Summer Weeds Research Articles

Summer Weeds as Hosts for Frankliniella occidentalis and Frankliniella fusca (Thysanoptera: Thripidae) and as Reservoirs for Tomato Spotted Wilt Tospovirus in North Carolina

In North Carolina, Tomato spotted wilt tospovirus (family Bunyaviridae, genus Tospovirus, TSWV) is vectored primarily by the tobacco thrips, Frankliniella fusca (Hinds), and the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). TSWV overwinters in winter annual weeds from which it is spread to susceptible crops in spring. Because most susceptible crops are destroyed after harvest before winter weeds emerge in the fall, infected summer weeds are thought to be the principal source for spread of TSWV to winter annual weeds in fall. A survey of summer weeds associated with TSWV-susceptible crops in the coastal plain of North Carolina conducted between May and October revealed that relatively few species were commonly infected with TSWV and supported populations of F. fusca or F. occidentalis. F. occidentalis made up > 75% of vector species collected from 15 summer weed species during 2002. The number of F. occidentalis and F. fusca immatures collected from plant samples varied significantly among plant species. Ipomoea purpurea (L.) Roth, Mollugo verticillata L., Cassia obtusifolia L., and Amaranthus palmeri S. Wats supported the largest numbers of immature F. occidentalis. Richardia scabra L., M. verticillata, and Ipomoea hederacea (L.) supported the largest numbers of F. fusca immatures. TSWV was present at 16 of 17 locations, and naturally occurring infections were found in 14 of 29 weed species tested. Five of the TSWV-infected species have not previously been reported as hosts of TSWV (A. palmeri, Solidago altissima L., Ipomoea lacunosa L., I. purpurea, and Phytolacca americana L.). Estimated rates of infection were highest in I. purpurea (6.8%), M. verticillata (5.3%), and I. hederacea (1.9%). When both the incidence of infection by TSWV and the populations of F. occidentalis and F. fusca associated with each weed species are considered, the following summer weed species have the potential to act as significant sources for spread of TSWV to winter annual weeds in fall: I. purpurea, I. hederacea, M. verticillata, A. palmeri, C. obtusifolia, R. scabra, Ambrosia artemisiifolia L., Polygonum pensylvanicum L., and Chenopodium album L.

Summer Weeds as Hosts for <I>Frankliniella occidentalis</I> and <I>Frankliniella fusca</I> (Thysanoptera: Thripidae) and as Reservoirs for Tomato Spotted Wilt Tospovirus in North Carolina

Summer Weeds as Hosts for <I>Frankliniella occidentalis</I> and <I>Frankliniella fusca</I> (Thysanoptera: Thripidae) and as Reservoirs for Tomato Spotted Wilt Tospovirus in North Carolina

Weed control in a pigeon pea–wheat cropping system

Pigeon pea ( Cajanus cajan (L.) Millsp.) seedlings compete poorly against the rapid growth of warm-season annual weeds. Weed control is required before this heat and drought-tolerant legume can be reliably grown in the U.S. southern Great Plains as a potential source of livestock hay between annual plantings of winter wheat ( Triticum aestivum L.). Currently, no herbicides are labeled for use on pigeon pea grown in the U.S. Three years of replicated field experiments were conducted to determine the effects of applications (1× and 2× rates) of herbicides (pre-emergence, sulfentrazone + chlorimuron and metribuzin; post-emergence, imazapic and sethoxydim) on weed suppression, pigeon pea dry matter, and carry-over effects on a winter wheat crop. The most abundant summer weeds were broadleaf, and all herbicide treatments, except sethoxydim (grass herbicide), reduced weed densities compared to untreated plots without adversely affecting pigeon pea stands. Imazapic treatments provided the most effective weed control. Overall average pigeon pea dry matter ranged from 75 to 256 g m −2 with sethoxydim and the untreated control ≤ metribuzin ≤ sulfentrazone + chlorimuron ≤ hand weeded control ≤ imazapic. Compared to the hand-weeded control, imazapic treatments greatly reduced wheat dry matter (1×, 65% and 2×, 91%) and grain yield (1×, 59% and 2×, 93%). Imazapic should not be used unless nontransgenic imidazolinone herbicide tolerant wheat cultivars are planted. While the other herbicides decreased negative effects of weeds on pigeon pea dry matter without greatly affecting productivity of a following wheat crop, appropriate labels for each of these herbicides will be required prior to their use by southern Great Plains pigeon pea producers.

WeedTurf: a predictive model to aid control of annual summer weeds in turf

Predicting weed emergence is useful for planning weed management programs. Unfortunately, our ability to anticipate initial emergence and subsequent levels of emergence from simple field observations or weather reports is often inadequate to achieve optimal control. Weed emergence models may provide predictive tools that help managers anticipate best management options and times and, thereby, improve weed control. In this study, the germination characteristics of four annual grass weeds (large crabgrass, goosegrass, green foxtail, and yellow foxtail) were investigated under different temperatures and water stresses to calculate base temperatures and base water potentials. These parameters were used to develop a mathematical model describing seedling emergence processes in terms of hydrothermal time. Hydrothermal time describes seed germination in a single equation by considering the interaction of soil water potential and soil temperature. The model, called WeedTurf, predicted emergence with some accuracy, especially for large crabgrass (lowest efficiency index [EF] value 0.95) and green foxtail (lowest EF value 0.91). These results suggest the possibility of developing interactive computer software to determine the critical timing of weed removal and provide improved recommendations for herbicide application timing.

Effect of reduced tillage on weeds and soil organisms in winter wheat and summer maize cropping on Humic Andosols in Central Japan

Although reduced tillage (RT) may preserve soil biota and improve the productivity and sustainability of arable lands in temperate regions, the extension of RT is limited by difficulties in controlling weeds. We studied the effect of RT without herbicide application on weed communities and soil biota in a 1-year 2-crop rotation system with winter wheat ( Triticum aestivum L.) and maize ( Zea mays L.) on Andosols in Japan. RT of the surface 3 cm and conventional moldboard plowing (CT) were conducted before seeding twice per year. For the first 3 years, from autumn 1997 to spring 2000, one field was managed with RT and another with CT. For the second 3 years, from autumn 2000 to spring 2003, RT and CT were conducted in two replicated plots in each field. Weed communities and soil biota were studied in the last 2 years. Dominant weed species in winter wheat cropping were Italian ryegrass ( Lolium multiflorum Lam.) in 2002 and common vetch ( Vicia angustifolia L.) in 2003, and their biomass was high where RT or CT was continuously conducted. Switching of tillage methods, from RT to CT or vice versa, reduced the biomass of winter weeds. In summer maize cropping, several annual and perennial weed species tended to increase under RT in the second 3 years. However, redroot pigweed ( Amaranthus retroflexus L.), the most dominant weed in 2002 and 2003, responded to tillage inconsistently and its biomass was not always increased by RT. Species diversity of winter weeds was decreased by CT conducted in the first 3 years, and that of summer weeds was decreased by CT conducted in the second 3 years. The seedbank in the 0–10-cm soil layer under recent RT was large (7200–16 300 seeds m −2) compared with that under CT (2900–7300 seeds m −2). The microbial substrate-induced respiration (SIR) and the population densities of nematodes and mites were higher under RT in the second 3 years and were not affected by previous tillage practices. Both were highly correlated with soil total nitrogen. The positive effect of RT on these soil organisms was primarily attributable to the accumulation of organic matter in soil, but not to plant cover as a result of incomplete weed control by RT. Occasional adoption of RT in current CT systems may be effective at enriching soil organisms with little risk of weed infestation.

Factors affecting the occurrence of western flower thrips, Flankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in persimmon orchards

Wakayama Prefecture is one of the main production areas of persimmon in Japan. However, western flower thrips, Flankliniella occidentalis (Pergande) has been causing serious damage to persimmon fruit, especially variety Tonewase, when the fruit color turned yellow in early September since 1997. F. occidentalis overwintered on the perennial weed such as chickweed, Stellaria neglecta, and had two peaks of population density on undergrowth of persimmon orchards: one in June when perennial weeds were growing and the other in July-August when summer weeds were growing. Thus F. occidentalis maintained its population through various undergrowth. Since the weeding time was different between persimmon and mandarin orange orchards, the adult F. occidentalis dispersed from an orchard where they existed at a higher density to the adjacent orchards. Therefore, the population density of F. occidentalis was higher in a persimmon-mandarin orange cultivation area than in a persimmon mono-cultivation area. The thrips density on undergrowth of foxtail ears, Setalia viridis, was higher in the persimmon orchard than in the grassland nearby. This is provably because pesticides applied to persimmon trees suppressed the occurrence of natural enemies such as the minute bug, Orius sauteri, on weeds by drafting, causing a resurgence of F. occidentalis in persimmon orchards.

Weed Control in Maize (Zea mays L.) Through Sorghum Allelopathy

ABSTRACT Sorghum allelopathy has been utilized as an economical and natural technique for controlling weeds in some field crops like wheat (Triticum aestivum L.), maize (Zea mays L.), rice (Oryza sativa L.), mungbean (Vigna radiata L.) and Brassica (Brassica juncea L.). It can be used as sorgaab (water extract of mature sorghum plants), sorghum mulch, sorghum soil incorporation or included in crop rotation. Two field experiments were conducted for two years in the summer of 1997 and 1998. In Experiment 1, the response of maize (Zea mays L.) and summer weeds to foliar applications of sorgaab, hand weeding and herbicide spray was studied. In Experiment 2, the comparative efficacy of sorgaab at 15, 30 and 45 days after sowing (DAS) and sorghum mulch for controlling weeds were studied. Sorgaab foliar spraying controlled from 18–50% weeds and increased maize grain yield by 11–44%. Mature and chaffed sorghum herbage (10–15 Mg ha−1) surface applied at sowing controlled up to 26–37% weeds and increased maize yield by 36–40%. Three foliar sprays of sorgaab at 15, 30 and 45 days after sowing was the most economical method for controlling weeds in maize as compared with hand weeding, chemical herbicides and sorghum mulch. Weed control through hand weeding and/ or chemical herbicides was found to be economically impractical due to higher costs involved in both cases. Sorgaab can be used as a natural weed inhibitor in maize.

Development and reproduction of Myzus persicae and Aphis fabae (Hom., Aphididae) on selected weed species surrounding sugar beet fields

Abstract: Myzus persicae (Sulzer) and Aphis fabae (Scop.) are two major aphid species colonizing sugar beet. They have a very wide host range adapting to a large number of plant families and species. A series of cage experiments, conducted under ‘winter’ and ‘summer’ growth chamber conditions, showed that both species have the potential to use winter and summer weeds that are usually present in the vicinity of and within sugar beet fields as secondary hosts. Among all the weeds tested, Veronica hederifolia L. and Solanum nigrum L. were the most suitable for M. persicae. Although Brassica kaber (DC.) Wheeler was the weed species associated to the highest reproduction rate of this aphid, V. hederifolia showed a higher intrinsic rate of population increase due to the shorter prereproductive period of the aphid. Amsynckia intermedia Fish. and Mey and Amaranthus retroflexus L. were the most suitable weed hosts for A. fabae.

Development of a rainfed lucerne-based farming system in the Mediterranean climatic region of southwestern Australia

In the southern coastal region of southwestern Australia with a Mediterranean-type climate, rising water tables prompted the owner of the farm, ‘Laurinya’, near Jacup, Western Australia (34°S, 119°E), to extend small plantings of lucerne near saline streams to large areas of the farm. In recent years, the area under lucerne has increased from 20 to 800 ha. The aim is to ultimately have all pasture on the property as lucerne-based perennial pastures. The lucerne is sown with a no-till seeder in rows 250 mm apart. In two contiguous rows in every five rows, barley is sown with the lucerne to provide protection to the young lucerne plants from sand particles carried by high winds in the sandy-surfaced soils of the region. The barley also provides an income stream in the year of establishment of the lucerne. The lucerne-based pastures are the foundation of a phase-farming system. A period of lucerne varying in length from 2 to 10 years is followed by a cropping phase of 3–10 years. The lucerne pastures are rotationally grazed for 1–2 weeks with 5–6 weeks between grazing. The lucerne provides nitrogen to subsequent crops and assists with the control of volunteer grasses and summer weeds. It also uses water that otherwise would leak past the root zone and lead to rising water tables and secondary salinity.

Identification of crop and weed hosts of Ralstonia solanacearum biovar 2 in the hills of Nepal

Common agricultural weeds and crops that grow in the high hills of Nepal were examined after artificial inoculation and under natural conditions in the UK and Nepal to determine whether such plant species could act as hosts to biovar 2 of Ralstonia solanacearum. Bacterial populations in the roots were determined 1 and 2 months after inoculation, and at various intervals after harvesting infected potato crops under natural conditions. Inoculated roots of the summer weeds Drymaria cordata and Polygonum capitata and the winter weeds Cerastium glomeratum and Stellaria media yielded 102−107 colony‐forming units per g root. High populations of the bacterium were recovered from these plants even after partial surface sterilization, indicating that systemic infection had occurred. Ralstonia solanacearum populations were recovered from root extracts of 75% of naturally growing D. cordata plants when sampled 3 months after harvest of a potato crop with bacterial wilt. Similarly, root extracts of 25% of P. capitata plants carried the bacterium. No potential winter weed hosts were infected under natural conditions when sampled 5 and 6 months after harvest of infected potato, indicating that winter conditions in the high hills of Nepal are not conducive to infection. Among crops, mustard (Brassica juncea cv. Fine White) developed typical wilt symptoms after artificial inoculation in warm glasshouse conditions (20–28°C). Mustard and barley are winter crops in Nepal. However, neither mustard (Brassica juncea var. Lumle Tori) nor barley (Hordeum vulgare cv. Bonus) was infected when planted into heavily infested plots under natural conditions. The results indicated that the role of nonsolanaceous summer weeds in the persistence of biovar 2 of R. solanacearum in the environment may have been previously underestimated.

Host suitability of two biotypes of Bemisia tabaci on some common weeds

AbstractSignificant differences in some reproductive parameters of the B and Q biotypes of Bemisia tabaci (Gennadius) with regard to four species of winter weeds were determined in a no‐choice assay. The highest fecundity (eggs) and fertility (pupae and adults) were obtained with Malva parviflora L. as host, followed by Capsella bursa‐pastoris L., Brassica kaber (DC) and Lactuca serriola L. The percentage of adult emergence (from egg to adult) was significantly higher (P < 0.001) with M. parviflora, C. bursa‐pastoris and B. kaber than with L. serriola. Except on L. serriola, the mean values of the reproductive parameters for the Q‐biotype were significantly (P < 0.05) greater than those for the B‐biotype. On the other hand, in choice experiments with summer weeds, both B‐ and Q‐biotypes preferred Datura stramonium L. and Solanum nigrum L. to Amaranthus retroflexus L., Chenopodium album L. and Echinochloa crus‐galli L. Significantly more males and females, and more pupae and empty pupal cases per plant were found on D. stramonium than on S. nigrum. Adult abundance on A. retroflexus, C. album and E. crus‐galli plants was very low. At a constant temperature of 26 ± 1 °C, the Q‐biotype developed significantly faster than the B‐biotype on S. nigrum and D. stramonium. Both biotypes required, for this development, significantly more days on D. stramonium than on S. nigrum. These results suggest that it is important to suppress the growth of M. parviflora, C. bursa‐pastoris, B. kaber, D. stramonium and S. nigrum in order to avoid the risk of further expansion of whitefly populations where these weeds and both B‐ an Q‐biotypes are present.

Selectivity of Cyhalofop-butyl in Poaceae Species.

Responses to foliar-applied cyhalof op-butyl of the seedlings of 29 Poaceae species at about 3- to 4-leaf stage were examined. Species belonging to subfamilies of Panicoideae, except for Imperata cylindrica, and Eragrostoideae were all susceptible, being completely controlled at 100g ha-1. Most of these species are important summer weeds in crops. Alopecurus aequalis (Pooideae) and Agrostis alba (Pooideae) were also susceptible. Six of 10 other Pooideae species and the two Oryzoideae species tested, as well as I. cylindrica, in which all treated plants survived at 300g ha-1, were shown to have tolerance to cyhalofop-butyl. The other four Pooideae species were less susceptible and incompletely controlled at 100g ha-1. Oryza sativa displayed the highest tolerance; plants treated at 300g ha-1 did not show any significant differences from untreated plants. The typical visual symptom common through all plants of affected species was withering of the emerging leaves. The critical response that led to plant death, however, appeared to be the suspension of new growth. Plant survival after this phase seemed to depend on whether new development was restored before unaffected leaves lost their activity, by resumption of healthy leaf emergence mainly by formation of tillers or rhizomatous shoots.

Observation of Vesicular-Arbuscular Mycorrhizal Formation in the Roots of Some Seasonal Weeds Proliferated in Citrus Orchards.

Weeds were collected from citrus orchards in April and July to investigate vesicular-arbuscular mycorrhizal (VAM) infection. The infection was found to be high in the roots of spring weeds : Rumex acetosa L., Agropyron tsukuhiense (Honda) Ohwi var. transiens (Hack.) Ohwi, Stellaria media Villars., Vicia cracca L., Lamium amplexicaule L., and Medicago polymorpha L., and in the roots of summer weeds : Erigeron canadensis L., Amaranthus lividus L., Cynodon dactylon (L.) Pers., Beckmannia syzigachne (Steud.) Fern., Commelina communis L., Oxalis corniculata L., and Digitaria adscendens Henr. Spore formation was mostly found in the roots of spring weed : Stellaria media, Vicia cracca, and Lamium amplexicaule ; no VAM infection was observed in the roots of Rumex japonicus Houtt., Equisetum arvense L., and Polygonum blumei Meisn.

Effect of Timing of Winter Weed Control on the Growth of Young Peach Trees under Sod Culture.

A census of the weed population by species and their coverage and heights was made periodically over the summer in fruit trees and grapevines to characterize the vegetation of winter annual weeds in sunny orchards (Exp. 1). The timing of herbicide applications on the reduction of competition between winter annuals and the growth of 1-yr-old 'Hikawahakuho' peach (Prunus persica Batsch. var. vulgaris Maxim.) trees was studied (Exp. 2). The competition between those weeds and 4- and 6-yr-old 'Hikawahakuho' peach trees was also examined incorporating various vegetation management practices (Exp. 3). When weed management allowed winter annual weeds to grow freely in young sunny orchards, Vicia angustifolia L. became dominant from March to June, followed by Stellaria media (L.) Villars, and Lamium amplexicaule L. Those winter weeds reduced the overall growth of 1-yr-old peach trees when they were not controlled by May. Growth inhibition of newly developing shoots and fine roots by winter weeds was not as strong as that by summer weeds. Shoot length was reduced significantly in 4-yr-old peach trees but not in 6-yr-old ones. The results indicate that winter weeds need to be controlled by early May to minimize inhibition of peach tree growth.

Effect of weed position on yield loss in soyabean and a comparison between relative weed cover and other regression models

SummaryThe importance of the position of weeds with respect to crop rows in the determination of crop yield‐weed density relationships and the usefulness of relative cover (RC) of the weeds as an explanatory variable were studied in soyabean [Glycine max (L.) Merrill] competing with two summer weeds with contrasting canopy structure (Xanthium strumarium L. ssp. italicum and Echinochloa crus‐galli L.). The position of the weeds was of little importance in the relationship between yield loss and weed density. This information is important because published experiments have used different types of weed distribution (e.g. evenly distributed or sown in rows). For both weed species it was possible to obtain a single relationship between yield loss and RC for measurements made from 30 days after crop emergence to soyabean canopy closure. The competitive effect of the weeds appeared to be strictly related to RC, indicating that for weeds growing taller than the crop the main competitive factor may be the shading caused by the leaves of the weeds situated above the crop canopy.

Herbicide tolerance and weed control strategies for Lesquerella production

Lesquerella fendleri (Gray) Wats, has the potential of being an economical, water-efficient source of hydroxy fatty acid that is useful in the production of specialty lubricants, plastics, coatings, and cosmetics. Lesquerella's slow initial growth habit makes it noncompetitive with most weed species. This is especially true during the spring when the more aggressive summer weeds begin to appear. Because the cost of hand-weeding is commercially prohibitive, the primary subject of this study was to develop effective weed control strategies for Lesquerella, including herbicide tolerance, efficacy, and application techniques. Three years of herbicide tolerance studies in the field and greenhouse have identified preplant incorporated (PPI), postemergence (POST), and layby (LAY) herbicides to which Lesquerella is tolerant (less than 15% damage, with 100% damage meaning complete kill). Because Lesquerella is a new crop, which also could be a potential weed, it was also necessary to note several herbicides to which it has no tolerance. Herbicides that appear to be excellent candidates for registration include, PPI: trifluralin, benefin, and ethalfluralin; POST: oxyfluorfen, fluazifop, clopyralid, and sethoxydim; LAY: pendimethalin and DCPA. Rates and timing of application are very important for some materials. Materials that are potential, but less likely, herbicide candidates include, PPI: pendimethalin; PRE: napropamide and pronamide; POST: pronamide and dicamba.

Effects of root diffusates of some weeds associated with corn plantations on the hatchability of the corn cyst nematode,Heterodera zeae

Twenty two summer weeds belonging to fifteen plant families and twelve winter weeds from eight plant families were tested to compare the effects of their root diffusates with the corn root diffusates (CRD) of cv. Giza 2 on the hatchability of the corn cyst nematode (CCN),Heterodera zeae.

Plant diversity in late medieval cornfields of northern Switzerland

Weed assemblages from late medieval cornfields have been studied for the first time in northern Switzerland. Eleven samples from at least two different grain stores were investigated. The samples were collected from the carbonised remains of six wooden houses built in the late 13th century A.D. and which burnt down in the middle of the 15th century. The weed floras found in the spelt (Triticum spelta) and oats (Avena sativa) indicate a high botanical diversity in the cornfields at harvest time. Although oats are normally a summer crop and spelt a winter crop, both summer and winter crop weeds (as well as many different present-day grassland taxa) were found in each type of grain. Most of the weeds found were perennial plants, which was interpreted as an indication of both extensive tillage of the arable land and application of the three-field rotation system (Dreifelderwirtschaft). The spectra of the two palaeophytocoenoses (assemblages of ancient plant remains) studied suggest that the phytosociological method may not be reliable for classification of the late medieval remains into “summer” and “winter” crop weed communities. These findings should provide a better understanding of the development of anthropogenic plant communities, and in particular, the development of crop weed communities.

Species richness and phenology of vegetation along irrigation canals and drains in the Nile Delta, Egypt

This study evaluates the species richness, phenology and effect of environmental factors on the composition of canal and drain vegetation in the Nile Delta, Egypt. Altogether, 365 stands were sampled along the terraces, slopes, littoral zones and water zones of 28 canals and 10 drains. Smooth species compositional changes were found in the first three zones. The slope plant community has the highest total number of species and species richness and a medium value of species turnover. The water zone has the lowest values of these variables. The number of species with seedlings and vegetative plants had two peaks: one in winter and the second in summer, which was related to the contrasted behaviour of the winter and summer weeds. The number of species with vegetative and fruiting plants was relatively higher, while the number with dormant plants was relatively lower in the canal vegetation when compared to that of the drains. The number of species with vegetative, flowering and fruiting plants increased with the decrease of canal-drain width.

Effects of soil solarization on arable weeds under Mediterranean conditions: control, lack of response or stimulation

Field experiments on soil solarization were conducted in a Mediterranean climate at ICARDA in northern Syria from 1985 to 1988. Fifty-seven species from 25 families were included in this study. Of these, 46 were reduced in numbers as a result of the treatment; five species were increased, six were unaffected. After 20, 30, 40 and 50 days of solarization, weed dry weight was reduced by 84, 87, 86 and 94%, respectively, in a lentil crop and by 61, 76, 81 and 85% in a faba bean crop. Most annual weeds, especially Sinapis arvensis, were controlled up to 100%. Low to zero control or even stimulation occurred with weed species having bulbs ( Muscari racemosum, Bellevalia sp., Ornithogalum narbonense), heat-tolerant seed ( Coronilla scorpioides, Scorpiurus muricatus), a deep-lying root system or other perennial organs (e.g. Gladiolus aleppicus, Aristolochia maurorum, Leontice leontopetalum, Geranium tuberosum). A higher number of Muscari racemosum plants m −2 was encountered after solarization, indicating stimulation by the treatment. The numbers and dry weight of this weed after 20 days of solarization were increased by 85 and 87% in faba bean and lentil, respectively. Dry weight of spring and summer weeds after 50 days of solarization decreased by 89.2 and 90.3%, respectively. The maximum temperature reached at 5 cm soil depth under the plastic was 57°C.