Spotty celery
Q I have a problem with what I think is celery rust which has confounded me forever since I won’t use chemicals on it. Can you tell me how to fix it organically?
Question from K. Jensen, via email
A This looks like septoria leaf spot caused by the fungus Septoria apiicola, a relatively common disease of celery, especially in damp conditions. The best approach is to try to avoid conditions that favour the disease, so grow your celery in full sun, in well-drained soil, adding organic matter, such as compost, so the soil is moisture-retentive, and provide extra water in summer to prevent any water stress. Space the plants well apart to allow good air movement through the foliage so it dries out quickly after rain. Some celery varieties seem to be more susceptible to the disease than others. ‘Elne’, available from Kings Seeds, is reported to show good resistance. It’s a vigorous grower which, if planted in spring, matures early in the season, before weather conditions favouring the disease become prevalent.
At the first sign of disease symptoms pick off affected leaves and dispose of them in the rubbish or burn them – don’t compost them. Spores from infected leaves can remain in the soil for several years so clean up old plant debris and practice crop rotation, allowing three to four years between celery crops in the same patch of soil.
Copper fungicides, such as Liquid Copper, can help control the disease and their use is acceptable to some organic gardeners. Follow the label instructions; you may have to spray every seven-10 days if wet weather prevails. Seaweed-based foliar sprays have proved effective at reducing the incidence of fungal diseases on many plants, so might also be worth trying on celery.
Septoria leaf spot can be spread on the celery seed itself. If you grow your own from seed rather than buy plants, you may be able to reduce the problem by heat-treating the seed, soaking it in hot water at 50°C for 30 minutes immediately before sowing. The temperature and timing needs to be accurate – too low it will not kill the disease spores, too high you may damage the seed embryo. Mix the wet seed with fine dry sand to make it easier to sow.
Answer by Andrew Maloy (The Plant Doctor)
