Article: Matshediso Motshabi
It’s that time of year when our fields frequently seem pretty fantastic, but naturally some plants are showing indications of what may appear to be a nutrient deficiency or a plant disease. There is a significant distinction between a plant exhibiting signs and one exhibiting symptoms in plant pathology. The term “signs” refers to the outward manifestation of physical harm caused by biotic or abiotic agents, such as the disease itself, pests, spores, fruiting bodies, chemical residue, bacterial slime, and so on. A plant’s observable response to biotic and/or abiotic elements that cause a change or abnormalities in the plant, such as wilting, discolouration, stunted development, and so on, is called a symptom. The question is, how can you know whether a plant has a disease or a nutritional deficit if it has a poor appearance?
The difficulty in answering this question is that many of the symptoms separating a disorder from a disease are general. For instance, the plant may show chlorosis, which is a yellowish discoloration frequently brought on by a deficiency in nitrogen, zinc, manganese, or iron, or even suggest that there is root damage, which invites pathogens like bacteria, viruses, and root nematodes. The plant won’t be able to utilize the necessary nutrients and will show its discontent in discolouration even if the pH of the soil or water is off, including the soil temperature. Necrosis of the leaves, which are leaves with yellow or brown blotches spreading in from the margins and tips, may be caused by a bacterial infection, excessive fertilizer use, drought stress, or all three.
However, many plant diseases can present with similar signs and symptoms as nutritional problems. The main distinction between a deficiency and a disease is that when the nutritional component is addressed, plants recover. For instance, blossom end rot on tomatoes may appear to be an infection, but it is usually a problem with how well the plant is utilizing calcium. One of the main causes is a lack of calcium. But uneven watering is also bad. Whatever the cause, the tomatoes will bounce back once the issue has been resolved. This isn’t the case if it’s a disease problem, and figuring out if it’s a disease or deficiency is one method to tell. When it is an infection, there are frequently multiple symptoms, which is a significant distinction. Even though the leaves may be going yellow, they frequently contain dots or streaks. The same is true with necrosis. It’s possible that some of the leaves are curling and turning reddish. Additionally, there may be signs of pest pressure, which raises the risk of bacterial, fungal, or viral transmission.
Another thing to think about is whether one plant in the field or multiple exhibit symptoms. Sometimes it is preferable to wait for the neighbouring plants to develop an immune system strong enough to prevent the spread, with the aid of precise agrochemicals, rather than pulling out the plants exhibiting signs and symptoms when they are below the economic threshold level and the disease is not easily transmissible from one crop to another. To the point where you are certain whether something is an illness or a dietary issue, it takes some practice. And there will surely be instances where speaking with a plant pathologist—the qualified expert to identify the problem with your crop and establish its cause—is the best course of action. Additionally, they can help you balance your soil to best fit the demands of your plants and recommend good farming techniques to ward against plant diseases. By doing a field or greenhouse inspection, you can see potential problems early on. The majority of the time, management strategies might be more successful the earlier you identify a problem. Abiotic elements also play a significant role in the identification of plant diseases and the success of your crop thriving, therefore it’s crucial that you verify the quality of your seed and seedlings, the soil’s quality and pH, and whether the water is suitable for irrigation.
