and 4 were situated with a grassed border area on the north (Position 1) and a corn field to the south (Position 4). Current data (
Total number of holes identified after harvest for tube thickness, field position, and treatment for Site 3. Column means followed by the same letter are not significantly different according to Tukey's HSD comparison test. Field position 1 was next to a grassy area and field position 4 was adjacent a corn field.
Total number of holes identified after harvest for tube location, field position, and chemical treatment for Site 4. Column means followed by the same letter are not significantly different according to Tukey's HSD comparison test. Field position 1 was next to a grassy area and field position 4 was adjacent a corn field.
Another hypothesis was that thicker walled tubing would help reduce rodent damage. Site 3 shows less damage to the thinner walled tubing compared to the thicker walled tubing (
The spraying of chemical on the drip tubing was to create a hostile environment such that mice would not inhabit the area near the SD tubing. By spraying the drip tubing just before canopy closure may also allow a short time period for the peanut canopy to cover the tubing for added protection and reduce the opportunity time for precipitation to wash the chemical off of the tubing. By creating this hostile environment with chemicals, rodent activity should decrease. However, there was no difference in the number of holes counted in any of the chemical treatments compared with the untreated tubing. At Site 4, the Ropel® did have less rodent activity (2392 holes/ha) than the untreated (6042 holes/ha) and about the same number that was found in Site 3 (1981 holes/ha). This can possibly be attributed to late installation of the tubing and that Ropel®, according to label, does not wash off during precipitation events, thereby repelling the rodents and increasing the rodent damage on the untreated tubing.
The rodenticide was not an effective control method. The cost per unit area for the rodenticide was the highest of all the chemicals selected (
Economic values for labor, repair equipment, rodenticides, insecticides, and animal repellents. Tubing installed in alternate row middles (1.83 m apart). About 15 cm of blank tubing is used for a repair splice for each hole.
A comparison of all four experimental sites indicates that a light covering of soil/plant debris on drip tubing can reduce rodent damage to an acceptable level. The cost associated with repairing drip tubing at Site 1 peanut (
Tubing (0.20 mm tube thickness) installed on a 1.83 m spacing would cost about $300/ha (
There was very little rodent damage to drip tubing in corn or cotton. In peanut, a light covering of soil or plant debris will keep rodents from damaging the drip tubing to acceptable levels. Spraying the tubing at canopy closure (peanuts) did not work with the two insecticides tested. The animal repellent, Ropel®, did seem to have less rodent damage on drip tubing at one of the sites but was not consistent across multiple sites. The rodenticide, Bromadiolone (Contrac Blox®), had no effect on reducing rodent damage. Since none of the insecticides, repellents, or rodenticides were effective in controlling rodent damage, the expense of purchasing and applying these chemicals would not be an option. Thicker walled tubing had over three times more damage than the thinner walled tubing implying that thinner wall tubing may be a better choice. Overall, lightly burying the tubing may be the only option available to reduce rodent damage in peanut fields. However, this light soil cover on the drip tubing may not be an option if clean tillage is the normal farm practice such that drip tubing would need to be destroyed and replaced each year. If the tubing could be installed and not removed for three to four years such as with strip tillage, this system would be a more cost effective irrigation system for installation and repairs.
The authors would like to thank Ernest Yoder, Larry Powell, and Jesse Childre for field layout, drip tube equipment design and maintenance, day-to-day data collection, and laboratory analysis.
USDA-ARS-National Peanut Research Laboratory. P.O. Box 509, 1011 Forrester Dr. SE, Dawson, GA 39842.
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