The process of diagnosing a plant health problem without any specialised laboratory equipment is called ‘field diagnosis’. Field diagnosis involves careful observation of the symptoms on a plant and linking those symptoms with possible causes. While some plant health problems are relatively easy to diagnose, others can be very difficult for a number of reasons. For instance, there may be multiple factors that cause similar symptoms, or the plant being examined may not show very clear symptoms. As a result, it will often not be possible to make a highly specific field diagnosis, such as giving the name of a nutrient that is deficient or the pest species causing the problem. However, in many cases a very specific diagnosis is not necessary to identify corrective measures. A diagnosis of a pest group, such as fungus or stem-boring insect, will provide a lot of useful information for developing an adequate solution. The precision and accuracy of the diagnosis ultimately depends on one’s knowledge of the plants and the known problems in the area, with additional support from tools like the PestSmart Diagnostic Field Guide. The first step in narrowing down the cause of a plant health problem is to determine if the symptoms are caused by a living organism (biotic) or by a non-living factor (abiotic).