Saturday, September 4, 2010

Plant pathology:Leaf roll on Broadbeans

My broadbean crop has developed 'leaf roll' disease. This is caused by Clover stunt virus which is transmitted by the Cowpea aphid (Aphis craccivora). The seed may have been infected with the virus before I planted it but the more likely cause is that I neglected this particular patch during the early months of autumn/winter and let some self sown zucchini grow and fruit, thus crowding out the developing broadbean plants. I also didn't keep up the water to them sufficiently as well. So I blame myself partly for their poor performance. This week, right on cue, black aphids made themselves at home on top of the already sick plants. What is interesting about these aphids is that they travel such great distances to get here. They migrate from western country districts (Western Slopes and Plains of New South Wales) after breeding on pasture legumes and other suitable plants , rising to the upper atmosphere and blown to the coast by north westerly or westerly winds which are common in early spring.
Aphis craccivora Cowpea Aphid(Photo: Zara Ludgate)

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