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Monitoring Incidence of Fusiform Rust in the South and Change Over Time
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Fusiform Rust in the South

Fusiform rust, caused by the fungus Cronartium quercuum (Berk.) Miyabe ex Shirai f. sp. fusiforme on slash (Pinus elliottii Engelm. var. elliottii) and loblolly (P. taeda L.) pines, is native to the Southern United States. Since the 1930's, fusiform rust has developed into the most destructive forest tree disease of southern pines (Dinus and Schmidt 1977). Widespread planting of slash and loblolly pines, coupled with forest fire control programs, has resulted in increasing acreages of susceptible pines and increasing populations of the fungus' alternate hostCoaks (Quercus spp.)Cwhich are necessary for the fungus to complete its life cycle and cause infections of pines. Infection by the fungus results in the formation of swollen galls on susceptible pine stems and branches. Main-stem infections in pines less than 5 years old are likely to kill the tree (Campbell 1965, Nance and others 1981, Wells and Dinus 1978). Main-stem and branch infections occurring after age 5 normally do not kill a tree, but they often result in breakage during storms or merchantable volume loss at harvest (Webb and Patterson 1983). Slash pine is generally more susceptible and more damaged by rust than is loblolly pine (Goddard and Wells 1977). Rust incidence varies greatly from year to year and across sites due to varying weather patterns and local conditions. Incidence and impact of rust may be reduced by management activities, particularly the planting of rust-resistant sources or genotypes in high-risk areas. It is important to attempt to track rust incidence across the South to detect any significant changes or trends in rust levels over time.

Estimating the incidence of fusiform rust for a region as large as the South is extremely difficult. The cost of making a large, single-purpose survey to obtain such data is prohibitive, so if Southwide estimates are to be made, other currently existing data sets must be used. The only regional data available for making such estimates can be obtained from Forest Inventory and Analysis (FIA, formerly known as Forest Survey) of the Digital Arborist, Southern Research Station (formerly the Southeastern and Southern Forest Experiment Stations). The FIA data is collected from several thousand sample plots in each Southern State on a 6- to 10-year remeasurement cycle. Fusiform rust infection has been recorded since 1973 in most States (Jacobi and others 1981) and is uniquely suited to such surveys because it has a symptom that can be easily identified year round. Rust incidence has been previously estimated for five Southeastern States (Florida, Georgia, North Carolina, South Carolina, and Virginia) using FIA data (Anderson and others 1986) with somewhat different procedures than employed here. Now, FIA data that includes fusiform rust incidence from two or more survey cycles is available for each Southern State where rust occurs, allowing new estimates to be made and new comparisons of change over time.

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