Identification plant symptoms of Disease and pest symptoms and environmental effects This 3 part videos series we explain how to distinguish plant symptoms. In this Part III, we will show symptoms caused by abiotic factors and give tips through which you can pin-point the cause of the symptoms and take corrective measures.
Namaskar, Welcome back to soulofkrishi.
This is the 3rd Part of our 3 part video series on Distinguishing Disease and Insect Problems from Nutritional and Environmental Stresses
In the first two parts of this video series we showed general types of plant symptoms due to various factors and deficiency, toxicity and environmental effect. In this part of the video we will show common symptoms caused by biotic factors and environmental factors and give tips through which you can pin point the cause of the symptoms and take corrective measures.
First let us distinguish between symptoms caused due to biotic and environmental reasons.
If the symptoms are caused due to biotic factors like diseases and insects, then on close observation we would see presence of fungal spores, powdery or downy growth, depressions, shape changes, insect, cast skins and things like that. On regular observation we would find such symptoms spreading progressively on the plant and spread to other nearby plants. We may also see that only this particular crop in the field or nearby fields are affected and not other types of crops. For example, if it is cotton, then only cotton is affected and not the jowar grown in the same area.
If the symptoms seen in the field are due to environmental effects like frost, lightning, sunburn and things like that then we would see only physical injuries and would find physical evidence not usually on the plant i.e. wind hail, sunburn, herbicide damage, etc. Such symptoms are irrespective of crop and affect all plants in the area and also such symptoms do not spread to other plants in that area.
We generally come across ten types of symptoms caused both due to biotic factors and environmental factors like Wilting – Browning, Necrosis - Browning, Chlorosis, Water Soaking – Lesions, Distortion, Deformation & Malformation, Defoliation, Bleeding and Gumming, Plant Galls or swelling and other physical damages. Let us discuss one by one.
Now Let us examine Wilting – Browning
If we see wilting and browning symptoms caused due to lack of water or inability of the plant to take up water then it might be due to drought and or caused by wilting diseases. If it is due to drought then in the whole area crops show the wilting and farmers can easily make up that it is due to lack of water. But if it is due to disease then only a particular type of crop is affected and that too in isolated plants here and there in the field. It happens at particular stages of crops like in some cases soon after planting and in some cases at flowering period. Farmers need to take up corrective measures by consulting an extension worker.
If symptoms start appearing slowly and affect the complete plant or tree then it might be due to Nematodes, insects and vertebrate animals damaging the root systems. In such cases farmers must closely observe the roots for gals, root grubs and other damages caused by rats, rabbits. On the stems, we must look for holes. If holes are seen then it must be caused by stem borers. Accordingly farmers must take up control measures.
Sometimes wilting and browning happens overnight or within a short period of one to two days. Then it might be due to frost caused due to exposure of plants to low temperatures
Let us now examine Necrosis – Browning
If we see Necrosis – Browning on leaf margins starting from older leaf extending to younger leaves then it is caused by soil salinity, excess salt in soil solution and in irrigation water.
If we find necrosis browning only on older leaf margins and leaves wither then it is caused due to potassium deficiency. We can apply potassium in such cases for correction
If we see the entire plants including leaves, flowers and fruits are turning to necrosis-browning then it is caused due to diseases. In that case consult an extension expert and take up control measures as per suggestions
Sometimes drought also causes necrosis-browning. In that case we would see large area in that region irrespective of crop types are affected by such necrosis-browning. Farmers can easily make it out as they experience drought in the region.
Some plants particularly the fruits on the plants if they show necrosis along with discoloration, turning brownish or yellowish white then it is caused due to sunburn which farmers can feel when they look at the prevailing weather in that area.
Exposure of plants to pollutant gases or chemicals also causes necrosis-browning. Sometimes it happens overnight as it happened in Visakhapatnam gas leakage or it might happen slowly as is seen in industrial areas with polluted waters.
Necrosis-browning is also caused some times by spray of excess herbicides or pesticides. In such cases only the sprayed area gets affected and other areas nearby will appear healthy. Farmers can realize their mistakes and identify the reasons for such damage themselves.
Next let us see Chlorosis or yellowing symptoms on plants
If the chlorosis appears on older leaves in some cases and younger leaves in some other case may be either on complete leaf or interveinal or intra-veinal chlorosis then it is caused due to nutritional deficiencies like nitrogen, sulphur, zinc and iron
If yellowing is accompanied by necrosis of leaf margins, blotches and spots with central blackening or browning then it can be due to diseases
Sometimes yellow mottles appear on leaves due to genetic characters like in many ornamental plants.
Chlorosis can also appear on leaves due to some insect damages
If chlorosis is on younger leaves with altering leaf shape and size or if yellow or white streaks appear or only veins turn yellow then it is caused by viral diseases. For this consult an extension worker for remedies.
In several plant diseases, incidence starts as water soaked lesions like erwinia rot, soft rots, bacterial blights and other diseases. With time these diseases spread fast and affect the plant as a whole. On the other hand if there are continuous rains and high humidity accompanied by high temperature then water soaked lesions appear on plants leaves and are most common in succulent ornamental plants.
Many times plants show distortions like twisted leaves, bushy and necrotic leaves, deformed leaves with spots, cupping of leaves and many such deformations and distortions. Most of these are caused by viral and mico-plasma diseases and physiological disorders in plants. For these, take expert advice to come to any conclusions in order to take remedial measures.
Plants exhibit de-foliations due to many reasons like drought, insect damage, herbicide sprays. All these can be identified by the farmers themselves by assessing the on ground situations. Similarly defoliation or drying of leaves may be caused due to high temperature or low temperature or exposures to pollutants. In such cases also farmers will be able to diagnose depending upon the prevailing conditions in the farm.
Plant stems show oozing of gums and fluids due to several reasons like mainly diseases like ganoderma in coconut, stem bleeding in coconut, gummosis in watermelon, oozing of gum from fruits due to insect damage, gum oozing due to stem borers or even due to insect damage by stem borers. Farmers must make a close observation of these symptoms to know the causes and consult specialists for taking up corrective measures.
Several plants exhibit gall formation. These galls are of various shapes and sizes. Galls may be caused mostly by insects, for example gall midge like insects or infections by agrobacterium. Sometimes mechanical injury may also lead to formation of gall like protrusions on healing.
Several other specific types of injury symptoms can be seen in plants like rabbit or wild boar damage, squirrel and termite damage, lightning damage, wind damage, birds damage, monkey and rat damage and even mechanical damages. Farmers must make a case to case verification of these reasons and preventive and corrective measures can be taken up accordingly.
Apart from all these, farmers can still expect additional problems when plants have been severely stressed due to flooding, cyclones, severe droughts and situations arising out of such natural calamities.
We hope with these tips and explanations farmers will be able to identify the symptoms and diagnose the problems and take remedial measures to overcome these problems for a profitable farming
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Happy farming. Thank you and Namaskar
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