Field and laboratory experiments were conducted to evaluate the effect of postemergence johnsongrass control on incidence of maize chlorotic dwarf virus (MCDV) and maize dwarf mosaic virus (MDMV) in corn and to confirm the presence and movement of the blackfaced leafhopper, the insect vector of MCDV. Corn plants surrounded by MCDV- and MDMV-infected rhizomatous johnsongrass were either treated or not treated with nicosulfuron at 35 g ai/ha. Corn tissue samples were taken at the time of treatment and 4, 9, 14, and 21 d after treatment and the presence of MCDV and MDMV was determined by enzyme-linked immunosorbent assay (ELISA). Virus incidence in treated experimental units was higher at the later sampling dates relative to the nontreated. Earlier differences in incidence of MCDV and MDMV double infection in corn were detected where johnsongrass was controlled. Movement of the insect vector of MCDV was observed within the experimental area after johnsongrass was controlled, but was not significantly different from that in nontreated areas.

Winter rape (Brassica napus L.) green manures have shown potential for erosion control and suppression of weeds and other pests in potato cropping systems. However, little information on residue cover, biomass production, glucosinolate concentration, and glucosinolate production with winter rape grown as a green manure is available. In field trials in southern Idaho, ‘Aspen,’ ‘Bridger,’ ‘Cascade,’ ‘Dwarf Essex,’ and ‘Humus’ winter rape were planted in mid-August and incorporated the following spring in late April or early May. All five cultivars provided > 80% fall, winter, and early spring residue cover. Winter rape dry weight just before incorporation was 2,880 to 4,462 kg/ha in 1994 and 5,438 to 7,837 kg/ha in 1995. The major glucosinolate in roots of all five cultivars was phenylethyl glucosinolate; the major glucosinolates in shoots were 4-pentenyl, 2-hydroxybutenyl, 3-butenyl, and 2-hydroxypentenyl glucosinolate. Glucosinolate concentrations varied between years, but concentrations were higher in Dwarf Essex and Humus than in Aspen both years. Glucosinolate production per hectare also was highest in Dwarf Essex and Humus and lowest in Aspen. Dwarf Essex and Humus produced higher amounts of isothiocyanate (ITC) and oxazolidinethione (OZT)-producing glucosinolates than Aspen, Bridger, or Cascade, and therefore may be better biofumigants.

A soil bioassay experiment was conducted in Blacksburg, VA, to determine the effect of isoxaben application timings and rates on duration of weed control. Flats containing soil were imbedded into the field. Isoxaben was applied in the spring, fall, and spring followed by fall (double application) at 0.56, 0.84, and 1.12 kg ai/ha. Flats were moved to a greenhouse at 0, 1, 3, 6, and 9 months after treatment (MAT) and seeded with yellow rocket, buckhorn plantain, and spotted spurge for the bioassays. Weed counts from treated flats were compared to those in untreated flats to determine percent control. Fall and spring followed by fall applications provided approximately 20% greater control of yellow rocket 3 MAT and 30% greater control 6 MAT, compared to a single spring application of isoxaben. Isoxaben at all rates controlled yellow rocket > 70% at 6 mo after fall application. At 3 MAT, fall and spring plus fall-applied isoxaben provided about 15 and 20% greater buckhorn plantain control, respectively, compared to spring application. The two highest rates of isoxaben controlled buckhorn plantain > 70% at 3 mo after fall application, but provided poor control at 6 MAT. Control of spotted spurge was similar among the three application timings for isoxaben and was unacceptable at most evaluation dates. Overall, isoxaben applied at 1.12 kg/ha provided better control of all three weed species for a longer time than the reference herbicide, oxadiazon, applied at 3.36 kg/ha.

Eight species of Tamarix were first brought to North America in the 1800s from southern Europe or the eastern Mediterranean region. Many of the species escaped cultivation and by the 1920s invaded about 4,000 ha of riparian habitat in the southwestern United States. By 1987, it was estimated to have increased to at least 600,000 ha. The success of saltcedar in the southwest can be attributed to several factors related to its growth habit, reproduction, water usage, ability to tolerate highly saline conditions, and redistribution of salt from deep in the soil profile to the soil surface. The flowers produce small, numerous, and tufted seeds that can be carried long distances by wind or water. The seeds, however, have a short period of viability, and must come in contact with suitable moisture within a few weeks of dispersal. Unlike obligate phreatophytes, such as willows and cottonwoods, saltcedar is a facultative phreatophyte and is often able to survive under conditions where groundwater is inaccessible. The high evapotranspiration rates of saltcedar can lower the water table and alter the floristic composition in heavily infested areas. Mature plants are tolerant to a variety of stress conditions, including heat, cold, drought, flooding, and high salinity. Saltcedar is not an obligate halophyte but survives in areas where groundwater concentrations of dissolved solids can average 8,000 ppm or higher. In addition, the leaves of saltcedar excrete salts that are deposited on the soil surface under the plant, inhibiting germination and growth of competing species.

Effectiveness of rotary hoeing with cultivation and comparison of an in-row cultivator with a standard row-crop cultivator were determined in dry edible bean. The effectiveness of in-row cultivation conducted at various timings and frequencies was examined. The in-row cultivator was more effective in reducing weed populations than the standard cultivator, although at least two mechanical weeding operations were needed to reduce weed populations to levels of the herbicide check (EPTC [S-ethyl dipropyl carbamothioate] plus ethalfluralin). When the in-row cultivation was delayed until the second trifoliolate stage or later, weed populations were greater than those in the herbicide check. In situations with high weed populations, rotary hoeing prior to cultivation was required to reduce weed populations to levels similar to the herbicide check. An in-row cultivator has potential to improve mechanical weed control options in a crop such as dry edible bean. The types of adjustments made in combination with soil textures, soil moisture, and operator experience affect overall weed control. Thus, it is expected that the level of weed control will vary from year to year and even field to field for the same operator.

In two separate field experiments conducted over time, at-planting preemergence (PRE) applications of sulfometuron at 110 to 150 g ai/ha followed by March applications of sulfometuron at 30 g/ha or metribuzin at 2,580 g ai/ha at the start of the initial (plant cane) growing season controlled more bermudagrass and johnsongrass emerging in sugarcane from rhizome and stolon pieces than standard at-planting followed by March applications of atrazine at 2,240 g ai/ha (no control), metribuzin at 2,580 g ai/ha, or pendimethalin at 2,240 g ai/ha. Treatments containing at-planting applications of imazapyr at 280 g ai/ha or thiazopyr at 560 g ai/ha did not provide levels of control similar to sulfometuron. Crop injury in excess of 10% occurred only when imazapyr at 280 g/ha (18 to 42%) or sulfometuron at 30 g/ha (11 to 32%) was applied in March to emerging sugarcane. Sugarcane stalk numbers, stalk heights, and ultimately cane and sugar yields were increased when compared to the standards with all sulfometuron treatments and when thiazopyr was applied at planting and again in March.

The isopropylamine salt of glyphosate at 420, 560, and 840 g ae/ha applied alone or mixed with the sodium salt of bentazon at 840 g ai/ha, chlorimuron at 9 g ai/ha, the sodium salt of fomesafen at 350 g ai/ha, or the ammonium salt of imazethapyr at 70 g ae/ha was evaluated for control of large crabgrass and broadleaf signalgrass. Neither grass was controlled by bentazon, fomesafen, or chlorimuron. Imazethapyr controlled large crabgrass and broadleaf signalgrass 30 and 72%, respectively, 3 weeks after treatment (WAT). Glyphosate at all rates controlled both grasses 100%. Control 3 WAT was unaffected by mixing bentazon, chlorimuron, fomesafen, or imazethapyr with glyphosate. Broadleaf signalgrass control 1 WAT was reduced 4 to 15% by mixing bentazon with glyphosate.

Florida has more non-native species of plants established in the state than has any other state in the continental U.S.; the vast majority of these species are harmless. As settlement and population increased and additional exotic species were introduced at increasing rates, some non-native species were able to obtain the edge needed for exponential growth. Among the weeds discussed are those that demonstrate different types of entry, ecological systems, and control. Weeds representing the potential of a small population, a major escaped ornamental, rapid expansion in vegetables, major pests in tree crops, utilization of a biocontrol, distribution in turf, major invaders along roadsides and into open lands and pastures, and exotic aquatic weeds are discussed.

During the 20th century, naturalized saltcedar has become common within major tributaries throughout the western United States. Often growing in nearly monocultural stands, saltcedar is suspected of lowering water tables, thus destroying wetlands and wildlife habitats. Management efforts have primarily relied on mechanical and cultural practices, but recent success in controlling saltcedar with imazapyr has led to wider herbicide use. Based on a number of research/extension field trials in New Mexico from 1987 to present, imazapyr applied alone or in combination with glyphosate was found to control saltcedar to levels of 90% or greater, especially when applied in August or September. For fixed-wing aircraft applications, we recommend applying imazapyr at 1.1 kg ai/ha or imazapyr plus glyphosate at 0.56 plus 0.56 kg/ha. For individual plant treatments, we recommend spraying the foliage to wet with imazapyr at 1% v/v in water, or imazapyr plus glyphosate at 0.5 plus 0.5% v/v. Herbicide activity may be reduced as saltcedar height and stem number increases.

The effect of bromoxynil on large crabgrass control by clethodim, sethoxydim, fluazifop-P, fluazifop-P plus fenoxaprop-P, and quizalofop-P was evaluated in 1996 and 1997 in bromoxynil-tolerant cotton and in fallow areas. Bromoxynil at 560 g ai/ha reduced large crabgrass control 4 weeks after treatment (WAT) when mixed with labeled rates of fluazifop-P, fluazifop-P plus fenoxaprop-P, or quizalofop-P. Control 9 WAT was reduced when bromoxynil was mixed with any of the graminicides. Antagonism with the mixtures was greatest with quizalofop-P, intermediate with fluazifop-P plus fenoxaprop-P and fluazifop-P, and least with clethodim and sethoxydim. Increasing the graminicide rate 50% in mixtures with bromoxynil alleviated antagonism only for clethodim. No antagonism was noted 9 WAT when bromoxynil was applied 3 d before or 3 d after application of clethodim or sethoxydim or when bromoxynil was applied 3 d after fluazifop-P plus fenoxaprop-P. Antagonism was observed when bromoxynil was applied 3 d before fluazifop-P plus fenoxaprop-P or when applied 3 d before or 3 d after fluazifop-P and quizalofop-P. Regardless of bromoxynil application, greatest yields were obtained from cotton treated with clethodim or sethoxydim. Bromoxynil applied 3 d before or 3 d after clethodim, sethoxydim, or fluazifop-P plus fenoxaprop-P did not reduce yield. Yield was reduced when bromoxynil was applied 3 d before or 3 d after application of fluazifop-P or quizalofop-P and when bromoxynil was mixed with any graminicide.

Vegetation development bordering the Middle Rio Grande, as with most major southwestern U.S. tributaries, has historically undergone rapid and dynamic change. The introduction of saltcedar (or Tamarisk, genus Tamarix) and other exotic species into this environment within the 20th century has contributed to this process. These plants are now an integral component of the riparian vegetation mix. Manpower, logistics, and financial resources constrain the degree to which a desired riparian habitat can be restored from saltcedar thickets on the Bosque del Apache National Wildlife Refuge near Socorro, NM. Saltcedar clearing is accomplished using a combination of herbicide, burning, and mechanical control techniques costing from $750 to $1,300/ha. Soil salinity and depth to water are the principal physical features limiting revegetation efforts. Cottonwood and black willow plantings and natural regeneration after timed irrigations have produced diverse habitats that support a wide array of faunal species in areas previously occupied by homogeneous saltcedar.

Until recently melaleuca was spreading at a rate faster than it was being controlled throughout the boundaries of the South Florida Water Management District (District). Although melaleuca is a difficult species to eradicate, apparently District efforts, along with those of other governmental agencies and private groups, are containing its spread within the Everglades Water Conservation Areas (WCAs) and the marsh of Lake Okeechobee. Melaleuca has been completely cleared from WCA-2A, -3B, and -3A, south of Alligator Alley. These areas are now under “maintenance control.” Maintenance control means applying management techniques in a continuous basis to keep an invasive plant population at its lowest feasible level. Today, the melaleuca infestation is no longer increasing; in many areas, it is being reduced. Preliminary results from the latest District survey indicate melaleuca infestation has decreased considerably in South Florida, especially in public lands. The intent of this paper is to provide an assessment of progress made by the District's melaleuca control program over the past 7 yr.

Field experiments were conducted at East Lansing and Clarksville, MI, to evaluate the efficacy of imazamox, imazethapyr, and CGA-277476 plus quizalofop applied postemergence in wide- (76-cm) and narrow- (19-cm) row soybean. Soybean injury from all herbicides was minimal 14 days after treatment (DAT), except for CGA-277476 at 79 g ai/ha plus 69 g ai/ha quizalofop, which caused 30% soybean injury at the Clarksville location. Adding 4 g ai/ha CGA-248757 to 65 g ai/ha CGA-277476 plus quizalofop reduced common ragweed control, but increased redroot pigweed control in wide rows compared to 79 g ai/ha CGA-277476 plus quizalofop. Imazamox at 35 and 45 g ai/ha provided greater common ragweed and common lambsquarters control than imazethapyr at 70 g ai/ha 28 DAT. All herbicide treatments controlled velvetleaf. Common ragweed and common lambsquarters control by all herbicide treatments was enhanced in narrow- compared to wide-row soybean 56 DAT as was redroot pigweed control by CGA-277476 treatments. Total weed biomass and soybean yield in wide-row soybean treated with imazamox at 45 g/ha was not different from the hand-weeded control. In narrow-row soybean, soybean yield was equal to the hand-weeded control for 35 and 45 g/ha imazamox and 70 g/ha imazethapyr. Postemergence herbicide treatments resulted in less weed biomass and greater soybean yield in narrow- compared to wide-row soybean.

The name Polygonum is a very ancient derivative, composed of the two Greek words, polys, many, and gony, knee or joint, alluding to the numerous and conspicuous nodes in the stems of many species. The Greek physician Heraclides Tarentina (third and second centuries BC) prescribed prostrate knotweed, P. aviculare L., as a remedy against bleeding from the ear. Dioscorides, a Greek botanist, was the first to characterize Polygonum as having “numerous slender branches, creeping on the ground like grass, with fruit at each leaf.” Subsequently, other Greek physicians, poets, and botanists applied the name to the knotweed/smartweed group, and in 1753, Linneaus adopted it for the genus. The species name for pale smartweed, lapathifolium, is from lapathi, meaning sorrel-like or dock-like (Gledhill 1985; Hyam and Pankhurst 1995; Small 1895).

Field experiments were conducted from 1987 to 1990 to investigate the combination of cultural and chemical methods for control of Amaranthus spp. in corn. The tolerance of corn hybrids to herbicides or herbicide combinations was dependent on application rate. The early season threshold level for a mixed population of Amaranthus spp. occurred 3.5 wk after emergence. Density of Amaranthus spp. from 155 to 495 plants/m2 caused corn yield reduction of 50%. A quadratic model was derived relating percentage of yield reduction vs. duration of weed competition. The results emphasize the importance of using herbicides, cultural practices, and competition thresholds for an integrated weed control approach of Amaranthus spp. in corn.

Diffuse knapweed, a biennial or short-lived perennial, and spotted knapweed, a perennial, are taprooted Eurasian weeds invading rangeland in the western United States and Canada. Knapweed (Centaurea spp.) invasion is associated with reductions in biodiversity, wildlife, and livestock forage, and increased erosion. Spotted knapweed grows to about 1 m and usually has purple flowers, whereas diffuse knapweed is slightly shorter, usually with white flowers. Persistent flower bracts on diffuse knapweed bear a rigid terminal spine about 8 mm long with four or five pairs of shorter lateral spines. Bracts on spotted knapweed have dark spotted tips. Knapweed management involves a combination of containing infestations and control efforts. Hand pulling in areas with small infestations can be effective for controlling spotted and diffuse knapweeds. Picloram applied at 0.28 kg ha−1 provides control for about 3 yr. Effective long-term control of knapweeds requires periodic applications of picloram, which are only cost-effective on highly productive range sites with a residual grass understory. About 12 insect species have been released for knapweed biocontrol. Seed production has been reduced by 46% by insects feeding in the flower heads. Although insects have not reduced spotted knapweed densities, they may stress the weed and shift the competitive balance to associated species. Sheep grazing reduces the density of very young seedlings and may limit seedling recruitment into the population. In areas without a residual understory of desired plant species, revegetation of knapweed-infested rangeland is required. Components of any integrated weed management program are sustained effort, constant evaluation, and the adoption of improved strategies.

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.