Orchards, spray depositions

Schulz, R., Peall, S.K., Dabrowski, J.M. and Reinecke, AJ. (2001) Spray deposition of two insecticides into surface waters in a South African orchard area, Journal of Environmental Quality 30 (3), 814-822. 

Full-size trees, such as are found in traditional orchards, provide a complex and three-dimensional target. Spray deposition often relies on air assistance, and the influence of the structure of the target is great. Thus, with applications to trees, the prospect for improving the targeting sprays and the likelihood of poor application is great. 

Table 3.8 summarises the deposition of spray on soil surface underneath apple trees in orchards. When spraying apple trees in full leaf, spray deposition on the ground is on average 25% (18-35%), (Heer and Schut, 1986 Crum and de Heer, 1991 Porskamp et al., 1994a, 1994/ Ganzelmeier and Osteroth, 1994 Heijne et al., 1995). Spray deposition on the soil is not significantly different between axial and cross-flow sprayers, but tunnel sprayers (Zande et al., 1998) can decrease soil deposition by 50%. When trees are not in leaf, spray... 

Table 3.8 Spray deposition (% dose) on the soil surface underneath orchard trees (apple) for different periods during the growing season, and different spray techniques...

Figure 3.10 Spray deposition on leaf tissue and ground related to LAI in orchard spraying...

At the start of the season, when branches are still without leaves, more spray will be deposited on the soil surface than on the crop. Most of the spray will deposit on the crop when the maximum LAI occurs. This diminishes towards the end of the season. From the data found in the literature, these effects are shown in Figure 3.10 for orchard spraying (Zande et al., 1998). 

Cottony Peach Scale Tests. Studies made on the cottony peach scale were limited, but the results obtained are considered reliable. All of the tests reported here were conducted in 1947 under orchard conditions. A heavily infested peach orchard at Hamlin, N. Y., was used for the experiment. Because the supply of the isoparaffins available was very limited, it was necessary to devise a procedure whereby satisfactory tests could be conducted with only 600 to 1000 ml. of spray mixture per test. Treatment was usually restricted in each test to two carefully selected attached branches 1 to 2 feet in length. A third branch was sprayed at the same time to provide leaves for oil deposit determinations. Treatments were applied on July 18 and 19, 1947. At this time all the eggs produced by the overwintering females had hatched, and the resultant new generation scales had largely moved to the leaves where they occurred on the lower surface along the midrib. A compressed air paint spray gun, operating at 30 pounds pressure, was used to apply the spray treatments. 

The Florida seed orchard project conducted in 1980 (16) provided an opportunity to study drop deposit on needles of two distinct pine species. Five gallons of a dyed water base tank mix was applied per acre by aircraft. Drop stains were counted on needles microscopically. The VMD of the spray as determined on Kromekote cards was approximately 350 ym. Depending upon tree species and crown level, drop stains per centimeter length of needle ranged from 0.5 to 17.7 drops. A higher drop density was observed on the sparsely foliated slash pine than on the dense foliated Ocala sand pine (Table XI). A significantly greater density of drops was observed in the upper crown of both species as compared to the lower crown. 

Within 3 years after DDT was used commercially in the two orchards, concern over its possible accumulation in the soil had developed. Investigations of DDT concentrations in the surface layers of the orchard soils began in 1947 and continued for the next five years. A summary of these analyses is given in Table V. Build-up of residues was rapid at first, with levels equivalent to approximately 60 pounds per acre attained by 1951. Comparing these estimates with those from the more recent analyses shows that the amount accumulated during the last 14 years (1951-1965) is approximately the same as that deposited in the first six years (1945-1951). Several factors can be suggested as causes for this decline in rate of accumulation. The older methods of application resulted in more waste by spray runoff from the trees. Some of this waste was eliminated when... 

Drift deposition samplers consisted of 15 cm diameter petri dishes holding a pre-cleaned film of teflon FEP. Three deposition samplers were placed at each field sampling location in order to receive impinging spray components and any subsequent fallout from our spray operation. The deposition samplers were located at 50, 150, 300 and 500m radians (N, NE, E, SE, S, SW, W, NW) from the orchard. Previous work by Currier a ( ) had shown that... 

The distribution of the preparation over the surface of a treated leaf depends on the application rate. For example, in spraying a cherry orchard with a 0.8% suspension of Sevin with an application rate of 565 liter/ha, all of the liquid falling on the plant leaves remains there. When the application rate is doubled, part of the suspension runs off, and the density of the deposit on the bottom side of the leaves is 1.3 times that on the top side. The addition of Plyac (a surfactant) made it possible to reduce the insecticide application rate by improving the adhesion. 

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