How much pesticide in my spray tank?

An accurate and easy way to suggest the amount of pesticide in low-volume sprays is the amount of pesticide per acre. We especially encourage all who use low-volume sprays (usually 20-100 gal spray/A) to calibrate and recalibrate sprayers accurately. When the sprayer is calibrated according to the methods suggested, you must determine the number of gallons of spray needed per acre. Choose this figure based on your sprayer's limitations, in order to adequately cover the most difficult plantings. Wide rows, dense or tall trees, and low-to-moderate air volumes require more water for best coverage. Then add the amount of pesticide wanted per acre to the amount of water to be used per acre. For example, if 6.5 pounds is wanted in 50 gallons of water per acre, then 13 pounds is added to 100 gallons of water for 2 acres, or 65 pounds to 500 gallons of water for 10 acres.

For those who want to make their own calculations, use the amount of pesticides in low-volume sprays on mature apples and sweet cherry trees based on the amount of pesticides suggested for 400 gallons of dilute spray per acre minus 20 percent. For example, captan 50WP usually is suggested for early season apple scab control at 2 pounds per 100 gallons of dilute spray. At 400 gallons per acre, this would be 8 pounds captan 50WP per acre. This is reduced by 20 percent for low-volume sprays to 6.4 or 6.5 pounds per acre. Variations from this formula can be made as needed or desired.

Further pesticide reductions per acre can be made where trees are open and less than 18 feet in height. Reductions in pesticides needed per acre due to minor variations in tree size or thickness can be accomplished by closing nozzles or increasing the rate of travel. It is not necessary to recalibrate the sprayer with every change from one tree size to another. For example, going from mature apple trees to peach trees, if you increase the rate of travel from 2 to 3 mph, you will reduce gallons per acre by 33 percent. One or more nozzles at the top or at the bottom of the manifold may not be needed and may be turned off. Determine the number of gallons of spray needed per acre for each orchard on the farm and mix the amount of pesticide needed in that amount of water. For example, it may be found by trial that the sprayer can be adjusted quickly to apply 65 gallons of spray per acre on peaches. Mix the amount of pesticide needed per acre in 65 gallons of water and apply that amount per acre.

In Part V of this guide, alternate row middle applications and half-spray recommendations are given as pesticide treatment options. Alternate row middle applications can result in more efficient pesticide use and lower application costs. This practice also helps protect beneficial insects and mites in the orchard. In the alternate row middle system, the sprayer is driven down every other row instead of every row. Most of the spray material is thus deposited on only one side of the tree, providing both adequate pest control until the next spray period and a refuge for beneficial insects. At the next spray period, the sprayer is driven down the rows that were not treated previously. This system not only uses half the amount of pesticide normally required per acre, but it also provides superior pest control when the spray intervals are kept relatively short, the sprayer is correctly calibrated, the orchard is properly monitored, and the correct chemical rates are used at the proper times.