Reduce environmental impact by spraying at the right time with help from GEWIS

Introduction
Many roads lead to Rome. One way to reduce environmental impact is to apply crop protection agents at a time when they are well absorbed and work well. Often this is linked to weather conditions. The weather conditions surrounding the application are important for the effectiveness of the crop protection products. Which meteorological conditions are important depends very much on the type (herbicide, fungicide, etc.) and type (the method of formulation). Some knowledge about these issues can ensure that wholly or partially unsuccessful sprays can be avoided. However, it is difficult for plant protection product applicators to estimate the ideal time to apply these agents. Therefore, a computer-assisted decision support model has been developed that combines the meteorological conditions in the crop with the physical/chemical/biological action of the crop protection products, named GEWIS. GE- WIS is an acronym and stands for Crop Protection and Weather Information System.

Crop weather
Meteorological quantities such as radiation, temperature, precipitation, wind and relative humidity (rv) strongly influence the effectiveness of a crop protection treatment. On the one hand because plants, fungi and insects are influenced by these conditions, on the other hand because pesticides are directly or indirectly influenced in their effect by these meteorological conditions. For proper interpretation, however, the meteorological conditions in the crop must be looked at. After all, that is where it has to happen. The meteorological conditions in the crop may differ significantly from the conditions measured at standard height (at 150 cm height).
On average, the relative humidity in a (full) crop is higher compared to the rv at standard height. However, early in spring or during periods when the crop is only partially covering the ground, the rv during daytime sunny periods is much lower than the rv at standard height. Important for the farmer to take this into account, as it has a major impact on the uptake potential of many crop protection products. Air temperature can also vary greatly. On clear, radiation-rich days, the air temperature can easily be 5°C to 10°C higher during the day than the air temperature at standard altitude; at night this can be the other way around. These deviations from meteorological conditions in the crop are important in order to make some assessment of whether a plant is growing well and whether agents can be easily absorbed and transported.

Relationship between weather and plants
Weather conditions between plants have a lot of in- fluence on the plants themselves. Poor conditions, i.e. conditions with low rv, a lot of radiation and a lack of moisture at the roots cause a strong hardening off of the plant. Hardening off is protecting the plant from too much evaporation and the plant therefore deposits a relatively thick layer of wax on the leaves. This wax layer is at the same time also armor against the absorption of a large number of (mainly polar formulated) crop protection agents. In a number of cases, the accumulated wax layer on the leaves of the cultivated crop must also protect the cultivated crop against absorption of too many (herbicides). If spraying takes place too soon after a dark rainy period, too much uptake by the leaves will take place and the cultivated crop will die.
Generally speaking, lack of moisture at the roots, high radiation and low rv result in a lot of wax deposition on the plants and difficult uptake of most agents by the plant. Growing, dark weather with regular precipitation provides good uptake opportunities by the plant.

Relationship between weather and agents
Virtually all crop protection agents, are strongly influenced in their action by meteorological conditions.

Herbicides
Soil herbicides (herbicides) are preferably sprayed on moist soil. A short dry period is then important to be followed by precipitation to allow the herbicide to penetrate deeper into the soil. These soil herbicides must be absorbed by the root hairs of the weed plants and not by the cultivated plants. The discrimination occurs due to the difference in depth of the root hairs, those of the weeds are not as deep as those of the cultivated plants. The absorption of contact herbicides and growth substances takes place through the leaf skin (not the stomata). This requires cloudy, growing weather and moist soil for 2-3 days before application. Clearly, when applying the polar (aqueous) formulated products, there is a relationship between weather and treatment result. Growing conditions before application produce good results even with (very) low doses. Conditions under which the plants harden off produce much poorer results.

Insecticides
For insecticides (insect protection products), it is important that they be applied during a period when precipitation is low. Many insecticides have a positive relationship with temperature. The warmer it is, the better they will work. Insects also have a positive relationship with temperature. The warmer it is the more active they become, they eat more, they move more and they ventilate more. Interesting here is that these are also the ways in which the insecticides must be absorbed.
Important here is that the agents are quickly broken down by (solar) radiation, the effect decreases quickly after application by (sun) light. The optimal application would therefore be at a time when the temperature is high enough and there is little radiation after application.

Fungicides
The meteorological conditions of the 2 to 3 days before application are also important for the uptake of fungicides (protectants against fungi) acting systemically (absorbed by the leaf skin and then dispersed by the sap flow). Furthermore, a precipitation-free period during and after spraying is important. The latter does depend on the formulation. The pesticide must be given time to be absorbed during and after spraying. With surface-acting contact fungicides, the weather prior to treatment is less important. Here, however, the weather during and (shortly) after application is very important. Dry, sunny weather ensures a very rapid docking.

GEWIS
In order to make this complicated, complicated knowledge more easily accessible, after many questions from the farmer-practitioner, the program GEWIS was developed within a project, in which this knowledge was made more understandable. In the project, a paper version and a computer-aided model were developed.

Paper version
The paper version of GEWIS indicates, by means of a folder containing per plant protection product via a number of pictures for the active substance and formulation, what the optimal conditions are for the absorption and functioning of the plant protection products. The disadvantage of this paper version is that there was no current link with the weather conditions at that time and the user still has to make a number of links himself.

Computer-assisted version
The computer-assisted version combines the physical/chemical/biological properties of the crop protection agents with the weather data surrounding the crop protection treatment. The required (historical) weather data comes from a weather pole that measures in a crop. The weather data of the past three days are used in the system. Furthermore, weather forecasts are used for predictive value. Once the user accesses the system, the measured weather data from the weather pole is retrieved via an electronic means (modem or Internet) and stored in the computer. The same happens with the weather forecast data. These are also retrieved via an electronic means. With this meteorological data, the program, through a number of procedures (3-10, depending on the type of plant protection product), calculates the effectiveness for the respective product in a given hour, see Table 1. These hourly values are then displayed in a graph, where the data are for five days, two and a half days backward and two and a half days forward.  

GEWIS users use the system as a clear guideline for planning to perform a crop protection treatment at the right time. Generally, several checks are made (several days before the treatment). Data coming from the user groups learn that especially the spray timing in terms of time has changed among GE WIS users. Also, fewer treatment failures have been mentioned by the users. Currently, the system has about 350 users.

GEWIS is a program that runs under Windows. Within GEWIS is a database of all authorized active ingredients. Besides the effectiveness calculation based on the weather, GEWIS also offers possibilities to view backgrounds (authorization and use manual) of crop protection products and to look up diseases, pests and weeds with the product to be used. Furthermore, it is easy to automatically calculate the number of points of the environmental yardstick of the various crop protection products. This also allows for choice. If at a certain moment a user does not have a high score for a certain pesticide he wants to apply, he can look for an alternative. He can use an updated effectiveness calculation to see how the alternative scores and also see what the alternative scores in terms of environmental impact points.

Lock
With GEWIS it is possible to choose the best time of application on the day for the pesticide to have its maximum effect. This allows unnecessary spraying to be avoided and often a lower dosage can also be used for spraying. Furthermore, with the automated form of the environmental metric, a product least harmful to the environment can be chosen.