Heather N. Kolich, ANR Agent, UGA Extension Forsyth County

A lawn spreader in action. Small granules are flying out of the spreader.
Calibrate rotary spreaders for each product to ensure correct application rate. Photo by Adam Russell, Texas A&M University Extension

Late February to mid-March, before plants emerge from dormancy, is the time prune trees and shrubs and apply pre-emergence herbicides to lawns.

Pruning basics

Pruning is healthy for plants. Strategic pruning stimulates growth and flowering and also opens the canopy to improve airflow and light infiltration for disease prevention. Aesthetically, pruning helps us maintain the size and shape of plants. Now is a good time to go out and look at landscape trees and shrubs to identify your overall pruning goals and how you’ll approach each plant to achieve your vision. As you make your tree pruning plan, target and remove dead and broken branches first. Then step back and look for branches that grow inward toward the trunk and mark them for removal. Next, inspect the canopy for branches that cross over and rub other branches and select one of them for removal. After this initial pruning, spend a day or two reevaluating the tree in keeping with your overall vision.

Weed prevention

Pre-emergence herbicides create a blanket-like barrier within the soil that stops broadleaf weed seedlings from popping up into the sunlight. In order to be effective, however, the herbicide must be evenly distributed across the lawn and applied before the soil warms up to 55 degrees Fahrenheit. Finding soil temperatures at 2-inch and 4-inch depths is easy; just visit http://georgiaweather.net/, find the weather station closest to your location, and use the calculator to find current soil temperatures. Calibrating your spreader is trickier, but it’s an essential step in making an effective herbicide (or fertilizer) application. Factors in calibrating the spreader include the product (fertilizer, lime, herbicide, or seed), the person (height and walking speed) and the type of spreader (rotary for lawns or drop for small areas). In a rotary or broadcast spreader, lighter products don’t fly as far from the spreader as heavier products do. This difference affects the swath width of product distribution. Using the same spreader on the same hopper setting, a person who walks fast will apply less product to the area than a person who walks slower. What this means is that the spreader needs to be calibrated with each change of product and/or person making the application.

A grid showing the correct way to apply lawn chemicals
Make two, perpendicular herbicide applications across the lawn to achieve full, even coverage. Image courtesy of UGA Extension.

Step one in calibration is determining how much product should be applied over a specified area. The application rate for granular herbicides will be stated as pounds per 1,000 square feet on the product label or in the Georgia Pest Management Handbook (https://ipm.uga.edu/georgia-pest-management-handbook/). But, because even, thorough application of the herbicide or other granular product requires two, perpendicular applications over the area, you’ll need to calibrate the spreader to deliver half the recommended amount of product.

For example, the herbicide label states an application rate of 4-pounds per 1,000 square feet of lawn. You’ll make one pass over the area applying the herbicide in a north-south direction, then turn and make a second pass over the area applying the herbicide in an east-west direction. To avoid over-application, the broadcast spreader needs to apply only 2-pounds of product per 1,000 square feet in each of the two application passes. 2 pounds of product x 2 application passes = 4 pounds of product broadcast over the 1,000 square foot area.

Step two involves determining how much product your spreader broadcasts over 1,000 square feet and adjusting the hopper setting as needed to apply the recommended amount. In this case, that will be 2-pounds as determined above. To accomplish this:

  1. Mark a test strip of 100 linear feet on a level area of pavement with clearly visible start and stop points.
  2. Adjust the spreader hopper opening to the setting recommended on the product label, or at a mid-level opening if there is not a recommended setting.
  3. Weigh out 10 pounds of the herbicide and pour that amount into the spreader.
  4. With the hopper closed, walk at your normal pace toward the start marker.
  5. Open the hopper at the start marker and walk toward the stop marker. Close the hopper as you pass the stop marker.
  6. Weigh the herbicide left in the spreader and subtract that weight from the 10-pound starting weight. This tells you how much product was applied in the 100-foot strip.
  7. Multiply the amount of applied herbicide by 10. This tells you how much product would be applied at the current hopper setting and your rate of walking over 1,000 square feet.
  8. Sweep up the granules from the pavement.
  9. Adjust the hopper opening and repeat as needed to reach the application rate you determined in step one.

For more information about calibrating lawn spreaders, see https://hgic.clemson.edu/factsheet/calibrating-spreaders/ or https://extension.psu.edu/calibrating-your-fertilizer-spreader.

Posted in: