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Impact of Leaf Mining on the Growth of Portulaca oleracea (Common Purslane) and Its Competitive Interaction with Beta vulgaris (Sugarbeet)
Robert F. Norris
Journal of Applied Ecology
Vol. 34, No. 2 (Apr., 1997), pp. 349-362
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2404881
Page Count: 14
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1. The combined attack by leaf mining larvae of the sawfly, Schizocerella pilicornis, and the weevil, Hypurus bertrandi, typically resulted in over 80% defoliation of fieldgrown Portulaca oleracea plants in the Central Valley of California. Incorporation of the insecticide aldicarb into the soil prior to planting protected the weed from attack by the insects. Comparison of insecticide-treated and non-treated plants demonstrated that the leaf mining reduced weed growth by 60-70%. 2. Under replacement series pot experiment conditions, leaf mining reversed the competitive interaction between sugarbeet and P. oleracea. Sugarbeet grew best in the presence of P. oleracea plants that were attacked by leaf miners; relative crowding coefficients for sugar beet exceeded 1.0. When P. oleracea was protected from leaf-miner attack, relative crowding coefficients for sugarbeet were all below 1.0. 3. Portulaca oleracea caused up to 80% yield loss in sugarbeet in additive field competition experiments. The magnitude of the sugarbeet yield loss increased with increasing density of P. oleracea; between 0.5 and 3.0 P. oleracea plants per m of crop row caused an economic loss depending on year. Soil-applied aldicarb insecticide did not alter the competitive interaction in 3 years out of 4, although the insecticide substantially protected P. oleracea from leaf mining. 4. Although P. oleracea was severely damaged by leaf miner feeding, this injury did not result in sufficient biological weed control to reduce the need for use of other weed management techniques.
Journal of Applied Ecology © 1997 British Ecological Society