Sumatran fleabane [Conyza sumatrensis (Retz.) Walker] is an emerging weed in the Australian cropping region. Populations resistant to glyphosate have evolved in Australia, creating the demand for information regarding the seed germination ecology of glyphosate-resistant (R) and glyphosate-susceptible (S) populations of C. sumatrensis. A study was conducted to examine the effects of temperature, light intensity, salt stress, osmotic stress, and burial depth on the germination and emergence of two populations (R and S) of C. sumatrensis. Both populations were able to germinate over a wide range of alternating day/night temperatures (15/5 to 35/25 C). In light/dark conditions, the R population had higher germination than the S population at 20/10 and 35/25 C. In the dark, the R population had higher germination than the S population at 25/15 C. In the dark, germination was inhibited at 30/20 C and above. Averaged over populations, seed germination of C. sumatrensis was reduced by 97% at zero light intensity (completely dark conditions) compared with full light intensity. Seed germination of C. sumatrensis was reduced by 17% and 85% at osmotic potentials of −0.4, and −0.8 MPa, respectively, compared with the control treatment. The R population had lower germination (57%) than the S population (72%) at a sodium chloride concentration of 80 mM. Seed germination was highest on the soil surface and emergence was reduced by 87% and 90% at burial depths of 0.5 and 1.0 cm, respectively. Knowledge gained from this study suggests that a shallow-tillage operation to bury weed seeds in conventional tillage systems and retention of high residue cover on the soil surface in zero-till systems may inhibit the germination of C. sumatrensis. This study also warrants that the R population may have a greater risk of invasion over a greater part of a year due to germination over a broader temperature range.

Susceptibility of a system to colonization by a weed is in part a function of environmental resource availability. Doveweed [Murdannia nudiflora (L.) Brenan] can establish in a variety of environments; however, it is found mostly in wet or low-lying areas with reduced interspecies competition. Four studies evaluated the effect of mowing height, interspecies competition, and nitrogen, light, and soil moisture availability on M. nudiflora establishment and growth. A field study evaluated the effect of mowing height on M. nudiflora establishment. In comparison with unmowed plots, mowing at 2 and 4 cm reduced spread 46% and 30%, respectively, at 9 wk after planting. Effect of mowing height and nitrogen fertilization on ‘Tifway’ bermudagrass (Cynodon dactylon Burtt-Davy×C. transvaalensis L. Pers.) and M. nudiflora interspecies competition was evaluated in a greenhouse trial. Murdannia nudiflora coverage was 62% greater in flats maintained at 2.6 cm than flats maintained at 1.3 cm. Supplemental application of 49 kg N ha−1 mo−1 increased M. nudiflora coverage 75% in comparison with 24.5 kg N ha−1 mo−1. A difference in M. nudiflora coverage could not be detected between flats receiving 0 and 24.5 kg N ha−1 mo−1, suggesting moderate nitrogen fertilization does not encourage M. nudiflora colonization. Effect of light availability on M. nudiflora growth and development was evaluated in a greenhouse study. Growth in a 30%, 50%, or 70% reduced light environment (RLE) did not affect shoot growth on a dry weight basis in comparison with plants grown under full irradiance; however, internode length was 28% longer in a 30% RLE and 39% longer in a 50% and 70% RLE. Effect of soil moisture on M. nudiflora growth and development was evaluated in a greenhouse study. Plants maintained at 50%, 75%, and 100% field capacity (FC) increased biomass>200% compared with plants maintained at 12.5% or 25% FC.

Intensive silvopastoral systems (ISS) are a sustainable alternative to monoculture systems (MS). The presence of trees and legumes improves animal welfare due to the increased food quality and quantity and the presence of shade while providing a variety of environmental services. As cattle behaviour is greatly affected by environmental conditions, knowledge on the behavioural trade-offs that cattle make to meet their demands while foraging in different grazing systems is important, as this will help us understand the perceived advantages of ISS. This pilot study assessed the behaviour of heifers in an ISS (n=8 heifers) and MS (n=8 heifers) in the Mexican tropics during the dry and rainy seasons, and its relationship with forage availability, mean travelled distance and the temperature humidity index (THI). In both seasons, daily foraging times were longer in the MS than the ISS (P<0.01). The duration of rumination was higher for ISS (P<0.01) and the duration of lying was higher for the dry season (P<0.05). The decrease in foraging times in relation to THI was significantly higher in the ISS than in the MS (mean slope±SE: ISS=−4.64±0.34; MS=−2.34±0.22; t=−14.20, P<0.001). The results suggest that the forage availability and access to shade in the ISS allow cattle to rest longer and increase rumination, whereas cattle in MS spend more time searching for food and foraging at times of the day were the temperatures were higher as a compensatory strategy, which potentially decreases cattle’s welfare and production qualities when compared with the ISS. In conclusion, ISS are likely to generate positive behavioural trade-offs that result in better welfare conditions and higher productive potential.

Common cocklebur root and shoot interferences were investigated as factors causing soybean yield reductions in the field. Significant decreases in soybean yield resulted from common cocklebur shoot interference when the two were grown together with the common cocklebur roots confined in plastic bags. Soybean yield decreased further when common cocklebur roots were not confined, but this decrease resulted, in part, from increased common cocklebur shoot growth. Wire mesh cylinders of varying diameters, placed in gaps in the soybean rows and designed to spatially restrict soybean shoot growth, reduced yield more than did gaps alone. When similar cylinders lined with black plastic were placed next to the soybean rows to restrict both within-canopy light and space for soybean shoot growth, soybean yield was reduced most (44%) with concomitant changes in stem height, stem diameter, lodging, and branches, nodes, and pods/plant. Interference of common cocklebur with soybeans resulted primarily from shoot interference, and competition for light within the soybean canopy implicated as the major factor causing the soybean yield reduction.

Photosynthesis and growth responses to irradiance level during growth were compared in soybean (Glycine max L. Merr. ‘Century’) and three broadleaf weeds to determine if these responses were associated with differences in shade tolerance among species. In response to reduced irradiance during growth, leaf thickness of all species decreased, while chlorophyll content per unit leaf volume and photosynthetic rate per unit leaf volume, measured at low irradiance, increased. Soybean and common cocklebur (Xanthium strumarium L. #3 XANST) also exhibited a decrease in soluble proteins on a leaf volume basis under reduced irradiance, and common cocklebur further exhibited a decrease in ribulose-1,5-bisphosphate carboxylase (RuBPcase) protein per unit leaf volume. Decreased irradiance during growth did not alter the content of RuBPcase or other soluble proteins per unit leaf volume in jimsonweed (Datura stramonium L. # DATST) or velvetleaf (Abutilon theophrasti Medic. # ABUTH). The superior shade tolerance of common cocklebur compared to the other species was attributed in part to the levels of RuBPcase and other photosynthetic proteins in leaves developed at low irradiance.

Field bindweed and Russian knapweed were grown from seed or rhizome segments under 520, 325, or 236 μmol·m–2 · s–1 photosynthetic photon flux density (PPFD) to determine vegetative and reproductive response. Flower production in both species declined with decreasing light level. Leaf area of field bindweed decreased as light level decreased, but Russian knapweed leaf area increased as light intensity decreased from 520 to 325 μmol·m–2 ·s–1 PPFD or from 520 to 236 μmol·m–2 ·s–1. Dry matter of shoots, roots, and rhizomes of field bindweed grown from seed declined as light level decreased, but the only response of plants grown from rhizome segments was complete inhibition of rhizome production. Dry matter of Russian knapweed shoots and roots in plants grown from seed or rhizome segments decreased as light decreased. In both species the total PPFD was more important than whether low or high light level occurred first.

Common cocklebur (Xanthium pensylvanicum Wallr. ♯ XANPE), velvetleaf (Abutilon theophrasti Medic. ♯ ABUTH), and jimsonweed (Datura stramonium L. ♯ DATST) are weeds that grow taller than soybeans [Glycine max (L.) Merr.] and compete for limited resources such as light. These weeds have an average area of influence of 0.5 m2, thus a density of 1 to 2 plants/m2 forms a full canopy of weed leaves above the soybeans that intercept 44 to 56% of the sunlight. Shade of 44 to 56% without weeds, placed above soybeans late in the season corresponding to times of weed shading, reduced soybean yield 19 to 26%. Since reported soybean yield reductions at weed densities of 0.7 to 2.5 plants/m2 were 18 to 54% for common cocklebur and 12 to 31% for jimsonweed and velvedeaf, it was concluded that most of the interference from jimsonweed and velvetleaf infestations in soybeans could be ascribed to competition for light, but only about one-half the interference was due to competition for light for common cocklebur. Soybean photosynthesis in the field was reduced about twice as much as soybean yield at equivalent levels of shading.

The optimum pH for germination of smallflower morningglory (Jacquemontia tamnifolia (L.) Griseb. # IAQTA] seed was 8.0. A scarification time of 25 to 60 s using a drum scarifier with medium grit provided the best germination, and the optimum temperature for germination was 35 to 40C. However, the optimum temperature for growth was 25 to 35C, with reductions in growth occurring above or below this range. Emergence after 14 days was 81 and 49% at planting depths of 1.5 and 10 cm, respectively. Shade levels of 30 to 92% reduced smallflower morningglory growth by 38 to 87% compared to plants grown in full sunlight.

Understanding patterns of shattercane and giant foxtail field emergence during the spring and summer in the Midwest is important to determine the best weed management programs for crop production systems. The primary objective of this study was to determine percentage emergence of shattercane and giant foxtail under field conditions as influenced by soil temperature fluctuations, in 1992 and 1993. A secondary objective was to determine the difference in emergence percentage based on shattercane and giant foxtail seed lots harvested in different years (1985, 1991, and 1992). Soil temperature fluctuations were manipulated by artificially shading the soil surface with plastic netting that provided 30, 60, and 90% of incident sunlight in addition to the full sunlight control (0% shade). Giant foxtail and shattercane seed was planted at depths of 1.25, 2.5, 5, and 10 cm under each shade, and emergence was monitored for 45 d. Soil temperature fluctuations were reduced by increasing depth and amount of shade. Increasing depth of seed significantly reduced percentage emergence by 63 and 54% for shattercane, and 71 and 73% for giant foxtail in 1992 and 1993, respectively. Decreasing light intensity significantly reduced percentage emergence of shattercane by 72 and 73% in 1992 and 1993, respectively, but did not decrease giant foxtail emergence. Seed lots of both species were different from one another both years. These results were consistent over years, even though 1993 precipitation was three times that for 1992. Therefore, shattercane seed uses diurnal fluctuations in temperature to sense proximity to the soil surface and covering vegetation to avoid germination when conditions are unfavorable for growth. In contrast, giant foxtail seed can germinate readily and grow when environmental conditions are within an acceptable range and when seed is not buried too deeply. Differences in percentage emergence between seed lots could play a major role in emergence patterns of shattercane and giant foxtail observed in the field and may be influenced by environmental conditions during seed development on parent plants.

Common waterhemp is a significant weed problem in Midwestern cropping systems partly because of its potential for multiple emergence events during the growing season. The effects of shade and time of emergence on this weed have not been characterized. In the field, common waterhemp vegetative and reproductive growth were evaluated under different irradiance levels at two emergence times. In full sunlight a common waterhemp plant emerging in late May produced 720 g of biomass and over one million seeds, and a plant emerging in late June produced 350 g of biomass and over 730,000 seeds. Plant biomass and seed production were lower as irradiance levels were decreased to 40, 68, and 99% shade. Mortality was high for common waterhemp grown in 99% shade; however, surviving plants produced some viable seed. Common waterhemp plants grown under reduced irradiance had higher leaf area ratios and lower relative growth rates.

Interseeded cover crops have the potential to maintain and improve soil quality, reduce the incidence of insect pests, and suppress weeds in vegetable production systems. However, the successful use of interseeded cover crops has been limited by their tendency to either inadequately suppress weeds or suppress both weeds and the crop. We hypothesized that in irrigated broccoli production, winter rye could suppress annual weeds through rapid emergence and shading, without adversely affecting the taller transplanted broccoli crop. In field experiments conducted in New York from 1999–2001, broccoli was cultivated at 0, 10, or 10 and 20 d after broccoli transplanting (DAT), with or without rye at the final cultivation. Rye interseeded at 0 DAT suppressed weeds and improved yields relative to unweeded controls but resulted in broccoli yield losses relative to weed-free controls in 2 of 3 years. Rye seeded at either 10 or 20 DAT did not reduce broccoli yields but had little effect on weeds for a given level of cultivation and resulted in Powell amaranth seed production of up to 28,000 seeds m−2. Rye interseeded at 0 DAT reduced light availability to weeds in 2000 but not in 2001 when Powell amaranth avoided shading from rye through rapid emergence and vertical growth. In greenhouse pot experiments, low temperatures for 7 d after seeding delayed the emergence of Powell amaranth by 3 d relative to rye and increased the suppression of Powell amaranth by rye from 61 to 85%. Our results suggest that winter rye may be more successfully integrated into broccoli production (1) when sown at higher densities, (2) in locations or seasons (e.g., spring) with lower initial temperatures, and (3) in combination with other weed management tools.

The development of optimal weed management strategies that rely, in part, on crop interference will require an understanding of how weeds compensate for limitations in above- and belowground resources. Trade-offs in the leaf morphology and biomass partitioning of rice and late watergrass were investigated under glasshouse conditions in 1999 and 2000. Both species responded to shade with increased height, reduced biomass, greater partitioning of biomass to leaves, and greater leaf area ratios. At the lowest light level (18% sunlight), plants of both species showed little response to nitrogen (N). However, height, tillers, biomass, and leaf area increased for plants grown at 50% and full sunlight as N increased from 0 to 224 kg N ha−1. Late watergrass exhibited more plasticity in specific leaf area and root weight ratio than rice in response to shade. This plasticity contributed to the ability of late watergrass to maintain a higher percent of its tillers and total dry weight than rice when sunlight was reduced by 50%. These results support the hypothesis that except at low light levels, limited N further reduces the growth of shaded late watergrass plants. Thus, weed management strategies that limit the plasticity of late watergrass by manipulating light and N availability are likely to be more effective than strategies that rely on manipulating a single resource.

Determining the nature of root and shoot competition can elucidate the competitive ability of an invasive species and direct management strategies. In a set of competition experiments, artichoke thistle (Cynara cardunculus), an exotic invasive perennial forb, was subjected to full or shoot competition with four species: black mustard (Brassica nigra), an exotic annual forb; ripgut grass (Bromus diandrus), an exotic annual grass; purple needle-grass (Nassella pulchra), a native perennial grass; and itself. For shoot competition, a smaller pot nested in a larger experimental pot sequestered the target plant root system. A bare ground invasion experiment, in which all plants were transplanted on the same date, and a community invasion experiment, in which competitor species were planted 1 mo before targets, were conducted. In the bare ground invasion experiment, target plant size was reduced (P ≤ 0.05) when exposed to full competition with the exotic species, but not purple needle-grass. Effects on target plants included reductions in height, number of leaves, rosette diameter, and shoot and leaf dry weight. In the community invasion experiment, full competition with all species reduced target plant growth (P ≤ 0.05). Shoot competition was more important when all species were planted synchronously, whereas root competition was more important when target plant establishment was delayed. In a separate experiment, artichoke thistle was grown under four light levels simulating field conditions under canopies of the same competitors. Midday carbon assimilation decreased linearly with increased shade, indicating the likely effects of shoot competition on artichoke thistle. Results indicated that exotic species are more competitive than native purple needle-grass against artichoke thistle and that restoration directly to native grassland after artichoke thistle removal might be difficult. However, artichoke thistle seedling growth is reduced by root competition from grasses that emerge earlier, indicating that early season management of grasslands to delay artichoke thistle establishment might provide effective control.

Horseweed has become increasingly common and difficult to control in San Joaquin Valley vineyards, due in part, to the evolution of glyphosate resistance. The development of weed-suppressive vineyard designs in which the trellis design, spacing, and row orientation combine to cast dense shade on the weed canopy zone (WCZ) may reduce weed growth. The relevance of such a system to horseweed, which can grow to be as tall, or taller, than a typical grapevine trellis, is uncertain. Also unknown is whether a glyphosate-resistant (GR) biotype and glyphosate-susceptible (GS) biotype would perform similarly under such conditions. Therefore, we compared the growth and development of two potted horseweed biotypes (GR and GS) in vinerows oriented east–west (EW) and north–south (NS). Rows oriented EW allowed less light penetration to the WCZ than NS rows throughout the study, and horseweed biotypes responded to low light levels by producing leaves with larger specific leaf area and leaf area ratios than those in the NS rows. Also, the leaf, stem, and root dry weight of the horseweed plants in the EW rows was reduced by 30% compared to the horseweed plants in NS rows. Leaf number was also reduced in the horseweed plants in the EW rows, but only for the GS biotype. Row orientation did not affect phenological development or the number of seeds produced by the GR or GS biotypes, but the GR biotype budded, flowered, and set seed approximately 1 wk earlier than the GS biotype. Thus, shade associated with the EW vinerows reduced horseweed growth, but not fecundity, and the GR biotype reached reproductive maturity earlier than the GS biotype.

Experiments were conducted on potted plants under field conditions in 2007 and 2008 at the Louisiana State University Agricultural Center's Northeast Research Station near St. Joseph, LA, to evaluate Texasweed response to shade. Shade levels of 30, 50, 70, and 90% were achieved using 1.8-m by 1.8-m by 1.8-m tents built using 2.54-cm-diam polyvinyl chloride (PVC) pipe and polypropylene fabric. Shade had no effect on Texasweed emergence but significantly reduced its growth. There were significant growth differences between plants transferred directly and gradually to a given shade level. At 100 d after emergence, plants gradually exposed to 30, 50, 70, and 90% shade had 13, 22, 37, and 58% less total dry matter per plants, respectively, than did those in 0% shade. Texasweed height in 70 and 90% shade was increased by 28 and 20%, respectively. Texasweed seemed to mitigate the adverse effect of shade by increasing specific leaf area (SLA) and percentage of leaf biomass. Increasing SLA and the percentage of leaf biomass appears to be a strategy for efficient allocation of biomass for light capture and carbohydrate synthesis, which can be used for height increase until the plant rises above the crop canopy. Although fruit production was significantly reduced, Texasweed was able to reproduce in 90% shade.

Heat stress has a significant impact on all livestock and poultry species causing economic losses and animal well-being concerns. Providing shade is one heat-abatement strategy that has been studied for years. Material selected to provide shade for animals greatly influences the overall stress reduction provided by shade. A study was conducted to quantify both the environment and animal response, when cattle had no shade access during summertime exposure or were given access to shade provided by three different materials. A total of 32 Black Angus heifers were assigned to one of the four treatment pens according to weight (eight animals per pen). Each pen was assigned a shade treatment: No Shade, Snow Fence, 60% Aluminet Shade Cloth and 100% Shade Cloth. In the shaded treatment pens, the shade structure covered ~40% of the pen (7.5 m2/animal). Animals were moved to a different treatment every 2 weeks in a 4×4 Latin square design to ensure each treatment was applied to each group of animals. Both environmental parameters and physiological responses were measured during the experiment. Environmental parameters included dry-bulb temperature, relative humidity, wind speed, black globe temperature (BGT), solar radiation (SR) and feedlot surface temperature. Animal response measurements included manual respiration rate (RRm), electronic respiration rate (RRe), vaginal temperature (body temperature (BT)), complete blood count (CBC) and plasma cortisol. The environmental data demonstrated changes proportional to the quality of shade offered. However, the animal responses did not follow this same trend. Some of the data suggest that any amount of shade was beneficial to the animals. However, Snow Fence may not offer adequate protection to reduce BT. For some of the parameters (BT, CBC and cortisol), 60% Aluminet and 100% Shade Cloth offers similar protection. The 60% Aluminet lowered RRe the most during extreme conditions. When considering all parameters, environmental and physiological, 60% Aluminet Shade Cloth offered reductions of BGT, SR, feedlot surface temperature and the best (or equal to the best) overall protection for the animals (RRe, RRm, BT, blood parameters).

Using behavioural indicators of thermal discomfort, that is, shade seeking, panting scores (PS) and respiration rate (RR), we evaluated the effect of hot summer conditions and shade, for a herd of adult Holstein dairy cows and a herd of Belgian Blue beef cows kept on pasture in a temperate area (Belgium). During the summer of 2012, both herds were kept on pasture without access to shade (NS). During the summers of 2011 and 2013 each herd was divided into one group with (S) and one without (NS) access to shade. Shade was provided by young trees with shade cloth (80% reduction in solar radiation) hung between them. For S cows, we investigated how shade use was related to hot conditions as quantified by six climatic indices. The heat load index (HLI), which incorporates air temperature and humidity, solar radiation and wind speed, was the best predictor of the six indices tested. In 2011, there was a relatively high threshold for use of shade. When HLI=90, shade use probability reached 17% for dairy cows and 27% for beef cows. In 2013, however, at HLI=90, shade use probability reached 48% for dairy cows and 41% for beef cows. For animals from the NS treatment we determined the effect of hot summer conditions on RR and PS (with 0=no panting and 4.5=extreme panting). In both types of cattle, an increase in black globe temperature was the best predictor for increasing RR and PS. Furthermore, we determined how the effect of hot summer conditions on RR and PS was affected by the use of shade. Under hot conditions (black globe temperature ⩾30°C), >50% of the animals under shade retained normal PS and RR (PS<1 and RR<90 breaths per minute), whereas normal RR and PS were significantly less prevalent for animals outside shade. Our findings suggest that, even in temperate summers, heat can induce thermal discomfort in cattle, as evidenced by increases in shade use, RR and PS, and that shade increases thermal comfort.

Research has addressed the issue of type of shade mainly on feedlots and high-producing dairy farms, but more studies are needed on the impact of shade on grazing beef cattle in a low-to-medium plane of nutrition. A 63-day grazing study using 24 British steers (268±4 kg) was undertaken in Uruguay (33°14'S, 54°15'W) to determine the effect of type of artificial shade on tympanic temperature (TT), behaviour and performance during summer. Cattle were allocated to six paddocks with an area of 2.5 ha each (four steers/paddock) continuously grazed. Treatments (two paddocks/treatment) were unshaded (US) and shaded with either 35% (35S) or 80% (80S) blockage of solar radiation. TT was recorded during 12 days placing an automatic device near the tympanic membrane inside the animal’s ear. Animal behaviours were measured by live observations of animals every 15 min from 1100 to 1600 h six times during the experimental period. According to the temperature–humidity index (THI), cattle was in the ‘normal’ category (THI<70, absence of heat stress) during 50% of the time, the rest being exposed to some degree of heat stress including 15% of the time with environmental conditions. Black globe temperature and surface soil temperature decreased as solar protection increased under the shade structure. Steers spent more time under the 80S structure than under the 35S between 1100 and 1600 h (83% and 49% of the time, respectively). Average 24-h TT did not differ among treatments (mean±s.e. 38.79±0.04ºC). Minimum TT was registered at 0700 h for all treatments (37.92±0.08ºC), whereas maximum TT was reached at 1700 h for both control group (39.73±0.18ºC) and 35% shade (39.48±0.12ºC) and at 1900 h for 80% shade (39.57±0.15ºC). Neither the provision nor the type of shade affected animal performance (0.622±0.060 kg/a per day), indicating the ability of cattle to acclimate and/or compensate for eventually short-term severe heat stress events. The results of this experiment suggest that the provision of shade with either 35% or 80% of blockage of solar radiation is recommended for the improvement of cattle well-being (expressed through changes in behaviour) without significantly affecting animal performance and TT. However, the overall results of the 63 days of the study can mask or dilute punctual effects of short heat stress events on cattle. More powerful experimental designs are required to address this issue in temperate regions.

Natural tree canopy gaps allow sunlight to penetrate to the forest floor, a major environmental component and resource for many tropical rain-forest species. We compare here how butterflies use sunny areas created by the natural gaps in canopies in comparison with adjacent closed-canopy areas. We chose butterflies as our focal organisms as they are taxonomically tractable and mobile, yet habitat sensitive. Previous studies have shown that butterfly diversity in tropical forests responds to varying degrees of canopy openness. Here we assess butterfly behavioural responses to gaps and equivalent sized closed-canopy patches. Butterfly occupancy time and behaviour were simultaneously observed 61 times in gaps and 61 times in equivalent sized closed-canopy patches across four sites in a tropical rain forest in northern Borneo. Out of the 20 most frequently recorded species, 12 were more frequently recorded or spent more time in gaps, four occurred more frequently in closed-canopy areas, and four showed no significant differences. Overall agonistic, basking, patrolling and resting were more common in gaps compared with the closed canopy. Many butterfly species have complex behavioural requirements for both gaps and closed canopies, with some species using these different areas for different behaviours. Each butterfly species had particular habitat requirements, and needed both canopy gaps and closed canopy areas for ecological and behavioural reasons, emphasizing the need for natural light heterogeneity within these systems.