Cornell University,

Department of Agricultural and Biological Engineering

Riley Robb Hall, Ithaca, NY14853-5701

Considerable pressures exist in the food and farming sector with many more challenges in prospect. Farmers are under great pressure when applying pesticides. An increasing awareness of environmental pollution, along with concern about operator contamination, has resulted in increased legislation concerning pesticide use.

There are many news developments in spray technology that will help reduce the costs involved in applying pesticides. The main costs associated with pesticide application are the cost of pesticides, which continue to rise in many cases. Any technology that reduces the amount of product necessary to control a weed, insect or disease, or improves its effectiveness, is welcome. The other major costs to consider are those of labour and timeliness.

New techniques, developed over the past five years, will be addressed in this paper.

In 1999 a number of pesticide manufacturers are adopting the BCPC nozzle selection system and stating on the pesticide label the spray classification needed for their product. Reference nozzles, tested in a laboratory using a laser analyser, are then classified according to the characteristics of the spray produced. Very fine, fine, medium, coarse and very coarse are the categories of spray. The label recommendation makes nozzle selection far easier for the sprayer operator. A general guideline is:

Fine classification for fungicides and insecticides

Medium classification for herbicides

Coarse classification for pre-emergent sprays

However, weather conditions, particularly wind and its effect upon drift, must be taken into consideration. If the label or supplier makes no recommendation concerning nozzles or spray quality, then a reasoned choice of spray quality must be made, taking three matters into consideration:

1. the target
2. the product
3. the risk of drift

Spray drift has long been a problem on many farms. Small droplets, less than 100 microns, drift in the air, whereas larger droplets, over 300 microns tend to bounce off leaves. A number of nozzle manufacturers offer low-drift nozzles to reduce drift.

Spraying Systems offer a pre-orifice flat fan, which reduces the internal operating pressure of a standard tip, producing a coarser spray at pressures between 30-60psi. The Drift Guard reduces drift by 50 %. The Turbo TeeJet contains a turbulence chamber to reduce drift by 50% at pressures between 15-90psi.

Air inclusion nozzles also reduce drift by allowing air to be incorporated into the liquid flow. The emitted spray contains large droplets filled with air bubbles and very few drift-prone nozzles. The droplets shatter on impact with a leaf, the air bubble absorbing the energy. Spraying Systems, Greenleaf Technologies, Lurmark and Lechler manufacture air inclusion nozzles.

The use of shielded booms improves deposition, reduces drift and increases the window of opportunity available for spraying. A finer spray can be used which will adhere better to the plant or insect and current research is looking at using reduced rates of pesticides as a direct result of using shielded booms. Research at the Alberta Farm Machinery Research Centre shows that a shield can reduce drift by 86% when using a medium spray at forward speeds in excess of 10 m.p.h. Farmers must consider if the benefit of a shielded boom outweighs the cost. Research also shows that choosing a nozzle with a larger flow rate may be as effective at reducing drift as constructing a costly shield around a boom. Forward speed and droplet size must be considered before a decision is taken.

Advantages include drift reduction, particularly useful when using non-selective herbicides in windy conditions, thus increasing the window of opportunity and improving timeliness. Band spraying is more economical than overall spraying; hoods ensure the pesticide goes where directed, resulting in a more effective application.

Hoods can be purchased as a kit for retrofitting to an existing sprayer or a complete spraybar with hoods can be purchased for varying row widths.

Hoods may also be used between the row; they limit pesticide drift, resulting in excellent crop safety, an important factor when considering quality control and accountability. An another advantage is that spraying is much faster than cultivating between the row and doesn’t cause moisture loss or bring up fresh weed seeds.

Many farmers are concerned with excess application of pesticides, particularly where light infestations of weeds occur and pesticides are sprayed onto bare ground. Patchen Selective Spray Systems of California market a sensor for fitting into spray hoods which will recognise the difference between weeds and bare soil. When the sensors detect green plant material (chlorophyll) under the hood, a spray nozzle is activated, applying pesticide to the plant in a 12-inch band. Each sensor emits light and then monitors the reflectance of that light, which will differ between soil and chlorophyll. Spraying can be carried out in the day or night as each sensor carries its own light source. Spraying is controlled by a solenoid valve that switches the spray on/off quickly, avoiding excess application.The sensor emit light and then monitors the reflectance of light, which will differ between soil and chlorophyll. The sensor emits light and then monitors the reflectance of light, which will differ between soil and chlorophyll.

An adjustable hood is available for different row widths.

Results from USDA-ARS and at the University of California show a 50 —85% reduction in pesticide use compared with a continuous sprayer, the variation depends on weed populations.

Sprayer tank washing has always taken a long time if the operator is careful about tank hygiene and is meticulous about cleaning out the pipeline, filters and nozzles. The operator is at great risk during tank washing from splashes of pesticide residue. Commonly, washing out may be carried out during overtime periods at the end of the working day, resulting in extra labour costs and employee concern regarding leaving the work place as soon as possible.

The use of built-in tank washers reduces the amount of water required resulting in less rinsate to dispose of. The other major advantage, particularly when used in conjunction with a second tank of clean water is that rinsing out can be done in the field without the need to return to the filling area. Operator contamination is minimised.

Tank washers can be easily fitted by farmers into the top of the sprayer tank. Plumbing of hoses is straightforward and the rinsing heads are relatively inexpensive to purchase.

A conventional crop sprayer is fitted with an injection system comprising one to four pumps which dispense pesticide at a known rate into the water stream within the sprayer pipeline. The main tank of the sprayer holds clean water only. The pesticide is mixed with the water, either in a manifold or at the main water pump and the resultant mix flows to the booms and nozzles.

An electronic controller adjusts the pesticide injection pump according to changes in operating requirements, e.g. changes in application rate and pesticide requirement. The major advantages of injection sprayers are:

i) reduction in environmental pollution due to the elimination of tank and pipeline washing.

ii) reduction in the operator contamination which occurs with conventional sprayers. Ideally the pesticide would arrive at the farm in large returnable and refillable containers and be connected directly to the pesticide injection pumps. The resulting closed system reduces operator contamination.

iii) the use of an electronic controller which allows each pesticide pump to deliver a specific product. The injection pumps can be switched on / off, as and when required, to spray various patches of weeds/disease.

iv) the amount of pesticide applied (dose rate) can be adjusted on the move, allowing a higher dose rate to be applied to a high infestation of weeds or disease and vice-versa.

1) Technology, in many cases, allows pesticide to be applied in a more efficient manner thus reducing application costs.

2) Nozzle selection, based on spray classification, will be made easier when the pesticide label carries a recommendation.

3) Drift is certainly reduced when shielded booms are used but the farmer must consider forward speed, droplet size, flow rate and low-drift nozzles as alternatives.

4) Direct injection sprayers enable farmers to rationalize their pesticide use, reduce environmental pollution and reduce operator contamination.