Efficacy of 1,3-dichloropropene plus chloropicrin application methods in combination with pebulate and napropamide in tomato

Small-plot research and large-field validations were conducted to determine the effect of 1,3-dichloropropene (1,3-D)+chloropicrin (Pic) application methods in combination with the herbicides pebulate and napropamide on pest control in fresh market tomato (Lycopersicon esculentum Mill.). In both the small-plot trials and the large-validation fields, various treatments compared the efficacy of soil fumigants and herbicides based on methyl bromide, in-bed and broadcast applications of 1,3-D+Pic, pebulate, and napropamide. The results consistently indicated that either in-bed or broadcast applications of 1,3-D+Pic in combination with pebulate and napropamide are equally effective against the weed Cyperus spp., the nematodes Tylenchorhynchus spp., Belonolaimus longicaudatus, and Meloidogyne spp., and the soilborne disease Fusarium oxysporum f.sp. lycopersici in fresh market tomato. Therefore, broadcast 1,3-D+Pic application can reduce personnel exposure and poisoning risks, without losing pest control efficacy.     

Effects of sulfosulfuron soil residues on barley (Hordeum vulgare), sunflower (Helianthus annuus) and common vetch (vicia sativa)

The phytotoxicity and sensitivity of succeeding crops to the new sulfonylurea, sulfosulfuron, have been reported although there is insufficient data on the phytotoxic effect of field soil residues. Growth chamber bioassays were conducted to detect the presence of residues in soil samples previously treated with sulfosulfuron at the recommended rate and double rate (20 and 40 g a.i./ha) that could affect the succeeding crop. Soil samples were collected between 7 and 9 months after sulfosulfuron application in field selectivity assays at nine different locations in Northern and Central Spain. The bioassay test species were barley (Hordeum vulgare L.) ‘Graphic’, sunflower (Helianthus annuus L.) ‘Albasol’ and common vetch (Vicia sativa L.) ‘Neska’, typical crops grown in rotation with wheat (Triticum aestivum L.) in this area. Sulfosulfuron residues did not affect barley and common vetch, but inhibited shoot length, root length and root dry weight of sunflower seeded into some soils treated with the 2× rate (40 g a.i/ha) 9 months earlier.     

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.     

A real-time PCR assay for the detection of azoxystrobin-resistant Alternaria populations from pistachio orchards in California

Azoxystrobin-resistant populations of Alternaria spp. in the alternata, tenuissima, and arborescens species–groups, the causal agents of Alternaria late blight of pistachio, have been selected in pistachio orchards in California. The azoxystrobin resistance in Alternaria spp. was found to be correlative to a single point mutation resulting in the replacement of a glycine by an alanine at codon 143 (G143A) in the mitochondrial cytochrome b (cyt b) gene. Based on this point mutation, a real-time PCR method was developed to rapidly detect azoxystrobin-resistant Alternaria populations in field leaf samples collected from pistachio orchards in California.     

Methyl bromide alternatives for weed and soilborne disease management in tomato (Lycopersicon esculentum)

Two field trials were conducted to examine the efficacy of methyl bromide (MBr) alternatives in the control of Cyperus rotundus L. (purple nutsedge) and Fusarium oxysporum Schlecht. f.sp. lycopersici (Sacc.) Snyder & Hansen (Fusarium wilt) in fresh market tomato (Lycopersicon esculentum Mill.). Various treatments compared combinations of soil fumigants and herbicides based on methyl bromide, chloropicrin, 1,3-dichloropropene, metam sodium, dazomet, and pebulate. The data show that consistently 1,3-dichloropropene plus chloropicrin at both doses in combination with the herbicide pebulate can be considered alternatives to methyl bromide in fresh market tomato. These treatments had excellent purple nutsedge and Fusarium wilt control, and marketable tomato yields were similar to that for methyl bromide plus chloropicrin.     

Aerial treatment of the migratory locust, Locusta migratoria (L.) (Orthoptera: Acrididae) with Metarhizium anisopliae (Deuteromycotina: Hyphomycetes) in Australia

Between November 1998 and March 1999, bands of nymphs of Locusta migratoria were aerially treated using a ULV oil formulation of strain FI-985 of Metarhizium anisopliae var. acridum. At a dose of 3–4×10¹² conidia/ha, there was <10% survival of locusts in treated sorghum crops, open grassland or open woodland with grass. Decline was less at lower doses or in dense woodland. During the first week after treatment, bands showed little change in numbers, but then rapidly declined in size and rate of movement. The decline was slower where vegetation was tall or dense, or where bands were large and moved out of the treated area a few days after spraying. In areas where bands were treated with Metarhizium, populations were suppressed in that few adult swarms formed. Adjacent untreated areas had many adult swarms which had to be controlled using chemical insecticides. Preventive locust control, as currently practised in Australia, involves beginning treatment when areas of band and swarm are small and the potential for direct damage limited. The clear demonstration that Metarhizium can suppress small local populations of L. migratoria indicate that it could be a valuable component of preventive control programmes against this species. The delay in mortality when treating with Metarhizium would be no impediment to its use in such programmes.     

Soil-applied herbicide use in wide- and narrow-row glyphosate-resistant soybean (Glycine max)

A field study was conducted in 2001 and 2002 at Blackville, SC, to compare the effectiveness of soil-applied herbicide programmes followed by glyphosate with sequential glyphosate applications in 19- and 97-cm row soybean. Treatments included pre-emergence applications of flumetsulam, chlorimuron plus sulfentrazone, metribuzin, or flumioxazin all applied with S-metolachlor with a subsequent application of glyphosate applied 5 wk after soybean planting (WAP). Additional treatments included sequential applications of glyphosate at 3 and 5 WAP and a non-treated control. Weed control was comparable in wide and narrow rows, and soil-applied herbicides were similar to sequential glyphosate applications in either row width. Amaranthus palmeri S. Wats., Digitaria sanguinalis (L.) Scop., and Cyperus rotundus L. control with all herbicides was 98–100%. All herbicide programmes provided at least 92% Ipomoea hederacea var. integriuscula Gray and I. lacunosa L. control. S-metolachlor plus flumetsulam followed by glyphosate provided 99% Senna obtusifolia (L.) Irwin and Barneby control, which was superior to the 88% and 90% obtained with chlorimuron plus sulfentrazone and metribuzin programmes, respectively. Flumioxazin and sulfentrazone caused up to 12% soybean injury. In 2001, soybean yields and gross profit margins were similar for soil-applied programmes followed by glyphosate and sequential glyphosate applications in wide and narrow rows. Conversely, soybean yields and profit margins in 2002 averaged across soil-applied programs were 380 kg/ha and $50/ha superior to sequential glyphosate applications in wide rows, but were similar in narrow rows. This research indicates a highly efficacious soil-applied herbicide program followed by glyphosate provides similar weed control to sequential glyphosate applications in wide- and narrow-row soybean; however, a soil-applied herbicide programme followed by glyphosate may improve yields and returns of wide-row soybean over sequential glyphosate applications alone.     

Overwintering and population dynamics of Bemisia tabaci biotype B in greenhouse during the spring in northern China

Since the sweetpotato whitefly, Bemisia tabaci (Gennadius) biotype B invaded southern China in the mid-1990s, it had spread to most other regions of the country, and become an important pest in agricultural and horticultural production. Investigations on overwintering of B. tabaci biotype B and its spring reproduction in northern China were conducted to determine the main factors that might contribute to an understanding of the population dynamics of this pest for developing improved pest control strategies. A cold hardiness test showed that when exposed for 10 h at −10 °C, mortalities of eggs, nymphs, and adults reached to 86.6%, 88.4%, and 100%, respectively, suggesting that it is probably impossible for feral populations of B. tabaci to survive in the winter under natural environmental conditions in northern China. A survey on vegetables, ornamental plants and weeds in greenhouses at Hebei Province and Beijing in northern China revealed at least 14 species of plants on which B. tabaci fed during the winter and spring. Lycopersicon esculentum Mill, Brassica alboglabra Bailey, Ficus carica L., Euphorbia pulcerrima Wild, and Hemelia patens Haence were the main host plants. Further research on the population dynamics of B. tabaci on three major greenhouse hosts; tomato, cucumber, and melon, indicated that densities remained at a low level during the winter, but increased steadily from February to March until migration into field crops in April. It is concluded that the control of the insect in greenhouse in winter and spring can play an important role for seasonal management of this pest in northern China.     

Comparing weed and crop seedling response to pre-emergence pendimethalin application in Corchorus olitorius and Abelmoschus esculentus

Field experiments and bioassay tests were carried out to evaluate the relative response of the crops, tossa jute (Corchorus olitorius L.) and okra [Abelmoschus esculentus (L.) Moench], and their associated weeds to pre-emergence application of pendimethalin at 0.33, 0.66, 0.99, 1.32 kg ai ha⁻¹ and a pendimethalin+atrazine tank mixture at 1.32+2.05 kg ai ha⁻¹. Bioassay tests were carried out using herbicide solutions of corresponding concentrations and herbicide-treated soil. Field application of pendimethalin at 0.66 kg ai ha⁻¹ and the herbicide mixture in both crops effectively controlled most seedling weeds including Rottboellia cochinchinensis. Euphorbia heterophylla and Calopogonium mucunoides, which persisted from 2 weeks after treatment (WAT) were not controlled. Herbicide application during crop establishment markedly inhibited the growth of both seedling weeds and crops. The mixture caused the highest weed and crop injury. Pendimethalin at 0.33 kg ai ha⁻¹ had minimal effect on these crops. Weed growth, weed tolerance of herbicide treatment and crop seedling injury were higher in tossa jute than that in okra, under the conditions of this study. The use of low pendimethalin doses in an integrated weed management system will ensure effective control of seedling weeds, and prevent crop injury and residue accumulation in edible plant produce.     

Algicidal effect of 3-(3-indolyl)butanoic acid, a control agent of the bacterial wilt pathogen, Ralstonia solanacearum

The chemical control agent 3-(3-indolyl)butanoic acid, previously reported as a control agent for the bacterial wilt pathogen Ralstonia solanacearum, was shown to suppress the growth of green algae during hydroponic culture of tomato. The algicidal activity of the compound was effective at 10 μg/ml, completely preventing generation of green algae under non-shaded greenhouse conditions. The algicidal effect was mainly due to suppression of the growth of motile unicellular algal cells tentatively identified as Chlamydomonas spp., which are commonly occurring in the hydroponic solution and vigorously multiply to form an algal mat on the sponge supports. The compound has potential as a non-phytotoxic algicide for hydroponically cultured crop plants.     

Control of Bromus species in winter barley in England using EPTC

EPTC was tested in glasshouse and field experiments for its potential as a herbicide to control Bromus species in winter cereals. Bromus hordeaceus, Bromus commutatus, Bromus pectinatus and Bromus sterilis were all selectively controlled in barley by EPTC. Winter wheat was found to be susceptible but winter barley tolerated doses up to 2·0 kg a.i./ha. The barley cultivar Sonja was more resistant than both Athene and Maris Otter. In the first field trial, 1·0 kg a.i./ha EPTC reduced B. sterilis plant numbers by 75% giving a barley yield increase of 2·84 t/ha. In the following year 2·0 kg a.i./ha reduced B. sterilis numbers by 54% and increased yield by 1·75 t/ha.     

Cotton leaf trichomes and populations of Empoasca lybica and Bemisia tabaci

Breeding cotton, Gossypium spp., for resistance to leafhoppers of the genus Empoasca and to sweetpotato whitefly, Bemisia tabaci (Gennadius), poses a dilemma. Glabrous (smooth-leaved) cotton plants have higher leafhopper populations but fewer whiteflies and less leaf and bract trash in mechanically harvested seedcotton than plants with pubescent leaves. In this study, both leafhopper and whitefly populations were observed in 31 cotton entries planted at Bet She'an, Israel, in 1987. Leafhopper populations decreased but the whitefly populations increased as the number of trichomes increased. At the end of June, plants with 40 trichomes per 13.7 mm² supported relatively low populations of both leafhoppers and whiteflies. However, the whitefly populations increased later in the season to 43 times the earlier population levels. Whitefly populations increased as the number of trichomes increased up to 70 trichomes per 13.7 mm² and then decreased as the trichomes became more dense. Various control measures and breeding schemes that might interact to provide an answer to the control of these pests are discussed.     

Interactions between glyphosate and imazethapyr on four annual weeds

Greenhouse and field experiments were conducted to evaluate the efficacy of various combinations of imazethapyr (0, 23, 46, and 70 g ai/ha) with glyphosate (0, 210, 420, 630, and 840 g ae/ha) on Setaria faberi, Amaranthus rudis, Abutilon theophrasti, and Ipomoea hederacea control. Additivity was the most frequently observed interaction and no synergistic interaction occurred throughout this study. The combination of imazethapyr with glyphosate at 210 g/ha caused an antagonistic response on Setaria faberi. Glyphosate at 420 g/ha with or without imazethapyr provided at least 95% control of Setaria faberi. The interaction between glyphosate and imazethapyr was additive on Amaranthus rudis control. Eight of the twenty-one herbicide combinations were antagonistic on Abutilon theophrasti control. Antagonistic interactions occurred when 46 or 70 g/ha of imazethapyr was added to 420 or 630 g/ha of glyphosate; while no antagonistic interactions were noted when glyphosate rate was 840 g/ha. The interactions on Ipomoea hederacea control were additive when the glyphosate rate was at least 420 g/ha. Glyphosate at 210 g/ha plus imazethapyr at 46 or 70 g/ha caused antagonistic interactions on Ipomoea hederacea control. Weed control tended to be more variable when the glyphosate rate was 210 g/ha and the imazethapyr rate was 46 or 70 g/ha. In general, the addition of imazethapyr to low rates of glyphosate improved control of Amaranthus rudis and Ipomoea hederacea and did not improve control of Setaria faberi and Abutilon theophrasti.     

Treatment decisions based on egg scouting for tomato fruitworm, Helicoverpa zea (Boddie), reduce insecticide use in tomato

Field experiments were conducted to evaluate the effectiveness of a tomato fruitworm, Helicoverpa zea (Boddie), management program where insecticide application was made only when fruitworm eggs were detected on tomato foliage. Fruit damage and number of insecticide applications were compared between the egg scouting program and a standard fruitworm management program where insecticides were applied on a weekly schedule. On average, 59 and 43% fewer insecticide applications (for esfenvalerate and Bacillus thuringiensis, respectively) were required in the egg scouting program, compared with the weekly spray program, without any reduction in marketable yield. The average seasonal insecticide cost savings associated with the use of the egg scouting program were $US109.33 and $US93.33 per ha for esfenvalerate and B. thuringiensis, respectively. When scouting was used, average net returns, considering machinery and labor costs, were $US146.45 and $US164.33 per ha higher for esfenvalerate and B. thuringiensis, respectively.     

Evaluation of Allorhogas pyralophagus Marsh (Hymenoptera: Braconidae) for the biological control of Diatraea spp. (Lepidoptera: Pyralidae) in sugar-cane in Guyana

In 1989, a mass production and field release programme of Allorhogas pyralophagus Marsh (Hymenoptera: Braconidae) for the control of the Diatraea spp., particularly D. centrella (Möschler) (Lepidoptera: Pyralidae) in sugar-cane, was initiated by the Guyana Sugar Corporation. The programme was terminated in 1995 after the release of approximately two million adult parasites resulted in a mean field parasitism in Diatraea spp. larvae of only 0.22%. In contrast, 62% of Diatraea spp. larvae were parasitised in vitro as were 32% of larvae in young cane shoots exposed to A. pyralophagus in the laboratory. Neither Diatraea larvae in young cane plants caged in the field nor those recovered from Echinochloa polystachya (Kunth) Hitchc. and Paspalum virgatum L. around release fields showed any parasitism by A. pyralophagus. The reasons for the low rate of host acquisition outside the laboratory are not known, but it is clear that A. pyralophagus offers little prospect for significant control of Diatraea spp., particularly D. centrella in sugar-cane in Guyana.     

Screening of allelochemicals on barnyardgrass (Echinochloa crus-galli) and identification of potentially allelopathic compounds from rice (Oryza sativa) variety hull extracts

Experiments were conducted to screen 23 known allelochemicals, including sinapic acid, and an equimolar mixture of the chemicals for potential allelopathy on barnyardgrass (Echinochloa crus-galli var. oryzicola), and to identify allelochemical(s) from hull extracts from three rice (Oryza sativa L.) cultivars. In a bioassay, the inhibitory effect was increased as the concentration of allelochemicals increased from 10⁻⁵ to 10⁻³ M. Ferulic, p-hydroxybenzoic, p-coumaric, and m-coumaric acids were the most active compounds and caused the greatest effect on seed germination, germination rate, and total seedling dry weight reduction. p-hydroxybenzoic acid (10⁻³ M; pH 4.1) showed the greatest inhibitory effect on the same parameters. HPLC analysis using three rice cultivars, Janganbyeo, Baekambyeo, and Labelle, showed that the concentration and composition of potentially allelopathic compounds depended upon the cultivar. Hull extracts from the allelopathic cultivar Janganbyeo contained higher levels of p-hydroxybenzoic acid than did those of the non-allelopathic cultivars Labelle and Baekambyeo. Nine compounds, including p-hydroxybenzoic acid (4.29 mg/g) in Janganbyeo, seven compounds including m-coumaric (0.43 mg/g) in Labelle, and five compounds including p-hydroxybenzoic acid (0.36 mg/g) in Baekambyeo, were detected. Preliminary identification by HPLC analysis resulted in peaks with retention times near those of standards, including p-hydroxybenzoic acid that was confirmed with EI/MS. It is suggested that these compounds may be, at least, a key factor in rice allelopathy on barnyardgrass, and the information presented may contribute to the development of naturally occurring herbicides.     

Yield responses of garlic (Allium sativum L.) to oxadiazon, date of planting and intra-row spacing under irrigation at Kadawa, Nigeria

Field experiments were conducted in the 2002/2003 and 2003/2004 dry seasons at the Irrigation Research Station of the Institute for Agricultural Research, Kadawa (11°39′N, 38°02′E, 500 m above sea level) in the Sudan Savanna Ecological Zone, Nigeria to study the effects of oxadiazon, date of planting and intra-row spacing on yields of garlic (Allium sativum L.) under irrigation at Kadawa, Nigeria. A uniform inter-row spacing of 15 cm was maintained in the two seasons. The results obtained showed that the hoe-weeded plots and application of oxadiazon at 1.5 and 2.0 kg a.i./ha resulted in comparable but significantly higher bulb yield per hectare, bulb diameter, bulb weight and number of cloves than oxadiazon at l.0 kg a.i./ha and unweeded check. Bulb yield per hectare, bulb diameter, bulb weight and number of cloves were higher at early November planting. Planting garlic at 5 cm intra-row spacing resulted in higher bulb yield in both seasons.     

Integration of Pseudomonas fluorescens and acibenzolar-S-methyl to control bacterial spot disease of tomato

Xanthomonas axonopodis pv. vesicatoria was isolated from infected tomato seedlings grown in an open field in Egypt. All the tested isolates infected tomato plants but with different degrees of disease severity. In an attempt to manage this disease, tomato seeds and/or seedlings were treated with an antagonistic local isolate of Pseudomonas fluorescens as a suspension or its formulation or acibenzolar-S-methyl (BTH). When the above three treatments were applied to tomato seeds under laboratory conditions, they improved seed germination and seedlings vigour relative to control seeds treated with sterile distilled water and pathogen but P. fluorescens culture was the most effective. Under greenhouse and field conditions, combinations of the above treatments were used. All treatments significantly reduced disease severity of bacterial spot in tomato relative to the infected control. The biggest disease reduction compared to seedlings inoculated with the pathogen alone resulted from a foliar application of P. fluorescens. Combined application of P. fluorescens or its formulation with BTH reduced the pathogen population and increased seedling biomass and tomato yield relative to control seedlings.     

Toxicity of Acorus calamus rhizome powder from Eastern Nepal to Sitophilus granarius (L.) and Sitophilus oryzae (L.) (Coleoptera, Curculionidae)

Powders prepared from sweetflag Acorus calamus rhizomes collected at both high (1700 m) and low (900 m) altitude in Eastern Nepal were admixed with wheat at concentrations in the range 0.05–2% w/w and the wheat infested with Sitophilus oryzae or S. granarius adults. Following a 7 day incubation, the mortality of both species was significantly lower at 20 °C than at 30 °C, and the material collected from high altitude was slightly less toxic than that from low altitude. The moisture content of the wheat (14 or 17%) and the part of the rhizome used to prepare the powder (young or mature growth) had no apparent effect on the toxicity of the preparation. Sitophilus granarius (L.) adults were more tolerant of the material than S. oryzae (L.), while the converse was true for larvae developing in treated grain. An admixture rate of approximately 2% w/w admixed rhizome powder was required to give complete kill of adults of both species following 7 days exposure at 20 °C, while a concentration of 1% w/w either prevented the emergence of adults or killed them rapidly following emergence when wheat containing eggs of either species was incubated for 7–8 weeks at 30 °C.

The β-asarone content of the rhizome powders was determined by GC-MS as 6.4 and 4.7% w/w (mature section of rhizomes collected at high and low altitudes, respectively) and 3.6 and 4.0% w/w (young sections of rhizomes collected at high and low altitudes, respectively). It is anticipated that, under field conditions and in the temperature range 20–30 °C, the initial residue of approximately 1300 mg/kg β-asarone required to disinfest wheat containing these weevil species would decline rapidly due to evaporation.     

Sclerotinia and Phomopsis — two devastating sunflower pathogens

Cultivated sunflower (Helianthus annuus L.) is prone to many diseases caused by fungi, bacteria, and viruses, of which the most detrimental are those caused by fungi. Two of the most important fungal pathogens are Sclerotinia and Phomopsis. Within the genus Sclerotinia, both S. minor and S. sclerotiorum cause a basal stalk rot and subsequent wilt of sunflower, with S. sclerotiorum more widely distributed around the world. Sclerotinia sclerotiorum also incites a head rot and mid-stem rot of sunflower. Since Sclerotinia spp. have a very wide host range and can persist in soil as dormant sclerotia for up to 10 years, the pathogens have been extremely difficult to control with either generic resistance or fungicides. The most effective control is the use of long rotations, tolerant hybrids, and sclerotium-free seed. Gray stem spot is a relatively new disease of sunflower first observed in the early 1980s in Yugoslavia and now considered the most devastating sunflower disease in eastern Europe. Symptoms include large stem cankers and subsequent wilt. Phomopsis helianthi has been identified as one incitant of gray stem spot, but another Phomopsis species may also be involved, both in Europe and in the United States. Foliar fungicides can control gray stem spot, but the development of resistant hybrids has been much more cost-effective.