Abstract: A laboratory trial was conducted to test the efficacy of OxiDate in controlling the late blight of potato and tomato fungus, Phytophthora infestans. In addition to the control, three OxiDate concentrations (1:150, 1:100 and 1:50 of OxiDate to water) were used in this study. A total of 17 different late blight isolates collected from New Brunswick, Prince Edward Island, Manitoba and Quebec (Canada) were subjected to various concentrations of OxiDate in a replicated experiment using a 2-way Completely Randomized Design. Growth of all isolates was inhibited when the 1:50 OxiDate concentration was used. At the 1:100 concentration, growth of 94.1% of the late blight isolates used was completely inhibited. At the lowest concentration of 1:150 OxiDate, the growth of 76.5% of the isolates tested was completely inhibited. The results of this study suggest that OxiDate has the potential to be used in preventing the occurrence of late blight in potato tubers if applied on potatoes in the proper manner after harvest and prior to storage.
Abstract: A long-term trial (5 years) is being conducted at a commercial property on land that has a history of high incidence and severity of soil-borne diseases. Five rotational crops (potato, pasture, brassica, cereal and squash) are being tested for their effects on pathogen inoculum. Soil applications of metalaxyl fungicide are used as a standard treatment for comparison. Soil samples are taken before and after each crop rotation cycle and plated on agar media for microbial enumeration, to study the changes in fungal pathogen populations. After three growing seasons, rotational treatment of potato and cereal + BQ Mulch (Brassica crop) reduced the level of Phytophthora and other (unidentified) fungi compared with the same rotation without BQ Mulch. Metalaxyl has had no effect on the soil levels of Phytophthora and Pythium spp.
Abstract: Formulated plant extracts and oils were investigated for control of diseases caused by Phytophthora spp. Soil infested with chlamydospores of Phytophthora nicotianae was treated by incorporating 1, 5, and 10% aqueous emulsions of formulations containing clove oil, neem oil, pepper extract and mustard oil, cassia extract, synthetic cinnamon oil, or the fungicide metalaxyl. Population densities of P. nicotianae were determined at 0 (before treatment), 1, 3, 7, 14, and 21 days after treatment. Treatment of the soil with 5 and 10% aqueous emulsions resulted in significant (P < 0.05) differences among treatment mean values at each assay date. After 1 day, population densities were reduced to below the limit of detection (<0.04 CFU/cm(^3)) in soil treated with 10% aqueous emulsions of two pepper extract-mustard oil formulations and two cassia extract formulations, and near the limit of detection for a synthetic cinnamon oil formulation. Over time, populations of P. nicotianae were detected in the assay; however, after 21 days, populations of P. nicotianae in soil treated with one of the pepper extract-mustard oil formulations still were not detected. Formulations of clove oil, another pepper extract-mustard oil combination, the two cassia extracts, and the synthetic cinnamon oil reduced populations 98.4 to 99.9% after 21 days compared with the nontreated control soil. The neem oil formulation and metalaxyl did not reduce pathogen populations at any rate tested. In the greenhouse after 35 days, 10% aqueous emulsions of a pepper extract-mustard oil formulation, a cassia extract, and the synthetic cinnamon oil formulation suppressed disease development in periwinkle 93.0 to 96.7% compared with the nontreated infested soil. The observed reduction in the pathogen population and significantly more healthy plants in the greenhouse indicates that these formulations of plant extracts and oils could have important roles in biologically based management strategies for control of diseases caused by P. nicotianae.
Abstract: Black pepper vines were less affected when the vines were treated either with metalaxyl gold MZ 64 WP (Ridomil gold) @2.5 g/vine or potassium phosphonite (0.5 per cent) as spray (@ 2 I-vine) and drench twice (@ 3 I-vine) during before on set of monsoon and second application in the month of August coupled with soil application of antagonistic organism i-e., Trichoderma harzianum @50g (cfu 107) along with 1 kg of neem cake to the root zone of the vine. Application of systemic fungicides alone i-e., metalaxyl MZ 68 WP (Ridomil gold) @2.5 g/vine or potassium phosphonate (0.5 per cent) as spray (@2 I-vine) and drench twice (@ 3 I-vine) also showed effectiveness in the compating the disease.
Abstract: The generation of dimethomorph resistance in Phytophthora infestans was attempted using ethidium bromide/UV light mutagenesis and repeated culturing on dimethomorph-amended medium. Ethidium bromide/UV mutagenesis created two isolates of P. infestans with resistance factors for dimethomorph >20, i.e., the ratio of the 50% effective concentration (EC50) of the mutant to that of the wild-type. With repeated culturing on dimethomorph-amended medium, the rate of growth (mm diameter/day) increased until the tenth subculture for most P. infestans isolates. Resistance factors generated from repeated culturing were <8 for all isolates. For most isolates, the generation of dimethomorph resistance resulted in reduced growth rates on nonamended medium, regardless of the level of resistance or induction treatment. Additionally, the frequency of infection of leaf disks and whole tubers was significantly reduced in >20% of the isolates repeatedly subcultured on dimethomorph-amended medium. Regardless of the induction treatment, reduced fitness was common for all P. infestans isolates, indicating a potential biological cost associated with dimethomorph resistance. Based on these results, the development of field resistance to dimethomorph in P. infestans is unlikely with the currently employed resistance management strategies.
Abstract: Isolates of Phytophthora infestans collected in Canada in 1997 from both potatoes and tomatoes, were tested on potato leaf discs for their response to an equal active ingredient concentration (10 μg a.i./mL) of the following commercial fungicides: Acrobat MZ (Dimethomorph and Mancozeb), Ridomil Gold (metalaxyl-m), Dithane (Mancozeb), Curzate (Cymoxanil), Bravo (Chlorothalonil), and Tattoo C (Propamocarb and Chlorothalonil). Relative percent leaf infection values, estimated on fungicide-treated vs fungicide-free leaf discs, were compared among isolates from the US-8 and US-11 genotypes isolated from the two host plants. Based on an equal concentration of each fungicide’s active ingredients, variations in relative percent leaf infection were recorded between US-8 and US-11 genotypes, and between potato and tomato isolates within each genotype. Bravo and Tattoo C used with similar active ingredients concentrations were the most inhibitory to all groups of isolates. Dithane and Ridomil Gold provided uniform low inhibition against P. infestans when tested on potato leaf discs. The different behavior of P. infestans isolates from potato vs tomato suggests that management of late blight in these two important crops must take such differences into consideration. In particular, the nature and concentration of the fungicides to be applied must take into account any information available about genotypes present on each crop.
Abstract: The ability of trans-2-hexenal, carvacrol and eugenol to control F. verticillioides was explored in vitro and in artificially infected kernels. The effect of the trans-2-hexenal fumigation on F. verticillioides control, fumonisin production and kernel germinationwas also investigated in naturally infected kernels. Trans-2-hexenal, carvacrol
and eugenol vapour showed fungicidal activity against F. verticillioides, in in vitro trials. Trans-2-hexenal was the
best pathogen inhibitor, followed by carvacrol and eugenol. In maize kernels, fumigations with trans-2-hexenal provided a high inhibitory effect on F. verticillioides growth and its efficacy depended on concentration and time
of incubation. Themost effective dose of trans-2-hexenal was 369 μL/L, but this concentration induced off-odourinmaize. The exposure to 246 μL/L trans-2-hexenal provided the best control of F. verticillioides and no phytotoxic symptoms or off-odour in kernels was observed. In contrast trans-2-hexenal fumigations were ineffective in the reduction of fumonisin concentration and high concentration (369 μL/L) stimulated fumonisin levels. Reduction or delay in the germinability of the kernelwas observed after trans-2-hexenal exposure. The results showed that trans-2-hexenal postharvest fumigation is effective in F. verticillioides control also in asymptomaticmaize kernels, but cannot reduce fumonisin production.
Abstract: Use of Fusarium-infected seed for cereal crops results in a reduced plant density due to seedling blight. This is especially a problem in organic agriculture, for which currently no practical seed disinfection methods are available. In the present paper we investigated whether spring wheat cultivars differ in tolerance to seedling blight in vivo, whether the possible differences could be linked to cultivar differences in initial growth rates, and whether differences in weed infestation were related to differences in emergence. Seed six spring wheat cultivars (Melon, Lavett, SW Kungsjett, Epos, Pasteur, Thasos), containing three Fusarium infection levels were obtained and sown in two field experiments in 2006 and 2007 and in an outdoor pot experiment in 2007. Results indicated that the six spring wheat cultivars differed in their tolerance to seedling blight, and consequently in the percentage of emergence of their seeds. The relative levels of tolerance to seedling blight of the six cultivars were robust in the three experiments performed. No clear relationship between initial growth rates and tolerance was found. In our experiments, no early and homogenous weed pressure was present, but in the 2007 field experiment a relationship between initial seedling emergence and weed infestation after anthesis was determined. Based on the presented results we suggest that additional to resistance to Fusarium head blight (FHB), differences in tolerance to seedling blight should also be considered during selection of wheat cultivars for organic agriculture.
Abstract: Leather rot, caused by Phytophthora cactorum , is one of the most important fruit-rotting diseases of
strawberry worldwide. Efficacy of mefenoxam and potassium phosphite against leather rot, when
applied in a post-infection fungicide program, made in response to rain events was evaluated over 3
years of testing. Post-infection treatments of potassium phosphite and mefenoxam were compared with
calendar-based treatments of azoxystrobin or potassium phosphite sprayed weekly, starting at late
bloom (fruit set). In order to obtain high-risk conditions for infection (splash dispersal of the pathogen
and subsequent infection periods), plots were flooded until standing water was observed between the
rows. Post-infection applications were made within 36 h after the initiation of a flooding event. Leather
rot incidence in the untreated controls ranged from 15 to 66% over the 3 years. All fungicide treatments
had significantly (P < 0.001) less leather rot incidence than in the untreated control. There were no
significant differences in leather rot incidence between the different fungicide treatments. Percent
control (the percentage reduction in incidence relative to the check) was as high as 100% with all
fungicide treatments. Mefenoxam and potassium phosphite post-infection (after flooding) provided
control equal to that obtained with a calendar-based spray program, but with from 1 to 3 fewer fungicide
applications.
Abstract: Coconut coir dust, commercially available as coco-peat, is used in raising the seedlings of vegetable crops in tropical countries. Coir-pith and other derivates of coconut husk have been well recognized as substrates for the multiplication of Trichoderma spp. and commercial nurseries use coco-peat for raising the seedlings. In the present study, coco-peat enriched with Trichoderma harzianum was used for raising tomato and chilli seedlings to test the effect of the same on managing wilt caused by Fusarium oxysporum f. sp. lycopersici in tomato and damping off and root rot caused by Phytophthora capsici in chillies in nurseries. The enrichment with T. harzianum, resulted in reduced wilt incidence (5-7.5%) compared to control (38.75%) in tomato with increased plant growth parameters. Though germination was reduced compared to control (without pathogen), there was reduction in P. capsici infection in chillies by up to 50% compared to coco-peat without Trichoderma enrichment. The use of coco-peat enriched with T. harzianum can be adopted by commercial nurseries for better plant growth and reduced incidence of tomato wilt and chilli root rot while raising disease free and healthy seedlings.
Abstract