Container-grown nursery crops in the southeastern United States are typically grown in a rooting substrate comprised primarily of the ground bark of pine trees. However, pine bark is becoming less available and more costly because of changes in production and marketing practices within southeastern pine forestry. This shortage has resulted in the economic incentive to seek pine bark alternatives. Two possible alternatives are clean chip residual and whole tree. These alternatives are like pine bark, because both are products of southern pine forestry. Unlike pine bark, which is a single part of the tree, these alternatives contain all parts of the tree, including wood and foliage in various portions. Registration of preemergence-active herbicides has been based solely upon data obtained from pine bark–based nursery production. Research was conducted to determine if the control of (1) large crabgrass with prodiamine, (2) eclipta with flumioxazin, and (3) spotted spurge with isoxaben would be comparable in these alternatives to what has been established in pine bark. Seed germination of all three weed species in no-herbicide controls was approximately 10% and equivalent between pine bark and the alternatives. Foliage fresh weight production of large crabgrass and spotted spurge was less in the alternatives compared to pine bark; eclipta was not affected. For all three weed species–herbicide combinations, weed control was nearly identical between pine bark and the alternative substrates, provided the herbicide had been applied at its registered rate. For all three herbicides, rates that are effective in pine bark substrates will be equally effective in the pine bark alternatives.

Greenhouse experiments were conducted to evaluate the response to halosulfuron of several smooth pigweed populations that had been shown to be resistant to acetolactate synthase (ALS, EC 2.2.1.6)-inihibiting herbicides. Five ALS-resistant smooth pigweed populations (R1, R2, R3, R4, and R5) and one susceptible (S) population were treated with halosulfuron POST at 0.27, 2.7, 27, 270, and 2,700 g ai/ha. Percentage injury and dry weight were used to determine resistance of smooth pigweed populations to halosulfuron. Populations of smooth pigweed with previous reports of resistance to ALS-inhibiting herbicides showed varying degrees of resistance to halosulfuron compared with the susceptible population. Concentrations of halosulfuron required to reduce ALS-resistant smooth pigweed dry weights 50% were 2 to 12-fold higher than that of the susceptible population. One population, designated R2, had increased resistance to halosulfuron applications, requiring 97 g/ha halosulfuron to reduce shoot dry weight 50% compared with only 8 g/ha for S. Our results show that populations of smooth pigweed with a history of ALS-inhibiting resistance can have differing degrees of resistance to halosulfuron.

A botanical survey conducted from 2003 to 2007 showed the occurrence of the acacia strap flower and the Oriental mistletoe plant in different regions in Jordan. Acacia strap flower was found parasitizing 26 plant species belonging to 12 families. Oriental mistletoe attacked 14 plant species from eight families. Parasitized species ranged from wild shrubs to fruit and forest trees. Eleven Fabaceae species were parasitized by acacia strap flower, whereas Oriental mistletoe parasitized six Rosaceae species. Caper, pomegranate, white weeping broom, and white willow were attacked by both parasites. Infection by both parasites resulted in mortality of host plants in many cases. Hosts severely attacked by acacia strap flower were African jujube, Australian pine, chinaberry, Christ thorn jujube, common jujube, oleander, poinciana, sumac, tamarisk, terebinth, and white weeping broom. Oriental mistletoe heavily parasitized almond, mosphilla, olive, Palestine buckthorn, pomegranate, and white weeping broom. Results indicated the high potential of both parasites to spread and attack new hosts in the absence of control measures.

A johnsongrass population from a cotton field in northern Greece along with a population from the university farm (“Control”) were evaluated for resistance to the herbicide quizalofop; cross-resistance to cycloxydim, propaquizafop, and fluazifop (acetyl coenzyme A [CoA] carboxylase [ACCase]-inhibiting herbicides), and multiple resistance to nicosulfuron (acetolactate synthase [ALS]-inhibiting herbicides). In greenhouse experiments, the application of four times the recommended rates of quizalofop and propaquizafop to suspected resistant rhizomatous plants resulted in 4 and 5% growth reduction, respectively. However, the growth of suspected resistant seedlings was reduced by 54 and 28% after the application of two times the recommended rate of the same herbicides. In contrast, the application of quizalofop and propaquizafop at recommended rates on rhizomatous plants and seedlings of the Control population reduced their growth by 97 to 100%. Also, the growth reduction of both populations by the application of cycloxydim, fluazifop, and nicosulfuron at recommended rates ranged from 93 to 100%. In the field experiment, quizalofop and propaquizafop applied at four times the recommended rate reduced growth of the suspected resistant population by 9 and 18%, respectively, whereas the recommended rate of fluazifop gave a 94% growth reduction of this weed. The herbicide rate required for 50% growth reduction (GR50) values for rhizomatous plants of the suspected resistant population were 0.90 and 2.465 kg ai/ha for quizalofop and propaquizafop, respectively, whereas the corresponding GR50 values for the seedlings were 0.074 and 0.185 kg ai/ha. These results indicate that a johnsongrass population developed cross-resistance to quizalofop and propaquizafop, but did not evolve cross-resistance to cycloxydim and fluazifop or multiple resistance to nicosulfuron.

WeedSOFT is a state-of-the-art decision support system for weed management in the north central region of the United States, but its accuracy to predict corn yield loss associated with later-emerging weed communities has not been adequately assessed. We conducted experiments in 2004 and 2005 to compare observed and predicted corn yield related to four establishment times of mixed-species weed communities for validation of competitive index modifier (CIM) values in WeedSOFT. Weed communities were established at VE, V2, V4, and V6 corn (emergence, second-leaf, fourth-leaf, and sixth-leaf stages, respectively), and consisted largely of annual grass and moderately competitive annual broadleaf species. Compared to weed-free corn, yield loss occurred in each of seven site-years for weed communities established at VE corn, but in only one site-year for communities established at V2 corn. No corn yield loss was associated with weed communities established at V4 or V6 corn. For communities established at VE corn, predicted corn yield differed from observed yield in all but one site year, with predicted yield less than observed yield in three site-years, and greater than observed yield in two site-years; however, nonlinear regression analyses of yield data pooled over site-years showed that fitted values were similar between predicted and observed yield. For communities established at V2 and V4 corn, predicted yield was less than observed yield in six and five site-years, respectively. For communities established at V6 corn, predicted yield was less than observed yield in three of six site-years, but was similar to observed yield in three of six site-years. These results indicated that the CIM values in WeedSOFT tended to overestimate the competitiveness of late-emerging weed communities. Corn yield data from a pooled analysis of all site-years were used to generate a revised set of growth stage CIM values, which improved the accuracy of predicted corn yield. These results should improve weed management decisions and reduce the need for herbicide applications to late-emerging weeds.

Sulfentrazone is a phenyl triazolinone herbicide used for control of certain broadleaf and grass weed species. Sulfentrazone persists in soil and has residual activity beyond the season of application. A laboratory bioassay was developed for the detection of sulfentrazone in soil using root and shoot response of several crops. Shoot length inhibition of sugar beet was found to be the most sensitive and reproducible parameter for measurement of soil-incorporated sulfentrazone. The sugar beet bioassay was then used to examine the effect of soil properties on sulfentrazone phytotoxicity using 10 different Canadian prairie soils. Concentrations corresponding to 50% inhibition (I50 values) were obtained from the dose–response curves constructed for the soils. Sulfentrazone phytotoxicity was strongly correlated to the percentage organic carbon (P = 0.01) and also to percentage clay content (P = 0.05), whereas correlation with soil pH was nonsignificant (P = 0.21). Because sulfentrazone phytotoxicity was found to be soil dependent, the efficacy of sulfentrazone for weed control and sulfentrazone potential carryover injury will vary with soil type in the Canadian prairies.

Glyphosate-resistant crops will be grown for the first time in Western Australia in 2009. A survey was conducted across 150,000 km2 of the southeastern part of the Western Australian grain belt in 2007 to determine whether glyphosate-resistant Conyza populations were present. Sixty-eight Conyza populations were collected from various fields and roadside locations. These populations were collected from areas where Conyza was known to exist. Populations were screened with glyphosate and all populations were found to be glyphosate-susceptible. While no glyphosate-resistant Conyza populations were found in the southeastern grain belt of Western Australia, it provides baseline data prior to the introduction of glyphosate-resistant crops in this region. It is important to monitor the efficacy of glyphosate as resistance becomes more prevalent in weeds of various cropping systems worldwide.