Broadleaf Weed Species Research Articles

Influence of Diflufenzopyr Addition to Picolinic Acid Herbicides for Russian Knapweed (Acroptilon repens) Control

Diflufenzopyr is a synergist that has improved the efficacy of certain auxin-type herbicides such as dicamba on many broadleaf weed species. However, little is known regarding the activity of diflufenzopyr with other auxin-type herbicides. Russian knapweed is an invasive creeping perennial that is susceptible to certain pyridine carboxylic acids, which are auxin-type herbicides. The objective of this research was to determine if the addition of diflufenzopyr to three pyridine carboxylic acid herbicides enhances long-term control of Russian knapweed in Wyoming. All treatments were applied in the fall. Treatments included aminopyralid (0, 0.05, 0.09, and 0.12 kg ae/ha), clopyralid (0, 0.16, 0.21, 0.31, and 0.42 kg ae/ha) and picloram (0, 0.14, 0.28, 0.42, and 0.56 kg ae/ha), applied with and without diflufenzopyr (0.06 and 0.11 kg ae/ha). Twelve mo after treatment (MAT), diflufenzopyr had no significant impact on Russian knapweed control with either aminopyralid or picloram, and had significant but inconsistent impacts on knapweed control with clopyralid. At 24 MAT, diflufenzopyr did not enhance Russian knapweed control with either aminopyralid or clopyralid and was slightly antagonistic with picloram. These results indicate that the addition of diflufenzopyr does not improve Russian knapweed control with fall applications of either aminopyralid, clopyralid, or picloram.

Development of a Laboratory Bioassay and Effect of Soil Properties on Sulfentrazone Phytotoxicity in Soil

Sulfentrazone is a phenyl triazolinone herbicide used for control of certain broadleaf and grass weed species. Sulfentrazone persists in soil and has residual activity beyond the season of application. A laboratory bioassay was developed for the detection of sulfentrazone in soil using root and shoot response of several crops. Shoot length inhibition of sugar beet was found to be the most sensitive and reproducible parameter for measurement of soil-incorporated sulfentrazone. The sugar beet bioassay was then used to examine the effect of soil properties on sulfentrazone phytotoxicity using 10 different Canadian prairie soils. Concentrations corresponding to 50% inhibition (I50values) were obtained from the dose–response curves constructed for the soils. Sulfentrazone phytotoxicity was strongly correlated to the percentage organic carbon (P = 0.01) and also to percentage clay content (P = 0.05), whereas correlation with soil pH was nonsignificant (P = 0.21). Because sulfentrazone phytotoxicity was found to be soil dependent, the efficacy of sulfentrazone for weed control and sulfentrazone potential carryover injury will vary with soil type in the Canadian prairies.

The biology of Canadian weeds. 65. Salsola tragus L. (updated)

This account updates that published by Crompton and Bassett in 1985 (classified then as Salsola pestifer A. Nels.). The taxonomy of this species has been controversial and confusing. Salsola tragus is an annual broadleaf weed species native to Eurasia and inadvertently introduced to the Americas in crop seed in 1873. This naturalized species is a common and economically important weed in crop production systems and non-cropped disturbed areas in semiarid to arid regions of western North America; in eastern North America, S. tragus commonly occurs along roadsides, railways, and other dry, stony, and sandy areas. Pollen-mediated gene flow and efficient seed dispersal aids both short- and long-distance spread. As a C4 species, S. tragus is highly competitive in semiarid and arid small-grain cropping systems because of its ability to emerge early, efficiently extract soil available water by its extensive root system, and tolerate heat, drought, and salinity. Moreover, the evolution of acetolactate synthase-inhibitor resistance has impacted herbicidal control of the species. The weed has been used as an emergency forage during drought, and is palatable when immature and non-toxic to livestock. Key words: Salsola tragus, Salsola pestifer, Salsola iberica, Salsola kali, Russian thistle, weed biology

The biology of Canadian weeds. 138. Kochia scoparia (L.) Schrad.

Kochia [Kochia scoparia (L.) Schrad.] is an annual broadleaf weed species native to Eurasia and introduced as an ornamental to the Americas by immigrants in the mid- to late 1800s. Although sometimes categorized in the genus Bassia, there is no compelling reason for this classification. This naturalized species is a common and economically important weed in crop production systems and ruderal areas in semiarid to arid regions of North America, and has expanded northward in the Canadian Prairies during the past 30 yr. Although primarily self-pollinated, substantial pollen-mediated gene flow and efficient seed dispersal aids both short- and long-distance spread. The weed is morphologically highly variable, and its growth and development are markedly affected by environmental conditions. Kochia, a C4 species, is highly competitive in cropping systems because of its ability to germinate at low soil temperatures and emerge early, grow rapidly, tolerate heat, drought and salinity, and exert allelopathic effects on neighboring species. Moreover, herbicidal control has been compromised to some extent by the widespread evolution of herbicide resistance in the species. Kochia is used as a forage, is palatable to livestock with nutritional value similar to that of alfalfa (Medicago sativa), but can be toxic if it comprises the majority of the diet. Although kochia pollen is an allergen, the seed is a source of phytochemicals including mosquito pheromones and saponins that are potentially beneficial to human health; kochia also is beneficial in phytoremediation of soils contaminated by hydrocarbons or pesticides. Key words: Kochia, Kochia scoparia, Bassia scoparia, herbicide resistance, soil salinity tolerance, weed biology

Seed Germination and Seedling Emergence of Nalta Jute (Corchorus olitorius) and Redweed (Melochia concatenata): Important Broadleaf Weeds of the Tropics

Abstract Nalta jute and redweed are widespread and significant broadleaf weed species of the tropics. Experiments were conducted to determine the effects of various environmental factors on seed germination and seedling emergence of these species. Light was not required for germination in either species. Germination was stimulated by seed scarification, suggesting that inhibition of germination in these species is mainly due to the hard seed coat. Scarified seeds of both species germinated over a wide range of alternating temperatures (25/15, 30/20, and 35/25 C). Both species were moderately tolerant of salt and osmotic stress, but nalta jute tolerated more stresses than redweed. Seedling emergence of nalta jute and redweed was greater than 87 and 93%, respectively, at soil depths of 0 to 2 cm but decreased as depth increased, with no emergence at 8 cm. Seedling emergence of both species was reduced by the addition of rice straw, though a high amount (4 to 6 t ha−1) of straw was required to suppress emerg...

A Unique Formulation of Glyphosate in the Acid Form

Abstract Glyphosate is a broad-spectrum herbicide effective on deep-rooted perennial species and on annual and biennial species of grasses, sedges, and broadleaf weeds. The solubility of glyphosate acid is relatively low in water, 12 g/L (25°C). Since glyphosate is an acid, however, numerous water-soluble salts can be formed. Recently, formulations have been developed that avoid the need to make salts. Instead, the glyphosate is presented in the acid form. Unlike traditional glyphosate salt formulations, that need surfactants to enhance their uptake, the acid formulation of HM-2028 does not rely on reduced surface tension or other surfactant effects to provide excellent uptake and herbicide efficacy.

Defining the Rate Requirements for Synergism Between Mesotrione and Atrazine in Redroot Pigweed (Amaranthus Retroflexus)

Joint action of the effects of atrazine and mesotrione can lead to synergistic herbicidal activity in broadleaf weed species. The objective of these experiments was to determine if specific rates are required to provide synergistic joint activity between mesotrione and atrazine in both triazine-sensitive (TS) and triazine-resistant (TR) redroot pigweed. Herbicide rates were evaluated in TS and TR redroot pigweed in two experiments: a dose response of mesotrione alone and in mixture with a constant rate of atrazine and a dose response of atrazine alone and in mixture with a constant rate of mesotrione. Results from these experiments revealed that synergism was detected in the TS pigweed when 56 g ai ha−1 mesotrione was mixed with 126 g ai ha−1 atrazine. In the TR pigweed, synergism was detected when mesotrione rate at 10 to 56 g ha−1 was mixed with a constant rate of atrazine at 126 g ha−1. Additionally, when mesotrione was held constant at 10 g ha−1, synergism was detected in mixture with atrazine from 31 to 3556 g ha−1 in TR pigweed. Furthermore, in TR pigweed, analysis of slope deviation across the dose-response curves of mesotrione with and without atrazine revealed a divergence that increased in magnitude as the rate of mesotrione increased. In other words, increased synergism was observed with increased mesotrione rate in the TR pigweed, which was also supported by biomass reduction and atrazine-like injury to the leaves. An additional experiment investigated synergism between mesotrione and bromoxynil in both TS and TR pigweed. Mesotrione at 10 g ha−1 was synergistic when paired with bromoxynil from 70 to 210 g ha−1 in both the TS and the TR pigweed.

RESPOSTA DE CULTIVARES DE SOJA À COMPETIÇÃO COM CULTIVAR SIMULADORA DA INFESTAÇÃO DE PLANTAS CONCORRENTES

As perdas de produtividade de uma cultura devido à competição variam de acordo com a(s) espécie(s) de planta(s) daninha(s) envolvida(s) e tendem a ser mais elevadas quanto mais semelhantes forem as espécies em competição, pois essas tenderão a usufruir dos recursos do meio a partir do mesmo nicho ecológico. O objetivo deste trabalho foi definir a resposta das cultivares de soja “IAS 5” e “Fepagro RS-10”, quando submetidas ao incremento de densidade da cultivar “Cobb”, simulando espécie daninha dicotiledônea. Para isso, foi conduzido um experimento em campo em Eldorado do Sul - RS. Os fatores e tratamentos utilizados foram: cultivares de soja (IAS 5 e Fepagro RS-10) e densidades da simuladora (Cobb), mais uma testemunha sem sua presença. As densidades de Cobb variaram de 5 a 36 plantas m-2. Os dados de perdas percentuais de produtividade das cultivares foram ajustados ao modelo de regressão não linear da hipérbole retangular. O modelo da hipérbole estimou em 6,8 e 5,9%, respectivamente, as perdas de produtividade sofridas por IAS 5 e Fepagro RS-10 quando a densidade da simuladora de plantas concorrentes se aproxima de zero. Constatou-se que a competição entre plantas de mesma espécie é elevada, uma vez que a presença de poucos indivíduos causa redução importante na produtividade de grãos. Cultivar de soja portadora de baixa estatura é afetada em maior grau pelo estresse competitivo imposto por plantas competidoras de estatura elevada.

Management of warm-season grass mixtures for biomass production in South Dakota USA

Switchgrass ( Panicum virgatum L.), big bluestem ( Andropogon gerardii Vitman), and indiangrass ( Sorghastrum nutans (L.) Nash) are native warm-season grasses commonly used for pasture, hay, and conservation. More recently switchgrass has also been identified as a potential biomass energy crop, but management of mixtures of these species for biomass is not well documented. Therefore, the objectives of our study were to: (1) determine the effects of harvest timing and N rate on yield and biomass characteristics of established warm-season grass stands containing a mixture of switchgrass, big bluestem, and indiangrass, and (2) evaluate the impact of harvest management on species composition. Five N rates (0, 56, 112, and 224 kg ha −1 applied annually in spring and 224 kg ha −1 evenly split between spring and fall) and two harvest timings (anthesis and killing frost) were applied to plots at two South Dakota USA locations from 2001 to 2003. Harvesting once a year shortly after a killing frost produced the greatest yields with high concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) along with lower concentrations of total nitrogen (TN) and ash. This harvest timing also allowed for the greatest percentage of desirable species while maintaining low grass weed percentages. While N rates of 56 and 112 kg ha −1 tended to increase total biomass without promoting severe invasion of grass and broadleaf weed species, N application did not always result in significant increases in biomass production. Based on these results, mixtures of switchgrass and big bluestem were well suited for sustainable biomass energy production. Furthermore, N requirements of these mixtures were relatively low thus reducing production input costs.

Leaf Appearance Base Temperature and Phyllochron for Common Grass and Broadleaf Weed Species

Base temperature (Tb) for leaf appearance and the thermal time interval between appearance of successive leaves (phyllochron) were determined for six common weed species from a series of growth chamber experiments. Mean leaf appearance Tbvalues for giant ragweed, velvetleaf, redroot pigweed, large crabgrass, woolly cupgrass, and wild-proso millet were 1.3, 8.0, 8.5, 4.5, 2.2, and 5.1 C, respectively, and mean phyllochron values were 37.2, 34.4, 17.3, 42.2, 65.2, and 34.2 growing degree-days per leaf, respectively. Phyllochron values increased slightly with mean temperature for each weed species. To our knowledge, these are the first reported leaf appearance Tband phyllochron values for giant ragweed, woolly cupgrass, and wild-proso millet. The results confirm leaf appearance Tband phyllochron values reported previously for velvetleaf and redroot pigweed. However, large crabgrass leaf appearance Tband phyllochron values in our study varied somewhat from those reported previously. The results provide information needed for parameterization of plant growth models that predict leaf development based on thermal time.

Cropping systems alter weed seed banks in Pacific Northwest semi-arid wheat region

Arable land weed seed banks are dynamic and reflect cropping history, current management, and environment. Changes in crop rotation and tillage system can alter weed seed density and species composition. In the semi-arid region of the Pacific Northwest, USA, no-till spring cropping is being studied as an alternative to the traditional winter wheat (Triticum aestivum L.)/dust-mulch fallow (WWF) rotation. Weed seed bank density and species composition were assessed during the first 6 years of an ongoing cropping system study comparing WWF with three no-till rotations; spring wheat (Triticum aestivum L.)/chemical fallow (SWF), continuous spring wheat (CSW), and spring wheat/spring barley (Hordeum vulgare L.) (SWSB). Soil cores were collected at depths of 0–8, 8–15, and 15–23cm in all plots during August each year following crop harvest. Weed seeds were washed from the soil, dried, and germinated in a glasshouse. Weed species most associated with the 0–8cm depth was Bromus tectorum L., the major winter annual grass weed in WWF. Species most associated with 8–15cm depth was Chenopodium leptophyllum (Moq.) Nut. ex S. Wats, a native warm season broadleaf weed that may have long seed bank persistence. An initial high density of B. tectorum was reduced with no-till spring crops and in WWF with intensive management strategies. In comparison an initial low weed seed density of B. tectorum remained low with no-till but increased in WWF with less management. Broadleaf weed species did not become management problems in no-till; however, seed bank weed shifts occurred where winter annual broadleaf species remained following reduction of high densities of B. tectorum. Summer annual broadleaf weed seeds such as C. leptophyllum and Salsola tragus L. were present but not at high densities. Summer annual grass weed seeds were not present and are not typical in this region. In this research, no-till spring cereal based systems did not result in an increase in total seed density at the soil surface. Results from this research show that no-till spring crop rotations are effective at controlling winter annual grass weeds as well as broadleaf weeds normally associated with WWF.

(220) Pelargonic Acid Weed Control Parameters

Producers and researchers are interested in pelargonic acid (nonanoic acid) as a broad-spectrum postemergence or burn-down herbicide. Pelargonic acid is a fatty acid naturally occurring in many plants and animals, and present in many foods we consume. The objective of this research was to determine the effect of pelargonic acid concentration, adjuvants, and application timing on weed control efficacy as a burn-down herbicide. Field research was conducted at Lane, Okla. (southeast Oklahoma), during the 2005 growing season. One month prior to spraying the weed control treatments, the land was cultivated to kill the existing weeds and provide a uniform seed bed for new weed growth. The factorial weed control treatments included three application concentrations of Scythe (57.0% pelargonic acid) applied at 3%, 6.5%, and 10%; three adjuvants (none, orange oil, and non-ionic surfactant); and two application dates. All herbicide treatments were applied with an application volume of 935 L/ha to seedling weeds. The experiment had a high weed density with multiple species of grass and broadleaf weeds. Weed control across species increased as the herbicide concentrations increased from 0% to 10%. At all concentrations applied, pelargonic acid produced greater weed control for a longer time period for the broadleaf weeds than the grass weeds. Visual damage to the weeds was often apparent within a few hours after application. There was a significant increase in weed control when applied to the younger weeds. In this research, pelargonic acid was effective in controlling both broadleaf and grass weeds as a burn-down herbicide, although crabgrass was tougher to control.

Comparison of Glyphosate Products in Glyphosate-Resistant Cotton (Gossypium hirsutum) and Corn (Zea mays)1

Wide-spread planting of glyphosate-resistant (GR) crops in the United States and glyphosate patent expiration has led to a proliferation of glyphosate products. Growers have questioned their advisors on efficacy and crop tolerance of the many products available. Field experiments were conducted to evaluate eight glyphosate products in 2002 and ten in 2003, representing isopropylamine, diammonium, and potassium salts, applied POST and postemergence-directed (PDIR) at 630 and 1,680 g ae/ha for GR corn and GR cotton tolerance and weed control. There were no differences among products for control of six annual grass and 10 annual broadleaf weed species. No injury to corn from any glyphosate product at 630 or 1,680 g/ha or to cotton from 630 g/ha was noted at any of seven locations. ClearOut 41 Plus™, an isopropylamine salt of glyphosate, and Roundup WEATHERMAX™, a potassium salt of glyphosate, applied POST at 1,680 g/ha injured cotton 27 to 30% and 10 to 17%, respectively, at 3 of 7 locations. No cotton injur...

Weed Control in Pea with Reduced Rates of Imazethapyr Applied Preemergence and Postemergence1

Broad-spectrum weed control options for pea are limited. Field experiments conducted from 1998 to 2000 evaluated reduced rates of imazethapyr for selective control of grass and broadleaf weed species in pea. Imazethapyr was applied preemergence (PRE) and postemergence (POST) at 20, 40, 60, 80, and 100% of the PRE rate of 75 g ai/ha currently labeled in Ontario. A rate of 45 g/ha or greater was required to maintain consistent control of common lambsquarters and wild mustard when imazethapyr was applied PRE. Green foxtail and redroot pigweed control was excellent at all PRE rates 56 d after treatment. The 75-g/ha rate was required to maintain effective and consistent control of common ragweed. No injury or yield reductions were observed for any of the PRE application rates of imazethapyr. Reduced rates as low as 30 g/ha of imazethapyr applied POST maintained high levels of weed control. Pea tolerance to low rates of imazethapyr applied POST was acceptable except when applied in a year of low rainfall when p...

Preemergence Weed Control in Soybean with Cloransulam

Field experiments were conducted from 1999 to 2001 to evaluate preemergence (PRE) activity of cloransulam on broadleaf weed species and to determine the effectiveness of cloransulam as a PRE herbicide in glyphosate-resistant soybean weed management systems. Cloransulam PRE controlled prickly sida, velvetleaf, and morningglory species even at reduced rates (recommended rate 36 g ai/ha) but only suppressed growth of Palmer amaranth, hemp sesbania, and sicklepod. Cloransulam applied PRE provided initial control or suppression of most weeds, but late-season control declined appreciably. Adding metribuzin to cloransulam PRE generally improved control of hemp sesbania, Palmer amaranth, annual grasses, and morningglory species, leading to soybean yield increases. Control of weeds was greater on a silt loam soil compared with a silty clay soil. Delayed herbicide activation by rainfall or irrigation reduced control of hemp sesbania and prickly sida and affected efficacy more than soil texture. Single postemergence (POST) applications of glyphosate or fomesafen plus fluazifop-P provided 90% or less control of most weed species. When glyphosate POST or fomesafen plus fluazifop-P POST followed PRE applications of cloransulam or cloransulam plus metribuzin PRE, control of all weeds was generally greater than 85%. The highest soybean yields were recorded from treatments that contained sequential PRE followed by (fb) POST herbicide applications. Composition of weed flora determined the effect of herbicide program on soybean seed yield. No yield benefit was gained from the sequential program when the dominant species was Palmer amaranth, which was controlled by glyphosate. When hemp sesbania was the dominant species, PRE herbicides fb glyphosate POST increased yield compared with total POST glyphosate.

Weed Seedbank Dynamics in Three Organic Farming Crop Rotations

Weed management is a primary concern of organic farmers. Crop rotation is an important potential management approach for regulating weed seed populations in the soil of organic farming systems. This research was conducted to determine the effect of three organic crop rotations on the weed seedbank during the first 6 yr of a long‐term cropping systems experiment at Beltsville, MD. The rotations consisted of (i) a 2‐yr corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation, (ii) a 3‐yr corn–soybean–wheat (Triticum aestivum L.) rotation, and (iii) a 4‐yr corn–soybean–wheat–red clover (Trifolium pratense L.)/orchardgrass (Dactylis glomerata L.) hay rotation. Weed seed populations were determined by a greenhouse emergence assay using soil samples taken in the early spring of each year. The seedbanks of smooth pigweed (Amaranthus hybridus L.) and common lambsquarters (Chenopodium album L.) preceding corn were usually lower following the hay years of the 4‐yr rotation or the wheat year of the 3‐yr rotation than following the soybean year of the 2‐yr rotation. However, annual grass seedbanks preceding corn tended to be higher following the hay years of the 4‐yr rotation than following the wheat year of the 3‐yr rotation or the soybean year of the 2‐yr rotation. Seedbanks in the 3‐ and 4‐yr rotations were similar to those of the 2‐yr corn–soybean rotation (higher smooth pigweed and common lambsquarters and lower annual grass) when these longer rotations began with a corn–soybean sequence than with other sequences. Sequences beginning with hay had lower smooth pigweed and common lambsquarters seedbank populations than all other sequences. The seedbank in spring significantly predicted weed abundance at maturity in corn in at least 2 of 4 yr for all species. Results show that longer rotations with more phenologically diverse crops can reduce seedbank populations and abundance of important annual broadleaf weed species in organic production systems.

Cloransulam absorption, translocation, and efficacy on common broadleaf weed species

Field and laboratory studies were conducted to evaluate herbicide efficacy, absorption, and translocation of cloransulam within broadleaf weeds. Control of morningglory species and velvetleaf with cloransulam was dependent upon application rate and timing. A reduced rate of cloransulam (9 g ai ha−1) was as effective as the labeled rate (18 g ha−1), when applications were targeted to small to midsize morningglory and velvetleaf. Prickly sida, hemp sesbania, and sicklepod were suppressed by cloransulam. Contour maps predicted accurately weed control for all species except tall morningglory. Cloransulam absorption and translocation provided some information about tolerance mechanisms. Susceptible species, entireleaf morningglory and velvetleaf, both rapidly absorbed14C-cloransulam. Absorption in the more tolerant velvetleaf was 20% lower than entireleaf morningglory at all harvest times. Absorption of14C-cloransulam in prickly sida was only 26% 6 h after treatment, and absorption did not increase with time. Differences in cloransulam absorption and translocation partially explained differences in susceptibility among some weed species but not others.

Evaluation of Organic Herbicides

Cover crops, cultivation, flaming, soil solarization, and mulching are commonly used for weed control in organic production systems. However, several new herbicides, approved by the Organic Materials Review Institute (OMRI), are recommended as contact, non-selective, post-emergence herbicides for annual grasses and broadleaf weeds. Citric acid (Alldown), clove oil (Matran 2), thyme/clove oil (XPRESS) were compared with glyphosate (Roundup Pro), a systemic broad spectrum herbicide, at three sites in southern and north central Florida during September and October, 2003. Treatments varied at each site but included glyphosate (5% a.i. applied to runoff) organic herbicides at recommended rates (undiluted citrus acid at 61 L·ha-1; 10% clove oil at 76 L·ha-1; 10% clove oil/thyme oil at 76 L·ha-1) and at twice recommended concentrations and application rates. Grasses and broadleaf weed species were different at each site but included Alexander grass, bahia grass, Bermudagrass, carpetweed, crabgrass, hairy indigo, lambs quarters, Florida pusley, goatweed, nutsedge, pigweed, shrubby primrose willow, broadleaf signalgrass, southern sandbur, spurge, torpedograss, and citrus rootstock seedlings. Weed control with the organic herbicides at all three sites at recommended and at higher concentrations and rates was inconsistent, ranging from 10% to 40%, compared with 100% control with glyphosate. Labels for the organic herbicides generally specify application to actively growing weeds less than 10 cm tall, emphasizing their use as early season herbicides. Fall applications to larger weeds, some within the specified maturity and size range and others taller and producing seed, could partially explain poor weed control.

Weed Seedbank Comparison in Conservation Reserve Program and Adjacent Fields Under Continuous Cultivation1

In 1998, 1,260 soil samples were collected from 63 of 99 Iowa counties to characterize the weed seedbanks in fields under the conservation reserve program (CRP) and adjacent fields under continuous cultivation. Five annual grass and 13 broadleaf weed species were identified in both the CRP and adjacent cultivated fields. Seedbank differences between CRP and adjacent cultivated fields were evident only for foxtails, common lambsquarters, pigweeds, and sweetclover, with the average of 3,288, 10,681, 38, and 1,709 seeds/m2, respectively; the corresponding seed population in adjacent CRP fields was 59, 57, 1,924, and 74%, respectively. However, weed species diversity was not significantly different between fields in CRP and continuous cultivation. Only CRP fields in the northwest Iowa crop-reporting district had a higher foxtail species seed population (4,915 seeds/m2) than the adjacent cultivated fields (1,782 seeds/m2). Land under CRP in northern (N), eastern, and southern (S) districts had 58% (4,158 seeds...

Discrimination of weed seedlings, wheat ( Triticum aestivum) stubble and sunflower ( Helianthus annuus) by near-infrared reflectance spectroscopy (NIRS)

The potential of using near-infrared reflectance spectroscopy (NIRS) to discriminate between seven broadleaf weed species, sunflower and wheat stubble was evaluated. Our results showed that the spectral window between 750 and 950 nm, which corresponds to near-infrared wavelength, was able to discriminate among wheat stubble, sunflower and the most problematic “hard-to-control” weeds in no-till sunflower, i.e. Little mallow ( Malva parviflora L.) and Ecballium elaterium L. These results are promising for further work in real-time remote sensing identification of weed patches in sunflower fields.