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DARD Horticulture Management Notes - June 2013 by Kieran Lavelle


Apple scab season
As any plant pathologist will tell you, three fundamental factors must coincide for disease to appear and spread successfully. The disease causing agent, for example, spores of the apple scab fungus, Venturia inaequalis, must occur at the same time as the susceptible host organism, for example, leaf tissue of ‘Bramleys Seedling’ apple trees, and in the correct environmental conditions for infection. In our apple scab example, this means long enough periods of leaf wetness and warmth for fungal spores to land, germinate and infect. 

Usually the season for scab ascospore release begins in late March and lasts until mid to late June, so the primary scab infection threat runs for up to three months (around 13 weeks). This year, however, persistently cold and relatively dry conditions at the start of spring meant there was little or no leaf and blossom bud expansion to coincide with the first spore outbreaks, which themselves were not recorded until 10 - 12 April. In addition, when these first spore releases occurred, temperatures were too low to give a definite risk of scab infection.

Hence apple scab control gave few serious challenges at first. But, as any Bramley apple grower will tell you, that didn’t remain the case! In the forty days from mid April until 22 May, there were ten confirmed apple scab disease alerts, one lasting more than 50 hours. In fact, during those six weeks there was no more than three days’ break between any two scab infection periods. It is a credit to local growers that they effectively managed this threat by maintaining tight fungicide protection regimes in their orchards.

Keeping the apple trees clean in this way until late June / early July should mean no lingering scab for the rest of the year, best quality Bramleys at harvest, and a reduced spore inoculum for spring 2014.

Under our feet

Soil is one of the most valuables resources and one we take for granted. When we think of soil microbes we only seem to think of those which cause damage to the crops we are producing. Evidence now indicates that only a few cause direct damage and that many are beneficially important in maintaining our soil health, nutrient availability and pathogen control. The relationship between soil and plant life is not something new. The relationship between nitrogen fixing bacteria and the roots of legumes plants is well documented. Nitrogen fixing takes place with, for example, bacteria species 

Rhizobium and Bradyrhizobium providing nitrogen to soils annually. Developments in scientific research are now providing us with a new armoury in maintaining quality production. Opportunities have now become available for using microbiology based controls as part of our defence systems. In the past we have had non -specific control by adding organic materials.

This encouraged microbiology activity which in turn provided us with less crop loss by the presence of unquantified micro activity. Today’s developments have allowed for the more specific application of microbes. Microbe agents such as bacteria Bacillus, fungi Gliocladium and species of Trichoderma have all been commercially developed which can be added to increase suppressiveness.

A number of commercial microbe based products are now becoming the norm in general production. Yes, some are still in the development stage and do require further assessment, but in some cases are the only form of control we have.

Maintaining and continuing to develop our understanding of what our natural resource soil holds is essential in providing a more sustainable control method for future production. As science develops it is hoped that many others will be found of benefit and will become common place in production.

Prepared by: Kieran Lavelle
e-mail : kieran.lavelle@dardni.gov.uk
telephone: 028 3752 9060


Source: HortiTrends News Room