Late blight on potato in Flanders, Belgium: field trials and characteristics of the Phytophthora infestans population

Commercial fungicides were tested in the field for efficacy on foliar late blight caused by Phytophthora infestans. The fungicide treatments for late blight control were conducted at either 7- or 10-day intervals. The effect of the fungicide treatments on epidemic development, tuber rot and blight incidence and tuber yields were determined. Last summer late blight development was arrested in July and at the beginning of August due to high temperatures and lasting drought. Foliar disease severity significantly affected potato tuber yields. Lowest tuber yield was noted in plots with high late blight infection levels (nontreated control and an experimental mixture of organic acids (Vi-Care, 1 l/ha)) while highest yields were recorded in plots with low late blight infection. Late blight infection on leaf level was not significantly correlated with % tubers that showed late blight symptoms. No fungicide scheme completely arrested epidemic development under the environmental conditions of the trial. The effect of propamocarb hydrochloride + chlorothalonil (Tattoo C, 2.5 kg/ha) was less suppressive for P. infestans than the other fungicides tested for both interval systems. However, fenamidone + mancozeb (Sereno, 1.5 kg/ha), zoxamide + mancozeb (Unikat Pro, 1.8 kg/ha), dimethomorph + mancozeb (Acrobat, 2 kg/ha), cyazofamide + heptamethyltrisiloxane (Ranman 200 ml A/ha + 150 ml B/ha) and cymoxanil + famoxadone (Tanos, 0.6 kg/ha) controlled P. infestans most effectively for both interval systems. Also the other fungicides controlled foliar late blight sufficiently. Only small differences were observed between the different treatments. A total of 51 isolates of P. infestans were collected from disease outbreaks in commercial potato crops and private gardens in 2003. Isolates were recovered successfully from single lesions of diseased potato foliage. Not from all isolates pure cultures were obtained due to contaminations with Fusarium species and bacteria. The structure of the population was analysed phenotypically. Characteristics of the isolates included in vitro growth rate, mating type, in vitro sensitivity to the phenylamide fungicide metalaxyl-M and allozyme genotype at glucose-6-phosphate isomerase (Gpi) and peptidase (Pep) loci

Study on the STOP effect of fungicide combinations to control late blight in potato

The effectiveness of different fungicide combinations to control late blight and the STOP effect of these fungicide combinations for the control of foliar and tuber blight under high infection pressure was investigated. Last summer late blight development was arrested in July due to high temperatures and lasting drought. In August the weather was cloudy, rather cold and a lot of rain. These weather conditions were very favourable for late blight. Due to the heat waves of June and July the foliage started to die allready in August and P. infestans developped very fast in the second part of August. Because of that no incidence of foliage blight was scored. No significant differences in yield were observed for the different treatments applied. The combination cyazofamid + heptamethyltrisiloxaan (Ranman) + propamocarb + chlorothalonil (Tattoo C) had the highest yield. The percent diseased tubers fluctuated between 14,9 and 45,1 % for the different treatments tested. The amount of blighted tubers was lowest for fluazinam (Shirlan) + cymoxanil +chlorothalonil (Mixanil) and fluazinam (Shirlan) + benthiavalicarb + mancozeb (Valicarb)

Study on the curative and eradicant action of fungicide combinations to control late blight in potato

Commercial fungicide combinations were tested in the field for efficacy on foliar late blight caused by Phytophthora infestans in substitution of tin. When the first disease symptoms appeared, the tested fungicide treatments for late blight control were applied 3 times at 3-day intervals. The effect of the fungicide treatments on epidemic development, tuber rot and blight incidence and tuber yields were determined. Last summer late blight development was arrested in June due to high temperatures and lasting drought. August was characterized by rather low temperatures and high rainfall. These weather conditions were very favourable for the development of late blight. The foliar protection against P. infestans was comparable for all the tested fungicide combinations. The effect of combinations with dimethomorph + mancozeb (AcrobatC, 2.5 kg/ha) was less suppressive for P. infestans than the other fungicides tested. Lowest foliar disease severity was recorded in plots treated with fluazinam (Shirlan, 0.4 l/ha) + cymoxanil + chlorothalonil (Mixanil, 2 l/ha). Furthermore, highest tuber yield was noted in plots treated with fluazinam (Shirlan, 0.4 l/ha) + cymoxanil + chlorothalonil (Mixanil, 2 l/ha). The percentage blighted tubers fluctuated between 5 and 11 %. No fungicide combinations completely arrested epidemic development under the environmental conditions of the trial. However, fluazinam (Shirlan, 0.4 l/ha) + cymoxanil + chlorothalonil (Mixanil, 2 l/ha) controlled P. infestans most effectively

Chemical weed control in triticale (x Triticosecale Wittmack): review of five years of field experiments

During 5 subsequent growing seasons field experiments were carried out at the experimental farm of the University College Ghent (Belgium) to evaluate the selectivity and efficacy of herbicides applied for chemical weed control in triticale (x Triticosecale Wittmack). The experiments were set up on a sandy loam soil, according to a completely randomised block design with 4 replicates. Several herbicides and combinations of herbicides were applied pre- and post-emergence, at different rates. The influence of the different treatments on weed diversity, weed density, growth inhibition and chlorosis of the crop and grain yield were studied. Results obtained from these field trials indicated differences between the different treatments

Stomatal behavior of cowpea genotypes grown under varying moisture levels

Drought is a major limitation to crop productivity worldwide. Plants lose most of their water through stomata, thus making stomata an important organ in the control of transpiration and photosynthesis. This study assessed the stomatal behavior of four cowpea genotypes grown under four moisture levels under hot semi-arid conditions. Stomatal conductance (gs) was measured at 47, 54, 70 and 77 days after planting (DAP). Biomass and carbon isotope composition (C-13) were also determined at flowering. Genotype and moisture level significantly influenced gs. Genotypes varied in gs at vegetative stages (47 and 54 DAP) only. TVu4607 had higher gs under severe drought conditions at both 47 and 54 DAP. On the other hand, moisture level influenced gs at 54 and 70 DAP only. Stomatal conductance was severely restricted in cowpea under both moderate and severe drought conditions as gs was mostly below the threshold 0.10 mol m(-2) s(-1). Relationships between: biomass and gs, and C-13 and gs were positive under severe drought only. The findings revealed that cowpea genotypes vary in gs under dry conditions and that the variation is more prominent at vegetative stage, suggesting that cowpea productivity in dry areas could be improved through selection of genotypes that maintain higher gs under dry conditions

Sensitivity towards DMI fungicides and haplotypic diversity of their CYP51 target in the Mycosphaerella graminicola population of Flanders

Septoria leaf blotch, caused by the fungus Mycosphaerella graminicola, is the most important wheat disease in Northwestern Europe, and is currently controlled by fungicide applications. Since the spread of resistance to methyl benzimidazole carbamates (MBCs) and quinone outside inhibitors (QoIs) in European countries, reliable control is mainly dependent upon sterol 14 alpha-demethylation inhibitors (DMIs). In the last decades however, a slow shift towards reduced sensitivity of M. graminicola to DMIs has been observed. This shift is caused mainly by mutations in the CYP51 gene encoding the 14 alpha-demethylase target protein for these fungicides. In this work, M. graminicola isolates were sampled at fields spread over Flanders, Belgium. In vitro assays were used to analyze the sensitivity of the Flemish M. graminicola population towards different DMIs. Sequencing of the CYP51 gene of these isolates allowed us to identify and map the haplotypes in this population. The results showed that there is a large variability in DMI sensitivity between the isolates, even within one field, which is reflected in a high diversity in CYP51 haplotypes within the M. graminicola population in Flanders. Next to some haplotypes that were not described in literature before, we found that the population is dominated by CYP51 haplotypes which were previously associated with increased resistance towards DMIs

Exploration of essential oils as alternatives to conventional fungicides in lupin cultivation

Lupin (Lupinus L.) has the potential to become a true alternative for soybean as protein source, especially in the more temperate regions in the world. However, diseases such as anthracnose (Colletotrichum lupini), gray mold (Botrytis cinerea), and root rot or brown spot (Pleiochaeta setosa) are important threats for lupin production, leading to yield and quality losses. Although conventional fungicides offer a solution to these problems, there is a growing interest in the use of alternative (biological) treatments. In this research, the applicability of four pure plant essential oils (clove oil, juniper oil, tea tree oil, and thyme essential oil) and timbor® (a Thymus vulgaris-derived plant extract) as alternatives for synthetic fungicides towards the lupin pathogens—C. lupini, B. cinerea, and P. setosa—was investigated. The anti-fungal effect of juniper oil was limited, whereas the other oils and timbor® clearly suppressed the growth and spore germination of all fungi. The in vitro experiments revealed that thyme essential oil and timbor® were most effective to inhibit conidial germination and mycelium growth. Furthermore, the results of the pot experiments demonstrated that these Thymus-derived compounds were able to suppress P. setosa brown spot and root rot symptoms. Additional trials are necessary to evaluate the effect of these compounds under field conditions. However, based on these in vitro and pot experiments, it can be concluded that pure essential oils and Thymus-derived plant extracts are promising anti-fungal agents, having the potential to become true alternatives for conventional fungicides in lupin cultivation. To the best of our knowledge, this is the first study demonstrating the potential of plant-derived compounds to treat the main diseases affecting lupin production

Congolese rhizospheric soils as a rich source of new plant growth-promoting endophytic Piriformospora isolates

In the last decade, there has been an increasing focus on the implementation of plant growth-promoting (PGP) organisms as a sustainable option to compensate for poor soil fertility conditions in developing countries. Trap systems were used in an effort to isolate PGP fungi from rhizospheric soil samples collected in the region around Kisangani in the Democratic Republic of Congo. With sudangrass as a host, a highly conducive environment was created for sebacinalean chlamydospore formation inside the plant roots resulting in a collection of 51 axenically cultured isolates of the elusive genus Piriformospora (recently transferred to the genus Serendipita). Based on morphological data, ISSR fingerprinting profiles and marker gene sequences, we propose that these isolates together with Piriformospora williamsii constitute a species complex designated Piriformospora (= Serendipita) 'williamsii.' A selection of isolates strongly promoted plant growth of in vitro inoculated Arabidopsis seedlings, which was evidenced by an increase in shoot fresh weight and a strong stimulation of lateral root formation. This isolate collection provides unprecedented opportunities for fundamental as well as translational research on the Serendipitaceae, a family of fungal endophytes in full expansion

Effect of adjuvants on the efficiency of dimethomorph plus mancozeb (Acrobat 2 kg:ha) on the control of late blight

Industrial adjuvants were tested in combination with dimethomorph plus mancozeb (Acrobat 2 kg/ha) in the field to investigate their efficacy on foliar late blight caused by Phytophthora infestans. The tested adjuvant fungicide treatments for late blight control were applied 5 times at 7-day intervals. The effect of the adjuvant fungicide treatments on epidemic development, tuber rot and blight incidence and tuber yields were determined. Last summer late blight development was arrested in July due to high temperatures and lasting drought. August was characterized by rather low temperatures and high rainfall. These weather conditions were very favourable for the development of late blight. Due to the heat waves of June and July the foliage started to die allready in Agust. Because of that no incidence of foliage blight was scored. No significant differences in yield were observed for the different treatments applied. The addition of an adjuvant had a clearly positive effect on the tuber yield. In the control 12,7 % infected tubers were observed. The mean tuber infection of plots sprayed with the Acrobat-adjuvant combinations was 7,4 %