D. Paul Jackson

Effects of Pythium Species and Time in Cold Storage on the Survival of Bareroot and Container-Grown Southern Pine Seedlings

Cold storing bareroot southern pine (Pinus spp.) seedlings for greater than one week after lifting in the fall can lead to poor outplanting survival when compared to seedlings that are lifted and stored in winter. In contrast, container-grown seedlings typically do not experience adverse effects from storing for periods greater than one week. The practice of lifting bareroot seedlings can cause wounds to root systems, which could allow soil-borne pathogens such as Pythium species to be used as infection sites. Once seedlings are placed in storage, the cool, moist environment may be conducive for zoospore activity, leading to root disease and outplanting failure. Bareroot and container-grown longleaf pine (Pinus palustris), loblolly pine (Pinus taeda), and slash pine (Pinus elliottii) and container-grown shortleaf pine (Pinus echinata) were inoculated with either Pythium dimorphum or Pythium irregulare, cold-stored for 3, 4, 6, or 12 weeks, and outplanted. Both Pythium species reduced survival of bareroot longleaf pine but not bareroot slash pine. Length of storage decreased survival for both seedling stock types. Pythium species did not affect the survival of container-grown seedlings. These results suggest that P. dimorphum and P. irregulare are more virulent to bareroot longleaf pine than the other pine species tested.

Planting Deep Increases Early Survival and Growth of Pinus echinata Seedlings

Two studies were established to determine the effects of planting depth on early performance of bareroot shortleaf pine seedlings (Pinus echinata). The studies involved planting seedlings either with the root-collar slightly below the groundline (GL) or with the root-collar planted about 11 cm below the soil surface (DEEP). After transplanting, DEEP seedlings had about 7.9 cm of shoot remaining aboveground. In one study, seedlings were planted in open sand pits where seedlings received 352 mm of rain by April 30. The second study involved planting seedlings in boxes (containing sand) in a roofed shade-house. Without rain, survival of DEEP seedlings in April was 96% which was significantly greater (P>F =0.007) than survival of GL seedlings (67%). With rainfall, survival (95%) was the same for both planting depths (P>F = 0.39). Therefore, planting seedlings with the root-collar level with the soil surface can, in some years, increase mortality. This might help explain why bareroot survival of shortleaf pine in some forest districts averages less than 80%.

Evaluation of Plastic Tarps, Reduced Rates and Low-Impact Application Methods of Soil Fumigants on Loblolly Pine Seedling Production

Due to the world-wide phase-out of (methyl bromide) MBr use and new soil fumigation rules established by the US Environmental Protection Agency (EPA) to reduce bystander risk, a large-scale study comparing five fumigants using new plastics, reduced rates and low impact application techniques over three growing seasons was installed to determine the effects that these factors have on seedling quality and quantity. Seedling densities at the end of the first growing season in 2010 ranged from 190-261 seedling/m 2 with some treatments out-performing others with respect to number of seedlings. At the end of the third growing season in 2012, the best soil fumigant for producing loblolly pine (Pinus taeda L.) seedlings was chloropicrin at 280 kg/h and MBr at 168 kg/h under totally impervious film (TIF). Overall, seedling root length, surface area, root diameter and root tips were similar to the standard MBr 280 treatment for all soil fumigants except for the Chlor 60 treatments under high density polyethylene (HDPE) plastic. The numbers of Culls was less with the higher rates and there was a corresponding increase in the number of Grade 1 and Grade 2 seedlings for each soil fumigant. These trials indicate that, while not the perfect replacement in all nursery soils, seedling production is still possible without MBr if alternatives such as chloropicrin are used and managers pay close attention to weed and nematode pests that are less susceptible to chloropicrin than MBr. Higher rates of each soil fumigant were better than the lower rates.