Fungicide Application Methods Research Articles

Evaluation of Fungicides and Fungicide Application Methods to Manage Phytophthora Blight of Pigeonpea

Phytophthora, a blight of pigeonpea caused by Phytophthora cajani, has been significantly increasing in major pigeonpea production regions of India. Limited information on infection with this pathogen and its epidemiology, as well as a lack of adequate resistant cultivars, is hampering the management of Phytophthora blight significantly. Therefore, five fungicides, viz., metiram + dimethomorph, cymoxanil + mancozeb, famoxadone + cymoxanil, mancozeb, and metalaxyl-M + mancozeb, were evaluated against P. cajani under control conditions to control zoospore induction, as well as the infection of zoospores, at the seedling stage. The half-maximal effective concentration (EC50) of fungicides for mycelial inhibition was calculated. The lowest EC50 was recorded in metiram + dimethomorph (0.17 µg/mL), followed by the metalaxyl-M + mancozeb (2.49 µg/mL) and cymoxanil + mancozeb (8.23 µg/mL) fungicides. The formation of the sporangium and zoospores was most significantly affected by metalaxyl-M + mancozeb, followed by metiram + dimethomorph and cymoxanil + mancozeb, in terms of sporangia viability and zoospore germination and encystment. Further, under glasshouse conditions, different fungicide application methods (e.g., seed-treatment; soil-drench; foliar-spray, either singly or in combinations) were evaluated with fungicides on susceptible (ICP 7119) moderately resistant pigeonpea (ICPL 99010, ICPL 20135 and ICPL 99048) cultivars. The seed-treatment + soil-drench, soil-drench + foliar-spray, and soil-drench of fungicide application methods were found to be effective in controlling the Phytophthora blight, at p < 0.001. A combination of the seed-treatment + soil-drench and soil-drench + foliar-spray methods, using metalaxyl-M + mancozeb or metiram + dimethomorph fungicides on moderately resistant cultivars (ICPL 99010), has a synergistic effect on the ability to control the Phytophthora blight at the seedling stage.

Effect of Fungicide Protection of Sugar Beet Leaves (Beta vulgaris L.): Results of Many Years Experiments

The rosette is the above-ground morphological part of sugar beet in the first year of its ontogenesis. The size and health of the leaves determine photosynthesis and the production of sugars and their redistribution throughout the plant and thus the yields and quality of individual organs. One means of protecting leaves is to apply fungicides. Their efficacy and effects of use depend on, among other things, the active ingredient and number of sprayings, as well as environmental conditions. The aim of the 11-year study was to evaluate the effect that the foliar application of fungicides in sugar beet cultivation had on leaf infestation and damage, the Leaf Area Index (LAI), leaf yield, and a plant foliage index (FI) expressed as the ratio of leaf mass to root mass. In field experiments, six treatments were compared: a control without fungicides; three sprayings with triazoles, benzimidazoles, and strobilurins as the active ingredients; and a single application of tebuconazole, epoxiconazole, strobilurin, and an epoxiconazole + thiophanate-methyl mixture. The efficacy and effects of the fungicide protection depended on its method of application and environmental conditions. Applying fungicides weakened the positive correlation of sugar beet leaf infestation and leaf damage to the sum of precipitation relative to the unprotected plants. In ten of the eleven years of the study, fungicide protection significantly increased leaf yields of plants and decreased their FI. In only three years did three sprayings increase leaf yield more than single sprayings, and, in six years, at least one of the active ingredients or the epoxiconazole + thiophanate-methyl mixture was as effective as triple sprayings. It is therefore warranted to permanently monitor the condition of plants and to select the fungicide application method depending on conditions.

The Impact of Fungicide Application Method on Soybean Canopy Coverage, Frogeye Leaf Spot, and Yield

Field trials were conducted across Iowa from 2017 to 2020 to investigate the effect of fungicide application methods (traditional and undercover) on coverage, disease severity, and yield. Foliar fungicides were applied at the soybean (R3) growth stage by a traditional ground sprayer with an overhead spray boom or a ground sprayer with 360 undercover sprayers that hang down into the canopy. Fungicide coverage was measured as milliliters per liter of pyrenetetrasulfonic acid dye detected on soybean leaves and as a percent coverage of water-sensitive spray cards from three canopy zones (upper, middle, and lower). Both detection methods showed that the upper canopy received significantly more coverage through the traditional sprayer than the undercover sprayer. The percent coverage in the middle canopy was not different between the two application methods. The tracer dye detected greater fungicide distribution in the lower canopy by the undercover than the traditional method ( P = 0.034). Greater disease severity was observed in 2018 and 2019 than in 2017 and 2020. Regardless of the year or application method, no location in the canopy had a significant difference in foliar disease control, nor did fungicide application affect yield. Results from these trials show adequate coverage of fungicide, but disease severity was not reduced, and yield was not improved.

Activity of the Novel Fungicide Mefentrifluconazole Against Colletotrichum scovillei.

The prevalence and destructiveness of anthracnose, caused by Colletotrichum scovillei, in pepper production regions seriously affects pepper yield and quality. Mefentrifluconazole, the first of the isopropanol-azole subgroup of triazole fungicides, was introduced for the control of pepper anthracnose. However, the growth characteristics of pepper fruit and rapid spread of anthracnose suggest that the fungicide application method must be optimized to enhance fungicide efficacy. The sensitivity of C. scovillei to mefentrifluconazole was determined by mycelial growth and germ tube elongation assays using 157 single-spore isolates with mean 50% effective concentration values of 0.462 ± 0.138 and 0.359 ± 0.263 mg/liter, respectively. The in vivo data also showed that mefentrifluconazole had favorable protective and curative effects against pepper anthracnose. Mefentrifluconazole significantly affected C. scovillei infection on pepper by reducing appressorium formation and sporulation, shriveling spores and germ tubes, and causing the abnormal development of appressoria and conidiophores. Mefentrifluconazole could move acropetally, horizontally, and basipetally in pepper plants. Compared with a knapsack sprayer, mefentrifluconazole applied by mist sprayer exhibited significantly better activity against pepper anthracnose. Additionally, as the spray volume increased from 45 to 150 liters/ha, the control efficacy of mefentrifluconazole first increased and then tended to be steady, with an optimal spray volume of 90 liters/ha. The difference in disease control efficacy was related to the deposition and droplet distribution of mefentrifluconazole on the pepper fruit. These results provide scientific guidance for the application of mefentrifluconazole in pepper fields and improved fungicide utilization.

Comparison of aerial and ground sprayer fungicide application technologies on canopy coverage, disease severity, lodging, and yield of corn

Fungicides may be applied to corn using an airplane or a ground sprayer. Questions regarding which technology is better at coverage throughout the corn canopy are common among farmers and agronomists. The objectives of this study were to compare the efficacy of three application technologies in terms of canopy coverage, foliar disease management, lodging and yield response. A fungicide was applied to corn at silking (R1) by airplane, a traditional ground sprayer with an overhead spray boom, or a ground sprayer with 360 Undercover sprayers that hang down into the canopy. Replicated on-farm and small-plot trials were conducted across Iowa in 2017 and 2018 for a total of nine site-years. Fungicide coverage was measured as ppm of pyrenetetrasulfonic acid (PTSA) dye detected on corn leaves, percent coverage of water sensitive spray cards, and percent of total application received. Foliar disease data were collected in three zones of the canopy: the upper canopy (UC), the ear leaf (EL), and the lower canopy (LC). Coverage and disease severity were not correlated with yield. In the 2017 on-farm trials, all three application methods delivered similar fungicide coverage on the EL and LC. In 2018, traditional and undercover methods provided greater coverage when compared to aerial application, however, fungicide distribution within the canopy was similar among the application methods. Overall trends indicated the traditional spray method delivered the best coverage to the UC. The aerial spray method delivered the least coverage to the EL and LC for three site-years. The undercover spray method resulted in greater coverage to the LC. Foliar fungicides applied by all three application methods significantly reduced foliar disease severity, and fungicide application methods did not differ from each other, and reduced disease severity to similar levels. Lodging was reduced approximately 50–75% by all application methods. For 8 of 9 site years, fungicide application did not affect yield significantly (P > 0.05), although numerically less yield was consistently recorded in the non-sprayed controls. Our findings indicate these three application technologies were similarly effective in reducing plant disease levels and lodging. But the reduction in disease due to fungicide application did not affect corn yield.

Spray volume deposits and fungicide efficacy on soybean rust (Phakopsora pachyrhizi)

Soybean rust (SBR), caused by Phakopsora pachyrhizi, is one of the most destructive fungal diseases affecting soybean yields in many countries. Fungicide application methods that provide better SBR control efficacy may reduce soybean losses due to this disease. We investigated the effects of spray volumes applying the fungicide pyraclostrobin plus epoxiconazol at 133 + 50 g a.i. ha-1 by a conventional sprayer (CS) and an air-assisted sprayer (AAS). Field experiments were conducted comparing the effects of spray volumes of 110, 160, and 210 L ha-1 and two application techniques (CS and AAS) on spray deposits and SBR control. Fungicide efficacies were measured by disease severity, thousand seed weight, and yield. Correlations between disease severity and yield were also assessed. All treatments were applied with an Advance 2000 AM18 sprayer. In general, SBR disease and yield did not differ significantly when fungicide applications were applied with AAS compared to CS. Increasing the spray volume from 110 to 210 L ha-1 did not increase spray deposit coverage on soybean leaves. Low disease severity was obtained by fungicide applications using a spray volume of 210 L ha-1. Safe recommendations of ground spray volumes for SBR control should be between 160 and 210 L ha-1, using hydraulic nozzles.

Influence of Nitrogen Rate and Timing, Fungicide Application Method, and Simulated Rainfall after Fungicide Application on Brown Patch Severity in Tall Fescue

Core Ideas Tall fescue lawns can be fertilized during the summer months at modest N rates without affecting brown patch severity. When an appropriate fungicide such as Heritage was used for brown patch management, the method of fungicide delivery did not affect brown patch suppression. Simulated rainfall up to 0.5 inches within 15 min of fungicide application did not compromise fungicide efficacy. In North Carolina, tall fescue (Festuca arundinacea Schreb.) is widely grown throughout the Mountain and Piedmont regions. North Carolina is in the transition zone, which is subject to hot, humid summers that predispose tall fescue to brown patch (Rhizoctonia solani Kühn). Field trials were conducted over a 2-year period (2015–2016) to evaluate the effects of nitrogen rate and timing, application method of a fungicide, and rainfall following fungicide application on brown patch severity on lawn height tall fescue. Seven rates of urea providing 0 to 6 lb N 1000 ft-2 year-1 were initiated each year in March with repeat applications monthly at 1 lb N 1000 ft-2. In a separate study, various timings of urea were conducted throughout the year for a total of 3 lb N 1000 ft-2 yr-1. In 2015, no significant differences in disease severity or turfgrass quality were observed among the seven N rates. Only the application of 6 lb N 1000 ft-2 yr-1 resulted in significantly higher brown patch compared with the non-treated control in 2016. No significant differences in disease severity or turfgrass quality were observed in the timing study in both years. Azoxystrobin was applied with a ride-on spreader/sprayer (11 gal water-carrier acre-1), a commercial applicator gun (130 gal water-carrier acre-1), and a research spray boom (88 gal water-carrier acre-1). No differences were detected among application methods. A rainfall event of 0.5 inches was simulated with overhead irrigation 30 min after application of fungicides. No differences were detected among the fungicide treatments, and all provided excellent control of brown patch.

Fruit and nut weight in pecan tree canopies in relation to the severity of pecan scab at different heights

SummaryFusicladium effusum is the cause of pecan scab, the most destructive disease of pecan in the south‐eastern USA. The aim of the study was to determine how scab severity at different sample heights in tall trees (14–16 m) affected fruit and nut weight at those same heights. Three experiments were performed in 2010‐2011 on trees of scab‐susceptible cultivars (cvs. Desirable and Wichita) and either received fungicide using an air‐blast sprayer or were non‐treated controls. Samples for measures of fruit and nut weight were taken at 0–5.0, 5.0+–7.5, 7.5+–10.0, 10.0+–12.5 and 12.5+–15.0 m (and were assessed for scab severity). A general linear mixed model analysis showed main effects of sample height, fungicide treatment and sample height × fungicide treatment interactions in all experiments on fruit and nut weight and on disease severity. Control trees had significantly more severe disease on fruit lower in the canopy, while fungicide‐treated trees either had similar disease severity at all heights or slightly more severe disease in the upper canopy. On control trees, where there was a linear relationships between fruit or nut weight and sample height, it was invariably positive (R2= .85–.94). On fungicide‐treated trees, fruit or nut weight most often had a negative linear relationship with sample height (R2=.69–.89). When significant, in control and treated trees, there was invariably a negative linear relationship between fruit or nut weight and scab severity (R2=.66–.94). Gradients in fungicide coverage and scab severity impact fruit and nut weights that can have ramifications on yield for a tree as a whole. Understanding the distribution of scab in pecan and other tall tree canopies provides a basis for developing management strategies and fungicide application methods to uniformly minimize disease.

Effectiveness of Nine Different Fungicides for Management of Crown and Root Rot of Chile Pepper Plants Caused by Phytophthora capsici

Bell and chile pepper plants are affected by the economically important disease Phytophthora blight, which is caused by the oomycete pathogen Phytophthora capsici. Greenhouse and field trials were conducted to evaluate and compare the ability of nine different fungicides to reduce development of the crown and root rot phase of Phytophthora blight and the resulting chile pepper plant death when applied at 2- and 4-week intervals. Overall, chile pepper plant mortality was significantly decreased in three greenhouse trials with soil applications of fungicide products containing ametoctradin + dimethomorph, cyazofamid, dimethomorph, ethaboxam, fluazinam, fluopicolide, mandipropamid, mefenoxam, and oxathiapiprolin. The same fungicides, excluding mandipropamid and oxathiapiprolin, also significantly reduced overall plant mortality in two field trials. No significant difference was found between 2- and 4-week fungicide application intervals with respect to chile pepper plant survival in any greenhouse or field trial. In general, the degree of reduction in chile pepper plant mortality was lower in field compared to greenhouse trials, probably due to the respective soil surface spray compared to soil drench method of fungicide application used in each instance. Accepted for publication 17 November 2015. Published 30 November 2015.

Timing and Efficacy of Fungicide Applications for Diplodia Ear Rot Management in Corn

Diplodia ear rot, a corn (Zea mays L.) disease caused by the fungus Stenocarpella maydis (Berk.) B. Sutton, has been a persistent ear rot across the United States. Management options are currently limited. Field trials conducted under inoculated and non-inoculated conditions were established at two locations in Indiana from 2011 to 2013 to test the fungicides azoxystrobin plus propiconazole and prothioconazole against Diplodia ear rot. Fungicides were applied at three individual growth stages during each year. Fungicides did not consistently reduce Diplodia ear rot compared to non-fungicide-treated controls in any year. Applications also did not consistently increase yield at any timing under inoculated and non-inoculated plots compared with the non-fungicidetreated control. Fungicides were tested in an in vitro assay to determine the effective fungicide concentration at which 50% of mycelial growth or conidial germination of S. maydis was inhibited (EC50). Propiconazole and prothioconazole EC50 values indicated efficacy in reducing fungal growth under controlled conditions; however, current fungicide application methods and plant barriers to fungicide contact with the pathogen may prevent these products from effectively reducing Diplodia ear rot in a field setting. Accepted for publication 23 August 2015. Published 1 September 2015

Evaluation of the profitability of a new precision fungicide application system for strawberry production

This study evaluates farm-level risk and profitability of a new web-based expert system developed for precision fungicide management for strawberry production in a humid and warm climate. The Strawberry Advisory System (SAS) examined in this study allows for a temporally-variable, weather-dependent fungicide application to manage anthracnose and Botrytis fruit rot diseases in strawberry production in the southern United States (U.S.) and specifically Florida. Using results from six-year production trials combined with historical state-level data, we simulate the distribution of the ten-year net present value (NPV) of profits for SAS-based and traditional Calendar-based strawberry fungicide management. The joint probability distributions of yields and sale prices driven by weather variability are modeled with Monte Carlo stochastic simulation. The new expert system is estimated to significantly reduce crop losses (23.7% on average for anthracnose and 20% for Botrytis) and decrease fungicide use (47% on average for anthracnose and 49% for Botrytis), while increasing profit 41.6% on average in the case of anthracnose and 16.8% for Botrytis. Although the use of the new expert system increases the variability of yield and profit, SAS significantly increases both yield and profit compared to those of Calendar-based method. Based on the risk-adjusted profitability analysis, SAS is a preferred method of fungicide application. Assuming a representative Florida strawberry farm of 10.5 hectares (26 acres), the value of SAS is estimated on average to be $1.76 million for anthracnose and $0.89 million for Botrytis, over a ten-year horizon of use. SAS fungi management is a viable and practical decision-support system for fungicide application that can increase profit, and potentially reduce the environmental footprint from strawberry production. It can add significant economic value to the strawberry producer in the United States and in other countries.

Using Soil-Applied Fungicides to Manage Phytophthora Crown and Root Rot on Summer Squash.

Phytophthora crown and root rot (Phytophthora capsici) of summer squash is especially difficult to manage because all commercial cultivars are highly susceptible to P. capsici. Producers have traditionally relied on foliar fungicide applications to control Phytophthora crown and root rot despite their limited efficacy. Soil fungicide applications, including via subsurface drip chemigation, have recently gained interest as a method of improving control of P. capsici infections. In this study, soil drenches and foliar applications of 11 fungicides were compared for control of Phytophthora crown and root rot of summer squash in replicated field and greenhouse trials. Fungicides were applied at 7-day intervals. Incidence (%) of plant death was assessed from 7 to 42 days post inoculation (dpi) in field trials. Crown rot severity was rated on a scale of 1 (no wilting) to 5 (plant death) from 5 to 21 dpi in greenhouse trials. Results of field and greenhouse trials were similar. Plant death of 'Cougar' following inoculation with P. capsici isolate 12889 occurred at all growth stages from first true-leaf to full maturity in field trials. Plant death 42 dpi differed significantly (P ≤ 0.0001) among fungicides and application methods. The fungicide-application method interaction also was significant. Some fungicides were ineffective regardless of application method. In general, soil drenches were more effective than foliar applications at limiting plant death but no treatment completely controlled disease symptoms. Mean plant death 42 dpi was 41% for soil drenches and 92% for foliar sprays. Drenches of fluopicolide, mandipropamid, or dimethomorph limited plant death to ≤10% and prevented yield loss associated with root and crown rot. Foliar applications generally did not reduce plant death compared with the untreated, inoculated control, and were unable to prevent yield loss in field trials. In greenhouse trials, crown rot severity differed significantly (P ≤ 0.0001) among fungicides, application methods, and cultivars when plants were inoculated with P. capsici isolate 12889 or SP98. Crown rot was less severe and disease progress was slower following soil drenches than foliar applications. Some fungicide treatments were more effective on 'Leopard,' which was less susceptible to P. capsici than 'Cougar.' Soil application methods, including soil drench and drip chemigation, should be evaluated when fungicides are registered for soilborne disease control, because these methods provide better control of Phytophthora crown and root rot than foliar application.

‘Fungicide application method’ and the interpretation of mycorrhizal fungus–insect indirect effects

Mycorrhizal fungi, by altering their host plant's physiology, can have indirect effects on insect herbivores. The ‘fungicide application method’ is a common approach used to investigate the indirect effects of mycorrhizal fungi on insects. This approach works by using initially mycorrhizal plants, and then generating a subset of these plants that are free of mycorrhizal fungi by applying fungicide to their roots. When insect feeding-bioassays are conducted using the resulting mycorrhizal and non-mycorrhizal plants, differences in insect performance are typically attributed to differences in mycorrhizal colonization per se, rather than the application of the fungicide. Thus, the fungicide application method relies on the assumption that there is no direct toxicity of the fungicide on the focal insect species, and no indirect effects on the focal insect resulting from effects of the fungicide on the host plant or on non-target soil micro-organisms. We tested this critical assumption by feeding Zygogramma exclamationis (Chrysomelidae) larvae on non-mycorrhizal Helianthus annuus (Asteraceae) plants whose roots were treated with a solution of the fungicide benomyl or with a distilled water control. Larvae fed on benomyl-treated plants had reduced survival, lower relative growth rate, and lower food conversion efficiency, compared to larvae fed on control plants. Hence, fungicides applied to roots can affect herbivorous insect performance even in the absence of the possibility of mycorrhizal fungi-mediated effects. We recommend caution when using fungicide application and suggest that selective inoculation is a preferable method of generating mycorrhizal and non-mycorrhizal plants when studying mycorrhizal fungi–insect indirect effects.

Evaluation of foliar fungicide application methods on soybean

A field trial was conducted at Fargo, North Dakota, in 2005 and 2006 to evaluate different fungicide application methods on soybean (Glycine max). Kromekote® paper cards were placed in the upper and lower canopy of soybean plants, and tebuconazole fungicide mixed with a blue dye was sprayed with different application methods at the R5 developmental stage. The applications were made with a conventional sprayer with Turbo TeeJet® 110015 flat-fan nozzles at 276 kPa liquid pressure, a conventional sprayer with XR TeeJet® 80015 flat-fan nozzles at 276 kPa liquid pressure, an AirJet® bifluid nozzle spray system with liquid pressure at 276 kPa and air pressure at both 76 and 48 kPa, or an air-assisted spray system with liquid pressure at both 221 and 83 kPa. An untreated control was also included to evaluate the effect of tebuconazole on soybean yield. Dye-sensitive Kromekote paper cards were analyzed to determine the percent coverage and the volume median diameter (VMD) of the droplets. Significant (P ≤ 0.05) interactions between year and application method were detected, most likely resulting from differences in plant height and development between the years. Droplet coverage in the upper canopy did not differ in either year among the application methods. Most application methods provided similar droplet coverage in the lower canopy in 2005, but the conventional sprayer with XR TeeJet 80015 flat-fan nozzles provided the greatest coverage in the lower canopy in 2006. Correlation analysis indicated that droplet coverage in the lower canopy increased with increased VMD of the droplets in 2005 (R = 0.91), and that yield increased with increased fungicide coverage in 2006 (R = 0.85). Visible symptoms of foliar fungal diseases were not present in either year, and tebuconazole had no effect on soybean yield, compared with the untreated control in either year.

Comparison of deposition patterns in two programs for applying protectant fungicides to potato stems and leaves for the control of late blight (Phytophthora infestans)

Fungicides are applied by air, chemigation, and ground in the Columbia Basin of Oregon and Washington. These methods of fungicide application differ in deposition of fungicide to the canopy and cost. This study compared the alternate use of air and chemigation application of fungicides (AIRCHEM) with chemigation alone (CHEM), by either measuring chlorothalonil or manganese (mancozeb) amounts in three canopy levels (upper, middle, lower), both on leaflets and stems, after multiple fungicide applications on a 7-day schedule. Greater amounts of chlorothalonil or mancozeb were usually found on the leaflets in the upper and middle canopy locations from AIRCHEM compared to CHEM, the day of fungicide application and 7 days later. Deposition of fungicides on stems generally follow the same pattern as leaflets, but the amount deposited and maintained on stems was significantly less than leaflets. Mancozeb deposition in the three canopy levels followed the same pattern as was found for chlorothalonil. The greater the amounts of chlorothalonil on leaflets and stems resulted in better disease reduction during inoculation assays. Reduced fungicide amounts on stems compared to leaflets may be the reason for increased stems infections in recent years by more aggressive strains of late blight. This is the first report quantifying chlorothalonil or mancozeb amounts on potato stems and the first to report amounts of mancozeb on potato foliage after fungicide application.

Low-drift fungicide application technology for sclerotinia stem rot control in canola

Five methods of fungicide application were made to canola ( Brassica napus) to determine the effect of nozzle type and pressure on sclerotinia stem rot ( Sclerotinia sclerotiorum) infection of canola and crop yield. Benomyl and vinclozolin fungicides were effective in reducing stem rot in treated plots and increasing yield over the unsprayed check in 2 of 3 years. Variation in product performance among years indicated that environmental conditions had a major effect on crop development, sclerotinia stem rot infection, the effect of fungicides and subsequent yield. Overall, conventional flat fan nozzles (TeeJet XR), low-drift venturi nozzles (CFFC TurboDrop) and hollow cone nozzles (TeeJet TXVS-8) were all effective at reducing disease symptoms. Both 275 and 550 kPa provided similar performance although increasing the venturi nozzle pressure to 550 kPa improved disease control slightly. These results indicate that venturi nozzle technology is appropriate for use with foliar fungicides for sclerotinia control in canola provided pressures are adjusted to optimize nozzle performance.

Application of chemical and biological agents for the management of frosty pod rot (Moniliophthora roreri) in Costa Rican cocoa (Theobroma cacao)

AbstractThis article describes two field trials carried out at La Lola, Costa Rica, to assess control measures against frosty pod rot of cocoa (Theobroma cacao) caused by Moniliophthora (Crinipellis) roreri. In the first, factorial, trial the control agents were applied using motorised mistblowers (MMs) and hydraulic sprayers fitted with a narrow angle cone nozzle. There was an interaction between agents and application methods; together with previous application data for the most active fungicide (copper hydroxide), these trials indicate that best yields are achieved with sprays that maximise deposits on pods. We describe the droplet size spectra produced by a Stihl SR400 MM under a range of conditions because this has become the standard method of fungicide application in this series of trials at La Lola. The factor that had the largest effect on droplet size spectrum was the presence or the absence of a detachable baffle plate in front of the air‐shear nozzle. In both trials described here, MMs were fitted with baffle plates, a formulation pump and restrictor transmitting 550 mL min−1 to deliver an estimated equivalent of 190 L ha−1. Copper hydroxide as prophylactic applications at 1500 g a.i. ha−1 have, to date, shown the most consistent (but incomplete) improvement in healthy pod yield. Use of copper fungicides may be cost effective when farm‐gate cocoa prices exceed approximately $1.25 kg−1. In these trials, isolates of the hyperparasitic fungi Clonostachys byssicola and Trichoderma asperellum and two off‐patent triazole fungicides (bitertanol and triadimenol) made no significant improvement to healthy yields. The systemic oxathiin fungicide flutolanil, at a dosage of 300 g a.i. ha−1, appears to protect pods substantially at early stages but gives proportionately less control of M. roreri than copper at later stages of pod development.

Efficacy, timing and method of application of fungicides for management of sorghum ergot caused by Claviceps africana

Trials conducted in Queensland, Australia between 1997 and 2002 demonstrated that fungicides belonging to the triazole group were the most effective in minimising the severity of infection of sorghum by Claviceps africana, the causal agent of sorghum ergot. Triadimenol (as Bayfidan 250EC) at 0.125 kg a.i./ha was the most effective fungicide. A combination of the systemic activated resistance compound acibenzolar-S-methyl (as Bion 50WG ) at 0.05 kg a. i./ha and mancozeb (as Penncozeb 750DF) at 1.5 kg a.i./ha has the potential to provide protection against the pathogen, should triazole-resistant isolates be detected. Timing and method of fungicide application are important. Our results suggest that the triazole fungicides have no systemic activity in sorghum panicles, necessitating the need for multiple applications from first anthesis to the end of flowering, whereas acibenzolar-S-methyl is most effective when applied 4 days before flowering. The flat fan nozzles tested in the trials provided higher levels of protection against C. africana and greater droplet deposition on panicles than the tested hollow cone nozzles. Application of triadimenol by a fixed wing aircraft was as efficacious as application through a tractor-mounted boom spray.

Effects of Nozzle Type and Spray Pressure on Control of Alternaria Leaf Blight of Muskmelon with Chlorothalonil.

Methods of fungicide application were evaluated for their influence on the chemical control of Alternaria leaf blight of muskmelon in 1997, 1998, and 1999. Chlorothalonil was applied through either flat-fan or hollow-cone nozzles and with spray pressures ranging from 207 to 1,034 kPa. In all 3 years, unsprayed controls had significantly more disease than any of the sprayed treatments. There was no significant effect of nozzle type on disease severity or yield in any year. Spray pressures of 207, 414, or 620 kPa did not significantly affect disease severity or yield in 1997. In 1998, the 827-kPa pressure significantly lowered disease severity compared with the 207-kPa and 414-kPa pressures, but a similar decrease in the number of lesions per leaf did not occur. Yield responses in 1998 did not support a relationship between spray pressures and disease control. In 1999, spray pressure of 1,034 kPa did not significantly decrease the area under the disease progress curve as estimated from weekly ratings of the disease severity ratings or counts of lesions per leaf made on two dates. Results indicate no differences in disease control due to any of the application methods examined.

Fungicide Application for Late Blight Management: A Boom Attached to a Center Pivot Irrigation System.

Chlorothalonil was applied to commercial potato fields of cvs. Russet Norkotah and Russert Burbank in replicated trials through either a center-pivot irrigation system or a spray-boom-attached-to-the-pivot system. Water rates were 26,192 and 675 liters/ha for the center pivot and attached boom, respectively. Three crop canopy levels were sampled within 2 h and again after 6 days following fungicide applications made at 7-day intervals. Efficacy of the two application methods was tested by inoculation of individual excised leaves with an isolate of strain US-1 or US-8 of Phytophthora infestans and by chemical residue analysis. Severity of late blight did not differ between the two fungicide application methods 2 h after application but, after 6 days, disease severity was significantly less on leaves where chlorothalonil was applied by the attached boom. Fungicide residues were three times higher on leaves where chlorothalonil was applied by the attached boom than with the center-pivot system. Significantly more disease occurred on fungicide-treated and non-treated leaves inoculated with the US-8 than the US-1 strain. Severity of late blight on inoculated leaves was inversely related to the amount of chlorothalonil residue on leaves.