Tuesday, 8 November 2005
14

Mowing Height and Urea Source Effects on Endophyte-Mediated Resistance in Four Tall Fescue Cultivars.

Cale A. Bigelow and Douglas S. Richmond. Purdue University, 915 W. State St., West Lafayette, IN 47907-2054

Endophyte enhanced grasses are desirable because their leaves contain alkaloids which enable them to resist surface feeding insect herbivory. Little information exists regarding the impact of common cultural practices like mowing height or nitrogen (N) fertilizer sources on endophyte mediated resistance. A greenhouse experiment studied the effect of two mowing heights (5.0 and 8.9 cm) and N supplied as urea or urea containing a nitrification inhibitor on black cutworm herbivory in four commercially available tall fescue cultivars (‘DaVinci', ‘Kentucky-31', ‘2nd Millenium'and ‘Plantation'). Turf was grown in pots from mature sod plugs taken from the field and pseudostem endophyte infection rates ranged from 44 to 100%. Turf was fertilized weekly with a liquid solution equivalent to 12.5 kg N ha-1. Analysis of the soil solution N did not show a predominance of nitrate or ammonium-N as N-source varied. The settling response of neonate black cutworms was markedly influenced by cultivar and mowing height. After 48 h in non-choice Petri dish assays, fewer larvae settled on clippings from 2nd Millenium which had the highest endophyte infection level. Larvae also displayed a strong preference for clippings taken from tall fescue maintained at 5.0 cm, regardless of cultivar. Survival of neonate larvae after 5 d, however, was not correlated with initial settling response but rather a significant interaction between cultivar, mowing height and N-source occurred. Larvae survival was significantly higher on clippings from plants mowed at 5 cm in 2 of the 4 cultivars tested (2nd Millenium and Plantation) and significantly higher on clippings from 2nd Millenium fertilized with urea without a nitrification inhibitor. This study demonstrates that in addition to choosing a high endophyte cultivar, manipulating basic cultural practices like mowing height and N-source can minimize potential insect damage and perhaps require fewer insecticide applications.

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