| | Introduction
Conservation farming and environmental concerns have driven technology towards reduced, more efficient pesticide use. One step in this drive has been the development of the Detectspray system. The system sprays only the part of the field which needs it, namely the weeds, not the ground.
Operation
Each Detectspray has four basic components:
- master controller;
- ambient sensor;
- multiple spray sensors; and
- multiple solenoid valves.
An individual spray sensor and solenoid valve are installed in line with each existing sprayer nozzle, normally at 50.8 mm (20 in) spacing along the boom. Each spray sensor includes an internal microprocessor. This microprocessor uses reflected light from the ground cover, along with information from the ambient sensor and operator settings on the master controller, to detect green plant growth, which activates the related solenoid valve. Green plants absorb light in the red waveband and reflect light in the near infrared waveband. On the otherhand, soil and dead vegetation absorb the near infrared waveband and reflect the red waveband. The Detectspray sensors distinguish green weeds from soil or stubble by how much red and infrared is reflected to the sensors. When a weed takes up 3 percent or more of any area under a sensor, the near infrared reflectance/red reflectance ratio increases. When the ratio increases above the value set for the particular soil surface where spraying is being done, the solenoid valve is opened and the weed sprayed. The area sprayed is: 0.5 m (nozzle spacing) x 0.8 m (at 20 km/h).
Weed detection and spray activation are virtually simultaneous. The period from detection to spraying the target is determined by the average spray velocity.
At 16 km/h, a new ground surface is scanned by each reflectance sensor every 1.3 cm of travel. At slower speeds, this scanning frequency is even greater. The ground area scanned by each sensor is a nearly rectangular area approximately 20 x 60 mm (8 x 24 in) when the sensor is mounted at a height of 50.8 mm (20 in).
This area approximates the coverage pattern of a flat fan nozzle operated at a similar height.
A continuous spray option can be used instead of the detection mode to spray with the entire boom. In addition, sensitivity of the system can be varied by increasing or decreasing a setting on the master controller. This means more green under the sensor is needed (larger weed) if a higher ratio value is selected.
Benefits
The main benefit of the Detectspray system is to support conservation tillage and fallow weed control. Detectspray has demonstrated particular benefits when used for pre-seeding herbicide application in direct seeding operations, chem-fallow and post-harvest weed control. Since the Detectspray sprays individual weeds, herbicide is applied over a reduced area, thus reducing the spray volume, cost of herbicide and time of operation. In some fields, this can mean a saving of over 75 percent in herbicide costs. However, producers should remember all spray savings are based on the number of weeds in the field.
There are a number of secondary benefits to spot spraying. These benefits include
- Reduction in residual herbicide rates, reducing the potential for carryover of phytotoxic residues.
- Non-target spraying will also be reduced since the potential for spray drift is reduced when applying less chemical.
- Chemical mixtures or products that were previously prohibitive in cost on an overall spray basis can now be considered when selective spraying, providing better control of difficult weeds and more flexibility in chemical use.
Potential problems
As with other spray operations, researchers have indicated weed control can be reduced because of rain and inadequate herbicide rates or mixtures.
Other typical spraying concerns become important when using the Detectspray system:
- An important factor with the system is stability of the spray boom. Variation in the height of the detectors significantly influences the sensors’ ability to detect weeds.
- Spray booms should have outrigger wheels to stabilize height. Vehicle mounted booms are not suitable for Detectspray systems unless boom stability can be ensured.
- Shadowing of the sensor can be caused by any obstruction of the sensor to the sunlight (incident light). This can be a concern in early morning or later afternoon when the sun is low. Shadowing can increase the background ratio and cause false triggers and spraying. Adjustment of the sensor sensitivity will help remedy this problem. Detectspray is looking for ways to make the sensors more reliable at lower light intensities through artificial lighting and other design changes.
- Maintaining nozzle pattern is crucial, especially in side winds. Pattern changes will result in poor coverage and control of weeds at the spray patterns edges due to misses. Therefore, using nozzles and pressures that produce a high percentage of small droplets that are susceptible to light winds is undesirable. If fine sprays are used or the sensors are located high above the weeds, radiance detectors should be located further in front of the nozzles to allow the slower droplets to reach the targets. The same is true if the sensors are located high above the weeds.
The manufacturer outlines the system can consistently detect 5 cm diameter weeds at 16 to 20 km/h. However, smaller weeds can be missed. To solve this problem, applicators have fitted spray booms with dual application systems. A dual boom system uses the conventional set of nozzles to broadcast at a relatively low rate (approximately 25 to 30 percent) of product for control of small emerging seedlings; and at the same time uses Detectspray to apply the balance of the normal rate (70 to 75 percent) to larger, established plants. Using two sprays enhances flexibility and reliability of control of small weeds without requiring two trips across the field. If the two boom system is not practical, detection of smaller weeds can be increased by lowering the sensor closer to the ground, which will decrease the area scanned. However, the sensor and nozzle spacing must be reduced.
Present research
At present, Detectspray systems are being used by 9 research organizations and approximately 12 farmers and custom applicators in Canada and the United States. Research activities are focused on varying agronomic issues in the respective areas, though most projects are assessing the level of weed control and chemical savings provided by Detectspray compared to broadcast herbicide application or to conventional tillage operations. Evaluation includes determining which weed size can be controlled most consistently, what is the best plumbing to use, climatic variations, corrosion concerns and other performancerelated issues.
Several farmers and custom applicators now have significant experience with Detectspray operating in field conditions. Most of these commercial size units have gained experience ranging from 3,000 to 30,000 ac.
Related systems
Detectspray is not the only selective system on the block. Similar packages are sold in Europe, including one unit said to be capable of distinguishing between weeds and crop. A Canadian company is testing a prototype which selectively sprays weeds. In the United States, a new sprayer has been developed which will selectively spray weeds that stick above the crop.
Distributor
Distributed in the United States by:
Concord Manufacturing
2800 Seventh Avenue North
Fargo, North Dakota USA 58102
Telephone:
Facsimile:
(701) 280 1260
(701) 280-0706
Cost: (As of 3 December 1993) Base Price: $3,253, plus $800 per nozzle. Prices are in U.S. dollars, f.o.b. Fargo, North Dakota, and include no brackets or plumbing attachments to hook up to the existing sprayer.
Information was obtained or rewritten from
Agricultural Engineering (Felton, W.L., and McCloy, K.R.) - November 1992
Agriculture Canada - Dwayne Chevalier
Concord Manufacturing - Gordon Hjertaas, Product Manager
Country Guide (Dave Wilkins) - February ‘93
Country Guide (Bryan Lyster) - June/July ‘92
Farm Chemicals (Dorothy Schmuck) - Aug.’92
Farm Journal (Larry Reichenberger) - Dec.’91
Gateway Fuel - Ken MacPhail
The Alberta Farm Machinery Research Centre now called Agricultural Technology Centre is at the forefront of machinery evaluations, applied and scientific research, and development of innovative agricultural technologies. |
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