Author: Ioannis Navrozidis MSc. | Remote Sensing Data Analyst | CERTH

Plant diseases have always been a major concern for agriculture and plant protection since they heavily and negatively affect crop quality and production. Effects of biotic crop stress, a.k.a. pests and diseases, vary from minor symptoms to severe damage in entire crops, which result in major financial costs for agricultural businesses and impact heavily agricultural economy, especially in developing countries that depend on a single or a few crops.

Prevention of major losses can be achieved by a number of methods aiming at timely stress factor identification. It is difficult, however, for the growers to apply these methods as many are unavailable and often require specific domain knowledge and are costly and resource-heavy to carry out.

According to FAO, a large portion of farms are small and operated at family level in developing countries. These families provide food for a significant part of the world’s population. Despite this, poverty and lack of food security are common and access to markets and services is limited. In an effort to support these families with an all-inclusive plant protection plan, a large amount of research has been carried out to produce accurate and accessible methods for the majority of farmers. It can be summarized that the ability to detect and identify variations in crop health status, preferably in real-time, is vital to avoid damage at critical time periods and optimize yield.

Remote sensing data is one of the main pillars in the field of crop health assessment and crop stress extent. Data derived from satellite and aerial imaging can then be used to determine the quality of the crop and make yield and price predictions. It also plays a significant role in the identification of stress factors in farmland and the gathered data can point to the most efficient stress-control mechanism to be used to get rid of the pests and/or diseases on the farm.

Commercial use of aerial imaging exists from around the 1920s. Although remote sensing technologies have come a long way in the past 100 years, there is still some difficulty in categorizing conflicting information about what’s currently applicable – and accurate enough – for in field applications. The use of remote sensing data for pest and disease management is considered quite mature and largely reliable.

It is generally accepted that satellite imaging is not able to achieve both high spatial resolution and high revisiting frequency as of yet. On the other hand, UAVs (Unmanned Aerial Vehicles) can detect vegetation health status in real time, but only covering local areas; thus, their utility is limited in scale or it becomes very costly.

We could identify two key areas where remote sensing imagery can be used for management of biotic stress factors, the first being the ability to apply site-specific treatments and the second to achieve early detection of stress. These key areas come with different levels of maturity for technology and application techniques:

Site specific treatments for stress factors

The area of stress management in which remote sensing is most reliably demonstrating its value is the targeted treatment of specific sectors of the field—areas that are the most susceptible to pests and diseases and the anticipated yield loss is high.

Regardless of the specific pest or disease threat, subtle variations in temperature, precipitation, humidity and other environmental parameters—specifically in crops with sparse or underdeveloped canopies—mean that some areas of a field are inherently more susceptible to infection than others. Moreover, the location of these high-risk zones might change in the course of a year.

Satellite imaging with the use of multispectral sensors can detect changes or patterns that indicate the presence of pests or disease. When combined with variable rate application, these remote sensing data that identify potential trouble spots, allows farmers to treat their crops only in the areas where an application is absolutely required. These precisely targeted applications are also enabled with other innovative equipment, such as sprayers with sectional or individual nozzle controls that sync with RTK (real-time kinematic) GPS.

The ability to avoid blanket applications helps not only in lessening environmental impacts from agrochemical use, but also provides an opportunity for significant cost savings, greatly enhancing the business’s financial health and growth.

Early Detection of Stress

It has been established that satellite and aerial imaging can locate areas susceptible to pests or diseases and can help farmers reduce the treatment costs. When it comes to early detection or prediction of these outbreaks, however, some work remains to be done.

Not all high-risk areas detected in satellite and aerial imaging are necessarily caused by pests or diseases. Even in the cases they are, it is not always possible to identify the exact source of crop stress based only on remote sensing. This fact points out that remote sensing data cannot completely remove the need for field surveys and ground-truthing by experts.

Emphasis should be given on research validation in order to prove untested methodologies in-field. That said, the shortcomings in these emerging scientific and applied technologies should not prevent professionals of the field from employing remote sensing services where their value has been proven: identifying stressed areas of a field that may be vulnerable to pests or disease, detecting changes in plant health in time to stop the spread of an outbreak and reducing costs by targeting treatment.

Ioannis Navrozidis

R&D in Agricultural Sciences | Remote Sensing Data Analyst