Combinations of Fungicide and Cultural Practices Influence the Incidence and Impact of Fusiform Rust in Slash Pine Plantations

Slush pine was grown in central Louisiana unrler,f?)ur levels c!f'culture with or without repeatc~d spmyings of the .sy.vten~ic ,fungicide triadimefhn , f i r protection against ,fusifi)rm rust. The eight treatment cornbinations were: ( I ) no,fungicide, weed control, or,fertilizer; ( 2 ) weeded; ( 3 ) weeded, applied irzorganic ,firtilizer, and bedded b<fi)replcrrlting; ( 4 ) weeded, bedded, and applied inorganic fertilizer in the sixth growing season (clel(.lcryedjkrtilizutioi~); ( 5 ) c~pplied fungicide but no weed control or,fertilizer; ( 6 ) applied fungicide and weeded; (7) czpplied ,fungicide plus treatment 3; and (8) applied fungicide plus treatment 4. Fungicide appliccrtions greatly reduced,fu.sijorm rust impact in 10-yr-old sla.sh pine stands. Fungicide treatments resulted in higher .survival, ,fewer trees with stem galls, fewer trees with gal1.s encircling 76%-100% c$' the .stem circumference, greater total volume/ac, and less volume/c~c among infected trees. The fungicide-treated trees had,fewer stem ga1l.s below 5 ft of tree height compared with untreated trees, indicating that the furzgicide treutmentprotectedpIc1nted seedlings through several growing seasons. Weed control increased fusiform rust incidence. The,fungicicle-treated plots receiving delayedfertilization yielded the most volume (3,018 ft3/ac) a$er 10 growing seasons because of high stocking and accelerated growth ji)llowing ,fertilization. South. J. Appl. For. (2):53-59. Fusi iorm rust, caused by Cronarrium yuercuum (Berk.) and severity on the survival, growth, and yield of planted Miyabe ex Shirai f. sp. ,fu.siforme, is the most destructive disease of slash pine (Pinus elliottii Engelm. var. elliottii). frequently causing mortality and reducing the value of surviving infected trees for sawtimber (Busby and Haines 1988, Webb and Patterson 1983). The incidence of the disease increases when certain cultural practices and fertilizers are used to increase seedling growth (Burton et al. 1985, Dinus and Schmidtling 1971, Froelich et al. 1983, Miller 1972, Rowan 1978). The incidence of fusiform rust is increasing in slash pine plantations in the West Gulf Coastal Plain (Hunt and Lenhart 1986). The systemic fungicide triadimefon ( ~ a ~ 1 e t o n O ) l i s effective against several plant diseases including fusiform rust (Snow et al. 1979). Triadimefon is translocated in plants from foliar sprays. Because the control of fusiform rust in slash pine stands would be beneficial, we applied triadi~nefon fungicide to measure the effects of fi~siform rust incidence No~r:: The authors wish to acknowledge the many contributions James D. Burton and Eugene Shoulders made toward this research and the study of Li~siform rust. slash pine growing under several other cultural practices. Materials and Methods Study Area The study area was cutover forestland in central Louisiana. The longleaf pine (P. pa1u.stri.s Mill.) sawtimber was harvested in the 1920s, and the land was grazed as open or fenced range until 1967 when livestock was excluded. In 1978, the natural pine-hardwood growth was cleared, debris or standing residual trees greater than 2 in. dbh were removed, and smaller trees were cut and left in place. The soil is a Beauregard-Caddo silt loam association. Slopes range from 1 % to 3% with a consistent western aspect. These soils are slowly permeable, low in organic matter and plant nutrients, droughty in summer (Burton et al. 1985), and intermittently water-logged in winter (Haywood et al. 1990). Chemical analyses were run on the surface 6 in. of soil collected from 10 random locations in the study area. Available phosphorus was very low averaging 0.9 ppm. Total nitrogen was 0.09% and soil organic matter was 5%. Cation ' Use ofregistered trademarks, or any other 11-adc, firm, or corporation name, exchange capacity was 7.1 n1eq1100 g of soil and the pH was does not constitute an official endorsement or approval by the USDA of ally 4.8. Soil phosphorus was extracted by shaking the soil with product or service to the exclusion of others that !nay he suitable. Discussion ofpesticides in this paper does not constitute recomrnend;rtion oftheir use or 0.3M NH4F + HC1 for and Kurtz 1945). ~rnply that dl\cu\\ed helc ,\re rcgl\tered Total nltrogen wa\ determined by macro-Kjeldahl (Bremner