Using a Hand-Cranked, Hand-held Spreader to Apply Herbicides in Container Nurseries

Transcription

1 Using a Hand-Cranked, Hand-held Spreader to Apply Herbicides in Container Nurseries Amy Barker and J.C. Neal Department of Horticultural Science North Carolina State University Weed management in nursery crops can be one of the most costly components of crop production. Producers of container nursery crops rely primarily on two methods of weed control multiple applications of preemergence herbicides and hand-weeding. Regardless of which herbicide is applied, the product must be applied accurately and uniformly to achieve effective weed control and protect the crop from over-application that may result in crop injury. Most preemergence herbicides used in container nurseries are formulated on granular carriers. The standard application method is with a hand-carried, hand-cranked belly-grinder -type rotary spreader. Some commonly used models include the Warren T7-II and Solo 421S. Other models are also available. The uniformity of spread using these devices has been shown to be quite variable. We have measured granular herbicide applications at nurseries and found up to 25% variability from one pot to another within a container block. Increasing the uniformity of herbicide distribution will improve weed control and decrease the potential for crop damage. The main key is to be as consistent as possible. The distribution pattern created by a spreader changes with differences in swath width, rudder Example of variable granule distribution setting, application pattern, walking and cranking speed, the amount of granule in the hopper, opening the hopper, and wind speed. Good herbicide distribution. Granular Distribution Granular spreaders typically have a distribution pattern with most granules directly in front of the applicator and tapering off farther away from the applicator (Figure A). In order to apply a uniform amount over an area, some overlap between passes is required. Overlapping each side of the distribution pattern by 3-35% for a total of 6-7% overlap, creates the most even application (Figure B.) How close together the passes are, and as a result how much the passes overlap, is called the effective swath width. Granular spreader use guidelines Page 1

2 Lb/acre Figure A. A typical pattern of granular distribution from a belly-grinder spreader Figure B. Overlapping passes by 3 to 35% will result in more uniform granular distribution Feet from Initial Starting Point Pass 1 Pass 2 Total Swath Width The distance between passes with a granular spreader (the swath width) has a large impact on application uniformity. For instance, with a 12 foot swath width, the average distribution pattern of Freehand granules using a Warren T7-II spreader is very uneven (Figure C). The gaps can be greatly reduced by using an 8 swath width instead (Figure D). A swath width of about 8-1 works best for the average granule carrier. Figure C. Spreader pattern using a 12' swath width; right, center, and left rudder positions; and the typical back & forth walking pattern Feet from Initial Starting point Granular spreader use guidelines Page 2

3 Lb/acre Lb/acre Figure D. Narrower swath width improves application uniformity. Spreader pattern using an 8' swath width; right, center, and left rudder positions; and the typical back & forth walking pattern Feet from Initial Starting Point Rudder Setting Some spreaders can be adjusted to throw granules more to the right or the left, reducing the amount of product applied outside the container beds. However, using these rudder positions creates spikes in the amount of product applied to the outer edge of the application area (Figure C & D). This can be avoided by using only the center rudder position on spreaders with multiple rudder options (Figure E). Holding the spreader at an angle while using the center rudder position also creates spikes in application. Figure E. Using only the center rudder position improved spreader uniformity. Spreader pattern using an 8' swath width, center rudder position only, and the typical back & forth walking pattern Feet from Initial Starting Point Application Pattern (the direction you walk makes a difference) There are two main application patterns, the back and forth method, and the parallel pass method (circuitous operation). How much product is applied to the right vs the left of the applicator (how skewed the distribution is) determines which method is better (Figure F). If the distribution pattern is symmetrical, the back and forth method is best. The more lopsided the pattern is, the Granular spreader use guidelines Page 3

4 better off you are using the parallel pass method (G). The Warren T7-II and Solo 421S spreaders with a variety of granules tend to produce skewed patterns, so on average you achieve better distribution by using the parallel pass method. Figure F. Sample granular distribution patterns. The skewed pattern has more product being applied to the right of the applicator than the left and would benefit from the parallel pass method Symetrical Distribution Skewed Distribution Figure G. Sample granular distribution with a Solo spreader, an 8 swath width, and only the center rudder position. The parallel pass method results in a more even distribution. Back & Forth Method Feet from Initial Start Parallel Pass Method Feet from Initial Start Granular spreader use guidelines Page 4

5 Lb/acre Rate lb/a Walking and Cranking Speed The amount of granules applied to a given area is influenced by the applicator s walking speed. The faster you walk, the fewer the granules put out (Figure H). A comfortable speed for most people is 3 mph, or 1 feet in 23 seconds. How fast you turn the spreader crank also influences the distribution of granules (Figure I). When calibrating your spreader, make sure to use a speed that is comfortable and then be consistent. A metronome may be used to help applicators maintain a constant walking and handle cranking speed. Figure H. The faster you walk, the lower the application rate. Maintaining the speed you used while calibrating the spreader is important to maintaining a uniform application rate Walking speed (mph) Figure I. Comparison of two different handle cranking speeds. The faster speed resulted in a wider spread and lower rate than the lower cranking speed. Maintaining the handle cranking speed used when calibrating the spreader helps keep the application rate and swath width consistent. (rpm: handle rotations per minute) rpm 99 rpm Granular spreader use guidelines Page 5

6 Amount of Granule in Hopper The amount of product in the hopper at any given time affects the rate of application. Application rates can be as much as 45% lower when the hopper is only 1% full than when the hopper is completely full (Parish, 1999). Don t wait until the spreader is empty to refill. Add more granules when the level in the hopper drops to about 25% full. Opening the Hopper Start walking and cranking the handle before opening the hopper. Otherwise, the spreader tends to drop a large amount of granule at the beginning. This also helps prevent the spreader from jamming and dropping large amounts in one spot. Difference in distribution as a result of opening hopper before beginning to walk and turn handle. Wind Speed If there are greater than 5 mph winds, do not use the granular spreader. Wind interferes with the uniformity of application. In the figure to the right one can see how the wind blew granules to the edge of the pot. This will result in root inhibition where the excessive herbicide is deposited and poor weed control where little or no herbicide is present. Tips for using Warren T-7 II and Solo 421S spreaders Wind blew granules to pot edge. 1. Size of the beds matters! Keep nursery beds between 6 and 8 feet wide (for an 8 to 1 ft swath width). 2. Center rudder position only. Do not use the spreader held at an angle. 3. Spread granules in one direction using parallel passes. 4. Maintain consistent walking speed. Use a metronome. 5. Maintain consistent cranking speeds. Use a metronome. 6. Refill the hopper when the level drops to about 25% full. Don t wait until it runs out. 7. Start walking and cranking before opening the hopper. 8. If the wind is 5 mph or more, don t make the application. Wait for a calmer day. 9. When possible, apply herbicide before spacing out containers to reduce herbicide losses between pots. Prepared: August 216 Granular spreader use guidelines Page 6