James H. Miller

Invasion of tallow tree into southern US forests: influencing factors and implications for mitigation

We identify species-environment relationships to predict the occurrence of Chinese tallow (Triadica sebifera (L.) Small) on forestlands in the southern US, where it has emerged as the most pervading, stand-replacing, alien tree spe- cies. Tallow invasions are more likely to be observed on low and flat lands, areas adjacent to water and roadways, sites re- cently harvested or disturbed, younger stands, and private forestlands. The winter extreme minimum temperature tends to restrain tallow northward migration. Increases in both range and severity of tallow invasions are predicted with a warming climate trend, and the situation could be worse if the warming is coupled with an increased frequency and intensity of dis- turbances. Monitoring and mitigation strategies are proposed to assist this region and other countries threatened by tallow invasions. Resume´ : Nous avons identifiedes relations entre lenvironnement et larbre a suif chinois (Triadica sebifera (L.) Small) pour predire loccurrence de cette espece sur les terrains forestiers du sud des Etats-Unis ouelle est devenue lespece darbre exotique la plus repandue capable de remplacer des peuplements. Les invasions de larbre asuif ont le plus de chances detre observees sur les terres basses et plates, dans les zones adjacentes aun plan deau et ala chaussee, sur des sites recemment recoltes ou perturbes, dans de jeunes peuplements et dans les boises prives. La temperature minimum ex- treme en hiver a tendance a limiter la migration de larbre asuif vers le nord. Une augmentation tant de letendue que de la severitedes invasions de larbre asuif est prevue avec la tendance au rechauffement du climat et la situation pourrait etre pire si le rechauffement est accompagnedune augmentation de la frequence et de lintensitedes perturbations. Des strategies impliquant le suivi et des mesures dattenuation sont proposees pour aider cette region et dautres pays menaces par les invasions de larbre asuif. (Traduit par la Redaction)

Invasion Dynamics and Genotypic Diversity of Cogongrass (Imperata cylindrica) at the Point of Introduction in the Southeastern United States

Abstract Nine sites of cogongrass were included in a study of genotypic diversity and spread dynamics at the point of introduction and its adjacent areas in the southern United States. Clones evaluated with two primer pairs yielded a total of 137 amplified fragment length polymorphism (AFLP) loci of which 102 (74.4%) were polymorphic. Genetic diversity was measured as the percentage of polymorphic, Shannons information index, Neis gene diversity, and panmictic heterozygosity. Neis gene diversity (HS) across all nine sites was estimated to be 0.11 and within site gene diversity ranged from 0.06 to 0.16. Bayesian estimate of gene diversity and Shannons information index were higher (0.17 and 0.17, respectively). The samples from the point of introduction (Pi) had the lowest genetic diversity for all types of estimates. Within site variance accounted for 56% of the total variation and among site variance 44% (Pu2009<u20090.05). Differentiation among sites was assessed using FST. The greatest difference was found between the Pi and the others. No relationship was found between genetic and geographic distances. Principal component analysis as well as cluster analysis separated individuals into three main clusters. The Pi formed a separate subcluster. Gene flow (Nm), inferred from Φ-statistics describing the genetic differentiation between pairs of sites ranged from 0.6 to 5.55. The lack of significant relationship between gene flow and geographic distance as well as genetic and geographic distances suggests that the invasion dynamics of cogongrass into the southern United States is primarily through anthropogenic activities and to the lesser extent through natural forces. Nomenclature: cogongrass, Imperata cylindrica (L.) P. Beauv; Brazilian satintail, Imperata braziliensis Trin.; satintail, Imperata brevifolia Vasey; satsuma orange, Citrus reticulata L.; CTAB, cetyltrimethyl ammonium bromide; DNA, deoxyribonucleic acid.

Pushing toward cogongrass (Imperata cylindrica) patch eradication: the influence of herbicide treatment and application timing on cogongrass rhizome elimination.

Abstract Cogongrass, an invasive grass native to Asia, has infested thousands of hectares in the southeastern United States. Although numerous studies have examined cogongrass control, no published studies, to our knowledge, have tested strategies for cogongrass eradication. Cogongrass has a persistent, thick rhizome mat but an ephemeral seedbank; therefore, successful eradication methods must largely focus on the rhizomes. A field study to evaluate specific herbicide treatments and application timings for cogongrass patch eradication was conducted at two locations in southwestern Alabama. Herbicide treatments included glyphosate at 4.48 kg ai ha−1, imazapyr at 0.84 kg ai ha−1, and a tank mix of glyphosate and imazapyr at the same rates. Treatments were applied in May, August, or October for 3 consecutive yr, and the May glyphosate treatment included a second annual application each October. Cogongrass visual control, shoot biomass, rhizome biomass, rhizome depth, and total nonstructural carbohydrate (TNC) content were sampled during the course of the study. Cogongrass response to treatments varied by location but by 36 mo after initial treatment (MAIT), complete elimination of cogongrass shoot and rhizome biomass and 100% visual control was achieved in several herbicide treatment–timing combinations at both locations. These included glyphosate plus imazapyr at any application timing, imazapyr in August or October, and glyphosate applied in May and October each year. TNC levels of surviving healthy rhizomes were not affected by herbicide treatments, but a seasonal pattern was observed. The maximum live-rhizome depth was not influenced by any treatment, indicating that herbicides were not preferentially leaving deeper, surviving rhizomes. These results demonstrate, for the first time, that the entire rhizome layer of cogongrass can be eliminated within 3 yr with multiple treatment options and that cogongrass patch eradication is possible for many land managers. Nomenclature: Glyphosate, glyphosate plus imazapyr, imazapyr, cogongrass, Imperata cylindrica (L.) Beauv. IMPCY. Management Implications: Cogongrass is one of the most difficult weeds to manage because of its aggressive growth and persistent rhizomes, which often survive initial herbicide treatments. Historically, research efforts have been focused on cogongrass control, but no published studies have tested strategies for eradication. The present study is the first documented research to demonstrate complete elimination of cogongrass in 18 to 36 mo using repeated, annual herbicide applications. Treatments included glyphosate, imazapyr, and a tank-mix of both applied in the spring, summer, or fall for 3 consecutive yr. Verification of eradication was based on a highly rigid criterion involving measurements of cogongrass visual control, shoot biomass, rhizome biomass, rhizome depth, and total nonstructural carbohydrate (TNC) content over 3 yr. Cogongrass response to treatments varied by location. By 36 mo after initial treatment, the glyphosate plus imazapyr treatment applied at any timing, the imazapyr treatment applied in August or October, and the glyphosate treatment applied in May and October each year resulted in complete elimination of cogongrass shoot and rhizome biomass. The maximum live-rhizome depth (16 cm ± 2 SE) was not influenced by any treatment. During the 3-yr period, herbicides did not affect TNC levels of surviving rhizomes, indicating that repeated treatments directly killed rhizomes, rather than slowly exhausting energy reserves. We are not suggesting that cogongrass can be eradicated from the southeastern United States; however, with repeated glyphosate or imazapyr herbicide treatments, land managers do have a feasible means of eradicating cogongrass patches.