Unsprayed Control Plots Research Articles

Fusarium head blight progression and yield response of bread wheat as affected by fungicides and spray regimes under field condition in southern Ethiopia

Fusarium head blight (FHB) is one of the destructive diseases in wheat-producing areas of the world. Field experiments were conducted during the 2019 main cropping season to determine an economically feasible time of application that consisted of fungicides and spray regimes to reduce FHB pressure and grain yield loss under field conditions at five locations in southern Ethiopia. The study was comprised of two fungicides and spray regimes. Totally seven treatment combinations were designed, including the unsprayed control plots. The field was designed by a randomized complete block design with four replications. Analysis of variance revealed interaction of fungicides and spray regimes significantly (P < 0.001) affected rates of disease progress, disease severity (DS), area under disease progress curve (AUDPC), and yield-related parameters. Lowest (0.0159 units day−1) and highest (0.0694 units day−1) disease progression rates were estimated from the application of Tebuconazole before disease onset and unsprayed control plots, respectively. Application of Tebuconazole before disease onset significantly reduced DS (67.68%), followed by application of Propiconazole + Tebuconazole before disease onset (67.16%) and Tebuconazole after disease onset (65.77%). Moreover, Propiconazole + Tebuconazole and Tebuconazole applications before disease onset considerably reduced AUDPC by 61.38%-days and 58.60%-days, respectively. The highest grain yield (5.02 t ha−1) was recorded from the application of Tebuconazole before disease onset. The grain yield loss of 44.22% was computed on an unsprayed plot compared to the plot protected with the application of Tebuconazole before disease onset. Overall, the application of fungicides' appropriate spray regimes reduces FHB pressure, and consequently, increases grain yields. However, the application of Tebuconazole before disease gave a better monitory advantage over the others. This could be suggested for the producers to manage FHB and enhance wheat production.

Effect of insecticides sprays on the field population of predators in okra crop

Pre-mix insecticide fipronil 4% + acetamiprid 4% SC (750, 1000, 1250 ml ha−1) and three other insecticides viz. emamectin benzoate 5% SG (170 g ha−1), acetamiprid 20% SP (75 g ha−1), pyriproxyfen 5% + fenpropathrin 15% EC (750 ml ha−1) were evaluated for combating pests in okra crop and effect on predators. These insecticides were sprayed twice at 10 days interval. The investigation results showed that predators’ populations decreased sharply after one day of each spray and increased gradually afterwards in subsequent days. However, populations in the sprayed plots at 10 DAS1 (Days after first spray) and 10 DAS2 (Days after second spray) were consistently less than the unsprayed control plots. Sprays of fipronil 4% + acetamiprid 4% SC (750 ml ha−1) caused minimum reduction in predators’ population at 10 DAS2 over pre-treatment (30.28%) and unsprayed control (50.60%) followed by pyriproxyfen 5% + fenpropathrin 15% EC (750 ml ha−1) with respective reductions of 35.56, 55.67% over pre-treatment and unsprayed control, respectively. On the other hand, sprays of fipronil 4% + acetamiprid 4% SC (1000, 1250 ml ha−1), emamectin benzoate 5% SG (170 g ha−1), acetamiprid 20% SP (75 g ha−1) caused 45.07 -49.62 and 55.74 -65.99% reductions in predators’ populations over pre-treatment and unsprayed control, respectively during the same time. In the mean time, the unsprayed control plots recorded overall 74.54% higher population of predators at 10 DAS2 over pre-treatment. By and large, amongst evaluated insecticides, fipronil 4% + acetamiprid 4% SC (750 ml ha−1) and pyriproxyfen 5% + fenpropathrin 15% EC (750 ml ha−1) appeared to be comparatively safer to prevalent predators in okra crop.

Repellency of insecticides and the effect of thiacloprid on bumble bee colony development in red clover (Trifolium pratense L.) seed crops

ABSTRACTThe study intended to compare repellency of three insecticides on bumble bees and honey bees in Norwegian red clover (Trifolium pratense L.) seed crops, and to examine effects of thiacloprid on bumble bee colony development in the field. The repellency study was carried out in a large-scale field trial in SE Norway in 2013. On average for observations during the first week after spraying, 17 and 40% less honey bees (P = .03) and 26 and 20% less bumble bees (P = .36) were observed on plots sprayed with the pyrethroids lambda-cyhalothrin and alpha-cypermethrin, respectively, than on unsprayed control plots. No pollinator repellency was found on plots sprayed with the neonicotinoid thiacloprid. Compared with unsprayed control the seed yield increases were 22% on plots sprayed with thiacloprid vs. 12–13% on plots sprayed with pyrethroids (P = .10). Follow-up studies in 2014–2016 focused on the effect of thiacloprid on bumble bee colony development in commercially reared nests of Bombus terrestris placed into red clover seed crops at the start of flowering. Unsprayed control crops were compared with crops sprayed either at the bud stage or when 18–44% of flower heads were in full bloom. Chemical analyses of adult bumble bees showed that thiacloprid was taken up in bees when crops were sprayed during flowering, but not detected when crops were sprayed at the bud stage. The bumble bees in late-sprayed crops also developed weaker colonies than in unsprayed crops. Dead bees with a high internal concentration of thiacloprid were found in one crop sprayed during the night at 35% flowering. This shows that thiacloprid is not bee-safe if sprayed after anthesis and that spraying has to be conducted at the bud stage to reduce its contamination of nectar and pollen.

Long-term ecological consequences of herbicide treatment to control the invasive grass, Spartina anglica, in an Australian saltmarsh

Invasive plants acting as habitat modifiers in coastal wetlands can have extensive ecological impacts. Control of invasive plants often relies on herbicides, although little is known about subsequent environmental impacts. Studying effects of herbicides on non-target species and long-term cascading consequences may yield insights into the ecology of invasive species by revealing interactions with native species. We conducted a long-term field experiment measuring effects of treating the invasive saltmarsh grass, Spartina anglica, with the herbicide Fusilade Forte®. No changes in sedimentary macrofaunal abundances or species richness, diversity, or assemblages were detected 1–2 months after spraying, despite known toxicity of Fusilade Forte® to fauna. This lack of impact may have been due to low exposure, since the herbicide was taken up primarily by plant leaves, with the small amount that reached the sediment hydrolyzing rapidly. Six months after spraying, however, total macrofauna in treated plots was more than four times more abundant than in unsprayed control plots, due to a fifteen-fold increase in annelids. This population growth correlated with increased sedimentary organic matter in treated plots, likely due to decomposition of dead S. anglica leaves serving as food for annelids. After another year, no differences in macrofauna or organic matter remained between treatments. The indirect effect on annelid populations from herbicide treatment could benefit management efforts by providing greater food resources for wading birds, in addition to improving birds' access to sediments by reducing plant cover. This study shows that an invasive grass can have a significant impact on native fauna through food-web interactions, influenced by herbicide usage.

Bio-efficacy of potassium phosphonate against nut rot disease of areca nut (&lt;em&gt;Areca catechu&lt;/em&gt; L.) in the northern Karnataka of India

Phytophthora arecaea, a causal agent of nut rot disease (koleroga) of areca nut (Areca catechu L.) is one of the major fungal pathogens affecting the crop in the northern Karnataka of India. The estimated loss associated with this disease extends up to 60%. In the endemic regions of India, the disease occurs immediately after the onset of the monsoon rains (June) and prevails till mid-August due to congenial weather conditions. For the effective management of this devastating disease, potassium phosphonate was tried during June and July 2013-2014 at the farmer’s fields. The results revealed that potassium phosphonate applied at the rate of 6.0 ml/L has reduced the per cent disease incidence (PDI) in areca nut (PDI=19.5%), where the results were on par (p&gt;0.05) with metalaxy MZ applied at 2.0 g/L (PDI=16.81%) and Bordeaux mixture applied at 1% (w/v; PDI=18.84%). However, potassium phosphonate at 3.0 ml/L (PDI=43.10%) and 4.5 ml/L (PDI=39.45%) was not effective in reducing the PDI. The maximum PDI of 52.87% was recorded in unsprayed control plots. The highest yields of 26.42 q/h was recorded from the plots sprayed with metalaxy MZ at 2.0 g/L, which is in par (p&gt;0.05) with potassium phosphonate applied at 6.0 ml/L (24.76 q/ha) and Bordeaux mixture at 1% (25.12q/ha). The lowest yield (12.48 q/ha) was recorded from the control (unsprayed) plots.

Field evaluation of a botanical formulation from the milky mangrove Excoecaria agallocha L. against Helicoverpa armigera Hübner. in Abelmoschus esculentus (lady's finger) and Cajanus cajan (pigeon pea)

ObjectiveTo evaluate a formulation from the milky mangrove tree Excoecaria agallocha L. (E. agallocha) against Helicoverpa armigera Hubner (H. armigera). MethodsAbout 3% aqueous ethanolic spray formulation derived from the lipophilic extract of E. agallocha (dry leaf) was evaluated against H. armigera in Abelmoschus esculentus (lady's finger) and Cajanus cajan (C. cajan) (pigeon pea), under field conditions. ResultsOn the 9th day of the 4th spray the larval count in the plot treated with 3% E. agallocha formulation drastically came down to 0.23 larva/plant, compared to 1.63 in the ethanol control plot and 1.60 in the unsprayed plot. Blocks sprayed with 3% E. agallocha formulation yielded 35.8 quintals/hectare (q/ha) of healthy pods compared to Ekalux® (pod yield: 60.7 q/ha), 3% Vijay Neem® (60.22 q/ha), yield plot (6 q/ha) and ethanol control (7 q/ha). In C. cajan, 1% E. agallocha, 3% Nimbecidine® and 0.07% indoxacarb were equally potent in reducing the larval population of H. armigera and the non-target pest Spilosoma obliqua to 0%, from the 9th day (3rd spray). Indoxacarb plot recorded the maximum yield of 16.1 q/ha with 2.4% pod damage. Plots sprayed with 1% E. agallocha yielded 14.7 q/ha with 2.32% pod damage. The effect of 3% Nimbecidine® spray (14.35 q/ha) was comparable to E. agallocha formulation. Unsprayed and ethanol control plots yielded 12.41 and 11.2 q/ha of pods with an average pod damage of 4.7%. ConclusionsE. agallocha formulation was found to be promising for the control of H. armigera, under field conditions.

Germination behaviour of seeds from herbicide treated plants of Chenopodium album L.

The carry-over effect of sub-lethal herbicides was investigated on the germination of seeds collected from surviving Chenopodium album plants, which had received 1/8, 1/8 twice, 1/8 three times, 1/4, 1/2, 1/1 doses of either pre-emergence ioxynil or post-emergence bentazone in a previous onion (Allium cepa) crop. Seeds were also collected from surviving C. album plants, which had received 1/4, 1/2, 1/1 of either pre-emergence pendimethalin, propachlor and linuron, or 1/8, 1/8 twice, 1/8 three times, 1/4, 1/2, 1/1 of post-emergence ioxynil or linuron in a previous leek (Allium porrum) crop. Seeds of surviving plants were collected and tested for germination at temperature of 5, 10, 15, 20 and 25 degrees C. The effect of different temperatures on the total number of germinated seeds was significant. Germination was minimum at low temperatures (5 degrees C or 10 degrees C). Herbicides did not show any effect on germination of C. album and resulted in the same final germination percentage as seeds collected from the unsprayed control plots.

Impact of two Insecticides Used in the Control of the Desert Locust onPsammotermes hybostomaDesneux (lsoptera: Rhinotermitidae) in Niger

The impact of chlorpyrifos ethyl (applied at a rate of 225 g a.i./ha) and fenitrothion (at 450 g a.i./ha), two insecticides commonly used to control desert locusts (Schistocerca gregaria Forskål), on the activity of Psammotermes hybostoma Desneux, a subterranean, wood-eating termite, were assessed in the Tafidet Valley in the Aïr area, during July–December 2005. Termite activity was significantly reduced with chlorpyrifos and fenitrothion compared with unsprayed control plots. Termite activity was most affected 1–30 days (Interval I) after treatment and thereafter for a period up to 60 days (Interval II) . Chlorpyrifos ethyl was the more toxic insecticide, leading to 75 % and 73 % reduction in termite activity during Intervals I and II, respectively. Recovery of the termite population occurred 60 days after treatment, as reflected by resumption of feeding activity. Both insecticides showed no effect on termite activity from 75–90 days after treatment.

Seed production of common bent (Agrostis capillaris) as affected by insecticides and plant growth regulators

The application of insecticides and/or chemical growth regulators for the control of arthropod-induced silvertop (whitetop) and/or lodging in seed crops of common bent (syn. browntop, US: colonial bentgrass, Agrostis capillaris L. syn. A.tenuis Sibth.) ‘Leikvin’ was investigated in 12 on-farm trials laid out according to five different experimental plans in SE Norway from 1993 to 1997. Seed yields on plots sprayed with insecticides were significantly higher than on unsprayed control plots in three out of nine trials; however, these seed yield increases were poorly correlated with silvertop frequencies which varied from 1 to 60% on untreated plots. Differences between various insecticides (two pyrethroids and one organophosphorus compound) and single versus split applications were mostly not significant. While seed yields on plots sprayed with ethephone (‘Cerone’, 0.5 kg a.i. ha−1) were not significantly different from those on unsprayed control plots, chlormequat chloride (‘CCC 750’, 1.0 or 2.0 kg a.i. ha−1 plus surfactant) minimized lodging and increased seed yield by 21% on average for five trials. When chlormequat chloride and the pyrethroid α-cypermethrin were combined in a tank mixture including surfactant at the crop growth stage Z 31-32, the effects of the two products were mostly additive. Based on these results, the application of the growth regulator chlormequat chloride (1.0 kg a.i. ha−1) is now recommended in Norwegian seed production of common bent. Although the effects of insecticides were often not significant, seed growers are further advised to add an insecticide (e.g., α-cypermethrin, 150 g a.i. ha−1) to the growth regulator as a precaution against silvertop, which otherwise seems to appear quite randomly in seed production of common bent.

Herbicide use, productivity, and nitrogen fixation in field pea (Pisum sativum)

Grain legumes grown in low-rainfall (&lt;300 mm per annum) cropping regions of southern Australia have at times failed to provide the rotational benefits observed in other regions, such as improved cereal yields in the season following a legume. ‘In-crop’ herbicides were identified as one possible factor that may have been negatively affecting the legume–rhizobia symbiosis. To test this hypothesis and identify possible mechanisms behind any observed effects, field trials were conducted at Waikerie (South Australia) in 2001, 2003, and 2004. Field pea (Pisum sativum L.) was grown and treated with one of several herbicides 5 weeks after sowing. Crop yellowing, biomass, nodulation, and nitrogen (N2) fixation were assessed 3 weeks after spraying, and biomass, yield, percent nitrogen derived from fixation (%Ndfa), and N2 fixation (2003, 2004) were assessed at the end of the season. Some herbicides stunted plant growth and caused crop yellowing 3 weeks after application; however, none of the herbicides affected N nutrition of peas. Despite this, in 2003, half of the herbicides assessed reduced the %Ndfa by 34–60% relative to unsprayed control plots. Herbicide effects on the measured parameters followed similar trends over each year of the 3-year study. However, effects were rarely significant in 2004 as the trials were primarily affected by low rainfall, indicating that environmental parameters play a key role in determining the severity of herbicide effects on symbiotic N2 fixation. The possible mechanisms behind herbicide-induced damage to the pea–rhizobium symbiosis are discussed, including reduced photosynthetic capacity of plants exposed to herbicides.

Mortality Factors of Eggs of &lt;I&gt;Leptocorisa chinensis&lt;/I&gt; (Hemiptera: Alydidae) in Rice Fields

To clarify factors causing mortality of Leptocorisa chinensis Dallas (Hemiptera: Alydidae) eggs in rice fields, sentinel egg masses were exposed for seven days in two rice, Oryza sativa L. (Poaceae), fields. An insecticide was sprayed to remove natural enemies in one-half of each field before exposing egg masses to predation. An egg mass containing 14 eggs was glued to a plastic label, and 21 egg masses each were placed in the sprayed and unsprayed control plots. During exposure, the number of hatched and missing eggs was observed daily. Egg predators were sampled in the fields before and after insecticide application. After the egg masses were retrieved from the fields, mortality factors of the unhatched eggs were assessed in the laboratory. The mean number of hatched and missing eggs was not significantly different between the sprayed and control plots in field A. In field B, however, the numbers were significantly different. The percentage of missing eggs in damaged egg masses ranged from 80 to 100%. In the laboratory, we observed that feeding marks caused by the grasshopper Conocephalus chinensis (Redtenbacher) were similar to those on the eggs exposed in the rice fields. The density of C. chinensis was low in control plots of field A. In contrast, the density was high in those of field B. These observations suggest that the density of egg predators, e.g., C. chinensis, is a mortality factor of L. chinensis eggs in rice fields.

Optimum timing and placement of a supplementary food spray Envirofeast® for the establishment of predatory insects of Helicoverpa spp. in cotton systems in Australia

Investigations to determine the optimum timing and placement of a supplementary food spray, Envirofeast® on the abundance of predatory insects on cotton was conducted in irrigated commercial cotton fields at Yarral near Narrabri, New South Wales, Australia, in 1998 v - v 99. Plots treated with the supplementary food product at the four-true leaf stage recorded a significantly higher number of predatory beetles, bugs and lacewings per metre compared with plots treated at two, six and eight-true leaf stages and unsprayed (control) plots. The cumulative total number of predatory beetles, bugs and lacewings recorded throughout the season in both treated and control plots was 23.81 per m. Of this total, plots treated at four true leaf stage recorded the highest (7.15 per v m) (i.e 30.03%), followed by two true leaf (5.81 per m) (24.41%), six true-leaf (4.31 per v m (18.12%), eight true-leaf stage (4.63 per v m) (i.e. 19.44%) and the unsprayed (control) plot recorded the lowest (1.91 per m (8.03%). The number of spiders per metre were not significantly different ( p v > v 0.05) among treatments and the control plots. The number of predators recorded in cotton crops treated with the supplementary food product as a band spray (33 v - v 50% band) or skip row spray (i.e. to every second row) was not significantly different ( p v > v 0.05) from plots where the product was applied as a solid spray to the entire crop (no skip row and/or no banding). Thus, tailoring Envirofeast® treatment in this way will ultimately reduce the quantity of product used, the cost of the product and allow cotton growers to adopt a multiple-use pattern for the product to support integrated pest management programmes in cotton.

Practical application of integrated disease management

A decision support system for cereal diseases and late blight of potatoes has been developed at the Chair of Phytopathology,&lt;br /&gt;Technische Universität München. The Wheat and Barley Prognosis System has been in use for many years by the&lt;br /&gt;Bavarian official advisory service. It is based on an exact diagnosis and established biological thresholds influenced by&lt;br /&gt;weather. Certain fungicides are recommended also covering diseases which have not reached the threshold. Diseases under&lt;br /&gt;consideration are eye spot disease, powdery mildew, Septoria leaf blotch, Septoria leaf and glume blotch, tan spot, brown&lt;br /&gt;and yellow rusts.The PhytophthoraModel Weihenstephan consists of two parts, weather based prognosis and monitoring in&lt;br /&gt;the unsprayed control plots. Spraying recommendations are given based on the results of the above-mentioned parts and&lt;br /&gt;considering cultivar behaviour and blight development in the field. The first spraying in the season as well as the timing&lt;br /&gt;of the following ones are crucial. This model does not give any recommendations regarding which active ingredient should&lt;br /&gt;applied. However there is a distinction made with regard to contact (protective) fungicides and systemic fungicides. The&lt;br /&gt;PhytophthoraModel Weihenstephan has been in use for several years in Germany as well as in Austria.

Detection and management of myclobutanil-resistant grapevine powdery mildew (Uncinula necator) in Ontario

Myclobutanil-resistant Uncinula necator (Schwein.) Burrill was present in western New York State in 1995. In a vineyard in neighboring Ontario, myclobutanil gave poor control of powdery mildew during 1999. In 2000, mildew prevention was assessed with four management programs on three cultivars using small plot, randomized complete block designs. Programs received six fungicide applications between immediate prebloom and early ripening. On vines of cv. Riesling, the cluster areas mildewed in the control and four management programs were: unsprayed, 96%; myclobutanil, 65%; sulfur, 0.2%; myclobutanil alternated with sulfur, 27%; and a rotational program (kresoxim-methyl, sulfur, myclobutanil, and mineral oil), 8%. Severe infections on vines of cvs. Vidal and Seyval confirmed the failure of myclobutanil at a rate of 80 g/ha per application. Using aseptic techniques, the sensitivities of single conidial chain isolates of U. necator to myclobutanil were assessed from their growth on myclobutanil-impregnated grape leaf disks. Thirty isolates from unsprayed control plots in June 2000 had a mean EC50 (effective concentration that gave 50% inhibition) of 0.24 µg myclobutanil/mL. Thirty isolates from myclobutanil-sprayed 'Seyval' secondary clusters in September 2000, had a significantly higher EC50 (0.54 µg myclobutanil/mL). Using a discriminating concentration of 0.18 µg myclobutanil/mL, the proportion of resistant isolates increased from 53% in control plots in June to 97% in myclobutanil-treated plots in September.

Optimal Fungicide Management of Purple Spot of Asparagus and Impact on Yield.

Purple spot disease of asparagus, caused by the fungus Stemphylium vesicarium, results in lesions on spears and ferns and defoliation of ferns. In two newly established commercial asparagus fields (cvs. Jersey Giant and Jersey Knight), chlorothalonil or mancozeb was applied every 7, 10, or 14 days or according to Tom-Cast with a threshold of 15 disease severity values, and not applied to the control. Tom-Cast prompted four sprays, resulting in a 60% reduction in the number of fungicide applications when compared with the 7-day-interval treatment. When disease pressure was severe, lesions on ferns were significantly less for both cultivars when fungicides were applied according to Tom-Cast or every 7 days compared with spray intervals of 10 or 14 days. Applying fungicides according to Tom-Cast or every 7 days resulted in an increased Jersey Giant fern stand compared with applying fungicides every 10 or 14 days. Unsprayed control plots yielded 77 to 83% (depending on cultivar) of those plots treated according to Tom-Cast using chlorothalonil. Significantly higher yields of Jersey Knight were obtained for chlorothalonil versus mancozeb. When mancozeb was used, Jersey Knight yield was significantly increased with a 7-day versus Tom-Cast application regime. Using chlorothalonil in a Tom-Cast program provided a benefit per hectare (BPH) of $1,005.24 (Jersey Knight) to $2,057.69 (Jersey Giant). In comparison, using mancozeb in a Tom-Cast program provided a BPH of -$484.27 (Jersey Knight) to $1,030.55 (Jersey Giant) over a 2-year period.

A Survey of Weeds in Organic Farming in Sweden

ABSTRACT The weed flora on 57 arable fields on 17 farms employing organic farming was recorded. With the ordination technique pCCA (partial Canonical Correspondence Analysis) the relative importance of some farming practices was evaluated (crop, preceding crop, ± undersown ley, ± weed harrowing, ± weed hoeing, ploughing regime, ± compost, ± animal husbandry, ± biodynamic agriculture). The variables that explained most of the variation in the weed flora in fields (along with typical weed species) were the crops ‘beans and peas’ (analysed together; Centaurea cyanus), ‘ley as preceding crop’ (Cerastium fontanum), ‘weed hoeing’, ‘fallowing in the preceding year’ (Lamium spp.) and ‘animal husbandry’ (Sinapis arvensis). A number of species considered endangered, rare or decreasing in Sweden were recorded on these farms, suggesting that organic farming can contribute to maintaining biodiversity in an agricultural landscape. The weed flora was also compared with that of unsprayed control plots in herbicide trials. Ranking of weeds according to either frequency or a pCCA both showed clear differences, with organic fields having much more weeds. Species typical of organic farming were Centaurea cyanus and Vicia hirsuta. There was a tendency for weed species that dominate in conventional farming to be more nitrophilous than those species characteristic in organic farming.

Spray-topping annual grass pasture with glyphosate to delay loss of feeding value during summer. IV. Diet composition, herbage intake, and performance in grazing sheep

We report the effects of spray-topping annual grass pasture with glyphosate (180 g a.i./ha as Roundup CT, at the seed head emergence stage) on the nutritive value of herbage and on subsequent performance of grazing sheep. Eight 1-ha plots, consisting of 4 sprayed and 4 unsprayed (control) plots, were set-stocked with Merino wethers (18 months old, 12 sheep/ha) from 8 days after anthesis in the control plots (late spring) until 165 days after anthesis (mid-autumn). In 4 periods (15–20, 36–41, 71–76, and 99–104 days after anthesis; Periods 1–4, respectively) sheep were dosed with synthetic alkanes and herbage and faecal samples were taken, in order to estimate diet composition (in terms of plant parts), faecal output, herbage intake, and the digestibility of the whole diet. As described in our earlier papers, spray-topping reduced the yield of pasture dry matter, but also slowed the loss of water-soluble carbohydrate (WSC) and digestibility during pasture senescence. The present paper shows that as a result, sheep grazing sprayed herbage in Periods 1 and 2 consumed significantly more organic matter (OM) and digestible OM (DOM) than sheep grazing the control pasture. Their diet contained a higher proportion of stem with a higher WSC concentration than that of the sheep grazing the control plots. The proportions of different plant parts (leaf blade+sheath, stem, seed head) in the diet of both the plot sheep and oesophageally fistulated (OF) sheep, which grazed treatments for short periods, differed significantly between treatments in all periods. However, the compositions of the diets selected by plot and OF sheep were similar. These results confirmed diet preferences measured using housed sheep and demonstrate the usefulness of alkane-based procedures for quantifying diet composition and intake in grazing animals. As a result of their higher intake of DOM, sheep grazing sprayed herbage had a significantly higher liveweight gain over the first 2 periods (40 g/day). In Period 3, sheep grazing sprayed herbage consumed more OM than sheep grazing control herbage. However, DOM intakes from sprayed or control plots were not significantly different in either Period 3 or Period 4, and were lower than in Periods 1 and 2. Sheep grazing both treatments lost liveweight at a similar rate over this time. Wool growth in sheep grazing sprayed herbage was improved by 10% during the experimental period; wool strength was also improved significantly. The implications for the management of sheep grazing spray-topped pastures over summer are discussed.

Field Evaluation of an Improved Formulation of Gypchek (a Nuclear Polyhedrosis Virus Product) Against the Gypsy Moth (Lepidoptera: Lymantriidae)

Prior to 1994, Gypchek® (USDA Forest Service, Washington, DC), the gypsy moth nuclear multicapsid polyhedrosis virus (LdMNPV), was used in operational programs against gypsy moth Lymantria dispar (L.) dispersed in a standard molasses-lignosulfonate tank mix and applied twice at the rate of 5 × 1011 polyhedral inclusion bodies (PIB) per ha per application in a volume of 19 liters per ha. In 1995, we evaluated a commercially-produced carrier and operational options that would make Gypchek application more efficient and less costly without reducing efficacy. Specifically, the standard tank mix formulation and application procedure was compared against a premixed commercial carrier, Carrier 038 (Novo Nordisk, Franklinton, NC) applied by three different application options. Option 1 consisted of double applications of Gypchek at the rate of 5 × 1011 PIB per ha per application in volumes of 9.5 liters per ha. Option 2 was identical to Option 1 except that application volume was reduced to 4.8 liters per ha. Option 3 consisted of a single application of Gypchek dispersed in 9.5 liters per ha at the rate of 1 × 1012 PIB per ha. There was also a fifth treatment consisting of unsprayed control plots. All treatments were evaluated in replicated 4-ha forest plots in southwestern Virginia. Levels of LdNPV-induced mortality, of larvae collected live 6 to 11 days after treatment, among treatments receiving a double application were not significantly different at α = 0.05 from such mortality resulting from the single application of Gypchek in Carrier 038. However, both of the double-application treatment options (but not the single application option) of Gypchek dispersed in Carrier 038 had significantly higher levels (α = 0.05) of LdMNPV than the double-application treatment of Gypchek dispersed in the standard tank mix. Defoliation was significantly different among the four Gypchek treatments, but all were significantly lower than the controls. These results indicated that all three options using Carrier 038 provided a level of efficacy equal to or better than the standard tank mix formulation applied twice at 19 liters/ha. Economic assessment indicated that the single application option was more efficient and/or less expensive than the other options.

Chlorpyrifos Effect on Armored Scale (Homoptera: Diaspididae) Populations in San Joaquin Valley Citrus

Portions of three citrus orchards infested with California red scale, Aonidiella aurantii (Maskell), and with yellow scale, A. citrina (Coquillett), were sprayed either with a commercial rate of chlorpyrifos or left unsprayed. The three orchards included a chlorpyrifos-susceptible A. aurantii population, a chlorpyrifos-resistant A. aurantii population, and a chlorpyrifos-resistant A. citrina population. The levels of efficacy of chlorpyrifos in the field trials confirmed the levels of susceptibility of scales in the laboratory bioassays. Susceptible A. aurantii were killed for 60 d after treatment with one application of properly timed chlorpyrifos. Chlorpyrifos-resistant A. aurantii were held at pretreatment levels for 30 d but increased in numbers similar to those of the unsprayed control plots by 60 d after treatment. There was no significant difference in percentage of parasitism between the sprayed and unsprayed treatments. Resistant A. citrina were unaffected by the chlorpyrifos treatment, both in the number of scales per plant structure as well as in the population structure. The percentage of parasitism was significantly greater in the unsprayed compared with the chlorpyrifos treatment in this population.

Effects of herbicides on wallaby grass (Danthonia spp.) 1. Establishment

Two experiments were conducted at Tamworth, New South Wales, to assess the effects of herbicides applied post-sowing pre-emergence, and at 2 post-emergence growth stages, on Danthonia (wallaby grass) dry matter yield, plant number, and plant phytotoxicity. Phytotoxicity was scored visually on a 0-5 scale (0, no phytotoxicity; 5, 100% phytotoxicity). In the post-sowing pre-emergence study, no Danthonia plants survived on plots sprayed with metribuzin (375 g a.i./ha), chlorsulfuron (45 g a.i./ha), or simazine (750 and 1500 g a.i./ha). Phytotoxicity was also high at lower rates of metribuzin (187.5 g a.i./ha) and chlorsulfuron (22.5 g a.i./ha). Dry matter yields and plant numbers on 2,4-D amine and ester treatments were not significantly different from those of unsprayed controls. On metsulfuron-methyl (3 and 6 g a.i./ha) and triasulfuron (21.4 g a.i./ha) treatments, plant numbers were similar to the controls, but Danthonia yields were lower (P&lt;0.05). In seedling stands, the only herbicide that reduced (P&lt;0.05) Danthonia dry matter yield compared with the unsprayed control plots was metsulfuron-methyl applied at 6, 12, and 18 g a.i./ha at the 2-4 tiller stage, and at 12 and 18 g a.i./ha at early stem elongation. At both times of application, Danthonia plant numbers were lowest (P&lt;0.05) on the metsulfuron-methyl 12 and 18 g a.i./ha treatments. Phytotoxicity scores were &gt;2 and highest (P&lt;0.05) on all metsulfuron-methyl plots. These studies indicated that a range of chemicals could be used to control broadleaf weed seedlings, without damaging Danthonia seedlings.