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Current Status of Rust in The South

Host acreage by state, ownership, and rust infection level are presented in tables 1-8. Southwide, the current estimate of slash and loblolly pine host types is 47.9 million acres (table 1). Georgia has the most, about 9.4 million acres, while Oklahoma has the least, 465,000 acres. The majority of the acreage is owned by nonindustrial private forest landowners (51 percent) and the forest industry (42 percent). Over 13.4 million acres (28 percent) southwide have >10 percent of the slash and/or loblolly pines infected (table 2), and the proportion of infected acreage on nonindustrial private and industrial forest land is about the same as for all host acres. These percentages, of course, vary somewhat among States. Georgia has the most, with about 4.5 million acres having >10-percent infection, and Oklahoma the least, with 34,000 acres having >10-percent infection.

Slash and loblolly pine plots with >10-percent rust incidence are distributed over nearly the entire range of each species, as shown by the maps in figures 1 and 2. These maps provide a good visual approximation of the distribution and frequency of rust occurrence but not an absolute one. Even though several thousand plots are established in each State, many areas of potential pine hosts may not be represented by a plot or plots. Because rust incidence can vary considerably over relatively small areas, areas of high or low rust can be closely associated but not accurately characterized by one or more nearby plots. Also, States in the eastern half of the region (Florida, Georgia, North Carolina, South Carolina, and Virginia) have a more random distribution of plots, whereas States in the western half of the region (Alabama, Arkansas, Louisiana, Mississippi, and Texas) have a more systematic distribution. Thus, plot densities on the map do not absolutely represent rust prevalence. Nonetheless, the maps provide a good, visual representation of where rust is most commonly found on FIA plots.

Of the 13.4 million acres southwide with >10-percent of the trees infected, 29 percent is slash pine type and 71 percent is loblolly (tables 3-6). About 34 percent of the 11 million acres of slash pine type (table 3) and 26 percent of the 36.6 million acres of loblolly pine type (table 6) had >10-percent of the trees infected. For the slash pine type, the proportion of planted acres with >10-percent rust was twice that for natural acres (41 vs. 21 percent; tables 4, 5) while for the loblolly pine type, the proportion with >10-percent rust infection was rather similar for planted and natural acres (23 and 29 percent; tables 7, 8). The highest proportion with >10-percent rust for the slash pine type occurred in Louisiana (85 percent, natural acres), while the highest levels for the loblolly pine type occurred in Georgia (58 percent, natural acres).

There were far fewer acres with >30- and >50-percent infection levels (tables 3-8). For slash pine, the proportion of acres with these levels of infection were 15 and 7 percent, respectively. In the loblolly type, only 9 and 3 percent, respectively, of the acres were at these levels. Individual State estimates varied considerably depending on species and stand origin. For instance, in Louisiana, the proportion of natural slash acres with a >30-percent rust level was 73 percent; at the > 50-percent rust level it was 32 percent. In Georgia, natural loblolly acreage at the >30-percent infection level was 24 percent; at the >50 percent level it was 9 percent.

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Figure 1. -- Locations of Forest Inventory and Analysis plots that have slash pine forest type and > 10-percent fusiform rust infection.

Figure 1

Figure 2. -- Locations of Forest Inventory and Analysis plots that have loblolly pine forest type and > 10-percent fusiform rust infection.

Figure 2

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