Organic is the ideal at the OPW’s walled garden, but its gardeners have had to spray the potato crop with a fungicide

PESTS, PARASITES, predators and pathogens – yes, it’s that time of year again when a bewildering variety of life forms (including a few so tiny that they can only be seen under a powerful microscope) fight to the death in the OPW’s walled kitchen garden. Some, such as the aphids (pest), are being devoured by the ladybirds (predator), but others, such as potato blight (pathogen) are far more tricky to treat, particularly when, like the OPW gardeners, you’re trying to use organic-only methods. So very tricky, in fact, that after much painful examination of their eco-consciences, OPW gardeners Brian Quinn and Meeda Downey have made the difficult decision to spray their entire potato crop with the fungicide Dithane.

“Although the walled garden isn’t certified-organic, we’ve always maintained it according to organic principles and avoided using any chemicals unless they were approved for organic use. But now, with the new threat of Blue 13 and Pink 6 , we’ve had to make an exception,” says Brian resignedly. “We’re not exactly happy about it but some of the traditional potato varieties that we’re growing, such as British Queen, are martyrs to blight and they just wouldn’t stand a chance without regular spraying. We thought about copper sulphate but it turns out that’s being withdrawn from use because of worries over toxic levels building up in the soil. So we didn’t have much choice.

Meeda is in full agreement. “Other organic gardeners have told us that they don’t even bother trying to grow British Queen, even in a tunnel, because the variety’s so vulnerable to blight. Plus there’s been a blight warning for the last few days because of the humid, moist weather . So we weighed things up and decided it was better to be safe than sorry.”

Dithane, the chemical Brian and Meeda are spraying on the potato plants, is a preventative fungicide, meaning it needs to be applied to the crop before any sign of disease and while the weather (and the plant) is dry, if it’s to be in any way effective. It also needs to be applied at very regular intervals (every seven to 14 days depending on weather conditions) if the plants are to remain protected.

“When the weather’s dry, the risk of blight isn’t a worry as the fungus only spreads when there’s regular rainfall along with daytime temperatures of 15-25C. But Dithane won’t work on plants that are already infected, so although the crop is blight-free at the moment, we need to keep spraying if we want a decent potato harvest”, explains Meeda.

Unlike the OPW gardeners, those urban farmers who chose to grow the exceptionally blight-

resistant Sarpo varieties won’t have to worry about such a rigorous spraying programme to protect their crop. Trials by its breeders in the Sarvari Research Trust (sarvari-trust.org) have proven that while the Sarpo varieties can become infected with the blight pathogen (including Blue 13 and Pink 6), it has little obvious effect on the plant’s vigour or on the production of healthy tubers. So why didn’t the gardeners try growing these Hungarian-bred potatoes, which have become the popular choice amongst most organically-minded gardeners? “We hadn’t heard great things about the flavour” says Brian, although this alleged lack of flavour is hotly disputed by both its breeders and other gardeners. Even the well-known Italian chef and cookery writer Antonio Carluccio recently gave the Sarpo potatoes the thumbs-up for tastiness . “As well as that, we really want to grow a range of potatoes in the garden, including early varieties such as Orla, but the Sarpo varieties available at the moment are both maincrop types.”

But what constitutes an early, a second-early or a maincrop potato has been turned on its head this year, as the cold spring delayed growth by many weeks. In the OPW’s walled garden, things have been further confused by the fact that Meeda and Brian began chitting some seed potato varieties well before others, with unusual results. “The British Queen seed potatoes (second-

earlies) we’d ordered were the first to arrive from the suppliers, so they were already chitting for about five weeks before the Orla (first-earlies) came in. They both went into the ground at the same time (mid-March) but the British Queens are well ahead because of the extra chitting. So I suppose you could say that our first-earlies are now our second-earlies and vice-versa,” grins Brian.

Aside from blight, the OPW gardeners have few worries about pests (such as potato eel worm) afflicting the crop. But if they did, they’d have sprayed it with the organically-approved, broad-

spectrum bio-pesticide, SuperNemos (nemo.ie), which kills a wide range of soil-based garden pests. This Irish invention is now being trialled in other areas of the walled kitchen garden, including in the strawberry beds against the vine weevil (yet another pest). And while the squeamish urban farmer might not like the idea of spraying millions of microscopic worms onto the ground (there’s a definite “yuck” factor), inventor Dr Abdul Hamid Al-Amidi swears these nematodes (a mix of predatory and parasitic pathogens) are entirely safe for people, animals, plants, bees, bumblebees, earthworms and other beneficial insects such as ladybirds. “You don’t even need to wear protective clothing while spraying them,” he says.

SuperNemos is effective against wireworms, weevils, leatherjackets, cutworms and cabbage worms as well as many other damaging pests, but not against slugs, the gardeners’ most hated enemy. Instead Brian and Meeda are enlisting the help of Nemasys (nemasysinfo.com), a different garden pest-control company, but one that also supplies a range of beneficial nematodes to gardeners. These include Nemaslug, which contains a soil-dwelling nematode called Phasmarhabditis hermaphrodita, a parasite that specifically targets slugs. Unlike SuperNemos, which kills targeted pests within 48 hours, Nemasys takes a little longer (7-21 days) to kill, although the slug damage slows almost immediately.

All nematodes are naturally-occurring in the wild, by the way, proving the grisly point (in case you hadn’t already noticed) that your vegetable garden is already choc-a-bloc with natural-born killers. Just because you can’t see them doesn’t mean theyre not out there . . .

• The OPW's Victorian walled kitchen garden is in the grounds of the Phoenix Park Visitor Centre, beside the Phoenix Park Café and Ashtown Castle. The gardens are open daily from 10am to 4.30pm

• Next week Urban Farmer in Property will cover growing tomatoes in a glasshouse

• Fionnuala Fallon is a garden designer and writer