Plant Surfaces. Although much work has been directed toward better application of 
pesticides to crop plants, very little effort has been made to more specific placement on 
the plant. Cooperative research by engineers and crops scientists may lead the way to 
material reductions in pesticide requirements by showing that the material is wholly or 
primarily effective on specific locations on the plant. One example is the development of 
granular DDT for placement inthe whorls of the corn plant. Similarly a report from North 
Carolina researchers states that:” 
‘The results indicate that commercial hornworm damage can be prevented with 
about one-fifth the recommended rate of insecticide if treatments are directed 
to the upper five or six leaves at the time the oldest larvae are in the third and 
fourth instar... .. Insecticide residues can be reduced considerably over those 
attained with grower treatments with no appreciable increase in insect damage.” 
Pesticide application requirements (on plant surfaces) may be differentiated according 
to the needs on the plant surface. 
Overall discontinuous application. For herbicides which are translocated in the plant 
or for insects which bite and chew, it is only necessary to have a distribution of the ma- 
terial so that sufficient quantities aremadeavailableto bring about the required reaction. 
This may be eithera relatively few large particles or a larger number of smaller particles 
reasonably well spread over the plant surface. It may be that application to the upper or to 
the lower surface may be of most benefit for a specific insect. 
Overall continuous application. For disease control or for sucking insects the re- 
quirement may be that the material be distributedalmost continuously, although in a very 
thin layer, over the plant surface. For example, one can calculate the necessary minimum 
size of particles and the distribution of those particles on a leaf to prevent the entrance 
of a disease spore of known dimensions. The requirements for 100 percent coverage can 
be very exacting and most likely unattainable in either a commercial or an experimental 
machine, but the requirements can be established as a goal to shoot for. 
On the Soil Surface. Increasing amounts of herbicides are being placed on the soil 
surface to control weeds, either as pre-emergence or as post-emergence sprays. The 
required amounts, the method of application, andthe kind of material depend upon soil and 
plant conditions which must be determined and defined. Again, concurrent and cooperative 
research by engineers and crop scientists is necessary for best progress. 
Sub-surface application. In some cases the pesticide, suchas a herbicide or a nemato- 
cide, may be placed under the soil. The optimum effect with the minimum amount will 
come about when the material is placed at the proper depth and distributed in sucha 
manner as to come in contact with the desired pest. In addition, a pesticide suchasa 
volatile liquid herbicide must be properly covered to obtain maximum results with mini- 
mum losses to the atmosphere. 
Other applications. Specialized applications such as on animals may require addi- 
tional precautions such as protecting the animal’s eyes and preventing excessive inhala- 
tion. 
BRIEF HISTORY OF EQUIPMENT PROGRESS TO DATE 
Although thousands of inventions and developments have been recorded, the following 
list shows typical examples indicative of the progress. 
1883 Hand sprayer 
1887 Traction sprayer 
1900 Gas engine power sprayer 
Engine duster 
2North Carolina Tobacco Reprint Series No, 65, May 15, 1959, 
72 
