Conference pears; work on system changes to enable better scab control in organic orchards in the Netherlands

Scab control in Conference pears is the bottleneck in organic growing. A group of growers, advisers and researchers in the Netherlands is working on new approaches to organic pear growing. Central to this approach is a reliable and good scab control. Changes in the system of cultivation are sought which will enable this scab control with less fungicide. This has become even more urgent since copper was banned as a fungicide in the Netherlands. First results from trials on vigour control show that there is potency for system changes that will enable a better scab control in organic growing. Scab incidence was reduced in three trials with 34, 58 and 82% respectively. The project, in which also other cultivation measures are being tested, will be continued

Susceptibility to Apple Scab, Nectria Cancer and Powdery Mildew of Different Unsprayed Apple Varieties

Twentyfive apple varieties were evaluated for Apple scab (Venturia inaqualis), Nectria canker (Nectria galligena) and Powdery mildew (Podosphaera leucotricha) for 4 to 7 years. The trees were grown unsprayed. The weather conditions at the experimental orchard normally results in high infections of apple scab and low infections of powdery mildew. Infections of Apple scab is often seen also in scab resistant varieties. Williams Pride, Katinka and Katrina (scabresistant varieties) were the only varieties not showing scab in the experimental period. The two scabresistant varieties Angold and Produkta (varieties having a poor fruit quality) was unsusceptible to Nectria canker. The reference variety Elstar/Elshof was in all plantings among the most resistant varieties. Powdery mildew is not a problem at the experimental orchard. Most varieties had low susceptibility to Powdery mildew. Varieties with low susceptibility to diseases in general were Angold, Produkta, Rajka, Rubinola, Ahrista, Gerlinde, Gul Richard, Sukkertop, Katinka, Katrina, Marian and Primicia

Resistance management in Vf apple scab resistant organic apple orchards

Modern Vf scab resistant apple varieties open the way for organic growers to lower fungicide input, higher yields, better skin quality, more biological control for mites and insect pests and better consumer acceptance of their management practices. Manny examples in the past years have shown however that the Vf resis-tance can be easily overcome by local scab populations in north-western Europe. Discussions during the meetings of the IOBC working group Diseases in Orchards in 2000 in Fontevraud (France) and in 2003 in Lindau (Germany) lead to a set of management practises necessary to prevent gene-fulx, and selection to-wards Vf virulence in the local apple scab populations. Eleven orchards of the Vf resistant apple variety Santana that where planted between 1998 and 2000 where monitored for apple scab lesions on fruits form 2002 to 2005. The results where evaluated in respect tot the applied resistance management practices. We conclude that fungicide treatments on the major primary scab infections are the key factor in the resistance management on Vf resistant apple varieties. From a practical viewpoint these early season fungicide applications are also necessary for the control of powdery mildew, as the main Vf- resistant apple cultivars appear to be relatively susceptible to powdery mildew. For private gardens apple varieties with field resistance to apple scab should be advised, not Vf resistant varieties

REPCO contribution to the development of products for apple scab control

Natural compounds were sprayed according the RimPro scab warning system from start of bud break until the mid of June. Scab incidence was measured on the leaves and the fruit. Phytotoxicitiy and russet-ing was assessed. The natural compounds were sprayed together with sulphur and were compared with the standard biological fungicides copper hy-droxide and sulphur alone. Compound E73 + sulphur was the most effective on fruit. Armicarb and Resis-tim both sprayed with sulphur were comparable in efficacy with Funguran-OH. In our study laminarin (GL 32) did not shown any effect on the control of scab on apple

Investigations on alternative substances for control of apple scab - Results from Conidia germinating tests and experiments with plant extracts

The intention of this research project, which was supported within the "Bundesprogramm Ökologischer Landbau", was to find alternatives for the control of Venturia inaequalis for the organic fruitgrower. Beside the investigations on reducing the ascospore potential on fallen leaves, experiments were conducted in laboratory, greenhouses and in orchard to test direct control of scab with different plant extracts, concentrations and methods of extraction. Extracts from Inula viscosa, Quillaja saponaria-bark, citrus-species (AGROMIL) and Saponaria officinalis revealed a distinct efficacy against apple scab in greenhouse studies on apple seedlings. ELOT-VIS, CHITOPLANT, COMCAT, MOOSEXTRAKT, SILIOPLANT und FZB 24 did not show sufficient efficacy with the application schedule used for control of scab. Mixtures of Quillaja-saponine and sulphur reduced effectively apple scab incidence. In an experiment concerning rain stability Citrus-extract and Quillaja-saponine showed a lower efficacy against scab after a simulated rain of 5 mm. The screening of different supplements to Citrus-extract as surfactants and adhesives revealed GREEMAX and BIOPLUSS as promising additives. Both combinations showed an efficacy comparable to copperoxychloride corresponding to 400 g elementary copper per ha

ECONOMIC IMPACTS OF FUSARIUM HEAD BLIGHT IN WHEAT

Fusarium Head Blight (FHB), commonly known as scab, has been a severe problem for wheat producers in recent years. This study estimates the economic value of crop losses suffered by wheat producers in the 1990s. Nine states and three wheat classes are included in the analysis, which considers the effects of scab on both production and average prices received. The cumulative value of losses (1991-97) in scab-affected regions is estimated at $1.3 billion. Two states, North Dakota and Minnesota, account for over two-thirds of these dollar losses.Fusarium Head Blight, scab, crop losses, wheat, Production Economics,

Assessment of the susceptibility to pests and diseases of 36 apple cultivars in four low-input organic orchards in France

One of the keystones of the organic orchard is the cultivar choice as one element of pest and disease control. However, few exhaustive data sets concerning the cultivar susceptibility to pests and diseases are available for growers. In order to identify cultivars adapted to organic production methods, the susceptibility to scab, aphids and powdery mildew and the agronomic properties of 36 cultivars were assessed in four French sites under different pedo-climatic conditions. Different levels of susceptibility to scab were observed for 23 scab Vf-resistant and 13 other cultivars. In the North of France where Vf resistance is overcome, the Vf cultivars displayed different levels of scab severity. A high variability in the susceptibility to aphids was observed whereas susceptibility to powdery mildew varied less. The analysis of susceptibility properties, yield and fruit quality, fruit storability and tree behaviour permitted to identify a set of interesting cultivars according to the site

New approaches in biological control of apple scab

Apple scab caused by Venturia inaequalis is a major disease in apple production. In organic farming scab control depends on the use of fungicides based on copper or sulphur. Since the use of copper will be restricted in the European Union and the use of sulphur often leads to insufficient control and phytotoxicity, alternative control measures are needed. The use of microbial antagonists may be an alternative to fungicides for scab control. Scab epidemics during summer are driven by conidia produced only on apple leaves. In this situation, antagonists present in the phyllosphere may interfere with conidia of the pathogen during sporulation or infection. Within the EU-funded project REPCO, more than hundred fungi were isolated from sporulating scab colonies and tested on apple seedlings for their potential to reduce sporulation of the pathogen. Since the aim of the study was to contribute to the development of a biocontrol product, only candidates were selected which fulfilled a range of additional criteria considering major constraints in development of biocontrol products. The best antagonists were applied under orchard conditions during two growing seasons. The antagonist H39 significantly reduced sporulation of V. inaequalis after most applications. However, in a few cases no effect was found

Control of apple scab by curative applications of biocontrol agents

In organic apple growing protective applications with copper, sulphur or lime sulphur are used for apple scab control. Protective applications have to be repeated when new leaves unfold. The timing of protective sprays depends on the weather forecast. If forecasted infection conditions fail to appear, treatments were for nothing. With curative control agents available, the number of treatments could be reduced. In greenhouse trials we tested control agents for their protective and curative efficiency against apple scab after artificial inoculation of potted apple trees. Applications were done 2 hours before inoculation, 5 hours after inoculation on wet leaves, 5 hours after inoculation during simulated rainfall or 24 hours after inoculation on wet or dry leaves. The optimal time of application differed between the preparations tested. Vitisan and OmniProtect had their highest activity when sprayed curative 24 hours after inoculation. Combinations were found, which revealed a high efficiency against apple scab from 2h before to 24 hours after inoculation. In a field trial apple scab was effectively controlled by curative applications of OmniProtect

Prospecting for organic fungicides and resistance inducers to control scab (Venturia inaequalis) in organic apple production

As a part of the REPCO project we are prospecting for plant extracts and other materials to control apple scab in order to find substitutes for copper fungicides in organic apple production. Two routine screening systems are used to evaluate the potential of materials to control apple scab; one testing the effect of materials on conidium germination on glass slides, and one testing the effect of materials on scab development on apple seedlings grown in growth chambers. Several interesting materials have been identified and a number have been selected for testing in experimental organic apple orchards. Studies of the mode of action of promising materials including induced resistance are on-going and work on improvement of timing and formulation is initiated at KVL