Growth, Survival and Physiological Effects of Hexazinone and Sulfometuron Methyl Applied Overtop of Longleaf Pine Seedlings

A field study was conducted in Santa Rosa County, FL to evaluate the effects of two herbicides, hexazinone and sulfometuron methyl, on longleaf pine seedling (Pinus palustris Mill.) survival, growth, and physiological functions over a 2 yr period (2001–2002). An old-field site was planted with 1-yr-old container-grown seedlings in January 2001, and herbicides were band-applied overtop of the seedlings in April 2001. Hexazinone rates were 0.56 and 1.12 kg ai/ha, and the sulfometuron methyl rates were 0.21 and 0.42 kg ai/ha. Volumetric soil moisture was also measured in May, July, August, and October in each treatment. At the end of the first growing season (2001), survival was not improved by any of the herbicide applications. However, root collar diameter (RCD) increased for hexazinone applied at 0.56 and 1.12 kg ai/ha, and sulfometuron methyl applied at 0.42 kg ai/ha at the end of the first growing season compared to the control. At the end of the second growing season, RCD was 28.7, 30.9, 30.5, 32.1, and 33.3 mm for the control, sulfometuron methyl applied at 0.21 and 0.42 kg ai/ha, and hexazinone applied at 0.56 and 1.12 kg ai/ha, respectively. Also, the percentage of seedlings out of the grass stage at the end of the study was 72, 74, 79, 81, and 89% for the control, sulfometuron methyl applied at 0.21 and 0. 42 kg ai/ha, and hexazinone applied at 0.56 and 1.12 kg ai/ha, respectively. Foliar responses, such as net photosynthesis, stomatal conductance, and transpiration were measured in October 2001. There was no evidence of herbicide injury on foliar physiological functions relative to the control seedlings 6 months after treatment. During 2001, soil moisture was related to hexazinone and sulfometuron methyl application rates in May and July, but not in August or October. Averaged across May and July, soil moisture increased from 5.4% in the control to 7.6 and 7.5% in the highest hexazinone and sulfometuron methyl treatments, respectively. Based on seedling survival, growth, and herbicide costs, the most effective treatment was hexazinone applied at 0.56 kg ai/ha. South. J. Appl. For. 28(1):48–54.

Estimates of genetic parameters for oleoresin and growth traits in juvenile loblolly pine

In southern pines of the United States, resistance to attack by southern pine beetle, Dendroctonus frontalis Zimmermann, is believed to principally involve flow of oleoresin to beetle attack sites. Both environmental and genetic factors are known to affect the quantity of oleoresin flow in loblolly pine, Pinus taeda L., but little is known about the genetic contribution to phenotypic variation in this trait. Here we report estimates of genetic variation in oleoresin flow and growth traits for a population of this species. Oleoresin yield, total height, and diameter were measured on 10- and 11-year-old trees from an experimental test in Santa Rosa County, Florida. Trees were from 72 full-sib families produced by mating 48 parents according to a disconnected partial diallel mating design. Resin yield was determined from breast-height samples collected at two times: once in the summer of 1999 when latewood was being produced (summer resin flow), and once in the spring of 2000 during earlywood formation (spring resin flow). All traits studied were found to be highly genetically variable and to have much greater additive than dominance variance. Estimates of narrow-sense heritability for spring and summer resin flow were in the moderate range and are comparable to values obtained for the growth traits. Additive genetic correlations between oleoresin yield and the growth traits were positive and moderately high, suggesting that directional selection to improve growth in loblolly pine will also result in increased production of oleoresin.