To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Doveweed is a problematic weed species in many agricultural ecosystems as well as on roadsides and rights-of-way. Effective POST chemical control options for doveweed are limited in many cropping systems. Greenhouse studies were conducted to evaluate the effectiveness of metsulfuron-methyl dose and the impact of mixtures and sequential applications of either trifloxysulfuron-sodium or bentazon with metsulfuron-methyl for doveweed control. By 14 d after the initial treatment, applying 0.04 kg ai ha−1 metsulfuron-methyl, either once or sequentially, provided 100% control of doveweed. Application of trifloxysulfuron-sodium at 0.04 kg ai ha−1 alone or in mixture with metsulfuron-methyl (0.04 kg ha−1) did not provide consistent doveweed control nor did it reduce biomass. Trifloxysulfuron-sodium applied alone at 0.08 kg ha−1 or in a mixture with metsulfuron-methyl (0.04 kg ha−1) provided consistent doveweed control (>80%). A single application of bentazon (0.56 kg ai ha−1) was ineffective at controlling doveweed. A single application of the bentazon and metsulfuron-methyl mixture (0.56 + 0.04 kg ha−1, respectively) or sequential applications of either bentazon alone (0.56 kg ha−1) or in mixture with metsulfuron-methyl (0.04 kg ha−1) provided excellent doveweed control (100%) by 35 d after treatment. Overall, single applications of metsulfuron-methyl (0.02 to 0.17 kg ha−1) or mixtures of metsulfuron-methyl with trifloxysulfuron-sodium (0.04 + 0.08 kg ha−1, respectively) or bentazon (0.04 + 0.56 kg ha−1, respectively) controlled doveweed and may be useful for enhancing the control spectrum for other weeds. Sequential applications of the bentazon and metsulfuron-methyl mixture (0.56 + 0.04 kg ha−1, respectively) provided doveweed control and are a resistance-management strategy for doveweed.
Postemergence weed control atop the bed during strawberry production is limited to hand-weeding, clopyralid, and acetyl CoA carboxylase inhibitors. Identification of additional modes of action is desirable to increase available options for producers and alleviate herbicide resistance concerns. The study objective was to screen sulfonylurea herbicides for strawberry safety and Carolina geranium efficacy. Herbicide treatments included metsulfuron-methyl, flazasulfuron, foramsulfuron, thifensulfuron-methyl, trifloxysulfuron-sodium, and rimsulfuron. Strawberry plants were heavily damaged by all herbicides apart from foramsulfuron. While the strawberry plant was dramatically impacted by the evaluated herbicides, demonstrating strong epinasty, there was no differences in resultant biomass at 31 d after treatment compared to controls. Carolina geranium was severely injured by metsulfuron-methyl, flazasulfuron, and thifensulfuron-methyl and moderately injured by foramsulfuron. There were consistent reductions in biomass by 31 d after treatment by metsulfuron-methyl and flazasulfuron. Overall, metsulfuron-methyl and flazasulfuron are suitable candidates for Carolina geranium control in row middles. Foramsulfuron is a suitable candidate for additional field-based screening for utility in postemergence use in strawberry production atop the bed. Consideration towards doses, surfactants, timings, and cultivar tolerance may be necessary due to minimize injury (15 to 20%) observed in the greenhouse.
Row-middle weed control in Florida vegetable production is challenging and often necessitates several PRE and POST herbicide applications. Coordinating POST spray applications with emergence timings should increase herbicide efficacy by targeting susceptible growth stages. Most published emergence models were developed in temperate climates, and adapting them to subtropical climates can be complex and requires reductionist insights into seed ecology, particularly germination and dormancy. The study objective was to examine the influence of temperature and osmotic potential on seed germination of carpetweed (Mollugo verticillata L.), Carolina geranium (Geranium carolinianum L.), eclipta [Eclipta prostrata (L.) L.], and goosegrass [Eleusine indica (L.) Gaertn.]. Mollugo verticillata seed germination was positively photoblastic, with increased germination at high temperatures (≥35 C), more so with high fluctuating temperatures (35/20 and 35/25 C), and occurred at osmotic potentials as low as −0.5 MPa. Geranium carolinianum seed germinated between 10 and 20 C in light or darkness and at osmotic potentials as low as −0.4 MPa. Eclipta prostrata seed germination was entirely positively photoblastic, occurring optimally between 15 and 25 C and at osmotic potentials as low as −1 MPa. Eleusine indica seed germination demonstrated some degree of positive photoblasticity, with greater germination in the light, peak germination at 35 C, and germination occurring at osmotic potentials as low as −0.5 MPa. Described germination ecology for selected species will provide insights for building ecology-based growing degree-day accounting restrictions for empirically derived emergence models.
Herbicides are the foundation for row-middle weed control in Florida plasticulture production. Paraquat is commonly used as a burndown herbicide, and resistance issues have subsequently developed. Halosulfuron is mixed with PRE and POST herbicides to provide additional control of nutsedge. The objective of the study was to determine glufosinate efficacy on weeds emerging in the row-middle and suitability in mixture with halosulfuron for nutsedge control. For total weed control, the high dose of glufosinate (983 g ai ha–1) gave the highest overall control (98% and 64% at 4 wk after treatment for experiments 1 and 2, respectively), and the low rate of glufosinate (656 g ha–1) (67% and 39%) gave results comparable to paraquat (57% and 44%). The high glufosinate dose and paraquat gave comparable control of Brazil pusley (74% to 77% control). Glufosinate + halosulfuron mixture had lower efficacy on Brazil pusley than halosulfuron + paraquat mixture. Glufosinate application reduced grass densities, whereas paraquat did not. Increasing the glufosinate dose did not further decrease grass densities. Similar trends in grass control were also demonstrated in their respective mixtures. Mixing halosulfuron with glufosinate or paraquat did not provide consistent reductions in nutsedge densities, nor did adding paraquat or glufosinate further reduce densities compared with halosulfuron alone for the 4-wk study period. Both paraquat and glufosinate antagonized halosulfuron and reduced efficacy on nutsedge. Compared to controls, there was a reduction between expected and actual nutsedge control for paraquat and glufosinate (25% and 36%), respectively. For total weed control, glufosinate is a suitable alternative to paraquat for row-middle weed management in vegetable production.
Broadleaf infestations interfere with Florida strawberry production. Broadleaf POST herbicide options applied atop the crop are limited to synthetic auxins and not suitable for conventional multi-cropping and organic systems. Reducing light access and interception during weed emergence may reduce interference. Light-limited growth of two problematic broadleaves, black medic and Carolina geranium, and the most commonly grown strawberry cultivar (‘Florida Radiance’), were examined in the greenhouse. The experimental design was completely randomized, and the trial was repeated. Black medic was susceptible to reductions in incoming solar radiation, wherein reducing the daily maximum available light from 331 to 94 µmol m−2 s−1 reduced leaf number and area by 93% and 89%, respectively. Carolina geranium growth was less susceptible to reduced-light treatments, with leaf area and number each reduced by 66% when light was reduced from 331 to 94 µmol m−2 s−1. Belowground, Carolina geranium biomass was similarly reduced between the 331 and 94 µmol m−2 s−1 treatments. Strawberry was relatively tolerant to shading at 155 µmol m−2 s−1, but further reductions did increase mortality. Shade-induced weed suppression is a promising alternative strategy for conventional and organic Florida strawberry production. Targeted application during periods of weed emergence may play a role within integrated pest management strategies. This approach is most feasible for black medic management but may be useful for Carolina geranium in concert with other strategies.
Black medic (Medicago lupulina L.) is a problem weed species in Florida strawberry [Fragaria × ananassa (Weston) Duchesne ex Rozier (pro sp.) [chiloensis × virginiana]] production. It competes with the crop and hinders harvest efficiency. A reductionist approach is being undertaken to predict M. lupulina field emergence to coordinate control tactics. Germination is the first model component to be developed. The objectives were to study the effect of osmotic potential and temperature on seed germination and to develop the germination component for reductionist emergence modeling. Trials were initiated using petri dishes in incubators to test M. lupulina germination in response to osmotic potential (0 to −1 MPa) and constant (5 to 40 C) and fluctuating temperatures (35/25, 35/20, 25/15, and 25/10 C, 12/12-h duration). Medicago lupulina germinated between 5 and 35 C. Optimal germination was between 10 and 20 C. Germination was negatively impacted by temperatures above the optimum. Fluctuating temperatures did not influence germination compared with constant temperatures. A reduction in osmotic potential from 0 to −0.25 MPa reduced germination from 43% to 14%. Three temperature-mediated germination trends were identified: standard increases and plateau up to 20 C, reduced germination between 20 and 35 C, and no germination at 40 C. A novel restriction to daily growing degree-day (GDD) accounting was developed for heat-limited germination. The germination restriction accounted for the optimum and maximum temperature, diminishing returns of exposure to higher temperatures, and the negative impact of higher temperatures above the optimum range. Determination logic and the new daily GDD accounting formula aligned GDD accumulation across all temperatures to be described by a Weibull formula (R2 = 0.5199). Results establish the germination component for reductionist emergence modeling, but further study is required to account for dormancy and PRE growth.
Weed interference during crop establishment is a serious concern for Florida strawberry [Fragaria×ananassa (Weston) Duchesne ex Rozier (pro sp.) [chiloensis×virginiana]] producers. In situ remote detection for precision herbicide application reduces both the risk of crop injury and herbicide inputs. Carolina geranium (Geranium carolinianum L.) is a widespread broadleaf weed within Florida strawberry production with sensitivity to clopyralid, the only available POST broadleaf herbicide. Geranium carolinianum leaf structure is distinct from that of the strawberry plant, which makes it an ideal candidate for pattern recognition in digital images via convolutional neural networks (CNNs). The study objective was to assess the precision of three CNNs in detecting G. carolinianum. Images of G. carolinianum growing in competition with strawberry were gathered at four sites in Hillsborough County, FL. Three CNNs were compared, including object detection–based DetectNet, image classification–based VGGNet, and GoogLeNet. Two DetectNet networks were trained to detect either leaves or canopies of G. carolinianum. Image classification using GoogLeNet and VGGNet was largely unsuccessful during validation with whole images (Fscore<0.02). CNN training using cropped images increased G. carolinianum detection during validation for VGGNet (Fscore=0.77) and GoogLeNet (Fscore=0.62). The G. carolinianum leaf–trained DetectNet achieved the highest Fscore (0.94) for plant detection during validation. Leaf-based detection led to more consistent detection of G. carolinianum within the strawberry canopy and reduced recall-related errors encountered in canopy-based training. The smaller target of leaf-based DetectNet did increase false positives, but such errors can be overcome with additional training images for network desensitization training. DetectNet was the most viable CNN tested for image-based remote sensing of G. carolinianum in competition with strawberry. Future research will identify the optimal approach for in situ detection and integrate the detection technology with a precision sprayer.
Black medic (Medicago lupulina L.) infestations are a concern for Florida strawberry [Fragaria×ananassa (Weston) Duchense ex Rozier (pro sp.) [chiloensis×virginiana] producers. Current control techniques rely on hand weeding or clopyralid application. Coordinating POST control measures with emergence timing can reduce crop competition duration and increase control. The objective of this study was to evaluate M. lupulina emergence in response to burial depth and temperature and to model M. lupulina cumulative field emergence under subtropical Florida conditions using growing degree days (GDDs) as a predictor. Two studies were in controlled environments and looked at factors affecting emergence, burial depth, and temperature. A third experiment was a 2-yr emergence study conducted on four commercial strawberry fields in Hillsborough County, FL. Emergence was modeled as a function of accumulated standard and restricted daily GDD accounting, based on M. lupulina dormancy and germination. In Experiment 1, M. lupulina only emerged when seed was deposited on the surface. In Experiment 2, there was three-way interaction among temperature, burial depth, and measurement timing (P<0.0001). Medicago lupulina emerged from as deep as 2 cm at a temperature range between 15 and 25 C. Medicago lupulina field emergence was not consistent between years, although emergence was consistent across four sites in year 1, with 0 emergence in year 2. Dormancy and germination restrictions increased calibration and validation model fit and reduced GDD inflation, making models usable between years. Medicago lupulina primarily emerged during crop establishment, between mid-November and late-December, which corresponds to an ideal timing for control measures before the harvest period.
Fomesafen is a protoporphyrinogen oxidase–inhibitor herbicide with an alternative mode of action that provides PRE weed control in strawberry [Fragaria×ananassa (Weston) Duchesne ex Rozier (pro sp.) [chiloensis×virginiana]] produced in a plasticulture setting in Florida. Plasticulture mulch could decrease fomesafen dissipation and increase crop injury in rotational crops. Field experiments were conducted in Balm, FL, to investigate fomesafen persistence and movement in soil in Florida strawberry systems for the 2014/2015 and 2015/2016 production cycles. Treatments included fomesafen preplant at 0, 0.42, and 0.84 kg ai ha−1. Soil samples were taken under the plastic from plots treated with fomesafen at 0.42 kg ha−1 throughout the production cycle. Fomesafen did not injure strawberry or decrease yield. Fomesafen concentration data for the 0.0- to 0.1-m soil depth were described using a three-parameter logistic function. The fomesafen 50% dissipation times were 37 and 47 d for the 2014/2015 and 2015/2016 production cycles, respectively. At the end of the study, fomesafen was last detected in the 0.0- to 0.1-m depth soil at 167 and 194 d after treatment in the 2014/2015 and 2015/2016 production cycles, respectively. Fomesafen concentration was less than 25 ppb on any sampling date for 0.1- to 0.2-m and 0.2- to 0.3-m depths. Fomesafen concentration decreased significantly after strawberry was transplanted and likely leached during overhead and drip irrigation used during the crop establishment.
OBJECTIVES/SPECIFIC AIMS: This case-control study aims to determine the relationships among childhood adversity, attachment style, and the likelihood of accepting or declining a referral for HV. The study will serve as a pilot to inform the power analysis of a subsequently proposed full-scale study. METHODS/STUDY POPULATION: Using a case-control study design, 25 women who decline HV referral (cases) will be compared with 25 women who accept HV referral (controls) on their exposure to childhood adversity and attachment style. Women who are eligible for the study are English-speaking mothers who have been offered HV services by Health Care Access Maryland. Surveys are administered in-person, either in the participant’s home or at another location (e.g., public library), based on participant preference. The dependent variable is participant’s verbal response to the HV referral (accept/decline). The independent variable, childhood adversity, will be measured using the Philadelphia Urban Adverse Childhood Experiences (ACEs) Survey and the Attachment Style Questionnaire (ASQ). Control variables include demographics (i.e., age, race, education, employment, housing, marital status), obstetric history (i.e., previous preterm birth, miscarriage, fetal death, infant death, abortion), and current psychosocial risk factors (i.e., history of substance use, intimate partner violence, depression). Descriptive comparisons will be done for the independent and control variables in controls versus cases. Bivariate analysis will examine associations between the odds of being a case and ACE score and ASQ score. Multivariate logistic regression models will be used to examine the relationship between ACE total and ASQ score; exposure to ACE in cases versus controls; and the odds of an avoidant and anxious attachment styles in cases versus controls. RESULTS/ANTICIPATED RESULTS: We hypothesize that (a) higher ACE scores will be positively associated with a higher level of avoidant attachment; (b) higher ACE scores will be positively associated with declining a HV referral; and (c) higher levels of avoidant attachment will be associated with declining a HV referral. DISCUSSION/SIGNIFICANCE OF IMPACT: Racial inequities in birth outcomes are pervasive and unjust. Non-Hispanic Black women experience births that result in infant mortality, fetal mortality, preterm birth, and low birth weight babies at more than double the rate of non-Hispanic White women in Baltimore and nationally. Prenatal and early childhood home visiting programs have been found to decrease maternal smoking and hypertensive disorder which are associated with PTB, reduce closely spaced births which is associated with fetal and infant death, and improve women’s long-term economic self-sufficiency, child health and social outcomes. However, as community-based programs, these services are not reaching the majority of eligible women in low-income urban settings—women who are also disproportionately burdened with poor pregnancy-related health outcomes. Considering the potential to improve outcomes, the importance of eliminating health disparities, and the national and local investment in HV services, it is vital to understand why some women are not enrolling in prenatal HV programs. The findings from this and subsequent studies will inform the translation of evidence-based HV program outreach efforts for women with complex social history. It will inform the design of enhanced outreach and engagement efforts of HV programs to more reliably engage women.
Broadleaf species escape current integrated weed management strategies in strawberry [Fragaria×ananassa (Weston) Duchesne ex Rozier (pro sp.) [chiloensis×virginiana]] production. Clopyralid is a registered POST control option, but current application timings provide suppression of only some species. Earlier clopyralid application timings may increase spray coverage to weeds at the planting hole, but strawberry plant tolerance to applications shortly after transplant is unknown. The objectives of the study were to determine the degree of clopyralid tolerance when applied to mature strawberry plants according to current management strategies, whether clopyralid absorption and translocation were involved in the tolerance response demonstrated by mature strawberry plants, and whether clopyralid could be safely applied to immature strawberry plants shortly after transplant. Clopyralid caused no damage when applied to mature strawberry plants and did not affect crop height, number of crowns, flowers, immature berries, or yield. Maximal strawberry absorption of radiolabeled clopyralid was 82% of the recovered radioactivity and reached peak (90%) absorption at 15 h. Maximal total translocation of radioactivity from the treated leaf was 17% and reached peak translocation at 52 h. Translocation was primarily to the new leaves and reproductive structures. In the early-application experiment, damage induced by clopyralid for all application timings reached 0 by 8 wk after treatment. Across all timings, maximal damage at 140 g ha−1 was 17% when applied 14 d after transplant (DATr) and 56% at 28 g ha−1 when applied at 21 DATr. Clopyralid dose did not affect the number of crowns, aboveground biomass, or yield. There was some stunting in plant height (3%) by the high labeled dose of clopyralid. Labeled dose clopyralid applications appear safe for application timings closer to strawberry transplant, though considerations of leaf cupping should be taken under consideration for label changes.
Strawberry is an important horticultural crop in Florida. The long growing season and escapes from fumigation and PRE herbicides necessitate POST weed management to maximize harvest potential and efficiency. Alternatives to hand-weeding are desirable, but clopyralid is the only broadleaf herbicide registered for use. Weed control may be improved by early-season clopyralid applications, but at risk of high temperature and increased strawberry injury. The effect of temperature on clopyralid safety on strawberry is unknown. We undertook a growth chamber experiment using a completely randomized design to determine crop safety under various temperature conditions across acclimation, herbicide application, and post-application periods. There was no effect of clopyralid on the number of strawberry leaves across all temperatures. Damage to the strawberry manifested as leaf malformations. Acclimation temperatures affected clopyralid-associated injury (p=0.0309), with increased leaf malformations at higher temperatures (27 C) compared to lower (18 C) temperatures. Pre-treatment temperatures did not affect clopyralid injury. Post-application temperature also affected clopyralid injury (p=0.0161), with increased leaf malformations at higher temperatures compared to lower ones. Clopyralid application did not reduce flowering or biomass production in the growth chamber. If leaf malformations are to be avoided, consideration to growing conditions prior to application is advisable, especially if applying clopyralid early in the season.
The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (~2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
Paratuberculosis (Johne’s disease) is a chronic invariably fatal enteritis of cattle caused by the bacterium Mycobacterium avium subspecies paratuberculosis and has recently been isolated from wild rabbits. One potential route of transmission of M.a.paratuberculosis from rabbits to cattle is the ingestion of rabbit excreta contaminating pasture. Here we (1) determine the prevalence and level of infection in rabbits and their excreta (2) quantify the level of rabbit faeces contaminating cattle pastures and (3) determine the impact of rabbit faeces on cattle grazing behaviour.
Strawberries, an important Florida crop, are grown on raised beds covered with plastic mulch. The plastic mulch provides good control of many weeds, but some problem species can emerge from the transplant hole during crop establishment. POST herbicide options for broadleaf weed control within the strawberry bed is limited to clopyralid, which only provides suppression. Strawberry canopy shielding may be responsible for the observed incomplete control with clopyralid application for problematic broadleaf weed species such as black medic and Carolina geranium. Two field experiments were established on mature strawberries to evaluate spray penetration through the canopy. The first examined spray penetration through the canopy of multiple strawberry cultivars at various distances from the crown. The second examined the effects of application volumes and nozzle selection on spray penetration. Cultivar selection had no effect on spray penetration through the canopy. In the first study, when applying at 281 L ha−1, the area around the planting hole (0 to 5 cm from the crown) had 8% coverage below the canopy while the area below the canopy edge (10 to 15 cm from the crown) had 27% coverage. In the second study, increasing the application volume from 187 to 375 L ha−1 increased coverage by 81%. Increasing the application volume from 375 to 740 L ha−1 increased coverage 33% with maximal coverage of 53% at 740 L ha−1. Nozzle type (standard even flat spray tip, Drift Guard, or TwinJet nozzles) did not affect coverage or deposition volume below the canopy. Overall, mature strawberry canopies demonstrated similar spray droplet penetration across cultivars with increased penetration with increased distance from the crown. Penetration increased with increasing application volume, but the nozzle types used in this experiment did not affect penetration. Additional research is needed to better define the effect of application volume on herbicide efficacy.
Body dissatisfaction and depressive symptoms are commonly experienced during adolescence and increase the risk of adverse health outcomes, especially eating disorders. However, the dominant temporal associations between these two experiences (i.e., whether one is a risk factor for the other or the two are mutually reinforcing) has yet to be fully explored. We examined the associations between body dissatisfaction and depressive symptoms assessed at baseline and 5- and 10-year follow-up in younger (M age = 12.9 years at baseline, 56% female, n = 577) and older (M age = 15.9 years at baseline, 57% female, n = 1,325) adolescent cohorts assessed as part of Project Eating Among Teens and Young Adults. Associations between body dissatisfaction and depressive symptoms were examined using cross-lagged models. For females, the dominant directionality was for body dissatisfaction predicting later depressive symptoms. For males, the picture was more complex, with developmentally sensitive associations in which depressive symptoms predicted later body dissatisfaction in early adolescence and early adulthood, but the reverse association was dominant during middle adolescence. These findings suggest that interventions should be tailored to dynamic risk profiles that shift over adolescence and early adulthood, and that targeting body dissatisfaction at key periods during development may have downstream impacts on depressive symptoms.
Strawberries are an important horticultural crop in Florida. Black medic is among the most problematic weeds within the production system. To better coordinate control measures, black medic growth and development while in competition with strawberry was studied. Twelve plants were randomly selected at each of four field sites in Hillsborough County, FL, in 2014. Plants were repeatedly measured over the growing season for stem length and number of primary branches, flower buds, flowers, and seed clusters. Growing degree days (GDD) were calculated (Tbase=0 C) starting from the hole-punch application of the plastic mulch (October 8, 2014, to October 10, 2014) from weather station data generated from the Florida Automated Weather Network. Strawberry height and width increased consistently across all sites, but black medic growth and development varied considerably. Strawberry suppressed black medic growth up to 1,805 cumulative GDD at three of four sites where black medic remained beneath the strawberry canopy. After 1,805 GDD, the black medic stems still remained below but experienced exponential growth for total stem length and, in turn, flower buds, inflorescence, and immature seed clusters. Ideal clopyralid spray timing based on susceptible plant size was 890 to 1,152 GDD. Optimal hand-weeding time frames would likely occur as the plant stems expand beyond the strawberry canopy (to improve visibility) and before flower production to prevent seed return to the seedbank. First seed production was observed at 1,200 GDD at the earliest site and between 1,966 to 2,365 GDD across all the other sites. Overall, consistent trends were observed across sites, but between-site variability was observed that could not be accounted for by differences in temperature.
Net changes in glacier area in the region 50–51˚ N, 116–125˚W, which includes the Columbia and Rocky Mountains (1951/52–2001) and the Coast Mountains (1964/65–2002), were determined through a comparison of historic aerial photography and contemporary Landsat 7 ETM+ imagery. The volumes of individual glaciers were estimated using an empirical volume–area scaling relationship. The area of glaciers in the Coast Mountains decreased by 120±10km2, or 5%of the initial ice-covered area here. The areas of glaciers in the Columbia and Rocky Mountains decreased by 20 and 6km2 respectively, corresponding to relative changes in total area of –5% and –15%. The estimated total ice volume loss from the whole region was 13 ±3 km3. In all parts of the study area, the relative changes in area of individual glaciers showed considerable variability, while the smallest glaciers remained essentially unchanged. This suggests that local factors unique to individual glaciers largely determine their sensitivity to climatic change, and that the very small glaciers are collectively less sensitive to such change.
An analysis of the local topographic setting of very small (<0.4 km2) glaciers within a small region of the Monashee Mountains, British Columbia, was conducted to investigate its influence on recent changes in the extent of these glaciers. Net changes in glacier extent were determined from a detailed manual comparison of remotely sensed imagery acquired in 1951, 2001 and 2004. Most of the 86 glaciers included in the study showed no observable net change in area over the study period, while six glaciers retreated, four disappeared entirely and only one advanced. Indices derived to characterize elements of the local topographic setting that might affect the local mass balance suggest that most of the glaciers are situated in locations that favor ice preservation by enhancing mass input and/or reducing ablation rates. Glaciers situated in less favorable settings generally either decreased in area or disappeared. The results suggest that most of the glaciers studied have retreated as far as they are likely to under the climatic conditions of the late 20th century.