To estimate the potential growth and distribution of itchgrass (Rottboellia exaltata L. f.) in the United States, we grew the plant in 36 combinations of day and night temperatures in controlled-environment greenhouses. Day temperatures ranged from 17 to 32 C and night temperatures from 11 to 26 C. Total dry weights, leaf areas, heights, and numbers of tillers were determined at 3, 31, and 58 days after emergence. Mathematical growth analysis techniques were used to calculate net assimilation rates (NAR) and leaf area durations (LAD). Maximum dry matter production (the product of NAR and LAD) and maximum leaf area production occurred at 32/26 C. Dry matter production and leaf area production were greatly reduced by day temperatures below 29 C and night temperatures below 23 C. The retardation of dry matter production by low night temperature was due mainly to reductions in LAD rather than to reductions in NAR. Low day temperatures reduced dry matter production through combined effects on LAD and NAR. At the warmer day temperatures, tiller production increased with decreasing night temperature. Flowering occurred at all day temperatures and at all night temperatures of 14 C or greater. Based on its growth responses to temperature, itchgrass would reach 75 to 100% of its maximum potential growth in the Gulf Coast states, the lower Midwest, the South Atlantic states, and the Southwest. Therefore, it represents a serious potential weed problem in these regions.

Environmental factors that affect the growth and development of onionweed were evaluated in order to predict its potential range and impact in the U.S. In controlled-environment experiments, onionweed achieved 60 to 100% of its maximum vegetative growth at temperatures ranging from 18/11 to 30/23 C day/night. The greatest biomass was produced at day temperatures of 18 or 24 C and night temperatures of 11 or 17 C. Leaf production and reproductive development were greatest at 18/11 C. Plants eventually flowered also at 18/17, 24/17, and 24/11 C but not in any regime with a 30 C-day or a 23 C-night. Flowering occurred earlier in 16-h photoperiods than in 16-h photoperiods than in 8-h photoperiods. Climatic analyses revealed no U.S. analogs of the principal Australian onionweed sites. Based on its environmental responses and its pattern of distribution as a weed in Australia, onionweed will likely remain confined to the southwestern U.S.

Responses of the vegetative growth of cogongrass [Imperata cylindrica (L.) Beauv.] to temperature and photoperiod were studied in plants grown from stem and rhizome propagules collected from plants originating at four locations in southern Alabama and Mississippi. The plants were grown in four controlled-environment chambers with day/night temperature regimes of 23/17 C and 29/23 C, photoperiods of 12 h and 16 h, and photosynthetic photon flux densities (PPFD) of 650 μE(einsteins)m−2s−1. After 87 days, heights, leaf areas, total dry weights, rhizome numbers, and rhizome dry weights were significantly greater in plants grown at 29/23 C than at 23/17 C. Total dry weights, rhizome numbers, and rhizome dry weights were greater at the 16-h photoperiod than at 12 h. Plants grown from propagules from the McNeil, Mississippi population, which originated from an introduction from the Philippines, were significantly smaller than plants grown from propagules collected from populations thought to have originated from an introduction of cogongrass from Japan. Mathematical analysis of the growth data showed that the observed differences in dry matter production were more closely related to differences in leaf area duration than to differences in net assimilation rate.

Mathematical growth analysis techniques were used to study the effects of simulated field temperatures and chilling events on the growth of the exotic noxious weed itchgrass (Rottboellia exaltata L. f.) and adapted varieties of corn (Zea mays L. ‘DeKalb XL43’ and ‘DeKalb XL395′), and soybean [Glycine max (L.) Merr. ‘Corsoy’, ‘Williams', and ‘Tracy’] in climate-controlled greenhouses and growth chambers. Itchgrass grew vigorously and produced seed in temperature regimes simulating the warmest 4 months of the growing season in the Gulf Coast states (30/25 C, day/night), the central Midwest (27/21 C), and the northern Midwest (23/18 C). At 30/25 C day/night, itchgrass produced 707 g of dry matter and 1907 seed per plant after 119 days. Itchgrass produced 621 g dry matter and 1429 seed at 27/21 C and 499 g dry matter and 1160 seed at 23/18 C. Itchgrass and adapted varieties of corn and/or soybeans were grown in four additional temperature regimes simulating the first 5 weeks of the growing seasons for corn and soybean at Madison, Wisconsin (19/11 C day/night); for soybean at Carbondale, Illinois (24/20 C); for corn at Waycross, Georgia (20/14 C); and for soybean at Baton Rouge, Louisiana (27/23 C). After 24 days of growth, half the plants in each regime were exposed to 3 days of chilling (11/4 C for Madison, 17/10 C for Carbondale, 15/6 C for Waycross, and 24/18 C for Baton Rouge) and returned to the original growth regimes for recovery. The chilling treatments reduced dry matter production, net assimilation rate, and leaf area duration more in itchgrass than in corn or soybean. After recovery, the previously chilled itchgrass plants had greater reductions in height, leaf area, and dry weight, compared to unchilled controls, than did corn or soybean. Weed/crop ratios in height, leaf area, and dry weight for itchgrass/corn were significantly reduced by chilling. In the two cooler regimes, weed/crop ratios in leaf area and dry weight for itchgrass/soybean were significantly reduced by chilling. Because of its sensitivity to cool temperatures, itchgrass, is unlikely to be an important early-season competitor with corn or with soybean outside the South.

Catclaw mimosa, an exotic member of the Leguminosae, occurs in three areas of Florida. Propagation is by seed only. Seeds collected from Florida were used for germination, growth, and herbicide evaluation studies. Seeds germinated at 75 to 94% but were not influenced by different environmental conditions under which they were stored. Greenhouse-grown plants cut or burned off at ground level failed to regrow. However, plants cut at 2 cm or more above ground level regrew from lateral shoots. Sixteen herbicides were evaluated to determine their effects on 6- to 8-wk-old plants grown in the greenhouse. Catclaw mimosa was killed by picloram, tebuthiuron, hexazinone and sulfometuron at 0.4, 0.07, 0.14, and 0.56 kg ha-1, respectively. Dicamba at 1.12, triclopyr at 1.12 (Garlon 3A and 4), linuron at 4.48, and glyphosate at 8.96 kg ha-1 were also effective. Chlorsulfuron and metsulfuron killed 9 out of 10 plants at the highest rates tested. Four herbicides, imazapyr, thifensulfuron, DPX-L5300, and atrazine killed 50% or less of the plants at the highest rates of each compound tested. Fosamine did not kill catclaw mimosa at the rates tested.

Ethylene-stimulated germination of witchweed [Striga lutea Lour. = S. asiatica (L.) O. Ktze.] seed first occurred after 13, 10, 6, 3, and 2 days of conditioning in moist sand at day/night temperatures of 20/14, 23/17, 26/20, 29/23, and 32/26 C, respectively. Maximum germination percentages in these regimes were 0.5, 3, 20, 24, and 37%, respectively. No germination occurred at 17/11 C. Witchweed seed survived in sand frozen for 7 weeks at −7 or −15 C and subsequently germinated in response to ethylene or in the presence of corn (Zea mays L., ‘DeKalb B73 × Mo.17H′) roots. The parasites emerged from the soil and flowered when maintained at 29/23 C after the termination of the freezing treatments. In other experiments, witchweed parasitized corn and/or sorghum [Sorghum bicolor (L.) Moench ‘DeKalb E-59+′] root systems in a sandy loam under 26/17, 26/20, 29/20, 32/23, and 32/26 C day/night regimes. Witchweed emerged from the soil with 26/20, 29/20, 32/23, and 32/26 C and flowered with 26/20, 32/23, and 32/26 C day/night regimes. Underground development and subsequent emergence of the parasites were substantially reduced with day/night temperatures below 29/20 C. Winter soil temperatures and growing season soil and air temperatures are unlikely to limit the spread of witchweed into important corn- and sorghum-producing areas of the United States.

Tropical soda apple is an exotic perennial pasture weed currently reported in the U.S. only from Florida, Georgia, Alabama, Mississippi, and South Carolina. In experiments to determine its environmental requirements and potential range, tropical soda apple was grown in growth chambers in 16 day/night temperature regimes ranging from 18/8 to 36/26 C. After 100 d of growth, maximum height, leaf area, and shoot biomass occurred at day/night temperatures ranging from 24/26 to 36/26 C. The plants achieved 50% or more of maximum leaf area, biomass, and height at 18/26, 24/20, 24/26, 30/26, and 36/26 C. Plants survived in 8 C nights with day temperatures of 18 to 36 C, but biomass and leaf area were only 3 to 10% of maximum. Leaf appearance rate was linearly related to mean temperature over the range of 11.3 to 29.3 C, with a slope coefficient of 0.018 leaves/day/degree C. Flowering was delayed by photoperiods shorter than 10 h or temperatures lower than 24/20 C. In favorable temperatures, plants flowered within 60 d after emergence in photoperiods ranging from 8 to 16 h. Artificially pollinated flowers produced fruit with germinable seeds within 6 to 7 wk, at temperatures ranging from 23/17 to 32/26 C. A regression equation relating vegetative growth to day and night temperatures indicated that tropical soda apple could achieve 30% or more of its maximum growth rate during 7 mo of the year in southern Alabama, Louisiana, and Texas and during 4 to 5 mo of the year at sites in Georgia, South Carolina, North Carolina, Virginia, Tennessee, Kentucky, Illinois, Arkansas, Missouri, Kansas, and Oklahoma. Neither temperature nor photoperiod will limit its further spread in the southern U.S. and adjacent regions.

In controlled-environment chambers, serrated tussock achieved maximum growth in temperature regimes of 18/11, 18/23, 24/23, or 24/17 C day/night. Growth was significantly reduced at 30/11 C, and no plants survived at 36/29 C. Serrated tussock seedlings grew slowly at first but eventually produced vigorous tussocks with as many as 2800 tillers after 140 d in the 24/17 C regime. Comparisons of climatic conditions in New South Wales, Victoria, New Zealand, South Africa, and the United States revealed that similar temperature conditions occur during the warmest eight mo of the year in areas as diverse as Oregon, Washington, the Sierran Nevada foothills of California, upper elevation rangelands in Arizona, and the southern Appalachian highlands. None of these areas has a precipitation pattern similar to those of the sites of serrated tussock weed infestation in the Southern Hemisphere. However, poorly managed pastures and unimproved rangelands in these diverse areas may be vulnerable to invasion by serrated tussock, should the weed become established in the United States.

Tropical soda apple (SOLVI) is an introduced, perennial broadleaf plant that has invaded Florida agricultural land and natural ecosystems and has spread to other states (Georgia, Alabama, South Carolina, Louisiana, North Carolina, Tennessee, and Pennsylvania). Tropical soda apple was first collected in Florida in 1988. In 1990, SOLVI-infested land was approximately 10,000 ha, in 1993, 162,000 ha, and in 1995, approximately 0.5 million ha were reported infested in Florida. Rapid spread of this invasive plant has occurred from seeds transported in cattle, hay, sod, grass seeds, water, and wildlife (deer, feral hogs, birds). Animals will not eat the foliage but will consume the fruits and spread the seeds in their feces. This exotic weed is an indeterminate plant with seed production averaging 50,000/plant/yr, seed germination of 70–90%, and seed longevity in soil of up to 1 yr. Integrated weed management strategies include prevention (avoidance of contaminated hay or grass seed, control of movement of cattle), control (mechanical, chemical), and monitoring. Seed production must be prevented and landowners should adopt a zero tolerance toward SOLVI. During the time (1990–1995) research (biology, ecology, control) was being conducted to control SOLVI from Florida, this weed had infested the entire state and escaped into other states. Risk assessment criteria for new plant introductions must be developed and implemented to prevent future biological pollution.

Benghal dayflower (formerly known as tropical spiderwort) is one of the most troublesome weeds in Georgia cotton. Field studies were conducted from 2003 to 2005 to evaluate the relationship between the duration of Benghal dayflower interference and cotton yield to establish optimum weed-control timing. To determine the critical period of weed control (CPWC), Benghal dayflower interference with cotton was allowed or prohibited in 2-wk intervals between 0 to 12 wk after crop planting. Maximum yield loss from Benghal dayflower in May-planted cotton was 21 to 30% in 2004 and 2005, whereas cotton planting delayed until June resulted in maximum yield losses of 40 to 60%. June-planted cotton had a CPWC of 190 to 800 growing degree days (GDD) in 2004 (52-d interval beginning at 16 d after planting [DAP]) and 190 to 910 GDD in 2005 (59-d interval beginning at 18 DAP). In contrast, May-planted cotton in 2005 had a narrower CPWC interval of 396 to 587 GDD (18 d) that occurred 3 wk later in the growing season (initiated at 39 DAP). May-planted cotton in 2004 did not have a critical range of weed-free conditions. Instead, a single weed removal at 490 GDD (44 DAP) averted a yield loss greater than 5%. It is recommended that fields infested with Benghal dayflower be planted with cotton early in the growing season to minimize weed interference with the crop.

The management of exotic, invasive plants is among the most challenging undertakings of natural resource managers, particularly in large, remote landscapes. The availability of information on the distribution and abundance of invasive plants is vital for effective strategic planning yet is often unavailable because of high costs and long procurement times. This paper presents results of a large-scale invasive plant mapping effort in the Florida Everglades utilizing digital aerial sketch mapping (DASM) and evaluates its utility for guiding management decisions. The distribution and abundance (cover) of four priority invasive plant species—Australian pine, Brazilian pepper, melaleuca, and Old World climbing fern—were mapped over 728,000 ha in the Everglades during 2010 to 2012. Brazilian peppertree was the most widely distributed and abundant species, occupying 30,379 ha. Melaleuca was also widely distributed and occupied 17,802 ha. Old World climbing fern occupied only 7,033 ha but its distribution was generally concentrated in heavy infestations in the northern Everglades. Australian pine was the least abundant of the mapped species and tended to be limited to the southeastern Everglades region. DASM proved to be a cost-effective means of obtaining region-wide distribution and abundance information for these species at broad scales (> 500 m), but detection rates and positional accuracy declined at finer scales. Both canopy type (forested vs. unforested) and distance from flight transect appear to be important factors for detection accuracy.

The potential dispersal of Benghal dayflower seeds by mourning doves was studied in southern Georgia, U.S.A. The gut contents (both crop and gizzard) of mourning doves harvested in the autumn months were investigated to determine if mourning doves fed on Benghal dayflower and whether seeds can survive conditions in the bird gut. Research indicated that mourning doves fed selectively on Benghal dayflower with some harvested birds containing hundreds of Benghal dayflower seeds and capsules in their guts. Further, some seeds recovered remained highly viable. Germination rates in seeds taken from bird crops were similar to controls over the first 4 wk of germination and enhanced over control treatments during the latter 16 wk of a 20-wk germination study. Ultimately, seeds extracted from dove crops had 92% germination as compared to 80% for control seeds. Seeds extracted from dove gizzards had 45% germination, about half that of controls. Benghal dayflower seeds have a structurally reinforced seed coat that probably aids in survival of mechanical damage through bird intestinal tracts. Benghal dayflower seeds exposed to 1.0 M HCl treatment for 2 h had little loss in viability, successfully germinating after such treatment. When evaluating mechanisms for the eradication of Benghal dayflower from agricultural crops, consideration needs to be given to the large number of mourning doves and other bird species that visit cropland and potentially aid in its dispersal.

Both phenotypic and genetic variation can affect the establishment success of exotic species. Using the weed Senecio vernalis Waldst. & Kit. with a continuous westward expansion of the native geographic range, we asked to what degree seed traits and germination patterns differ among different habitat disturbance types in the introduced region. We hypothesized that seed traits and germination pattern differ between different disturbance types, with lighter seeds and enhanced germination speed in highly disturbed habitats. Since S. vernalis colonizes successfully various disturbed habitats, we expected to find a high phenotypic genetic variation. Individuals from 19 populations were sampled from one region in Eastern Germany to study seed trait variation and germination success by means of a germination experiment and to assess genetic patterns using amplified fragment length polymorphism (AFLP) markers. Contrary to our expectation, habitat disturbance types did not differ in seed traits, germination characteristics or genetic variation. Instead, we found highest phenotypic and genetic variation within populations. Maximum percentage of germination was positively affected by seed mass. In addition, there was a weak but significant association between AFLP band patterns and population size and seed width, indicating that some variation in seed traits has a genetic component. In conclusion, the absence of a population differentiation at this geographic scale makes it unlikely that adaptation to different disturbance regimes is involved. Instead, a high variation in seed traits, overall high germination and genetic variation within populations under a wide range of habitat disturbance conditions seems to enable the offspring to colonize various habitat disturbance types.