Spray deposition data

To estimate amount of spray penetrating the canopy and depositing on the ground, we collected spray on Kromekote paper cards. Tables I-IV provide deposit data from several aerial application projects. As expected more spray was recovered on the ground in the open forest than was recovered beneath trees. 

It is expected that at the start of the season more spray will be deposited on the soil surface than on the crop. Since most of the spray deposits on the crop when the maximum LAI occurs, and this diminishes towards the end of the season, we can expect that deposition on the soil will show the inverse of this. From the data found in the literature, these effects are shown in Figure 3.8, for potatoes (Zande et al., 1998). 

Resistance to corrosion Most authors who compare resistance to corrosion of electroless nickel with that of electrodeposited nickel conclude that the electroless deposit is the superior material when assessed by salt spray testing, seaside exposure or subjection to nitric acid. Also, resistance to corrosion of electroless nickel is said to increase with increasing phosphorus level. However, unpublished results from International Nickel s Birmingham research laboratory showed that electroless nickel-phosphorus and electrolytic nickel deposits were not significantly different on roof exposure or when compared by polarisation data. 

Table III. It is obvious from the data in Table III that the housefly and the mosquito, in both the adult and larval stage, are susceptible to insecticides of the DDT type. However, the extravagant claims that DFDT is far superior to DDT as a contact insecticide against flies are not borne out by the results of controlled laboratory tests. The Peet-Grady testing technique used by Prill (92) would indicate that in the presence of added pyrethrins DDT is definitely superior to DFDT when applied as a spray. On the other hand, DFDT gave higher percentage kills than DDT when flies were placed under a Petri dish and held in contact with deposits of the compounds on glass surfaces. A comparison of the activity of these compounds against adult mosquitoes has not been reported.

The modeling results of the spray stage provide input data and initial conditions for the modeling of droplet-substrate interactions in the ensuing deposition stage of the spray forming process. 

The early development and present status of petroleum oils as insecticides for use on deciduous fruit trees are reviewed. The biological groups of insects most susceptible to oil sprays are listed. Factors affecting oil deposit are discussed and data are cited to establish relationships between oil deposit and control. The relationship between chemical composition and control efficiency is also discussed. The possible modes of action by which petroleum oils kill insects are considered. Specifications are given for improved dormant spray oil. Current recommendations ifor the use of oil sprays in control of fruit pests occurring in New York State are listed. The possibility of developing more effective hydrocarbon insecticides is discussed. 

Mortalities observed in tests of a series of oil dosages against adult female California red scale or eggs of the citrus red mite indicated a positive relation between increased dosage and increased kill. The fit of the points to the line was much better for oil dosages expressed as deposit than for those expressed as spray concentration. However, the variance observed indicated that statistical procedures would be required to arrive at the best fit for a line through the observed points. The method of probit analysis chosen was that proposed by Bliss (2) and modified by Finney (11) for data adjusted for mortality in the controls. 

To estimate inhalation contact exposure, some assumptions must be made which err on the side of conservatism and which should be modified as more complete data become available. It is necessary to know the droplet size spectrum of the spray because the diameter of the droplet influences its movement down the respiratory system (11). The functional unit of the lung is the alveolus, which is the terminal branch in the system. It is presumed that pesticide particles which are soluble in respiratory tract fluid and are 5p or less in diameter will reach the alveolus where they will be readily absorbed through the cells of the alveolar membrane into the pulmonary capillary beds and hence into the circulatory system. A recent review by Lippmann at al. (12) discusses in depth the deposition, retention and clearance of inhaled particles. 

The deposit of active chemical, the drift losses and drop size range can be found and would be functions of the spray formulations and application equipment which are under test In a given weather and application terrain. In order to compare different test run data, the results may be plotted as a series of 2nd degree polynomial regression curves (6). Actual chemical analysis of the released spray caught on the samplers provides the most accurate measure of deposit and airborne losses, but calculation of these functions from the drop sizes found can also be done. A total deposit recovery as a % of the amount released can be determined. 

Figure 3 shows data for a spinner atomizer in a 110 mi/hr airstream. The vmd is 140 microns, the % volume in drops less than 122 microns is now 24% while the relative span has increased to 1.23. It is this tremendous increase of drops (less than 122 microns dia.) from 2.0% for the 300 microns spray to 24% for the 150 microns spray that is a potential source of trouble from airborne transport of these small drops. These are carried away from the treatment area and a potential exists for contact with humans and animals as well as unwanted deposit on non-target crops. These small drops have been found at distances of several miles from the actual applications (5). If the material being released is of low toxicity, or in a remote area, the problem is not serious. But for high toxicity materials the 24% loss which is not controlled, poses a serious problem. 

Data from Tables I-V show that deposits in the open from low-volume aerial sprays range from 8 percent to 82 percent and beneath trees from 3 percent to 39 percent. The percentages vary due to drop size of the spray, meteorology, properties of the tank mix, and release height. Improved formulations, uses of low volatile tank mixes, attention to atmospheric conditions which support deposition, and improvement in sampling methods should increase accountancy. 

The data sets reviewed, document our knowledge on the deposition of aerial sprays released over coniferous forests. Conifers are relatively efficient collectors of spray drops as more drops are consistently observed on the ground in open areas than beneath trees. Spray which penetrates the upper canopy, and is unaccounted for on samplers in the lower canopy, probably was filtered out by foliage. More deposits are observed in the upper crown than in the lower crown. Data are lacking, however, on the fate of drops which do not penetrate the canopy. There is a potential for these drops to penetrate the canopy downwind or to drift off target. 

Another factor that will increase the drift is the target size or number of spray swaths. If the spray block is more than about 200 yards wide, then the expected deposit amount could increase by a factor of 2- to 10-fold. There is a need for a great deal more drift data and for it to be summarized into generalized drift curves with some limitations placed on them as to the upper and lower limits of expected spray drift amounts under a variety of conditions so that they can be applied to various spray situations. There is not a great deal of drift data specific to forest spraying. 

The interpretation of the effects of such drift, particularly its potential for adverse effects on human health, is dependent on some of the parameters of environmental behavior shown on Table VIII. The dose is given at 2 lbs/acre and translated into a deposit level of 20 mg/square foot, which is more useful in the interpretation of exposure data. The figures given for the deposit amount from spray drift at 100 yards and 1/2 mile are the figures for drift from a coarse spray on flat land for small target areas and are average drift amounts. The figure of 20 mg/kg is the NOEL for 2,4-D. 

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