Autumn control of rosy apple aphid,Dysaphis plantaginea (Passerini), with aphicides

Rosy apple aphid, Dysaphis plantaginea (Passerini), is normally controlled in commercial apple orchards by an application of an aphicide in the spring. Control is often inadequate, especially in organic production where the range of aphicides permitted, which are only contact acting, is very restricted. A series of eight large-scale replicated orchard experiments evaluated control of rosy apple aphid by autumn applications of aphicides. The experiments showed that control of the aphid in the autumn with pirimicarb or pirimicarb+cypermethrin can be highly effective and, with 2–3 sprays of the organically permitted insecticide pyrethrum, moderately effective. The optimum time for spraying was week 40–41 (early–mid October), coinciding with the start of migration of males and before mating and egg laying, as indicated by Rothamsted Insect Survey suction traps at 8 sites throughout England. The other organically acceptable materials tested (potassium soap, rotenone, garlic extract, kaolin, neem extract, starch-based plant extracts) did not give useful control.The vulnerability of gynoparae and oviparae on the flat undersides of leaves (i.e. leaves not curled by aphid feeding) in the autumn where they can be directly intercepted with sprays, compared to the inaccessibility of fundatrices and fundatrigeniae enclosed in blossom clusters and leaves curled by aphid feeding in spring, is discussed. The need to develop assessment methods and treatment thresholds for autumn treatment so routine spraying can be avoided, is highlighted.     

Effect of codling moth exclusion nets on the rosy apple aphid, Dysaphis plantaginea, and its control by natural enemies

Exclusion nets aimed at controlling populations of the codling moth, Cydia pomonella are increasingly used in French apple orchards. The secondary effects of these so-called Alt’Carpo nets on other apple pests have not yet been thoroughly determined. This study was carried out to evaluate whether the presence of white nets (mesh size: 3 × 7.4 mm) affects the population dynamics of the rosy apple aphid (RAA), Dysaphis plantaginea and the abundance and composition of associated arthropod communities. We surveyed 50 infested shoots on a weekly basis throughout spring in 2008 and 2009 on apple trees with or without (control) nets in one insecticide-free orchard located in south-eastern France. At three dates in 2009, the RAA infestation rate was also computed by counting the total number of infested shoots per tree. The nets were installed at three different dates during the RAA lifecycle: September (September Netting Plot (SNP)), March (March Netting Plot (MNP)) and mid-April (April Netting Plot (ANP)). The abundance of RAA in the uncovered plot in 2008 was 1.75-fold higher than in the ANP. In 2009, this abundance was 1.39-fold higher than in the ANP and MNP, and slightly lower than in the SNP (1.07-fold). The nets (MNP and SNP) decreased the number of RAA colonies present in early spring. Interestingly, the nets reduced the duration of RAA infestation by 7–10 days. The highest reduction in RAA abundance and infestation rate was observed when nets were closed during the RAA development phase (ANP). The nets significantly reduced the abundance of ants on the marked shoots, especially in the ANP compared to the control. In addition, this study showed that nets have a significant negative influence on the abundance and richness of RAA-natural enemies. There was a significant decrease in the abundance of predators but no effect on the abundance of parasitoids. Syrphidae, Forficulidae and Coccinellidae were the most abundant natural enemy groups in the uncovered plot. Netting the plots led to a pronounced decrease in Coccinellidae abundance, a slight but significant decreased in Syrphids and had no effect on earwigs. Overall, Alt’Carpo exclusion nets had a direct negative impact on RAA population dynamics especially in the presence of at least one active natural enemy per marked shoot. These promising findings suggest that the combination of physical and biological control methods has potential for regulating RAA populations in organic orchards.     

Incidence and severity of powdery scab on potatoes in Pennsylvania

Studies were conducted in Potter Co., Pennsylvania to investigate the effect of powdery scab (Spongospora subterranea) on five potato cultivars (Norchip, Rosa, Kennebec, Katahdin, and Monona) at two planting dates. Soil temperature was within the range of 15–18 C and soil moisture was within 15–19% based on dry weight throughout the season. The effect of planting date was significant at each disease assessment, except for the severity on the fourth assessment. By the end of the season, incidence of scab was 66% or more for all cultivars. Rosa, Kennebec and Katahdin had a greater scab incidence over both planting dates and a greater severity at the first planting date than Monona and Norchip.     

Evaluation of Lecanicillium longisporum, Vertalec against the cotton aphid, Aphis gossypii, and cucumber powdery mildew, Sphaerotheca fuliginea in a greenhouse environment

The commercial mycopesticide, Vertalec^® based on Lecanicillium longisporum, was evaluated for simultaneous control of aphids and powdery mildew on cucumbers in a greenhouse setting where temperature and RH were allowed to fluctuate within normal operating ranges. Five to six week old cucumber plants were inoculated with either Sphaerotheca fuliginea (Sf) spores, cotton aphids (Aphis gossypii) or both. Vertalec, Vertalec containing irradiation-inactivated blastospores (II Vertalec) or sterilized water (control) were applied to the plants 1, 4, and 7 days later. Vertalec treatment provided complete control of aphids 16 days after aphid inoculation, whereas effects of the II Vetalec were not significantly different from the water-treated control. The number of powdery mildew spots on cucumber leaves and the number of S. fuliginea spores in each spot were significantly lower in Vertalec-treated plants than II Vertalec-treated plants or the controls, whereas numbers in the II Vertalec treatment were lower that the untreated control. These results demonstrate that Vertalec has potential for simultaneous management of both cotton aphid and powdery mildew in greenhouse cucumber production.     

The effect of irrigation and nitrogen on powdery scab and yield of potatoes

Summary Powdery scab, caused by the fungusSpongospora subterranea, has developed in the Cappodocia region of Turkey because of changes in agronomic practices, such as excessive irrigation and nitrogen fertilizer use and growth of highly susceptible cultivars. The most suitable irrigation and nitrogen application levels were established to maintain powdery scab at minimum levels without affecting potato yield. Three irrigation levels were used in 1998 (673, 897, 1121 mm) and five in 1999 (329, 494, 658, 823, 987 mm). Nitrogen levels were applied 150, 300, 450, 600 kg N ha⁻¹. In 1998, least powdery scab occurred with 673 mm irrigation, which yielded 41 t ha⁻¹ potatoes. The lowest disease severity occurred in 1999 with 494 mm irrigation and 150 kg N ha⁻¹. At these levels, tuber yield was 34 t ha⁻¹ which was not significantly different from the highest yield measured. In 1999 and at two of the three irrigation levels inl998, nitrogen increased disease severity.     

Effect of planting date and inoculum level on incidence and severity of powdery scab on potato

Summary Powdery scab incidence and severity was examined on six potato cultivars planted at two different dates in a naturally infested field. There were two sub-plots; one where seed was exposed prior to planting to spores ofSpongospora subterranea from scabby peels, which were then added to the furrow at planting, and another where seed was exposed only to natural inoculum within the field. The later planting data reduced incidence and severity, but there were no differences between sub-plots. All cultivars became infected, but ‘Rosa’ was the most susceptible and ‘Katahdin’ the most resistant. Contribution No. 1720, Department of Plant Pathology, The Pennsylvania Agricultural Experiment Station. Authorized for publication September 22, 1988 as Journal Series Paper No. 8007.     

HvWRKY2 acts as an immunity suppressor and targets HvCEBiP to regulate powdery mildew resistance in barley

Plants use a sophisticated immune system to perceive pathogen infection and activate immune responses in a tightly controlled manner. In barley, Hv WRKY2 acts as a repressor in barley disease resistance to the powdery mildew fungus, Blumeria graminis f. sp. hordei(Bgh). However, the molecular features of Hv WRKY2 in its DNA-binding and repressor functions, as well as its target genes, are uncharacterized.We show that the W-box binding of Hv WRKY2 requires an intact WRKY domain and an upstream se...     

Short-term response of soil spiders to cover-crop removal in an organic olive orchard in a mediterranean setting

Abstract This study shows that disturbance caused by cover-crop removal (CCR) in an organic olive orchard affects ground-spider populations. The effect of CCR on various organic olive-orchard plots was assessed by monitoring the abundance and diversity of ground-dwelling spiders. Covered plots in the organic olive orchard were compared with uncovered plots where the covers had been removed mechanically. CCR positively affected the most abundant spider species Zodarion styliferum (Simon) (Araneae: Zodariidae) as well as other species of running spiders belonging to the families Gnaphosidae and Lycosidae. Over time, the two types of plots did not significantly differ in diversity or dominance. Similarly, no differences were detected between the study plots in terms of the distribution of individuals when a cluster-similarity analysis was performed. This lack of difference in diversity might be due to the spatial scale used in the study or climatology. Because of their general effects, CCR profoundly changed the abundance of spiders in the olive orchard, but with no clear impact on spider diversity.     

Effects of inoculum density and cultivar resistance on common scab of potato and population dynamics ofStreptomyces scabies

The interaction ofStreptomyces scabies, causal agent of common scab, and its potato host was examined under scab-conducive conditions in the greenhouse. Three potato cultivars with different levels of resistance to common scab were inoculated with four levels of two rifampin-resistant strains ofS. scabies. In general, scab severity increased linearly with an increase in log₁₀ of the inoculum, but both cultivar resistance and strain ofS. scabies affected the slope of the regression line. Rhizosphere and rhizoplane populations ofS. scabies also increased with increasing soil population. One strain ofS. scabies consistently had higher rhizosphere and rhizoplane populations than the other strain. However, rhizosphere population was not consistently related to scab severity, scab incidence, cultivar resistance, or strain virulence.     

Aircraft-applied sulfur for control of powdery mildew (erysiphe cichoracearum) on potato in washington state

Aircraft-applied dust and liquid sulfur sprays were evaluated for control of powdery mildew (Erysiphe cichmacearumDC), on rill irrigated potatoes (cv. Russet Burbank). Either form of sulfur applied weekly or biweekly usually controlledE. chichoracearum through September, but not in October. Significant yield increases were obtained in only two of five trials. The small differences in disease severity between weekly and biweekly applications of sulfur were not significant. Sulfur gave very little control if applied after infection was established. Applications of liquid sulfur, the formulation less likely to cause environmental problems, should be started at the first trace of stipples on stems and continued biweekly throughout the season.     

Animal and forage responses on Maximus,a tetraploid cultivar vs Marshall,a diploid cultivar of annual ryegrass

This 2‐year grazing study carried out at Raymond, Mississippi, USA, evaluated animal performance and forage characteristics of a tetraploid (“Maximus”) vs a diploid cultivar (“Marshall”) of annual ryegrass at three stocking rates (SR; 3.5, 5.0 or 7.5 animals per ha). Angus cross‐bred heifers (Bos taurus; initial body weight [BW] = 240 kg) were continuously stocked on pastures at set stocking rates for the duration of the study. Stocking rates and cultivars were arranged in a 3 × 2 factorial design that was completely randomized with two replications. There was no cultivar effect (p = .449) on average annual herbage mass (HM). However, HM decreased linearly with increasing SR (p = .001) from 3.8 to 2.5 t ha^?1 during Year 1 and 4.4 to 3.8 t ha^?1 during Year 2 (p = .028). In Year 2, there was a difference in water‐soluble carbohydrates (WSC) between cultivars (p = .012; Marshall, 117.0 vs Maximus, 139.0 g/kg). There was no cultivar effect (p > .10) on average daily gain (ADG) in either year of the study. In both years, ADG decreased linearly with increasing SR (p = .001) from 1.22 to 0.98 kg/d during Year 1 and 1.31 to 1.08 kg/d during Year 2. Across years, gain ha^?1 increased linearly (p < .001) with increasing SR. Our results showed no difference in animal performance and HM between the two cultivars. Producers’ choice of annual ryegrass cultivar should be based on seeding cost and agronomic traits that allow for better adaptation of the forage.     

Evaluation of triadimenol seed treatment for early season control of tan spot,powdery mildew,spot blotch and Septoria nodorum spot on spring wheat

Triadimenol seed treatment was evaluated for control of early infections of spring wheat (Triticum aestivum L. cultivars Max and Sinton) by Pyrenophora tritici-repentis (causal fungus of tan spot), Erysaphe graminis f. sp. tritici (causal fungus of powdery mildew), Leptosphaeria nodorum (causal fungus of Septoria nodorum spot), and Cochliobolus sativus (causal fungus of spot blotch). In controlled environment studies, triadimenol seed treatment controlled both tan spot and powdery mildew up to 20–30 days and 40–50 days after sowing, respectively. However, triadimenol seed treatment provided no control of early infection by airborne inoculum of L. nodorum and C. sativus. Powdery mildew-resistant cv. Max was completely free of symptoms or signs of E. graminis f. sp. tritici. In field experiments, triadimenol seed treatment controlled early development of tan spot and powdery mildew for 5 and 10 days longer, respectively, than in controlled environment studies. Control of both diseases in cv. Sinton and tan spot control in cv. Max resulted in yield increases of approximately 20% and 15%, respectively, at two different field locations.     

Reduction of scab incidence (Venturia inaequalis) in apple with prohexadione-Ca and trinexapac-ethyl,two growth regulating acylcyclohexanediones

Prohexadione-calcium and trinexapac-ethyl, inhibitors of 2-oxoglutaric acid-dependent dioxygenases, were tested for their efficacy in controlling scab infection on apple (cv. Golden Delicious) scions under greenhouse and field conditions. Their effectiveness was compared with other types of growth inhibitors (chlormequat chloride and paclobutrazol). Furthermore, to determine the time required to build-up plant resistance against scab, the compounds were applied at different concentrations and timings prior the inoculation with Venturia inaequalis. Prohexadione-calcium and trinexapac-ethyl significantly reduced scab incidence starting approximately 10 and lasting for approximately 25 days after application. In field conditions, the practical application of these compounds may result valuable both to control the vegetative/reproductive balance of the trees and to effectively reduce the amount of fungicides used to control scab.     

Optimization of d-pinitol extraction from vegetable soybean leaves and its potential application in control of cucumber powdery mildew

d-pinitol is a bioactive compound with an important application in both food and nonfood industries. In the present study, the leaves of twelve vegetable soybean cultivars that are usually treated as agricultural waste were screened for the presence of d-pinitol. The results showed that the d-pinitol content in these 12 cultivars ranged from 1.32 to 3.04% (w/w) of dry weight, and the cultivar Z98002 was found to contain the highest amount of d-pinitol. Response surface methodology (RSM) was used for optimization of d-pinitol extraction conditions by the Box–Behnken design. The predicted extraction efficiency, which is at least 1.3-fold that of the previously reported typical method, reached to 3.27% under the following optimal conditions: temperature of 65.5 °C, extraction time of 86.8 min, and dilution rate of 1:10. The test in the growth chamber showed that the efficacy of soybean extracts in cucumber powdery mildew control was dose-dependent on the d-pinitol concentration, and the formulated extracts clearly increased the control compared to the crude extract. This effect of the d-pinitol formulation in a greenhouse was confirmed in four provinces of China over a period of two years. Our present study provides the optimized extraction conditions for a selected agricultural waste—vegetable soybean—to obtain a high yield of d-pinitol. Results from the growth chamber test and the greenhouse bioassay will be useful in exploring a low-cost phytochemical fungicide for cucumber powdery mildew control.     

Scale and spatial structure effects on the outcome of barley cultivar mixture trials for disease control

The effects of field-trial scale, including plot size, and its interaction with fertiliser level and barley germplasm on mixture efficacy in controlling powdery mildew were investigated. Two groups of cultivars, one from cultivars grown in the UK and the other from cultivars grown in Poland, along with all their respective three-component mixtures, were grown in three field trials, one with 13.5 m² plots, one with 0.4 m² plots, and the third in intermediate size plots, which included a mixture of all the cultivars in both groups in equal size treatments of structured spatial arrangements. Another trial utilised similar structured spatial arrangements to trial 3 was carried out using a combination of cultivars with appropriate matching virulence levels (trial 4). Mixtures showed either a reduction in powdery mildew infection compared with the component monoculture mean, or no significant effect. There was a trend towards greater reductions at the low fertiliser level and smaller plot size. The most structured spatial arrangement was most effective for reducing infection in trials 3 and 4, but the complex-homogeneous arrangement in the fourth trial was also effective. Rhynchosporium was reduced by a similar and substantial amount by both spatial treatments in trial 3. The plot size and structuring effects may be explained by the interaction between host heterogeneity structure and pathogen dispersal scale effects, but resource exploitation for yield was best in the complex-homogeneous arrangement in trial 3 where all components were present to respond directly. These findings have implications for methods of trialling mixtures for large-scale field use and for testing component combining ability.     

Genetic resistance to and effect of leaf rust and powdery mildew on yield and its components in 50 soft red winter wheat cultivars

Effects of leaf rust (caused by Puccinia triticina f. sp. tritici Eriks.) and powdery mildew [caused by Blumeria graminis (DC.) E. O. Speer f. sp. tritici Em. Marchal], on performance of 50 soft red winter (SRW) wheat (Triticum aestivum L) cultivars were evaluated under natural field conditions. Widely grown cultivars released from 1919 to 2009 with varying disease resistance were grown in split-plot experiments in 2010 and 2011. Treated replications received seed treatments of triadimenol, captan and imidacloprid and foliar applications of propiconazole and prothioconazole + tebucanazole fungicides. Non-treated replications received only tebucanazole + metalaxyl + imazalil seed treatments. Final mean disease severity, agronomic, yield-related traits, yield components and spike characteristics were analyzed to determine individual and combined effects of leaf rust and powdery mildew on the cultivars. Yield losses as high as 54% were observed in the susceptible cultivar Red May. Average yield losses ranged from 1% to 21%. Yield losses primarily due to powdery mildew were as high as 14%, and losses primarily due to leaf rust were as high as 33%. Powdery mildew had the largest negative correlation with harvest index and seeds/spike. Leaf rust was most negatively correlated with plant biomass and harvest index, with a less consistent negative relationship with kernel weight.     

Identification of powdery mildew resistance loci in wheat by integrating genome-wide association study(GWAS) and linkage mapping

Wheat powdery mildew(Blumeria graminis f.sp.tritici, Bgt) is a disease of increasing importance globally due to the adoption of high yielding varieties and modern sustainable farming technologies.Growing resistant cultivars is a preferred approach to managing this disease, and novel powdery mildew resistance genes are urgently needed for new cultivar development.A genome-wide association study was performed on a panel of 1292 wheat landraces and historical cultivars using 5011 single nucleotide polymorphism(SNP)markers.The association panel was evaluated for reactions to three Bgt inoculants, OKS(14)-B-3-1, OKS(14)-C-2-1, and Bgt15.Linkage disequilibrum(LD) analysis indicated that genome-wide LD decayed to 0.1 at 23 Mb, and population structure analysis revealed seven subgroups in the panel.Association analysis using a mixed linear model(MLM) identified three loci for powdery mildew resistance on chromosome 2 B, designated QPm.stars-2BL1,QPm.stars-2BL2, and QPm.stars-2BL3.To evaluate the efficacy of GWAS in gene discovery,QPm.stars-2BL2 was validated using F2 and F2:3 populations derived from PI420646 × OK1059060-126135-3.Linkage analysis delimited the powdery mildew resistance gene in PI 420646 to an interval where QPm.stars-2BL2 was located, lending credence to the GWAS results.QPm.stars-2BL1 and QPm.stars-2BL3, which were associated with four SNPs located at 457.7–461.7 Mb and two SNPs located at 696.6–715.9 Mb in the Chinese Spring reference IWGSC RefSeq v1.0, respectively, are likely novel loci for powdery mildew resistance and can be used in wheat breeding to improve powdery mildew resistance.     

Impact of pesticide seed treatments on aphid control and yield of wheat in the Sudan

Mixtures of imidacloprid and tebuconazole, were evaluated for three consecutive growing seasons, to determine the effects on plant stand, aphid control and wheat grain yield. At rates of 1.05/0.04 and 0.7/0.04 g a.i of pesticide, respectively, per kg of seeds, plant stand per unit area increased compared with their respective untreated control. Both rates of imidacloprid efficiently controlled the maize aphid (Melanaphis maidis) and suppressed the green bug (Schizaphis graminum) for 6–8 weeks after sowing. There were substantial differences among the different treatments in the number of grains/ear and the 1000-grain weight. These differences were reflected in 90% and 30% average increase in the total grain yield of the wheat crop raised from seeds treated with the mixture relative to the corresponding untreated control and a standard mixture of lindane plus thiram, respectively. This strategy of using imidacloprid as seed dressing allowed easy application, gave adequate reliable control of aphids and less hazardous to the environment.     

Effects of relative humidity and high temperature on spore germination and development of tomato powdery mildew (Leveillula taurica)

The effects of relative humidity (RH) and temperature on tomato powdery mildew (Leveillula taurica) were studied in controlled environments to define conditions that affect disease development in fresh market tomatoes in California. Gradients of RH (20–90%) at constant temperatures (20–30°C) were generated in single growth chambers to determine their effect on mildew development on mature tomato plants. Temperatures of 30°C and above were deleterious for spore germination, germ tube elongation, and disease development. Lesion growth and rate of disease progress were significantly higher at 20°C than at 25°C. Low RH levels (20–40%) reduced spore germination and lesion growth, accelerated host tissue death and reduced disease progress. Intermediate RH levels (50–70%) increased spore germination and optimized disease development, provided temperatures were maintained within favorable limits. High RH levels (80–90%) were favorable for spore germination but continued exposure to these conditions led to a limited lesion growth and disease progress. Short daily periods (two or three daily exposures of at least 2 h) of high temperatures (35°C) suppressed disease development by 70–92%.     

Local and systemic control of powdery mildew (Leveillula taurica) on pepper plants by foliar spray of mono-potassium phosphate

A foliar spray of 1% (w/v) solution of the fertilizer mono-potassium phosphate (MKP) (KH₂PO₄) on the upper surfaces of lower leaves of greenhouse-grown peppers induced local and systemic control against Leveillula taurica, as compared with control plants. This protection was expressed by a reduction in the leaf area covered with sporulating colonies and in conidial production on leaf tissue, 24 or 48 h post-treatment, when MKP was applied on lower leaves of plants that had been exposed to the source of inoculum. Foliar application of MKP, initiated before or after exposure to heavily diseased plants as the source of inoculum, was effective in controlling powdery mildew. Application of MKP efficiently suppressed powdery mildew as expressed by inhibition of the development of new sporulating colonies, as well as the conidial production of the fungus on infected tissue. Microscopic examination indicated destruction of both hyphae and conidial structures on MKP-treated leaves. The efficacy of MKP in controlling powdery mildew on greenhouse-grown plants was compared with a sterol-inhibiting systemic fungicide. Both treatments significantly inhibited powdery mildew as compared with non-treated control plants, although the fungicide-based treatment seemed to be slightly more effective (not significant) in controlling the disease. Phosphate solutions were not phytotoxic to plant tissue and did not affect the yield, as compared with the fungicide treatment. However, a lower yield was recorded for the non-treated control plots because of mildew infection on leaves. These data indicate that MKP spray may be applied as an alternative practice for the control of powdery mildew in peppers.