The Challenges of September
September brings the onset of Autumn the, ‘season of mists and mellow fruitfulness’. Our gardens are hopefully bursting with plentiful harvests of fresh fruit and vegetables, but unfortunately for us gardeners, there are plenty of fungal diseases waiting for a suitable opportunity to attack our cherished crops.
Early Blight
Summer 2023 has seen one of the worst years for Potato Blight I can remember. I subscribe to a blight forecasting service and for my locality (North Shropshire) virtually every day since late June as seen conditions suitable for blight spores to germinate and establish within the crop.
The local farmer has been applying fungicides to a nearby field of potatoes every week during this period to try and avoid infection, but we both now have blight in our potato crops!
I have had early blight (Alternaria solani) on my second early Potatoes and maincrop potatoes for a couple of weeks. This disease tends only to attack foliage that is beginning to yellow.
As the crop has usually finished growing by the time this disease attacks, removal of the foliage will not have any detrimental impact on yield and a full crop can be harvested with little tuber blight present.
Much more devastating is the presence of late blight (Phytophthora Infestans). this one will quickly sweep through a crop of potatoes.
Its prolific spore release will not only infect the leaves but spores washed into the soil will also infect the tubers turning them into a slimy rotting mass.
Cutting Back & Preventing Spores
I have two infected plants, ironically two mid-June planted potatoes of the cultivar ‘Vivaldi’ on the end of the row!
Everything else, namely all the main crop potatoes are now starting to naturally yellow and die back as part of the natural plant senescence.
So what is the best course of action now? Although the plants would grow for another 7-10 days , before they go completely yellow, I shall not run the risk of the late blight spreading to the tubers.
I remove the haulms cutting them back to around 6 inches of stem, making sure all the leaves are removed and deposited in the green waste bin.
This will prevent any spores released being washed into the soil and infecting the tubers.
Whilst there have been some significant improvements in blight resistant potato cultivars in recent years, there are no completely resistant cultivars and potato blight is constantly evolving into new races, which will prove challenging for the future.
Companion Planting
One great success though for disease control by plant breeding, is in peas.
Peas which are sown from Mid-May onwards will in most years succumb to Pea Powdery Mildew, although it rarely results in a total crop fail. I grow two cultivars of peas ‘Oasis and ‘Terrain’. As you can see from the image ‘Oasis’ is now heavily infected with Powdery Mildew’ which has turned the plants white, whilst ‘Terrain’ is totally clear despite being grown in the same row.
I have not tried it but it is claimed that ‘Terrain’ will crop until November and still be disease free! I have grown it for three years now and can certainly say it will out-perform all other peas for later sowings as the high disease resistance means the pods will fill.
Next year I will grow ‘Oasis’ for the earlier sowings and ‘Terrain’ for any sowings after late April.
The September greenhouse is always challenging, cooler and longer nights are ideal conditions for the spread of grey mould (Botrytis Cinerea). Although it is tempting to close windows at night only do this if frost is expected as ventilation and good air circulation is really important to control this disease.
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