Each olive grower knows that the yield of the olive orchard can be affected significantly from the most important disease of the olive, which is called Verticillium wilt and is characterized as the HIV of olive. Verticillium wilt is the most important factor of yield reduction in the olive growing because it causes plant losses. The appearance of this disease increases with high intensity and severity in many olive growing regions of the country, due to the intensification of the olive growing and the disease transmission because of non-using appropriate cultural practices. The fungus establishment in the xylem of tree, which is the ascending supply system from the root to the canopy, leads in stress of the infected tree or branch. The result can be so serious that even entire branches of the plant or the entire tree can die in one growing season. The infection symptoms progress gradually until the entire wilting of the branch or the tree.

The detection of the disease with the eye is very difficult at the early stages of the infection. It is though very important to detect the disease at early stages because in this way the management cost of the fungus and the probability of yield reduction are reduced. With the recent level of methodology available for the identification of the fungus in the field, either an experienced plant pathologist should detect the pathogen in the field with visual observation or the fungus should be detected using laboratory techniques, such as in vitro cultures or molecular techniques. All these methodologies are expensive and, furthermore, they cannot provide spatial information for the precise location of the fungus in the field.

eleagro service has developed a diagnostic tool to detect timely the problem of Verticillium wilt in the field, using remote sensing means. The digital mapping of the field parcels with remote sensing methods is a cutting-edge technology for the modern agriculture, for which precision agriculture techniques are expected to be applied, and provided as a digital service by eleagro. Today, it is necessary to look for diagnostic methods which should give specific quality information for the problems that the crops are facing (stage of plant pathology infections), but also spatial information (location of the plant pathology problems within the field), so that targeted applications and treatments to be recommended. 

The grower receives on his hands a map and a report. The field is displayed in the map as an appropriate color image through which the levels of stress within the field are defined spatially. The spatial representation of stress through a color scale (that is the areas of the field parcels requiring treatment are presented through the map) is explained in the report that the grower receives along with recommendations of the treatment for the stress. Thus, the digital imaging converts in valuable information for application of specific management practices for the grower. 

The digital imaging of the field allows the mapping of stress, so that the grower can restrict it or eliminate it, through management practices which are also recommended to him. Thus, the grower receives an image or more (depending what he has asked to examine in his field, i.e. nitrogen, water or disease stress) and a report with management recommendation for the factor causing the stress. The big advantage of remote sensing is that the potential of collecting information and data from large agricultural areas within short time is provided and thus it is a much more productive method of sampling and financially sound compared to the traditional procedures of sampling in the field. Thus, the grower can increase the yield from his field, while in parallel will reduce the inputs (pesticides, fertilizers, energy and water).

Remote sensing is the science of observation and detection of a phenomenon remotely, that is through images which are received from remote sensors. Remote sensing, and its products offered through appropriate processing, find applications in many areas. More specifically, in the agricultural sector remote sensing can provide information for the status and the distinctive features of a crop. Each plant has a different spectral signature (differ in the reflectance and the absorbance of the incident irradiance) and through the calculation of spectral indices specific characteristics of the plants can be detected. More specifically, the application of remote sensing tools and methods provides the potential of vegetation stress detection in the field, but also the detection of the cause of this stress. 

An advantage also of remote sensing is that its products are georeferenced taking advantage of global positioning system (GPS) measurements and can be incorporated in geographic information systems (GIS). This provides the potential to the grower of knowing the precise location of the problem (i.e. Verticillium wilt infection, nitrogen deficiency, faulty fertigation equipment, water stress, weed detection), and thus dealing with it easier. The knowledge of the size and the location of the problems increases the yield of the olive orchard, reducing the management practices (reduced sprayings and fertilization only where needed, etc.), the water use (because of the targeted repair of the irrigation system or the targeted application of water on plants suffering by water stress) and finally energy consumption due to the use of agricultural machinery only in the areas needing treatment. 

Absolutely not. Remote sensing follows a procedure which requires many steps until the final result is achieved: aerial vehicles, satellites, extended experimental data from the field so that remote sensing information can be interpreted, algorithms and correlation equations of the reflectance values with infections, diseases etc., management practices coming after long time experimentation, measurements and spatial correlation techniques of the images, lab techniques of pathotype identification etc. All these though have to do with us.   

For the grower, the procedure is absolutely simplified. He has to follow four steps: a) he is registered in the service, receives a personal password and is logged in, b) he chooses through a digital map the area where his field parcel is found and we undertake the application of the remote sensing diagnostic tool, c) using the same password that he was given to log in and choose the area where his field parcel is found, he is logged in after he has informed through e-mail that the diagnosis in his area has been conducted and downloads the data and finally d) receives a report with digital images and recommendations practices (a spraying schedule, fertilizer recommendations, fertigation scheduling, recommendations for repair of faulty irrigation equipment etc.) which can discuss with the support group of consultant agronomists of the company.

In parallel, the grower can download in his tablet, his smartphone or his computer the software, which is provided to him by the company, with which he can see the digital map with color scales for the level of stress and the level of management required. 

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Generally plant analysis should be conducted in close time intervals (every two years), unless there are remote sensing data, which detect nitrogen deficiency or sufficiency, and thus, in this case, plant analysis should not take place so frequently.

Separate plant analysis samples should be taken from areas of the field parcel where different varieties are grown, having soils with different properties, different irrigation systems are applied, different microclimate or soils having different slope. In these cases, remote sensing facilitates the grower significantly, because image acquirement takes place for the whole field parcel and the information extracted refers to the total area, enabling the calibration of sufficiently supplied zones of the field parcel compared to deficiently supplied zones. Plant analysis also requires that no sample is taken by tree not growing well (that is a tree which is infected by a disease or pest) and thus the grower fertilizes the tree based on the sample taken from the rest of the field (thus he applies uniform fertilization). On the other hand, by using remote sensing, the status of each tree in the field is provided and fertilization is adjusted on the natural variation of the field, but also on the requirements of each tree separately, according to its age, physiological status, productivity, location etc.

The end of the growing season, which is after fruit harvest, is the best time to take a plant analysis sample, because at that time nutrient concentration stabilization in the olive leaves takes place. The leaves for the sample are taken from the middle of healthy current year’s branches and average vigorousness of the size of 30-50 cm, which do not bear fruits. In order to have higher representation in the sample, the leaves collected should have come from as many as possible trees within the field parcel. The leaves should be closed in paper bags (for maintaining in the sample high moisture) and sent to an analytical laboratory through mail within no more than 3 days.   

There is a root watering and sprayings’ recommendation schedule which indirectly achieves integrated management of the olive orchard through the reduction of excessive vegetative growth of olive and thus prevention of Verticillium wilt. The sound nitrogen management also using remote sensing provides increased yields, reduction of nitrogen fertilization and thus financial profitability and environmental protection through the reduction of nitrate leaching. 

The detection of nitrogen deficiency and nitrogen fertilization recommendation leads indirectly in the integrated management of the olive orchard through the reduction of excessive vegetative growth and thus in the prevention of Verticillium wilt. Sound nitrogen management using remote sensing also leads to increased yields, reduction of nitrogen fertilization, and thus in the reduction of cost production, and in the environmental protection through the reduction of nitrate leaching.

Nitrogen is the most important macronutrient and in case of deficiency can lead to yield losses. In parallel, while it is necessary in higher concentrations compared to other nutrients, it is the most mobile element in the soil with its nitrate form. Thus, the excessive use of nitrogen can lead directly in income losses for the grower, since the nitrogen fertilizers are one of the basic inputs in farming, but also indirectly due to the reduction of production (diseases, excessive vegetative growth etc.).

The traditional procedures of nitrogen requirements monitoring include soil nitrate analysis, plant analysis and total nitrogen analysis or nitrates in plant tissue, chlorophyll content meter and finally lysimeters established densely within the field. These procedures though are time consuming, laborious, and require careful sampling so that the sample is representative and are referred to a mean of 10 stremmas area, and, thus, the soil variation within the field parcel cannot be determined, which is anyway large and changes from meter to meter. Thus, they lead in a uniform management of the field parcel eliminating for the grower the possibility to define uniform management zones (i.e. some trees within the field which need more nitrogen and some other trees which need less nitrogen) and finally save money from the sound management of nitrogen. Remote sensing acquires information from the whole field parcel, looking the field as a single sample and, thus, can define the variability that is the non-uniform variation of nitrogen within the field parcel.