Certis UK

Dealing with difficult powdery mildew infections on ornamental crops

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Source: Certis UK

We are now at the peak of the powdery mildew season and, with increasing temperatures and dry weather conditions, susceptible crops are likely to be at high risk of infection.

The pathogen

There are five different powdery mildew species which attack ornamental crops in the UK.

  • Erysiphe ssp. – this pathogen is mainly found during cooler periods and is relatively sensitive to fungicides with most of the available products being able to control it. It’s most commonly found on Acanthus, Dahlia, Alder, Phlox, Aster, Artemisia, Begonia, Solidago, Hollyhock, Hebe, Lavatera, Salvia, Achillea, Delphinium, Clematis, Coreopsis, grasses, oak, herbs, Geranium, Verbena, Berberis, Potentilla, rosemary, Verbascum, Rhododendron
  • Microsphaera ssp. – can be found during cool and warm periods, but the pathogen is sensitive to long wet spells. Only a few of the conventional fungicides have efficacy against this pathogen. It affects Acer, lilac, oak, alder, elder, Ribes, marigold, Arbutus, Hydrangea, Kalmia, Mahonia, Ilex, Akebia, Catalpa, Carpinus, ash, Berberis, elm, hawthorn, rose and crabapple crops.
  • Sphaerotheca ssp. – prefers warm, windy and dry weather conditions especially when these conditions occur after a wet spell. It is mainly found on Hops, Viola, Euphorbia, rose, poplar, Spiraea, Ribes, laurel, Potentilla, Fragaria, Photinia and crabapple crops.
  • Podosphaera ssp. - there is known resistance to some of the conazole based active ingredients in America. It affects Malus, Prunus, Crataegus, Amelanchier, Photinia, Sorbus, Pyracantha, Cotoneaster, Spirea and hawthorn crops
  • Oidium ssp. – this pathogen disperses long distances. There are a small number of fungicides controlling this powdery mildew from FRAC groups 3, 8 and 11. Crops affected are Begonia, Euonymus, plane, Citrus, Antirrhinum Chrysanths, Hydrangea, Lonicera, vines, Sedum, carnation, Verbascum

Control options

Takumi SC (cyflufenamid) is particularly effective on these powdery mildew species when used at lower water volumes of between 500 and 800 L/ha for existing infections and 1000 L/ha for preventative applications. To obtain adequate control, applications should be made on the underside of leaves where possible and on leaves low in the plant canopy because the fungus prefers these surfaces. Takumi SC provides translaminar and vapour action which helps it move through the leaves as well as volatilise to the undersides of higher leaves.

Top tips to minimise the potential risk of resistance developing:

  • Apply systemic fungicides with contact fungicides in programmes or tank mixes
  • Maximise spray coverage
  • Apply fungicides only when needed
  • Use full label rates
  • Alternate between systemic fungicides with different modes of action as indicated by their FRAC code
  • Incorporate nonchemical control practices

Remember…

Do not use Takumi SC in two consecutive spray applications. Always use Takumi SC as part of a fungicide resistance programme by using products from different mode of action groups.

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