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Ground Spraying

In fruit production, chemical weed control is usually the least expensive option. Controlling weeds underneath fruit tree plantings benefits the plantings, as well as production, in several ways: (1) Herbicides reduce injury from mice by keeping vegetation away from the tree trunk; (2) herbicides prevent root and bark injury caused by disking; (3) herbicides allow the soil to remain undisturbed, helping to prevent weed seed germination and soil erosion; (4) reducing vegetation around fruit plants can help prevent virus, disease, and insect problems.

Before establishing any fruit crop, it is important to eliminate persistent perennial weeds from the field. For tree fruits it is best to establish the grass cover crop the year before planting. The cover crop will help prevent erosion and allow you to get into the field earlier in springtime to plant. The fall before planting, treat the field with a 2,4-D herbicide to eliminate any perennials that were established with the grass cover. Immediately before planting, treat rows where trees will be planted with glyphosate or paraquat, to kill grass and aid in planting.

Getting the most from herbicides requires good management. Sprayer calibration, dosage, soil type and organic matter content, and rainfall all affect the success of a weed control program. Below are cautions and reminders to be aware of before applying herbicides:

Sprayer calibration
Always calibrate sprayers before each season of use. During the season periodically check calibration. Replace worn nozzles and check pressure gauges at least once a year. (See Calibrating sprayers for orchard applications below.)

Correct dosage
Newly established plantings are more susceptible to overdoses than established plantings. On young plantings use the lower suggested rates. Rates listed in this publication are given as pounds of material per treated acre. The actual area of land treated in a fruit planting may be one-third of the land surface covered by trees. Avoid overlapping or doubling dosages. If a tank runs out in the middle of a block, carefully mark the last treated area.

Soil type and organic matter
Sandy soils or soils low in organic matter allow easy penetration and quick uptake, which can damage plants. Clay soils or soils high in organic matter require higher rates of materials for adequate control to be achieved. Read the herbicide label and adjust rates, if needed, based on soil type. Applying certain herbicides to soils having less than 0.5 percent organic matter is apt to damage plants. Most chemicals will not damage plants in soils with 2 percent or more organic matter. Some herbicides give poor results when used on soils with organic matter over 4 percent. Under these conditions, select herbicides that are systemic or that are absorbed through foliage.

Rainfall (irrigation)
Most residual herbicides work best when incorporated into the soil by rainfall or irrigation. They will have maximum effect if the water is applied within 4 to 10 days after application. Failure to water adequately can diminish the herbicide's effectiveness. Generally, 0.5 inch of water is sufficient.

Tank-mixing of herbicides
Concentrated herbicides should never be added directly to an empty tank. Add one-half of the necessary water to the tank, then the herbicide concentrate, and finally the rest of the water. Never allow a sprayer with mixed chemicals to stand without agitation.

When applying combinations, add them to the tank in this order: (1) wettable powders, (2) flowables, (3) water solubles, (4) adjuvants, (5) emulsifiable concentrates. Constant agitation is especially important when combinations of pesticides are in a tank.

Combining two different preemergent materials at lower rates or a preemergent and a postemergent will usually give broader-spectrum control. A labeled herbicide may be tank-mixed with any other labeled herbicide to be applied at the same time, provided both materials are being applied according to their respective labels. All precautions and limitations respective of both materials must be followed when they are applied together. If there is a days-to-harvest limitation on either or both materials, you must follow the more stringent one--that is, the longest limitation.

Before tank mixing, be sure to check the compatibility of the materials. If you are unsure of the compatibility, use the following test: (1) At rates proportional to field use, add herbicides to 1 pint of water in a quart jar. (2) Close the jar and mix contents by inverting jar 10 times. (3) Inspect immediately. (4) Allow jar to stand quietly for 30 minutes and inspect again.

If the mixture remains uniform for 30 minutes, the combination can be used. If it does not, add a surfactant or compatibility agent to the jar and test again. If the mixture separates after 30 minutes but remixes readily with 10 jar inversions, the mixture can be used if good agitation is maintained in the tank.

Herbicide sprayers
Herbicides may be applied with a hydraulic sprayer operating at pressures ranging from 10 to 40 psi. Flat-fan, flooding, or off-center nozzles should be used for spraying herbicides. Flooding nozzles permit complete coverage with the boom located nearer the ground to avoid low-hanging limbs. For more information on operating herbicide sprayers, see Penn State Agricultural Engineering Fact Sheet B-56, Herbicide Application Equipment for the Orchard, available from your county extension office.

What size of area should be treated with herbicides? What is a sprayed acre? The area to be treated may be a continuous strip along either side of the tree row or an area around the trunk of each tree. In general, the treated area should be wide enough so that all grass is kept away from the trunk (to reduce the possibility of mouse damage or mower damage to the trunk).

To avoid confusion about the meaning of "treated acre," use the following to calculate the area to be treated in your orchard. One acre equals 43,560 square feet. The area in each example equals a treated acre:

• A 2-ft-wide strip on either side of the row (4 ft overall) and 10,900 ft long (43,560 sq ft/4 ft)
• A 3-ft-wide strip on either side of the row (6 ft overall) and 7,260 ft long
• A 4-ft-wide strip on either side of the row (8 ft overall) and 5,500 ft long
• A 5-ft-wide strip on either side of the row (10 ft overall) and 4,360 ft long
• An area 2 ft x 2 ft under 10,900 trees
• An area 3 ft x 3 ft under 4,840 trees
• An area 4 ft x 4 ft under 2,720 trees
• An area 5 ft x 5 ft under 1,740 trees
• A 2-ft-diameter circle under 13,870 trees
• A 3-ft-diameter circle under 6,170 trees
• A 4-ft-diameter circle under 3,470 trees
• A 5-ft-diameter circle under 2,220 trees
  (Area = 0.79 x diameter)

For selective-area spraying, such as in tree rows, a special boom with nozzle(s) mounted on the end or a hand-held gun is satisfactory. A swivel nozzle with an off-center nozzle tip can be used. The band width can be increased by adding flat-fan tips along the boom. The application rate per treated acre should be the same from all nozzles. Use low pump pressures, in the range of 20 to 40 psi.

When wettable powders are applied, agitation in the tank is required to maintain the suspension. Jet or mechanical agitation is recommended. Agitation is easily accomplished by placing a jet in the bottom of the tank to provide a stirring action. On a sprayer equipped with either a roller or a piston pump, run a separate line from a point between the pump and the pressure regulator to the jet agitator in the tank. If a centrifugal pump is used, there is adequate volume from the bypass line, and the jet agitator may be attached directly to the end of the line. For uniform mixing, the agitator should be operating with some water in the tank when the chemical is added.

Calibrating sprayers for herbicide applications
1. Measure band width covered by all nozzles and express the width in feet; for example, 34 inches = 2.8 feet. If mixing nozzle types (e.g., OC and flat nozzles) make sure that the gallons per acre (GPA) of all nozzles is the same. Record tractor rpm's and pressure at the pump or boom.
2. Divide 340 square feet by the band width (in feet) determined in step 1. This gives you the distance to drive to cover 340 square feet.
3. Measure a course of that distance.
4. Drive the course (without the sprayer running) and determine the time to cover the course. If you are calibrating a PTO weed sprayer, you must drive with the tractor operating at the same rpm's as it did in step 1.
5. With the tractor stopped (brakes locked, please) and the sprayer operating as in step 1, catch the nozzle output for the time determined in step 4 (the same nozzles used for determining band width in step 1).
6. The number of fluid ounces caught equals the GPA applied by making an application with the nozzle setup and pressure used in step 1 and the driving speed used in step 4.
7. To increase GPA, either increase pressure or drive slower.
8. To decrease GPA, either decrease pressure or drive faster.

Minimizing spray drift. It is important to minimize drift for economical, effective control and to protect the environment. Small droplets tend to drift, so it is better to use nozzles that produce a large droplet. Use low pressure, large orifices, and drift reduction adjuvants, and avoid spraying on windy days. For more details see Agricultural and Biological Engineering Fact Sheets B-110, Spray Drift Control, and B-78, Sprayer Nozzles, available from your county extension office.

Cleaning the sprayer
Cleaning the sprayer is very important. At the end of each day's spraying, completely rinse the inside and outside of the sprayer with clean water. When changing from one chemical to another, or at the end of the spraying season, give the sprayer a thorough cleaning according to manufacturer's recommendations. If these are not available, use the following procedure:

Remove the nozzle tips and screens and clean them with a toothbrush, using a detergent and activated charcoal solution, ammonia solution, or trisodium phosphate. Flush the system with clean water. Rinse it thoroughly with a detergent solution. Rinse again with clean water.

It is difficult to remove 2,4-D compounds from sprayers; therefore, sprayers used for applying these compounds should not be used for any purpose other than applying herbicides. The 2,4-D-type materials can be removed if the following steps are taken immediately after use:

• Flush the entire system with a detergent solution.
• Fill the tank and prime the spray system with a 10 percent ammonia solution and let stand for 12 to 24 hours.
• Disassemble nozzles and soak caps, screens, etc., in the ammonia solution.
• Rinse thoroughly with water and circulate it through sprayer. A weed sprayer should not be used for any other purpose.

For more details about cleaning, obtain a copy of Penn State Agricultural and Biological Engineering Fact Sheet B-72, Sprayer Cleaning, from your county extension office.

Granular applicators and their calibration
Instead of sprayers, granular applicators may be used to apply certain herbicides in orchards. Special spinner spreaders can be attached to a telescopic boom, or commercial units are available that can be mounted directly on the tractor. For small orchards, a hand-carried spinner spreader, which gives satisfactory results, can be used. Uniform distribution of the granules is necessary and application should be made only when there is very little or no wind.

Granular applicators may be calibrated by operating equipment over a known area, such as 0.1 acre. There are 43,560 square feet in an acre. Disconnect the spinner and catch the granules in a plastic bag. Make adjustments and repeat until desired rate is obtained. Remember to maintain the same travel speed at all times.

Granular applicators must be calibrated with the same material that is to be applied. Therefore, a check test must provide some means to collect and weigh the granules. When herbicides are applied in a band along the tree row, it is important to understand that only a portion of the orchard floor is being treated. This portion, called the treated acreage, receives the same rate of application as if broadcast application were being used. The importance difference is that only part of the orchard acreage is treated and therefore band application requires less chemical than broadcast application.

Disconnect the spreading mechanism (if one is used) and attach a catch pan, plastic or paper bag, pail, or other appropriate container to catch the granules. Select a test plot of known area. Select an area large enough so the amount of granules collected can be accurately weighed on an available scales. Remember that an acre is equal to 43,560 square feet. Operate the equipment at the recommended settings and ground speed for the desired rate. Be sure to operate only over the measured course and to catch all the material that flows through the applicator.

For example, if you want to apply 150 pounds per treated acre in a 4-foot band, you will travel 10,890 feet per acre (43,560 ÷ 4). For the test, however, you can select a smaller area. The ideal choice is a plot large enough to minimize errors and small enough to be practical. Assuming scales are available to accurately weigh samples in the 5- to 15-pound range (1/30th to 1/10th acre), let's select a 1/20-acre test plot. One-twentieth of an acre is a band 545 feet long (10,890 ÷ 20). When the check is run, 7.5 pounds (150 ÷ 20) of granules should be collected. If the actual amount is different, adjust and rerun until the desired rate is obtained.

Repeat calibration for any change in conditions (temperature, humidity, lot number of granules), when you use a different chemical, drive at a different speed, or change the agitator speed.

CAUTION: Strict control of herbicide application is necessary, as weed killers can injure trees. Proper design and calibration of the equipment are necessary. Always read the label on the herbicide container and follow the directions. Assistance is available from your county extension office.