You are here.
Tree row volume
Fruit growers face the challenge of accurately applying pesticides to fruit trees of various sizes and shapes. For environmental and economic reasons, it is essential to apply enough pesticide for good control without being wasteful. To aid in this effort, the tree row volume (TRV) concept was developed. As an example:
Imagine two 1-acre blocks of fruit trees. Block A has very large trees, while block B has much smaller ones. Obviously, these two blocks should be sprayed differently, since there is "more tree" to spray in block A than in block B. But how do we decide how much liquid it will take to spray these different blocks, or how much pesticide should be applied to the trees?
One way is to try different amounts of water in the orchard until optimum coverage is obtained. This method is time-consuming and usually requires years of experience. The other method is to calculate the actual volume of the tree canopy--the tree row volume. In such calculations a row of trees is considered as a continuous hedge of foliage, and the volume is calculated as shown in Table 3-4. These calculations take into consideration tree height, width, and distance between rows in a particular orchard. The methods for determining the proportion of the acre sprayed are shown in Figure 3-1.
Adjusting gallons per acre with TRV
Once you have calculated the volume of foliage to be sprayed, you must determine the volume of water applied per acre based on the dilute (400 gal/acre) spraying of "standard-sized" trees. In other words, if an orchard with standard-sized trees (height = 20 ft, width = 23 ft, space between rows = 35 ft) is sprayed at 400 gallons per acre, then another orchard with half the TRV of the standard would be sprayed at 200 gallons per acre. This means that every 1,000 cubic feet of foliage is sprayed with 0.7 gallon of spray solution. This technique of adjusting gallons per acre for differences in TRV has been used in North Carolina for applying chemical thinners. Recommendations in North Carolina also include a range of rates from 0.7 to 1.0 gallon per 1,000 cubic feet to account for differences in canopy density. Recent studies conducted in Pennsylvania indicate that canopy density is not an important factor to be considered in TRV calculations in well pruned orchards.
Adjusting chemical rates per acre with TRV
Another way to use TRV is to adjust the amount of chemical mixed in the spray tank. For example, the label for NOVA 40 WP carries the recommendation of 0.1 to 0.2 ounce of product per 10,000 cubic feet of canopy volume. If you want to spray an orchard that has 500,000 cubic feet per acre and you choose the lower rate of 0.1 ounce per 10,000 cubic feet, then you should apply 5 ounces per acre. Keep in mind that when using TRV this way you must be sure that the spray rate in gallons per acre used is sufficient to ensure adequate coverage of all areas of the tree canopy and may vary from 20 to 100 gallons per acre.
For pesticides that do not offer TRV rates the rate per acre may be calculated by first determining the proportion of your orchard size to a standard orchard. Then multiply this figure by the pesticide rate per acre recommended. The TRV for a standard mature orchard is approximately 570,250 cubic foot per acre, requiring 400 GPA of dilute spray. A pesticide labeled for use at 1.5 pounds per 100 gallons dilute would be used at 6.0 pounds per acre. If the TRV for your orchard is 427,688 cu ft, its proportion to the standard would be:
427,688 / 570,250 which is equal to 0.75
The amount of pesticide to apply per acre at the 6.0 poundsper- acre rate would then be:
6.0 lb X .75 = 4.5 lb/A
This amount would be mixed and applied in the desired mount of spray volume per acre for your sprayer type. The distribution and canopy coverage with conventional airblast sprayers are better at rates above 50 GPA. Low-volume sprayers are designed to apply rates from 20-40 GPA. Recent research results show that pest control is poor to inadequate when pesticide rates are adjusted below a proportional rate of less than 0.50. Until additional results are obtained, caution should be used in using pesticide less than 50 percent below label amounts unless TRV rates are given on the label.
The pesticide rates given in the Pennsylvania Tree Fruit Production Guide have been adjusted for Pennsylvania orchards and may be listed at below labeled rates. In TRV calculations full rates on the label should be used.
Chemical thinning tree row volume
Old standard-sized trees (height = 20 ft, width = 23 ft, tree rows = 35 ft) would be sprayed at 400 gallons per acre in a full dilute spray. This orchard has a tree row volume of 572,502 cubic feet. Therefore, it was felt that a full dilute spray would take 0.7 gallons of spray per 1,000 cubic feet of tree canopy. Table 3-5 is based on this assumption.
To use Table 3-5, compute the area of the trees (height times width) at the end of a tree row. For example, a tree 15 feet tall and wide would have a tree row end view area of 225 square feet. Then follow across from the 225 square feet, in the left-hand column, until you are under the row width for your block. If these trees were planted in rows 22 feet apart, then the tree row volume for that block would be 312 gallons. This figure is the volume of spray water needed to spray your block on a dilute basis. This dilute gallonage can be used to determine the quantity of thinners to apply to an acre of that orchard. For example, Ethrel is recommended at a dilute rate of 0.5 to 1.0 pint per 100 gallons, so for this example Ethrel should be used at from 1.6 (0.5 times 3.12) to 3.1 (1.0 times 3.12) pints per acre.
In a similar way, Vydate L is labeled at 1-2 pints per 100 gallons but not over 2-4 pints per acre. In this example, Vydate L should be applied at between 3.1 (1 times 3.12) to 4.0 pints per acre. Note that the higher rate is determined by the maximum rate of Vydate L allowed per acre and not by a tree row volume calculation.
Advantages and disadvantages
The TRV concept has several advantages. One is that TRV makes it possible to apply pesticides and growth regulators with greater accuracy. Therefore, you may attain better pest control while saving money and reducing pesticides in the environment. One disadvantage is that it takes time to make the volume calculations for each block. It also puts extra demand on spraying techniques. As pesticides are reduced, weak links in the system become noticeable. Improperly calibrated sprayers, worn nozzles, and varying travel speeds can seriously affect the distribution of chemicals within the tree and, ultimately, the degree of pest control.