Rhaponticum repens (Russian knapweed).

R. repens is a deep rooted perennial that is native to Eurasia. It was accidentally introduced into North America as a contaminant of seed and spread rapidly. R. repens can be a serious crop pest in its native range and elsewhere. It forms large monotypic stands that reduce diversity and degrade forage quality on rangelands. As it is allelopathic and survives under a variety of conditions, it has been become an invasive exotic wherever it is imported. It has been declared a noxious weed in 18 US states (USDA-NRCS, 2016) and four Canadian provinces (Rice, 2003).

New spider mites (Acari: Tetranychidae) of the genera Paraplonobia and Eurytetranychus from Iran, and a description of all life stages of Eutetranychus orientalis (Klein)

Two new species of Paraplonobia Wainstein and Eurytetranychus Oudemans are described from Iran: Paraplonobia (Paraplonobia) flechtmanni n. sp. from Russian knapweed Rhaponticum repens (Asteraceae) and Eurytetranychus aminii n. sp. from gum bushes Astragalus gossypinus (Fabaceae). We describe all life stages of Eutetranychus orientalis (Klein) and discuss variation within this polyphagous pest species. A key to all known species of the genus Paraplonobia (Paraplonobia) is given.

Invasive Russian Knapweed (Acroptilon repens) Creates Large Patches Almost Entirely by Rhizomic Growth

Russian knapweed is an outcrossing perennial invasive weed in North America that can spread by both seed and horizontal rhizomic growth leading to new shoots. The predominant mode of spread at the local scale and dispersal at the long-distance scale informs control but has not been quantitatively researched. We used amplified fragment-length polymorphisms (AFLPs) of DNA collected from 174 shoots in two discrete patches of Russian knapweed at each of three locations in Montana. Out of the 174 shoots collected, we found nine AFLP genotypes. Three out of the six patches were monotypic; the other three patches each had one rare genotype. No genotypes were shared between patches. The maximum diameter of a genet (a genetic individual) was 56.5 m. These results indicate that patch expansion at the local scale is almost entirely by rhizomes that spread and develop new shoots. At the long-distance scale, dispersal is by seed. Controlling seed development through biological control and herbicide use may be effective at stopping long-distance dispersal but may not affect expansion of existing patches.

Monitoring a Gall Midge Population on Russian Knapweed (Acroptilon repens)

This paper describes postrelease monitoring of a population of Jaapiella ivannikovi, a gall-forming midge that was introduced for biological control of Russian knapweed. In 2011 to 2013, from late May to early June through August, we monitored 100 permanent plots at one of the first release sites of J. ivannikovi in central Wyoming. Based on the phenology of gall formation, an appropriate window for collection of galls to distribute to new sites is from early to mid-June through early August. Although J. ivannikovi established successfully, 4 yr after release, the percentage of ramets that were galled remained low (1 to 2%), indicating that J. ivannikovi is not yet having a significant effect on Russian knapweed at the site.

Assessing Invasiveness of Exotic Weeds outside their Current Invasive Range

When exotic species invade a region, it becomes important to assess their invasiveness in adjacent uninvaded regions to determine if weed prevention measures are needed. Leafy spurge and knapweed species are absent from the vast majority of eastern Montana, but the region is surrounded by regions heavily invaded by these species. To assess invasiveness of leafy spurge and Russian and spotted knapweed in common eastern Montana grassland sites, I introduced these species to three sites as seeds (120 live seeds plot−1) and seedlings (6 plot−1). I assessed how common grazing regimes influenced invasiveness by imposing cattle, sheep, mixed grazing (i.e., cattle plus sheep), and grazing exclusion treatments for 7 yr. Invader survival did not appear to differ greatly among sheep, cattle, and mixed grazing treatments, but excluding grazing lowered probabilities that plots maintained invaders for the entire study period at two of three sites. At these same sites, grazing exclusion increased growth rates of those invaders that did survive, at least in the case of leafy spurge. Regardless of grazing treatment or site, however, large proportions of plots did not maintain invaders through the end of the study period. At one heavy clay site, only one small leafy spurge plant persisted through the end of the study. In the seventh study year, the plots with the most leafy spurge and Russian knapweed produced 222 and 112 stems, respectively, and the stems remained mostly confined to the 2- by 2-m plots. These findings suggest that, barring intense disturbance, leafy spurge and spotted and Russian knapweed might be incapable of invading some grasslands of eastern Montana, particularly upland sites with high clay content. Any upland sites in the region these species are capable of invading will likely be invaded only very slowly.