Species of the fungus Pestalotiopsis are often found associated with leaf spots and diebacks, not just of conifers but of a very wide range of woody plants. They are usually regarded as being weakly pathogenic, that is they require a plant to be weakened or damaged in some way in order to colonise it. However, once within the plant tissues they can sometimes cause quite extensive damage.

Pestalotiopsis is often found colonising the shoots of conifer hedges that have suffered initial damage from aphid infestation. Wet weather favours dispersal of the spores and their ability to infect the plant.

You may see the following symptoms:

• Leaves turn yellow and then brown, often progressing back from the tip of a shoot
• A constricted, girdling area of browning sometimes develops on a twig, with the entire twig dying beyond this point
• Numerous black, ‘pinhead’-sized fruiting bodies, just visible to the naked eye, develop within the affected plant tissues
• Under wet conditions, thin black tendrils of spores ooze from the fruiting bodies

N.B. The development of brown patches and shoot dieback in conifer hedges can have a number of different causes (e.g. aphid damage, Pestalotiopsis, pruning at the wrong time of year, or various interactions between these factors). Laboratory examination of samples of affected shoots may be required to determine the precise cause(s).

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Non-chemical control

Try to avoid or prevent any of the factors that can lead to plant damage or stress. For example:

• Prevent or control damaging invertebrates such as cypress aphid
• Ensure that newly-planted conifers establish well
• Water plants during periods of extended drought
• Avoid unnecessary physical damage
• Prune hedges at the correct time of year (hedge pruning times)
• Avoid pruning during prolonged periods of wet weather (which are suitable for spore germination and infection), or during drought conditions (which can itself result in dieback)

If dieback due to Pestalotiopsis is diagnosed, pruning out the affected shoots will reduce the number of spores available to create new infections. However, remember that many conifers will not produce new growth if they are cut back hard into old growth.

Fungicides

The RHS recommends that you don't use fungicides. Fungicides (including organic types) may reduce biodiversity, impact soil health and have wider adverse environmental effects. If you do intend to use a fungicide, please read the information given in the link and download below to ensure that use, storage and disposal of the product is done in a responsible and legally compliant manner.
  
The products listed in the ‘Fungicides for gardeners’ document below are legally available for use by home gardeners in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally. Homemade products are not recommended as they are unregulated and usually untested.

There is no specific information available on the efficacy of any home garden fungicide against Pestalotiopsis.

Download

Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)

Link

Chemicals: storing and disposing safely

Pestalotiopsis species are regarded as weak pathogens, requiring a plant to be physically damaged or stressed (which itself can lead to tissue damage) in order to colonise the plant tissues. Very occasionally, the fungus is thought to be capable of attacking intact, healthy shoot tips.

Factors that can predispose a plant to colonisation by Pestalotiopsis include:

• Invertebrate feeding damage – cypress aphid (Cinara cupressivora) and other conifer aphids, for example, can cause significant damage on conifers such as Cupressus and × Cuprocyparis
• Weather or soil conditions, e.g. drought, waterlogging, wind damage
• Other forms of physical damage, e.g. from pruning or hedge trimming
• Root disease problems such as honey fungus or Phytophthora root rot
• Stress caused by poor establishment

Once it is active within the damaged tissues, the fungus can use these as a foothold from which to progress into adjacent healthy parts, extending the dieback.

The black spore tendrils, which ooze from the fruiting bodies under wet conditions, contain huge numbers of microscopic spores. These are splashed around by rain droplets, and can germinate to cause new infections if the leaf or twig surfaces stay wet.