One of the biggest mistakes growers tend to make when applying crop protection chemicals is failure to achieve proper crop coverage when spraying the materials, says PCA Laura Breyer, Breyer’s Vineyard IPM Services, Windsor, Calif. That includes misapplication of fungicides, including those used to treat vineyards for powdery mildew.
“Many growers don’t want to admit they’re not getting good coverage with their sprays,” says Breyer, one of the 2007 winners of the annual IPM Innovator Award from the California Department of Pesticide Regulation. “They’ll blame poor control of powdery mildew on other factors, like buildup of disease resistance to the chemicals, instead of the actual cause.”
A common mistake is skimping on application rates by spraying only every other row, instead of each row, in an attempt to save money, she notes. Another is simply traveling too fast when spraying.
“That’s easy to do,” Breyer says. “You may be driving at 3 mph on level ground. But, if you’re not careful, you could be speeding up to maybe 5 mph when going downhill. As a result, you’ll apply less than the recommended rate of chemical per acre. Slowing the tractor speed by just half a mile per hour and spending a little more time in the field can make a huge improvement in coverage.”
In addition to the slope of the field, weight of the sprayer and wheel slippage of the tractor or spray rig will influence travel speed.
Chemical labels list the recommended application rate and the sprayer operator’s manual contains charts or tables showing the amount of solution sprayed per acre at various travel speeds.
One simple way to determine travel speed when using spray equipment without a speedometer is to check the time required to travel a given distance, such as from one end of a row to the other. The longer this run, the more accurate the calculation.
Fill the tank half full to get an average weight load. Next, measure the time it takes to run this test course in both directions. Then, average the two runs and calculate the speed in miles per hour (MPH) using the following formula.
MPH = ft. traveled X 60
sec. traveled 88
An even faster, simpler way to determine ground speed, Breyer says, is to use a handheld GPS receiver, like those hikers carry. It can be mounted on a tractor or ATV operator. The one she tried showed travel speed to 1/10th mile per hour and cost less than $100.
The amount of canopy growth in a vineyard also affects spray coverage.
“Most powdery mildew fungicides work on contact with the fungus,” says Mark Battany, University of California Cooperative Extension farm advisor for San Luis Obispo and Santa Barbara counties. “Getting the spray to penetrate the canopy and provide the desired coverage becomes more difficult as the canopy fills in and the foliage becomes denser.”
Another way to improve spray coverage is to do appropriate leaf removal and shoot thinning to produce the desired amount of canopy growth, he says. At the same time, this can improve air flow to reduce the risk of powdery mildew.
To check your spray coverage in terms of spray pattern, volume and canopy penetration, Battany recommends using indicator paper or water-sensitive cards. Place them within several vines in a representative place at various locations in the vineyard. Be sure to put some in the fruit zone to measure coverage of the clusters. Then, run the sprayer down the row as you apply plain water. “Wetted dots on the paper show what kind of spray pattern you’re getting,” he explains. “Large, single splotches on the paper show a large droplet size and indicate less effective coverage than smaller, more evenly distributed wet dots.”
Sprayer calibration is important to make sure you’re getting good, cost-effective control with your powdery mildew fungicide, Battany notes. Improperly calibrated sprayers will waste money by applying more material than necessary or risking a disease outbreak by not applying enough of the chemical
Sprayer calibration should be done at least once a season. Ideally, this should be done whenever the recommended spray volume changes. Effective treatment of a vineyard with a full canopy requires a higher volume of material than applying a fungicide earlier in the season when a lower volume would be enough to treat a smaller canopy.
Calibration covers all aspects of the sprayer’s operation. This ranges from cleaning filters, screens and hoses, checking sizes and types and condition of nozzle and measuring and adjusting, as needed, spray pattern, pressure and volume.
Check with your UCCE office or sprayer dealer for more details on calibration procedures and worksheets.