Spray deposition potatoes

During each of these periods, there are changes in coverage of the soil by the crop and LAI. This affects spray deposition both on the leaf canopy and on the soil beneath. This is shown in Figures 3.6 and 3.7 for conventional hydraulic spraying and air-assisted spraying. In Figure 3.5 the results are presented for the spray deposition in the potato plant. 

Figure 3.6 Spray deposition (% dose) on the total potato plant and soil surface underneath a potato crop for different growth stages, and different spray volumes...

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). 

Figure 3.8 Spray deposition on potato leaves and on the ground as percentage of the dosage, related to LAI of the crop...

Figure 3.9 Spray deposition on crop canopy and underneath on soil surface, related to Leaf Area Index when spraying potatoes (after Zande et al., 1998)...

Zande, JC van de, HAJ Porskamp, JMGP Michielsen, MT Van IJzendoom and R Meier, 1999. Spray deposition and biological efficacy in potatoes. In J Pabis and RS Rowinski, 1999. Papers Presented at the Techniques for Plant Protection Conference, IP I , International Conference Warsaw - Poland, 23—26.05.1999. Warsaw Agriculture University, Warsaw, 117-125. 

Bystanders. The bystander had the lowest exposure to carbaryl of all the workers monitored. In keeping the bystander within 100 feet and downwind of the ground applicator, the bystander often had to walk into the field while it was being treated. This practice resulted in exposure when the hands of the bystander touched the crop foliage. Thus, with peas, there was no exposure because the plants were too small at the time of spraying for any inadvertent contact, but with relatively mature potatoes, measurable residues were deposited on the bystander. For example, when 80S was applied to this crop, the bystander had a total HDE of 0.5 mg/h... 

Later in the growing season, when plant stems lie between the ridges (stage C) LAI falls again to 1-2. Deposition on the potato plant is also reduced and, for conventional spraying, it is around 56% (Porskamp et al., 1993a Wretblad, 1997 Zande et al, 1994a, 1998, 1999, 2000). 

Using air-assistance on field sprayers changes the deposition pattern within the potato crop canopy. Penetration of the spray into the canopy is increased and by using air-assistance more spray is deposited at the middle and lower levels (Figure 3.5). At early and late growth stages (A and C) deposition in the crop using air-assistance is about 6-10% lower than with conventional techniques. With a fully mature canopy (B), the use of air assistance increases spray... 

---