Wettable Sulphur Research Articles

EFFECT OF VARIOUS TREATMENTS ON REDUCTION OF LEUCOSPERMUM 'HIGH GOLD' MORTALITY CAUSED BY ROOT DISEASES

One of the major problems of Proteaceae cultivation in Madeira Island is the high incidence of root diseases caused mainly by Rosellinia necatrix and Armillaria mellea and secondarily by Fusarium solani and Rhizoctonia solani, which lead to the death of plants older than 2 years. The compactness of the soils as well as its richness in organic matter and in other nutrients, together with the climatic conditions of the island (moderate temperatures and a high relative humidity), facilitate the development of root diseases. The aim of this experiment was to study the effect of various treatments in the reduction of mortality of 5-year-old Leucospermum 'High Gold' plants. The treatments consisted of the application to the roots of 1 L of the following solutions: iron sulphate (30 g/L) plus wettable sulphur (10 g/L) (T2 and T6), copper sulphate (25% copper) (20 g/L) with foliar application of Alga-E (15% of algae extracts) (1.5 ml/L) (T3 and T7), commercial bleach (30 ml/L) (T4 and T8), and Talosint (50% cubiet) (10 ml/L) (T5 and T9); the solutions were applied every 3 months (T2 to T5) or every 6 months (T6 to T9). After one year there were no significant differences between treatments, with a plant mortality of 4.8 to 14.3%. After two years, the lowest mortality was obtained with the application of commercial bleach every 6 months (T8) (28.6%); the other treatments gave higher mortality values but with no significant differences between them, except for treatment T5. Treatment T5 was the worst with 66.7% mortality which was statistically different from T4, T8 and T9. None of the treatments were effective in the reduction of the annual plant mortality; treatment T8 gave more consistent results in the two years of trialling period, with 9.5 and 21% for the first and second year, respectively.

Reducing russeting of Golden Group Apple Cultivars organically grown with Potassium Bicarbonate

One of the biggest problems for organic apple growing is the quality of fruits that means size, color, and shape characteristic to the cultivar, without russeting. The fruits are very sensitive six weeks after bloom (Gildemacher, 2000). Sensitivity to russeting can be built in the period before bloom (Babin, 1977, Berkett, 2005. The effects are more visible when the cooper based fungicides before bloom are used. When the copper was replaced with sulphur or lime sulfur, better results were obtained (Jong, 2008). Experiments were conducted in 2008 in a commercial orchard at SC Agroindustriala SA ClujNapoca. The former is 5 ha of five years old trees on M9 spaced at 3,5 X 0,9 m including five cultivars of Golden Group: Golden Delicious, Golden Reinders, Lysgolden, Smoothee. The objective of this study was to test the effect of potassium bicarbonate in reducing apple russeting in comparison with classical product used in organically apple grown The experimental applied products were: copper hidroxid, 50%, wettable sulphur 80%, potassium bicarbonate 20% . Best results in reducing russeting to Golden Group were obtained in variants treated with potassium bicarbonate, where values obtained were ranged in scale between light and moderate russet, with differences statistically insured against variants treated with copper hydroxid. Treatment with wettable sulphur were less indus russeting than those with copper hydroxid.

Mating and Oviposition Behaviors and Rhythms of Delphastus catalinae (Horn)

Thirty nine agrochemicals comprising eighteen fungicides, eleven insecticides, six fertilizers and four herbicides were evaluated at different concentrations against two isolates of Trichoderma spp., and EC 50 and EC 90 values were calculated based on inhibition in radial growth. Isolate T. virens TV9, obtained from citrus orchard-relatively less exposed to agrochemicals was found more sensitive compared to isolate T. harzianum Th4, obtained from cotton ecosystem relatively more exposed to agrochemicals. Among fungicides, benzimidazoles showed higher toxicity followed by chlorothalonil and triazoles when mean EC 50 values were compared. Wettable sulphur, Bordeaux mixture, azoxystrobin and mancozeb were found to be less toxic to Trichoderma spp. Among insecticides, organophosphorous group was found more toxic while carbofuran followed by spinosad were least toxic. Among fertilizers Zinc sulphate and diammonium phosphate were found highly toxic whereas potassium nitrate, muriate of potash and ammonium sulphate showed less toxicity. All the four test herbicides, i.e., pendimethalin, alachlor, glyphosate and 2, 4-D were found to be toxic to Trichoderma spp.

Management of Okra Powdery Mildew Using Ampelomyces quisqualis

The fungus Ampelomyces quisqualis is a naturally occurring hyperparasite of powdery mildews. Stanes Bio-Dewcon is a talc- based biological fungicide that contains the spores and mycelial fragments (1 x 10 8 CFUs g -1 ) of A. quisqualis . Bio-Dewcon at three different concentrations, viz., 2.0, 2.5 and 3.0kg ha -1 significantly reduced the okra powdery mildew incidence. The product was applied to plants as preventive spray at 30 and 45 days after sowing. Among the three doses tested, 3.0kg ha -1 was found to be on par with wettable sulphur (0.4%). Even though both Bio-Dewcon and wettable sulphur were found to be equally effective in controlling powdery mildew, Bio-Dewcon may be preferred due to its non-residual and odourless properties, especially in vegetables.

Management of Okra Powdery Mildew Using Ampelomyces quisqualis

The fungus Ampelomyces quisqualis is a naturally occurring hyperparasite of powdery mildews. Stanes Bio-Dewcon is a talc- based biological fungicide that contains the spores and mycelial fragments (1 x 10 8 CFUs g -1 ) of A. quisqualis . Bio-Dewcon at three different concentrations, viz., 2.0, 2.5 and 3.0kg ha -1 significantly reduced the okra powdery mildew incidence. The product was applied to plants as preventive spray at 30 and 45 days after sowing. Among the three doses tested, 3.0kg ha -1 was found to be on par with wettable sulphur (0.4%). Even though both Bio-Dewcon and wettable sulphur were found to be equally effective in controlling powdery mildew, Bio-Dewcon may be preferred due to its non-residual and odourless properties, especially in vegetables.

Integrated disease management of powdery mildew (Leveillula taurica (Lev.) Arn.) of Chilli (Capsicum annuum L.)

Chilli (Capsicum annuum L.) powdery mildew incited by Leveillula taurica (Lev.) Arn. ( = Oidiopsis taurica (Lev.) Salmon.) is one of the most serious diseases in Tamil Nadu. The leaf extracts of Azadirachta indica A. Juss. (10%) and bulb extracts of Allium sativum L. and A. cepa L. (5%) were highly effective in inhibiting conidial germination of L. taurica under greenhouse and field conditions. Among the antagonistic microorganism screened, maximum reduction in conidial germination was recorded by the culture filtrates of T. viride Per. ex. S. F. Gray., T. harzianum Rifai. and P. fluorescens Migula. under greenhouse and field conditions. Spraying of dipotassium hydrogen orthophosphate and monopotassium phosphate were highly effective in reducing chilli powdery mildew under greenhouse and field conditions. Among the chemicals tested, dipotassium hydrogen orthophosphate significantly increased the protein, total phenol, phenylalanine ammonia lyase, polyphenol oxidase and peroxidase activity of the leaves. In an integrated disease management, foliar spraying with sulphur alternating with dipotassium hydrogen orthophosphate or plant extract Azadirachta indica was as effective as alternating with wettable sulphur fungicide.

Post-harvest management of ber ( Ziziphus mauritiana Lamk) fruit rot ( Alternaria alternata Fr. Keissler) using Trichoderma species, fungicides and their combinations

Isolates of Trichoderma species from hot arid regions, fungicides and their combinations were evaluated for the management of ber fruit rot at post-harvest stage. Out of 16 isolates of Trichoderma species, six isolates checked growth of mycelia of Alternaria alternata by more than 55%. A distinct variation in the inherent level of resistance in these six isolates was recorded against 13 common fungicides. None of the Trichoderma species grew in PDA amended with carbendazim even at a very low concentration. In contrast, 100 per cent radial growth was observed in Trichoderma citrinoviride isolate T.c-CIAH224 in the presence of copper oxychloride (250 μg g −1) and mancozeb (100 μg g −1) in PDA medium. Isolate T.v-CIAH240 was antagonistic against A. alternata and tolerant to most of the fungicides tested. This isolate was highly compatible with chlorothalonil, dinocap and wettable sulphur even at 1000 μg g −1 and produced yellowish instead of normal green coloured conidia. Isolate of Trichoderma koningii – T.k-CIAH176, T. citrinoviride – T.c-CIAH224 and those of Trichoderma viride – T.v-CIAH181 and T.v-CIAH240 with inherent tolerance to some of the fungicides have shown better efficacy to suppress the fruit rot pathogen in dual cultures. However isolate T.v-CIAH240 was significantly superior in vitro in the suppression (71%) of the A. alternata through mycoparasitism and apparent secretion of secondary metabolites in the growth medium. Mycoparasitism and competition with the fruit rot pathogen were the mode of action in the majority of the isolates. The growth of A. alternata was completely inhibited in PDA amended with dinocap, propiconazole and tridemorph irrespective of the concentrations. In experiments in vivo, isolate T.v-CIAH240 was significantly effective (75% PEDC- Per cent Efficiency of Disease Control) against post-harvest infection by A. alternata followed by T.v-SBI48 (62 PEDC) and T.v-CIAH149 (44 PEDC). Among the individual fungicide treatments, dinocap and copper oxychloride (50 μg g −1) resulted in 52 PEDC. However, dinocap caused a scorching effect and a foul smell in fruits. Fruit rot control efficacy was enhanced to >70% by T.v-CIAH240 with tridemefon, thiophanate methyl, mancozeb or alcidine at 50 μg g −1 and to >80% with 100 μg g −1 of thiophanate methyl, chlorothalonil, mancozeb and alcidine in ber fruits (cv. Gola). There was a non-significant latent infection caused by isolates T.k-CIAH176, T.c-CIAH224 ( T. citrinoviride) and T.v-CIAH240. Such a latent infection was completely suppressed by low concentrations of fungicides when used in combination with T.v-CIAH240. The possible hypothesis involved in management of A. alternata in ber fruits at post-harvest stages using fungicides, Trichoderma species and their combinations is discussed.

Demographic effects of pesticides on biological control of Pacific spider mite ( Tetranychus pacificus) by the western predatory mite ( Galendromus occidentalis)

The western predatory mite, Galendromus occidentalis (Nesbitt) (Acari: Phytoseiidae), is a predator of Pacific spider mite, Tetranychus pacificus McGregor (Acari: Tetranychidae), in California vineyards. We evaluated the effects of six pesticides on biological control of T. pacificus on grape plant microcosms in a two-way design: presence and absence of G. occidentalis crossed with presence and absence of pesticide. The insecticide imidacloprid did not affect T. pacificus population growth rate, but it led G. occidentalis populations close to extinction. As a result, T. pacificus populations grew significantly higher in microcosms with release of G. occidentalis and treated with imidacloprid than with G. occidentalis alone. The fungicide wettable sulfur significantly decreased T. pacificus population growth rate but it did not affect G. occidentalis. Consequently, T. pacificus populations were significantly lower in microcosms with release of G. occidentalis and treated with wettable sulfur than with G. occidentalis alone. The insecticide buprofezin had no effect on T. pacificus population growth rate. Although buprofezin did not impact the ability of G. occidentalis to suppress T. pacificus, it negatively affected G. occidentalis population growth rate. The fungicides trifloxystrobin and tebuconazole and the insecticide methoxyfenozide had no influence on T. pacificus or G. occidentalis population growth rates. Furthermore, none of the pesticides affected the sex ratio of G. occidentalis, but buprofezin, methoxyfenozide and trifloxystrobin affected its stage structure. Our study demonstrates that simultaneous testing of the demographic effects of pesticides on pests and natural enemies is essential for a full assessment of pesticide impacts on biological control.

Activity of a microencapsulated mixture of constituents of essential oils against grey mould and powdery mildew in grapes and vegetables

In an effort to fend off microbial invaders, plants have evolved biosynthetic pathways to produce a variety of products, such as essential oils, that act as natural pesticides. In the current study, the in vivo activity of a microencapsulated mixture of eugenol, thymol and geraniol that are constituents of essential oils against grey mould (Botrytis cinerea) and powdery mildew (Uncinula necator, Sphaerotheca fuliginea) in grape and vegetables was investigated. Wine grape (cv. Agiorgitiko) field trials showed that the mixture, applied curatively close to harvest, was significantly (P=0.05) more effective in reducing B. cinerea bunch rot (43% reduction) than the fungicide iprodione (26%). Preventive spray applications of the mixture to greenhouse grown tomato (cv. Kalisti) had an overall efficacy of 30% under conditions of high grey mould pressure (max 74% infected leaf area on control). However, when the mixture of essential oils was applied curatively the gray mould severity on treated tomato (cv. Optima) plants did not differ significantly (P=0.05) from that of the control. Preliminary studies showed that the mixture did not affect the must/wine quality or the concentration of antioxidants in tomato fruit. In in vitro bioassays, B. cinerea mycelial growth was inhibited by 95% at the concentration of 0.14µg ml-1 (EC95 value) of the mixture. Although the mixture was less effective than wettable sulphur against powdery mildew (U. necator) on wine grape (cvs Merlot, Syrah) leaves, it reduced disease severity on bunches at the same level as sulphur. In greenhouse trials, the mixture had no effect against powdery mildew (S. fuliginea) in potted zucchini (cv. Pepo) plants.

A during-infection spray strategy using sulphur compounds, copper, silicon and a new formulation of potassium bicarbonate for primary scab control in organic apple production

In a field experiment conducted over two growing seasons, the effectiveness and phytotoxicity of inorganic fungicides such as sulphur, lime sulphur, copper, silicon and Armicarb (a new formulation of potassium bicarbonate) was compared with water for the control of primary apple scab infections in Belgium on high, medium and low scab-susceptible cultivars (cvs ‘Pinova’, ‘Pirouette’ and ‘Reinette des Capucins’, respectively). In order to drastically reduce the amount of fungicide applied in the orchard, two approaches were used: (1) a strategy involving spraying during the infection process, before fungal penetration and (2) a tunnel sprayer machine for treatment applications. Under field conditions highly favourable for disease, low rates of elemental sulphur (31.8 and 38.6 kg ha−1 year−1 in 2005 and 2006, respectively) combined with low rates of copper (2.1 kg ha−1 year−1 in both years) provided the best scab control and reduced scab severity on the fruits of cv. ‘Pinova’ by 97 and 98% compared with water control in 2005 and 2006, respectively. Lime sulphur was much more effective than wettable sulphur and appeared to be efficient at temperatures below 10°C, but its effectiveness against apple scab decreased if the treatments were applied 12–24 h later than in the ‘during-infection’ spray strategy. Armicarb used alone significantly reduced apple scab severity on the leaves and fruits of the three cultivars compared with the water control. Its effectiveness was as good as wettable sulphur applied using the same timing and dosage. Silicon reduced apple scab on fruits very slightly, but not on leaves. The amounts of wettable sulphur, lime sulphur, copper, silicon and potassium bicarbonate used in this experiment to control apple scab were not phytotoxic, did not increase fruit russet, did increase the yield of each cultivar and did not affect summer density of the beneficial Typhlodromus pyri. The potential and limitations of ‘during-infection’ spraying as a protection strategy against apple scab in organic farming are discussed.

Impact of sulfur on density of Tetranychus pacificus (Acari: Tetranychidae) and Galendromus occidentalis (Acari: Phytoseiidae) in a central California vineyard

Sulfur is the oldest and most widely used fungicide in the vineyards of California, where it is used for control of powdery mildew (Uncinula necator [Schw.] Burr). For decades, sulfur use has been associated with outbreaks of Tetranychus pacificus McGregor (Acari: Tetranychidae) on cultivated grapes in the San Joaquin Valley. I undertook large-scale field studies to test this association, to evaluate the impact of sulfur on Galendromus occidentalis (Nesbit) (Acari: Phytoseiidae), a major predator of T. pacificus, and to determine if timing of sulfur applications with respect to grape bloom has an impact on T. pacificus density. The studies took place in a 32 ha vineyard in Fresno County, and all fungicide applications were made with commercial-scale equipment. In 1998 a 'high sulfur' treatment, a combination of wettable sulfur and sulfur dust, was compared to 'low sulfur,' in which demethylation inhibitor (DMI) fungicides partially substituted for sulfur. In 1999 treatments were 'sulfur,' 'DMI,' 'sulfur pre-bloom' (here sulfur was applied prior to grape bloom, in late May, and then DMIs were applied until mid-season) and 'sulfur post-bloom' (the reverse of 'sulfur pre-bloom'). In each year, the T. pacificus population increase came after the end of fungicide applications, and results clearly show a relationship between sulfur use and T. pacificus density. In 1998, mean T. pacificus density was 2.7 times higher and mean G. occidentalis density 2.5 times higher in 'high sulfur' compared to 'low sulfur.' In 1999, the highest T. pacificus counts were in the 'sulfur' and 'sulfur pre-bloom' treatments, 4.8 times higher than 'sulfur post-bloom' and 2 times higher than 'DMIs.' Density of G. occidentalis was 2.3 times as high in 'sulfur' or 'sulfur pre-bloom' than 'DMIs.' The predator/prey ratio was not significantly different among treatments in 1998, but in 1999 it was highest in the 'sulfur pre-bloom' treatment. In 1999, density of Homeopronematus anconai (Baker) (Acari: Tydeidae) was 2.7 times higher in 'sulfur pre-bloom' compared to 'sulfur,' and higher by 2.7 times in 'DMI' compared to 'sulfur post-bloom,' suggesting a negative effect of sulfur on this tydeid. These results do not support the hypotheses that the cause of the increase in T. pacificus density is due to negative effects of sulfur on phytoseiids or tydeids. Rather, it appears that a plant-based explanation is likely, first, because of the differences in pre-bloom versus post-bloom sulfuring, and second, because of the long lag time between the end of the sulfur applications and the corresponding increase in spider mite density.

Management of powdery mildew disease of rambutan (Nephelium lappaceum L.) in Sri Lanka

Powdery mildew disease is the most destructive disease of rambutan in Sri Lanka, which seriously threatens quality fruit production. Therefore, studies were conducted to identify the causal agent, cross infection potential of pathogen with other crops, resistant/tolerant germplasm and safer chemicals for management of powdery mildew of rambutan.Pathogen of powdery mildew of rambutan was identified as Oidium nephelii. Pathogen did not show infection on leaves of rubber, mango, durian and orange which are potential hosts for Oidium species. All germplasm including recommended varieties were susceptible to the disease. Therefore, studies were directed to identify safer chemicals to control the disease. Spraying of wettable sulphur (5g/l.) at young foliage stage, at flowering, just after fruit setting and 3 weeks after fruit setting on to the plants completely controlled mildew disease of rambutan.

Efficacy of Milsana®, a Formulated Plant Extract from Reynoutria sachalinensis, against Powdery Mildew of Tomato (Leveillula taurica)

The efficacy of Milsana® VP 1999 and 2000 (a formulated plant extract of Reynoutria sachalinensis), known to induce resistance to powdery mildew on cucumbers, was tested against Leveillula taurica (Lev.) Arn. on greenhouse tomato. In four out of five trials, Milsana® achieved a disease reduction ranging from 42.2 to 64.6%. In one trial only, its efficacy was exceptionally low (23%). Application rates and disease pressure proved to be the main factors affecting the level of control. Milsana® was significantly less effective than fungicides (alternated DMIs and penconazole) in situ. In contrast, Milsana® was equally effective to wettable sulphur indicating that its effect was rather preventive than curative. The level of efficacy achieved by either Milsana® or fungicides did not result in a significant increase of yield. Laboratory tests showed that Milsana® (VP 1999) had a direct effect on conidial germination. Whether this effect significantly contributes to its field efficacy, remains to be elucidated. Overall, results indicate that Milsana® could play an important role in disease management of powdery mildew in organic and low input tomato production.

Effect of Fungicide Treatments and Sanitation Practices on Brown Rot Blossom Blight Incidence, Phytotoxicity, and Yield for Organic Sour Cherry Production.

Demand for organically grown fruit, including sour cherry, is rising in Europe and the United States, but the limited tools for disease management have not been thoroughly investigated. In this study, management of brown rot blossom blight, caused by Monilinia laxa, was examined for organic sour cherry production in Hungary. Combinations of sanitation practices and fungicide treatments, including copper hydroxide, lime sulfur, and micronized and nonmicronized wettable sulfur, were investigated in 2 years and two cultivars. The effect of fungicide treatments on yield and phytotoxicity on spur-leaf clusters was also determined. Among fungicide treatments suitable for organic production, copper hydroxide and lime sulfur alone or in combination with micronized wettable sulfur were most effective for blossom blight control when applied twice (at closed blossom and full bloom) or three times (at closed blossom, full bloom, and petal fall) during bloom. Both treatments were not as effective as the conventional standard and caused more damage on spur-leaf clusters during wet weather conditions, but significantly increased crop yield compared with the untreated control or wettable sulfur treatments. Micronized and nonmicronized sulfur applied up to three times during bloom were equally effective, did not impact yield, were not phytotoxic, and reduced blossom blight compared with the untreated control. Sanitation (the removal of blighted twigs and mummified fruit) reduced blossom blight in both cultivars compared with nonsanitized plots when disease pressure was high. The need for an integrated approach to effectively manage blossom blight in organic sour cherry production is discussed. This is the first in-depth characterization of cultural and chemical brown rot blossom blight control options for organic sour cherry production.

Early‐Season Applications of Sulfur Fertilizers Increase Potato Yield and Reduce Tuber Defects

Sulfur recommendations are based on avoiding deficiency. Since S may have additional effects, the objective was to determine whether S fertilizers increase yield and reduce tuber defects. Potato (Solanum tuberosum L.) cultivar Atlantic was treated with wettable sulfur (WS), ammonium sulfate (AS), and ammonium thiosulfate (TS) at 0, 28, 56, 84, and 112 kg S ha−1 applied at planting [in‐furrow (IF)], 11 d later [pre‐emergence (PE)], 11 d after emergence [postemergence (PT)], and at tuber initiation (TI). Separate trials were conducted for each fertilizer and application. Ammonium nitrate and urea were added to AS and TS to equalize N. Yield of U.S. “A” potato was increased 11 to 34% by fertilizers at S rates greater than 56 kg ha−1 at IF, PT, and by AS and WS at TI. These fertilizers applied IF and at TI reduced the incidence of common scab (Streptomyces scabies) on tubers. When applied PT, AS and TS reduced common scab; WS did not. The incidence of black scurf (Rhizoctonia solani) on tubers was reduced when AS and TS were applied PT but not when applied IF and at TI. Pre‐emergence application had no effect. Other tuber characteristics, e.g., specific gravity and vascular discoloration, were unaffected. Plant growth was inhibited by TS applied after emergence but recovered. Yield was increased by S at 56 kg ha−1 applied IF, PT, and at TI except for TS applied at TI. Common scab and black scurf were reduced depending on application timing and fertilizer.

Comparison of Reduced-Application and Sulfur-Based Fungicide Programs on Scab Intensity, Fruit Quality, and Cost of Disease Control on Peach.

The costs of two reduced-fungicide programs (5 applications each) and two micronized wettable-sulfur programs (6 or 11 applications each) and their impact on scab control and fruit quality were evaluated on 'Contender' and 'Cresthaven' peach over two growing seasons. The reduced-fungicide programs consisted of applications of chlorothalonil and captan or chlorothalonil, azoxystrobin, and captan. All programs provided excellent scab control when disease pressure was low to moderate; however, six sulfur applications did not adequately control scab under high disease pressure. The product cost of the reduced-fungicide chemicals was higher, but comparable with six applications of micronized wettable sulfur or nine hypothetical applications of nonmicronized wettable sulfur per season. The reduced-fungicide programs were preferable to weekly applications of sulfur (11 applications) because they equally controlled scab at a reduced cost and have greater potential to protect against other summer diseases. The fungicide program effects on fruit quality were inconsistent. A more detailed study is needed to determine if a relationship between fungicide programs and fruit quality exists.

Evalulation of acaricides and TNAU neem oils against spider mite, Tetranychus urticae (Koch) on bhendi and brinjal

Field and pot culture experiments were conducted to evaluate the bioefficacy of acaricides and TNAU neem oils against Tetranychus urticae (Koch) on bhendi and brinjal. Dicofol, monocrotophos, phosalone, wettable sulphur, Tamil Nadu Agricultural University Neem oil (TNAU NO 60 EC), Neem oil + Pungam oil (NOPO 60EC) and Neem seed kernel extract (NSKE) were used for the study. Dicofol 0.05% proved to be the most effective causing 70.56 to 91.85 per cent reduction of mites in blendi and 66.99 to 99.20 per cent reduction in brinjal both under field and pot culture conditions. The insecticides viz. wettable sulphur, phosalone and monocrotophos were next in order. The descending order of effectiveness was found to be NOPO, NSKE and TNAU NO.

New Fungicides and Application Strategies Based on Inoculum and Precipitation for Managing Stone Fruit Rust on Peach in California.

In greenhouse and field studies, rust on cling peach caused by Tranzschelia discolor was significantly reduced on leaves and fruit compared with that on controls by foliar applications of wettable sulfur, an agricultural oil, a substituted aromatic (e.g., chlorothalonil), as well as benzimidazole (e.g., benomyl, thiophanate-methyl), sterol biosynthesis inhibiting (e.g., myclobutanil, propiconazole, tebuconazole), and strobilurin (e.g., azoxystrobin) fungicides. The timing of treatments was a significant factor in reducing disease in most trials. Protective programs using wettable sulfur, tebuconazole, or azoxystrobin applied after stem lesion detection (ASLD) and before forecasted rains were highly effective. In the most effective programs for managing the disease, however, these fungicides were applied after stem lesion detection and occurrence of rainfall. Under highly conducive field environments for disease, single applications of azoxystrobin or tebuconazole at ASLD were significantly more efficacious than sulfur. Dormant treatments of liquid lime sulfur, chlorothalonil, or thiophanate-methyl/agricultural oil, however, were ineffective in reducing the disease during the subsequent spring and summer seasons. This is the first management program for rust on cling peach that utilizes inoculum and precipitation events to optimize timing of fungicide applications.

Variations in acaricidal effect of wettable sulfur on Tetranychus urticae (Acari:Tetranychidae): effect of temperature, humidity and life stage.

Under laboratory conditions, the acaricidal effect of wettable sulfur is influenced by climatic conditions and the stage of development of Tetranychus urticae. Its ovicidal effect results from the combined action of temperature and relative humidity (RH). Wettable sulfur becomes effective at 27.5 degrees C and 75% RH. Beyond this threshold, the acaricidal effect increases with rising temperature or humidity, to become complete at a temperature of 35 degrees C and 90% RH. Within the range of temperatures and humidities 20 degrees C/30% RH and 35 degrees C/90% RH the mortality of immatures (from protonymphs to teleiochrysalis) was total. Under similar experimental conditions, females usually died before the end of the experiment. Temperature and relative humidity increased the adulticidal potential of wettable sulfur. The fecundity of the sulfur-treated females and the viability of their progeny was found to depend on temperature and RH. According to the same climatic conditions, eggs were less susceptible than females, which were in turn less susceptible than juvenile stages.

Efficacy and phytotoxicity of lime sulphur in organic apple production

SummaryCurative and preventive efficacy and phytotoxicity of lime sulphur spray schedules, based on a warning system, were evaluated in the Netherlands during two growing seasons under field conditions. In most cases, lime sulphur treatments applied either curatively or preventively resulted in significantly lower scab damage on both the leaves and fruits compared to wettable sulphur treatments. However, all lime sulphur treatments showed high phytotoxicity values, reduced leaf size and had a tendency to a reduced yield quality compared to all other treatments. For curative schedules of lime sulphur on scab control, phytotoxicity and yield did not differ significantly from preventive schedules of lime sulphur. However, the use of a warning system combined with curative schedules of lime sulphur saved one and two lime sulphur sprays in 2000 and 2001, respectively, compared to the preventive treatments of lime sulphur. Our results demonstrated that a curative spray programme with lime sulphur at 0.75–2%, applied 35–45 h after predicted infection periods, can provide effective primary apple scab control, but no benefit in either yield or fruit quality was reached under organic growing conditions. Moreover, research herein clearly showed that organic growers are forced to find a balance between good efficacy and phytotoxic effects of lime sulphur.