We modified soil water supply to two groups of juvenile loblolly pines,Pinus taedaL., by sheltering or irrigating root systems in early summer or in late summer and measured oleoresin flow (primary defense), net photosynthesis, xylem water potential, and cambial growth throughout the growing season. When consistent significant differences in oleoresin flow and water potentials were detected between treatments, we induced attack by the southern pine beetle,Dendroctonus frontalisZimmermann. Compared with irrigated trees, sheltered trees had lower xylem water potentials, reduced cambial growth, reduced photosynthesis, and reduced resin flow. In terms of response to beetle attack, sheltered trees had fewer attacks and less total gallery constructed, but those beetles that did attack sheltered trees were more successful (50–100% more eggs per attacking pair). However, the success of attacking beetles was generally very low, even in sheltered trees (only three to eight eggs per attacking pair). This performance, along with water deficits that strongly affected tree physiology, growth, and development, indicates that juvenile loblolly pine can make internal adjustments that limit the success of southern pine beetle attack.