Remote sensing in plant disease management

Abstract

Remote sensing is now widely used in order to identify record and analyze soil and vegetation. There is an increasing interest to its application in plant pathology, for studies of damage caused by plant diseases and pests and physiological stress caused by pollution, water and nutrient problems. By remote sensing we study the multispectral signatures of a target area and its components. The electro-magnetic radiation from the object can be recorded and analyzed by optic- electronic instrument system. Multispectral signatures can also be recorded on photographic films, but the result is much dependent on the quality of the film, its grain size and resolution as well as its spectral sensitivity. By the use of suitable film/filter combinations and film types of various spectral sensitivity, however, we can get good information on the multispectral signature of the target area. Near infrared and infrared light is reflected deeper in the leaf tissue than visible light and may thus give complementary information on the physiological condition of the leaf and the plant. A leaf under stress is in many aspects also different from a normal leaf. Its size, shape, morphology and anatomy as well as its angle and thus its light absorption, transmission and reflection are different. A leaf under stress may close its stomata more or less which influences on its evapotranspiration. Such a leaf may have a slightly different temperature which may influence on germination of fungal spores on the leaf surface, the infection process and symptom development, etc. By infrared photography and spectroradiometry including thermography plant disease symptoms can be recognized and identified much earlier than they can be noticed by our eyes, and then the symptoms can be analyzed quantitatively and qualitatively. It is easy to understand that remote sensing has many applications in plant pathology and plant protection. Conventionally, remote sensing is referred to as a method to study a target area from high altitudes, from aircrafts and satellites. However, the technique and the methods can also be used at lower levels, over field experiments as well as at microscopic levels.