Guide for Spraying Fruit Trees

Agdex#:	210/606
Publication Date:	03/00
Order#:	00-035
Last Reviewed:	08/09
History:	Replaces Factsheet "Guide for Spraying Fruit Trees", Order No. 93-121
Written by:	Paul Goodwin - formerly OMAF; Ken Wilson - formerly OMAF

Table of Contents

1. Introduction
2. Maintenance
3. Safety
4. Application
5. Tree-Row-Volume Concept
6. Sprayer Set-Up
7. Precautions
8. Related Links

Introduction

A thorough understanding of the fundamentals of pest control is required if you are to be a good steward of the land. Correct timing of a pesticide application, based on a pest management program, is only one component of pest control. Timing, plus proper application, is the key to success. To do a satisfactory job of application a sprayer must be properly matched to tree size, spacing, pruning practices, ground conditions, acreage and weather conditions. A sprayer must also be kept in good operating order to ensure proper spray coverage for good pest control. [Figure 1]

Equipment should be in top condition, maintained regularly and calibrated at least once a year. Never assume that because you have followed the service instruction manual for winterizing your sprayer, the machine will be ready for instant hook-up and use in the coming season. You need to check for several common start-up problems before using the sprayer. If the sprayer is not checked, unnecessary and costly breakdowns, improper pesticide application and even a shortening of the life span of the machine may result.

Maintenance

Before the first spray application of the year, pump clean water through the system until the discharge is clear of all dirt, sludge and scale that may be present in the tank, pump, hose lines, and nozzles. Check the sprayer thoroughly for worn belts, pulleys, bearings and hoses.

Steps:

1) Check the pump. If you use a centrifugal pump, check for the correct operating pressure. With a piston pump check the packing for water or oil leaks. Be sure to check the valves, seats and "O" rings on the valve seats for damage or excessive wear. With a diaphragm pump, check the diaphragm(s) very carefully. If one is worn, replace them all. The valves and seats are also an integral part of this type of pump and should be checked. [Figure 2]

2) Examine all hoses and connections for leaks, especially the suction hose. An air leak in the suction line would seriously interfere with the operation of the pump and the pressure gauge.

3) Check all strainers throughout the delivery system, including the suction strainer, particularly in the early season when scale from the tank and lines may break free. If a strainer contains any sort of deposit, clean the tank and lines thoroughly. Replace all cracked or poorly fitting strainers. [Figure 3]

4) On regulators with stem packing, be sure to have the packing adjusted properly. If the packing is too tight, it will interfere with the movement of the stem. This interference will cause fluctuations in pressure and may allow a dangerously high pressure to build up. If the packing is too loose, there may be leakage. If you are unsure of the pressure for which the regulator is set, slacken off the pressure adjustment before starting the pump. Gradually adjust to the required pressure. The adjustment must be made each time the stem, valve, or seat is replaced.

Figure 2. All pumps should deliver the necessary flow rate required at the boom at the desired pressure, and have sufficient flow to provide proper agitation.

Figure 3. Inspect and clean the strainer early in season to ensure free flow of the pump.

5) Be sure to check the pressure gauge. If its accuracy is doubtful, replace the gauge. Check the pressure at the nozzle manifold by removing a nozzle body and inserting a good pressure gauge. [Figure 4]

6) Check all belts for wear and proper tension to be sure the power created is being transmitted efficiently. Tighten or replace the belts if necessary. [Figure 5]

7) Materials in the tank must be completely and uniformly mixed. Be sure the paddles are secure on the agitator shaft, the shaft bearing is lubricated, and the seals adjusted to prevent leakage. For hydraulic or jet agitation, you must ensure that the pump is operating to specifications: the pump capacity must be sufficient for the total nozzle output, flow to the agitator and some overflow if you are to maintain pressure.

Figure 4. If gauge needle is bouncing, compare with a known working gauge. Check to see if your pulsation dampener is malfunctioning.

Figure 5. Inspect belts regularly.

8) Check nozzle discs and swirl plates for signs of wear and replace before serious wear occurs. Worn nozzles will produce an irregular droplet pattern causing an excessive number of coarse and very fine droplets. [Figure 6]

Extra large droplets do not produce a uniform coverage of the target area, and a large percentage of the very small droplets drift away and do not make it to the target area at all. Worn nozzles can result in application rates that are different from the label rates. These rates could be excessive and therefore in contravention of the label. Harm could result to the environment and grower costs could increase. The rate of nozzle wear will vary with the abrasiveness of the spray fluid, pump pressure, and the hardness of the material used for the nozzle components. Replacing nozzle discs and swirl plates is a cheap investment when compared to the overall cost of pesticides for a season.

Routinely clean nozzles throughout the season using a toothbrush or other soft material. Never use a piece of wire, a nail, or other metal object because any of these could damage the orifice, distort the spray pattern, and greatly alter the spray output. [Figure 7]

Figure 6. A pesticide spray is a pressurized application of a liquid solution or suspension of pesticide product. Sprays are actually atomized solutions consisting of a range of droplet sizes.

Figure 7. Use a soft-bristled brush to clean nozzle tips.

9) Using clean water, perform a volume output check at the beginning of each season and at least once during the season to make sure the sprayer is putting out the desired amount of spray.

Safety

Along with calibrating and adjusting the sprayer for spring you should refresh your memory regarding pesticide safety. Pesticide storage, handling, transportation, disposal and the proper use of protective clothing are adequately covered in the Grower Pesticide Safety Course manual. Remember to heed all label warnings and carefully adhere to mixing instructions. Check current publications and product labels for precautions. Review these safety items carefully at the beginning of every growing season.

Application

When you are trying to apply a pesticide to a crop canopy, it is important to consider the density of that foliage barrier. Cultural practices play an important role in achieving optimum spray coverage. Sprayers that are calibrated in the spring to deliver excellent spray coverage may show poor coverage by the end of the growing season if attention is not paid to proper pruning practices. [Figure 8]

Keep in mind the changing shape of the tree canopy during the growing season and eliminate the limbs that may create a dense canopy of foliage. Often the same practices that promote better light penetration into the canopy to produce a better quality fruit will permit better spray penetration and coverage, as well.

Travel speed is another important factor to consider when spraying. Although this is governed by a number of factors (i.e., time constraints), be aware that the ground speed must be slow enough to allow the spray-laden airstream to penetrate the foliage. This spray-laden airstream must travel the required distance and be deposited on all parts of the trees, especially the tops and particularly on the underside of the leaves.

Figure 8. Coverage increases when canopies allow for better penetration. Pruning helps.

Tree-Row-Volume Concept

Tree-Row-Volume (TRV) is an estimate of the volume of foliage in a hectare of trees. Unlike row crop spray applications, orchard applications involve the spraying of a series of rectangular-shaped boxes full of foliage. Because of this, it is important to obtain maximum spray coverage while minimizing wasted spray material on the alleys between the rows. In OMAF publications, recommended pesticide application rates are based on spraying trees 4.5-5.5 m in height. Experience has shown that under Ontario conditions, a hectare (ha), or 10,000 square metres (m2) of properly maintained, fully-grown, standard-size apple trees can be effectively sprayed using 1,000 L of water. The height of these trees is typically 4.9 m and the cross-row limb spread is usually about 7.9 m, with 11 m between rows. By using the TRV concept, simple calculations can be made to determine the volume of foliage present in a standard hectare of trees. [Figure 9]

Figure 9. Tree-Row-Volume calculation (standard trees). This picture illustrates the spraying of a rectangular box full of leaves that would be 35,191 m3 in volume, or the TRV of that hectare. As previously mentioned, approximately 1,000 L of water is necessary to effectively spray this TRV, that is, about 28.4 L per 1,000 m3 of TRV.

However, as the industry moves towards size-controlling rootstocks and medium to high density plantings, standard orchards are becoming less common. Adjustments to reflect the changing tree size are necessary.

For example, a TRV formula applied to a size-controlled planting with a tree height of 3.0 m, a cross-row limb spread of 3.4 m, and 5.5 m between rows shows that sprays should be applied to a foliage volume of 18,545 m3. This TRV is only 53% (18,545\35,191 x 100) of the previous standard tree example. To spray each cubic unit of leaf volume in these size-controlled trees the same as the standard-size trees, adjusting the volume would seem appropriate. This would result in the use of 53% of the water and 53% of a pesticide, as otherwise required. This would mean significant economic savings for growers and a lower pesticide load on the environment. Without this correction, the TRV would equate to a significant over-spraying of these smaller trees.

All orchard blocks are different in respect to TRV. To be accurate, measure the exact dimensions of the trees before calculating the TRV for each block. Keep records and use them during the growing season to ensure the sprayer is accurately calibrated. Recognize that as the trees grow, the amount of water and pesticide required will need to be adjusted for the different tree sizes.

Agricultural chemical suppliers cannot be held liable for a failure, when rates below those recommended on their labels are used. Do not use TRV considerations if a label indicates doing so is inappropriate and never exceed full label rates.

Sprayer Set-Up

Once the decision has been made about how many litres per hectare are needed, a simple calculation is required to obtain the Litre-per-minute discharge rate for each side of the sprayer. Choose an appropriate ground speed (e.g., 4.8 kph), and do the following calculations:

 L/min/side =  L/ha X spacing between rows (m) X ground speed (kph) ÷ 1200

Note: The total discharge for two sides must not exceed the capacity of the pump.

Using the nozzle discharge chart for your sprayer, choose a combination of disc and swirl plates (cores) for each nozzle position at a selected pressure, in order to give the desired Litre-per-minute discharge. Choose nozzles so that a larger portion of the output is emitted from the centre nozzles of the sprayer, and choose nozzles with progressively smaller outputs as you move away from the centre position to the top and bottom of the nozzle bank. The total output for all nozzles must not exceed the desired Litre-per-minute discharge. If the output per minute is higher than required, reduce the nozzle sizes in the bottom half of the banks. If lower than required, increase the size of nozzles near the centre position.

Figure 10. A rule of thumb for volume distribution for full-sized trees is to apply two-thirds of the volume in the upper half of the boom.

Adjust the nozzle selection so that a larger portion of the output is emitted from the centre nozzles of the sprayer. Choose nozzles with progressively smaller outputs as you move away from the centre position to the top and bottom of the nozzle bank.

Many variations are possible to suit different tree shapes and densities. For smaller trees and supported planting systems, a smaller number of progressively smaller nozzles may give the desired coverage.

When the appropriate nozzle selections have been made, and they approximate the required Litre-per-minute discharge, a calibration of the sprayer will be required. Fill the tank with water and spray for 3 minutes. Then use a flow metering device or a pail that is calibrated in litres to refill the tank to its original level. The results should be close to the desired discharge. A slight increase or decrease in pressure could be used to adjust the volume discharge.

Precautions

When calibrating sprayer delivery, be sure the pressure gauge is accurate and all nozzles, screens and filters are clean. When making large adjustments to the sprayer volume, only 2 factors matter:

• the nozzles' size and configuration and
• the ground speed of the tractor.

Adjusting the pump pressure is not an effective way to make large adjustments to the spray volume.

Water volumes of less than 300 L/ha are considered inadequate if there is fruit to protect. The lower the volume of spray, the more critical the accuracy of the application and rates become.

Higher volume sprays are important to control some pests. Low volume applications and/or low rates of certain pesticides have resulted in poor control of insect pests like scale, mites and woolly aphids, particularly in treetops. For oil sprays, spray volumes must be high enough to soak the bark completely. When spraying streptomycin for the control of fire blight, or applying chemical thinners, higher water volumes may be required.

Remember, TRV serves as a guide for calibration. Recognize that as the tree canopy density increases throughout the season, an adjustment to the volume of water and pesticide may be necessary in order to maintain good coverage. Increased pest pressure and past experience may also influence the actual amount applied. Accurate calculation of TRV will not compensate for poor coverage, timing, pesticide choice, or weather conditions.

For more information on orchard sprayers, see OMAF Publication 310, Integrated Pest Management for Ontario Apple Orchards, or the Best Management Practices publication Pesticide Storage, Handling and Application (Order No. BMP 13)

Related Links

• Best Management Practices: Pesticide Storage, Handling and Application (Order No. BMP 13)