How to avoid potato blight

I can’t remember a worse year for growing potatoes than 2012 – spring droughts, late frosts, low temperatures and high rainfall resulted in poor growth, high levels of disease and disappointingly low yields. But while we can’t do much about the weather except pray to the sun gods, there are many ways in which gardeners can minimi se the risk of blight damage this summer. It’s all a question of “knowing thy enemy”.

Potato blight

Potato blight, or phytophthora infestans , is a genetically complex, highly adaptable fungus that can wreak great damage on unprotected potato crops, as evidenced by the Famine of the 1840s. The bad news for gardeners is that blight researchers have discovered that new, more aggressive strains of the disease continue to evolve.

Traditionally, blight has been controlled by the regular use of a preventative fungicide such as Dithane or copper-based sprays, but a growing band of gardeners are choosing to avoid the use of such chemicals. Capitalising on the fact that different potato varieties vary greatly in terms of their resistance to the disease, they’re instead switching to those with good blight resistance such as the Sárpo range. Developed by the Sarvari Research Trust in Wales, these spuds are the result of a decades-long breeding programme begun by the Sárvári family in Hungary.

The Sárpo "family" includes Sárpo Mira and Sárpo Axona (both main crop, red-skinned and floury), Sárpo Una and Kifli (earlier and waxy), Sárpo Shona (white-skinned) and Blue Danube (blue-flowering and blue-skinned). They're available as seed potatoes from a variety of stockists including Mr Middleton (mrmiddleton.com) and the Secret Garden Centre in Cork
(the secretgardener.com).

A handful of other maincrop varieties also showing excellent blight resistance include Bionica (early main crop and floury), available from Fruithill Farm (fruithillfarm.com). Dermot Carey, the market gardener who tends Harry’s Bar and Restaurant’s walled kitchen garden in Donegal, also highly recommends Tibet, another dark-skinned maincrop variety only available as a seed potato to members of the Irish Seed Savers’ Association.

For information on the Sustainable Potatoes United Development Study (Spuds) campaign to encourage Irish gardeners to grow blight-resistant varieties of potatoes , check out spuds.ie.

Blight-resistant varieties aside, there are a number of other important ways in which gardeners can protect their potato crops. First, always source good-quality, certified seed-potatoes from a reliable supplier and plant as early as possible.

Second , concentrate on early varieties, which have a far shorter growing season (roughly 14 weeks) than main crop potato varieties ( 18-20 weeks), making them less vulnerable to attack. Third , always practi se good garden hygiene. Be mindful of crop rotation – the longer the cycle, the less chance of passing on disease. Old potato “dumps” on the ground from last summer as well as any “volunteers” left in the soil to re sprout can act as a source of re-infection, so remove these by burning or bagging them. Plant at extra generous spacings, to discourage blight . Watch out for signs of disease (dark-brown patches surrounded by a pale “halo”, visible on wilting foliage and stems) and pay attention to blight warnings. If blight hits, cut stems back to ground level and dispos e of them .

While the risk of blight will still be greater than for crops regularly sprayed with a fungicide, careful hygiene controls like these can allow organic gardeners to grow potato varieties with only average blight resistance.

One example is the walled kitchen garden of Ballymaloe House. Here, heritage but blight-prone varieties prized for their tastiness, such as Home Guard (first-early), Sharpe’s Express (first-early), British Queen (second-early) and Pink Fir Apple (late main crop), are successfully grown alongside Sárpo Mira, Sárpo Axona and Blue Danube without any recourse to sprays. Other organic gardeners such as Dermot Carey also grow early varieties such as Orla and Setanta without spraying, reserving the limited use of copper-based sprays for vulnerable maincrop varieties such as Pink Fir Apple .

Top planting tip

Potatoes like a free-draining, very fertile, deep soil in full sun, and can be planted from mid-March onwards, ideally after being “chitted” for a few weeks indoors. If the soil is particularly cold or wet, postpone planting until conditions improve. Planting depth and spacing vary according to the variety, with “earlies” planted more closely (25-30cm apart, 45-50cm between rows) than main crops (40cm apart, 75cm between rows).

Useful to know

For those gardeners who want to buy only small amounts of a wide variety of seed potatoes, QuickCrop has a very useful Pic’n’Mix potato-picker web tool (see quickcrop.ie). School gardens interested in growing the historic, much-maligned Lumper potato can contact the Tops Potato Centre, Raphoe, Co Donegal, which will send on free seed samples while stocks last.

DATES FOR YOUR DIARY

Sonairte's Potato Day, March 23rd, 11am-4pm - for talks, displays and rare seed varieties (sonairte.ie). Daffoldil Day coffee morning, March 22nd, at Lodge Park Walled Garden beside the Steam Museum, Straffan.