A weed wiper is an agricultural machine that applies herbicide directly to weeds by physical contact instead of spraying it through the air. It is useful when weeds grow taller than the crop, because the applicator can touch the weed leaves while passing safely above the shorter crop plants. This targeted method can reduce herbicide waste, drift, and crop injury.
Weed wipers are used in pastures, row crops, orchards, and conservation areas where selective weed control is important.
The main working part is a horizontal bar, roller, rope, or sponge material that is kept moist with a herbicide solution. As the tractor or ATV moves forward, taller weeds brush against the applicator and receive a thin film of chemical on their stems and leaves. The herbicide is then absorbed and moved through the plant, often reaching growth points or roots depending on the product used.
Effective operation depends on proper wiper height, travel speed, solution concentration, plant contact, and weather conditions.
Understanding Agricultural Machines: Weed Wipers
Most weed wipers use a tank, a hose, a control valve, and an absorbent applicator. Some applicators are carpet strips that hang down. Others are rollers covered with fabric or foam.
The liquid must wet the outer surface evenly. If one end is dry, weeds in that part of the machine receive too little chemical. If the material is soaked beyond its holding capacity, liquid can run off onto soil or nearby plants.
The delivery system may use gravity, a small pump, or both. A steady flow matters more than a fast flow. Operators often check the applicator after a short distance to see whether it remains evenly moist.
Plant growth affects the result. Young, actively growing weeds usually take in more herbicide than drought stressed or damaged weeds. A waxy leaf surface can shed liquid, while hairy leaves may hold it near the surface.
The direction of travel can matter because stems and leaves bend differently when struck from opposite sides. Many growers make a second pass from the other direction when weeds have thick foliage.
They must follow the herbicide label closely. Labels state which plants can be treated, the correct mixture, the waiting period before grazing or harvest, and rules for protecting water.
Good setup begins before the machine enters the field. The operator measures crop height and weed height at several places, not just near a gate. Fields are uneven, and plant height changes across slopes, wheel tracks, and wet patches.
The applicator needs enough clearance to avoid ordinary crop leaves, yet it must reach a useful part of each weed. Travel speed should stay steady. Sudden speeding up reduces contact time.
Sharp turns can swing a long boom into plants that would normally be clear. Turning off the flow during transport and headland turns prevents unwanted deposits.
Maintenance is part of accurate treatment. Dried chemical can block hoses, stiffen rope wipers, or make rollers uneven. The machine should be cleaned using the method stated on the product label.
Gloves, eye protection, and clean water for washing are sensible precautions when mixing or handling solution. Operators should inspect hoses for leaks before filling the tank. They should record the field, date, product, mixture, and weather.
These notes help explain later results. They can reveal whether poor control came from missed weeds, unsuitable plant growth, rain soon after treatment, or herbicide resistance. Repeated use of the same herbicide group can select resistant weeds, so weed control plans often include crop rotation, mowing, cultivation, and different approved herbicide groups.
Key Facts
- Weed wipers work best when weed height is greater than crop height, so the applicator contacts weeds but not the crop.
- Application rate per area depends on wiper width, travel speed, solution flow, and contact time.
- Area covered per hour = width x speed / 10, where width is in meters, speed is in km/h, and area is in hectares per hour.
- Contact selectivity comes from height difference, not from a nozzle spray pattern.
- Too much solution causes dripping, which can injure crops and waste herbicide.
- A systemic herbicide moves inside the plant after absorption, while a contact herbicide mainly damages the tissue it touches.
Vocabulary
- Weed wiper
- A machine that wipes herbicide onto taller weeds using a moist bar, roller, rope, or pad.
- Applicator bar
- The horizontal part of the machine that holds or carries the herbicide solution and physically touches the weeds.
- Herbicide drift
- The movement of herbicide away from the target area, usually by wind or airborne droplets.
- Selective control
- A weed management method that harms unwanted plants while reducing damage to desired crop plants.
- Systemic herbicide
- A herbicide that is absorbed by plant tissue and transported within the plant to affect growth or survival.
Common Mistakes to Avoid
- Setting the wiper too low, which is wrong because the applicator can touch crop leaves and cause herbicide injury.
- Driving too fast, which is wrong because weeds may not stay in contact with the wiper long enough to receive an effective dose.
- Overfilling or oversaturating the applicator, which is wrong because dripping can contaminate the crop and soil below the bar.
- Using a weed wiper when weeds are shorter than the crop, which is wrong because the machine cannot selectively contact the target weeds.
Practice Questions
- 1 A weed wiper has a working width of 6 m and travels at 5 km/h. Using area covered per hour = width x speed / 10, how many hectares can it cover in 1 hour?
- 2 A field is 18 hectares. A weed wiper covers 3 hectares per hour. How many hours are needed to treat the field, not including refilling time?
- 3 A farmer has a crop that is 45 cm tall and weeds that are 35 cm tall. Explain whether a weed wiper is likely to be selective in this field and what adjustment or timing would improve its use.