 |
|
| The chemical management module also functions
at several levels. The module is subdivided into three submodules: 1) the chemical
selection module; 2) the chemical rate module and 3) the spray interval module. The overall output of the module is the determination of the chemical, its rate and the spray interval until the next application.
|
|
| The objective of this module is to determine
which insecticides, acaricides and fungicides registered for use on apples would be
effective in the control of the pests determined to be a problem by the expert system. The
control and use characteristics of each chemical is described within the dependency
networks. Critical factors which contribute to the selection of a chemical are: current
phenology of the orchard, the array of insects over threshold and disease levels in the
orchard, estimation of pathogen infection potential since the last spray, pesticides
applied in the last application, known fungicide or insecticide resistance in the orchard,
and the number of days until the orchard will be harvested. The appropriate use of benomyl
for the control of apple scab is described as an example and is shown in Figure 8. There
are two basic scenarios which describe the use pattern for benomyl. One describes
benomyl's use as a protectant fungicide, the other describes benomyl's use in a
post-infection situation. As a protectant benomyl is recommended from green tip to second
cover, when apple scab potential levels are from severe to moderate, there is no infection
potential since the last application of fungicide, a sterol inhibitor was not applied in
the last application as the first application following an infection period, no benomyl
resistance is known in the orchard, and the harvest date for the orchard is greater than 7
days from the present. The post-infection scenario described by the network is the same
except that the apple scab disease potential as determined by the system is high or low
post-infection and the beginning of the infection period which occurred since the last
application is not more than 24 hours from the current time. The output of the chemical
module is a list of insecticides, acaricides and fungicides which will control the pests
determined by the system under the current conditions.
|
|
| Once the chemicals have been selected the
system must determine which rate of chemical to recommend. This again is described in
dependency networks. For example, fungicides recommended for apple scab control early in
the season are generally recommended in combination to prevent resistance and to take
advantage of two modes of action. The rate for in-combination use are high, moderate and
low. Later in the season fungicides, generally protectants, are recommended alone. The
high fungicide rate is recommended from tight cluster through prepink, when the apple scab
severity level is determined to be high, and the chemical is to be recommended in
combination with another fungicide. A table containing the actual rates of each chemical
is built into the system. Within the system, Nova (myclobutanil) is an exception to this
method of rate determination. Since Nova is labelled according to tree row volume
calculations, it is recommended within the system according to tree row volume of the
orchard and the disease potential in the orchard. Tree row volume is automatically
calculated from information in the profile. |
|
| The system also recommends the date of the
next pesticide application. The factors used to adjust the spray intervals are phenology
of the orchard, disease potential rating, occurrence of an infection period since the last
spray, grower's spray interval preference, rainfall since the last application and the
chemical applied in the last application. Early in the season, the application timing is
mandated by the requirements to control apple scab. After second cover, insect control
requirements and weather conditions which affect summer apple diseases dictate application
timing. Grower application preferences are also considered due to the difference in the
ability of growers to spray an orchard at short notice and the necessity for some growers
to plan spray applications on a routine schedule in order to manage labor. This option
allows some growers to follow completely variable spray intervals based on pest and
weather circumstances and other growers to plan applications and be able to schedule labor
requirements. Even if a routine schedule is selected, spray intervals will be adjusted if
post-infection situations occur. The effect of rainfall on chemical residue is included in
the system based on heuristics. Growers have for a long period of time used the
rule-of-thumb that less than 1" of rain will not affect spray residue, 1 to 2"
will reduce spray residues by one half and 2" or more of rain will remove all of the
spray residue . As an illustration, the next pesticide application is recommended within 5
days of the last application if the orchard is green tip to petal fall, the apple scab
severity rating level is severe to low, there has been no infection potential since the
last appication, there has been 1 to 2" of rain since the last application, a sterol
inhibitor was not applied in the last application as the first application following an
infection period, and the last application was applied as an alternate side application.
All possible scenarios which describe situations which lead to spray intervals are
described within dependency networks.
|
|
| Once the pesticides have been selected they are checked for compatibility. Every chemical included within this system is compared before the recommendation is given. Dependency networks are used to describe which chemicals should not be mixed. Likewise, recommended chemicals are checked against the computer's calendar to determine if it is too close to harvest for application. | |
