abstract increased knowledge of russian knapweed biology would facilitate development of an optimum control program. to examine germination characteristic of this weed, several experiments were conducted in weed research department, plant pest and diseases research institute of tehran during 2003. first experiment was a factorial with 3 replications to break seed dormancy of this weed. first fa...

Biological control of spotted knapweed (Centaurea stoebe) is an ongoing topic of research that holds ecological importance due to the extent to which knapweed has spread across the Western United States. Using herbivores (insects) as biological controls of spotted knapweed can be successful at reducing plant density in certain habitats. However, the exact relationship among the insects, knapwee...

The influence of temperature, shoot age, and medium on gall induction by Subanguina picridis on Russian knapweed (Acroptilon repens) was examined in vitro. The optimal temperature for gall formation was 20 C. Gall induction was delayed as the temperature decreased, and decreased as shoot age increased. Bud primordia (0-day-old shoots and 5-day-old shoots) with an average length of 4.2 mm and 7....

Broadleaf herbicides are commonly used to suppress exotic weeds with the intent of releasing native species from negative impacts of invasion. However, weed control measures can also have unintended consequences that should be considered along with intended effects. We conducted a controlled field experiment within bunchgrass communities of western Montana to examine if broadcast application of...

Insects introduced as biological control agents of diffuse knapweed, Centaurea diffusa, primarily reduce seed production. Knapweed densities appear to be resilient to greatly reduced seed production. We have used measurements of seedling density and survival, and production of seeds by flowering diffuse knapweed plants to develop functions for a model of knapweed populations. These simulations ...

Hybridization has been hypothesized to influence invasion through the generation of novel phenotypes and/or increased levels of genetic variance. Based on morphology, hybrids between diffuse knapweed and spotted knapweed, two invasive plants in North America, are present in the invaded range. Some individuals within most diffuse knapweed sites in North America exhibit intermediate diffuse × spo...

Russian knapweed (Acroptilon repens [L.] DC.) and yellow starthistle (Centaurea solstitialis L.) are invasive weeds in the western United States, and both weeds are targeted for biological control. Cercosporella acroptili (Bremer) U. Braun was identified as a possible biological control agent for A. repens, and a morphologically similar Cercosporella sp. recently was found damaging to C. solsti...