Compensatory growth of potatoes (Solanum tuberosum L.) in response to defoliation

To be useful to an integrated pest management program, potato growth simulation models should incorporate the effects of pest defoliation on plant growth and development. There is evidence that plants react to defoliation with a variety of compensatory responses that can lead to replacement of biomass and productivity. To assess the type and degree of compensatory mechanisms in potatoes, field and greenhouse experiments were conducted with several levels of pest or artificial defoliation.;Field experiments in 1988 with controlled levels of defoliation by early blight (Alternaria solani) on 'Norchip' and late blight (Phytophthora infestans) on 'Katahdin' showed that late-season loss of lower leaves did not induce the compensatory responses seen from upper-canopy defoliation. Instead, tuber yield was related to time of epidemic onset and total defoliation.;Additional compensatory responses were detected in a series of greenhouse experiments with artificially defoliated 'Katahdin' plants. Photosynthetic rates increased 25% in older leaves and 13% in younger leaves on 50% defoliated plants. Stomatal conductance increased more in older than younger defoliated leaves. Specific leaf weight and nitrogen per unit area increased at all leaf positions in defoliated plants. Growth analyses revealed that defoliated plants had higher relative growth rates for leaf expansion and dry weight increase. Younger leaves recovered more leaf area than older leaves. Although initially depressed, tuber yields of defoliated plants recovered when harvest was delayed.;Results from this research are being used to modify potato growth simulation models as part of an interdisciplinary research effort to develop a regional potato pest management program.;Differential foliar applications of permethrin were made to 'Katahdin' potatoes in 1987 and 1988 to achieve three levels of defoliation by the Colorado potato beetle (Leptinotarsa decemlineata). In both years, delay of permethrin application until early August did not result in significant tuber yield decreases as compared to plots receiving season-long sprays, despite defoliation levels of up to 50%. However, season-long defoliation of up to 60% significantly depressed marketable tuber yield in 1987. Defoliated plants compensated for tissue loss via increased axillary branching, delayed leaf senescence, and late-season growth of branch leaves. Higher levels of blackleg, early blight, and aphids were noted in control plots.