a guide to the recognition and understanding of ramularia and other ...

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36 Physiological leaf spots Physiological leaf spots or abiotic leaf spots are common terms used to describe leaf spots for which there is no obvious association with a disease and their cause is not fully understood. Environmental conditions which may trigger physiological leaf spots include extremes of light, temperature, nutritional deficiencies or toxicity, pollutants and other crop stresses. Since ramularia leaf spot develops as a consequence of stresses on plants, it is common for ramularia leaf spot symptoms to develop alongside physiological leaf spots and for physiological leaf spots to be mistaken for ramularia leaf spots. Symptoms What are the symptoms of physiological leaf spots on barley leaves? Physiological leaf spots caused by light stress Early stages of physiological leaf spots caused by light stress include small brown “pepper spots” surrounded by a yellow halo. Symptoms are visible on the part of leaves exposed to light. These spots can superficially resemble the early stages of ramularia leaf spot and it is normal for them to occur on the same leaf as ramularia leaf spots. Physiological leaf spots will be clearly visible on the side of the leaf exposed to the light, but shaded parts of the leaf including the underside of the leaf may appear normal. Effect of variety PHYSIOLOGICAL LEAF SPOTS Symptoms of physiological leaf spots vary depending upon the variety. In some varieties they develop into regular brown spots or streaks which are confined by leaf veins and which are surrounded by a yellow halo. In others, they form brown irregular spots which are not confined by the leaf veins and which do not have a yellow halo. The reason why some varieties exhibit more physiological leaf spots than others is thought to be due to differences in the ability of a variety to produce superoxide dismutase enzyme. This enzyme produces antioxidants which absorb the harmful effects of superoxides, produced inside the plant as a consequence of prolonged exposure to sunlight.
Early development of physiological leaf spots Intermediate development of physiological leaf spots PHYSIOLOGICAL LEAF SPOTS 37
Page 1: A GUIDE TO THE RECOGNITION AND UNDE
Page 4 and 5: 2 Contents RAMULARIA Distribution C
Page 6 and 7: 4 RAMULARIA LEAF SPOT DISTRIBUTION
Page 8 and 9: 6 RAMULARIA LEAF SPOT DISTRIBUTION
Page 10 and 11: 8 Early stages SYMPTOMS What are th
Page 12 and 13: 10 SYMPTOMS Pepper spot symptom of
Page 14 and 15: 12 Later stage SYMPTOMS The rectang
Page 16 and 17: 14 SYMPTOMS Extensive ramularia lea
Page 18 and 19: 16 SYMPTOMS Ramularia leaf spot sym
Page 20 and 21: 18 SYMPTOMS Ramularia leaf spot sym
Page 22 and 23: 20 SYMPTOM APPEARANCE When do sympt
Page 24 and 25: 22 LIFECYCLE Disease lifecycle The
Page 26 and 27: 24 LIFECYCLE Spore dispersal Leaf w
Page 28 and 29: 26 LIFECYCLE Infection of barley by
Page 30 and 31: 28 LIFECYCLE Ramularia collo cygni
Page 32 and 33: 30 Ramularia Ramularia concentratio
Page 34 and 35: 32 CONTROL MEASURES Foliar fungicid
Page 36 and 37: 34 Fungicide choice CONTROL MEASURE
Page 40 and 41: 38 PHYSIOLOGICAL LEAF SPOTS Advance
Page 42 and 43: 40 PHYSIOLOGICAL LEAF SPOTS Physiol
Page 48 and 49: 46 Control of physiological leaf sp
Page 50 and 51: 48 PHYSIOLOGICAL LEAF SPOTS Magnesi
Page 52 and 53: 50 FUNGAL DISEASES CAUSING SYMPTOMS
Page 54 and 55: 52 FUNGAL DISEASES CAUSING SYMPTOMS
Page 56 and 57: 54 Septoria nodorum FUNGAL DISEASES
Page 58 and 59: 56 REFERENCES AND FURTHER READING R
Page 60 and 61: 58 ACKNOWLEDGEMENTS Acknowledgement
Page 62: The Chemical Company

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