5 February 1999

Falling pcn is down to fungal pathogens…

Potato cyst nematode

control without nematicides,

in a tight rotation?

Research at IACR-

Rothamsted suggests it is

possible, and one Lincs

grower is well on the way to

doing just that.

Andrew Swallow reports

FUNGAL control of potato cyst nematode could mean an end to nematicide use, says IACR- Rothamsted.

Seed inoculation with nematode parasitic fungi, or cropping to maintain the fungi in the soil, has been shown to reduce egg numbers to negligible levels without recourse to chemicals.

Lincolnshire Field Products is doing just that. It grows 200ha (500 acres) of potatoes for pre-packing near Spalding, on a one in four or five rotation. When all around pcn numbers were rising, their egg counts started to fall.

"In some fields potatoes were barely viable," recalls farm manager David Walker. "Then 10 years ago numbers started to decline, to the extent that we dont have to treat some fields now."

That saves the business about £270/ha (£110/acre) across 80-120ha (200-300 acres) a year, he estimates.

Tests by IACR-Rothamsted found fungal pathogens were attacking the female cyst nematodes. On one field egg counts had fallen from an average 35eggs/g in 1989, to 0-4egg/g in 1998, despite a number of potato crops in between.

Such fungal pathogens were known to exist, but in most rotations the level of fungus is insufficient to prevent rapid build up of nematode numbers.

"However, on the fields near Spalding we found about 10 eggs/g of the brassica cyst nematodes too," notes Dave Crump, research nematologist at Rothamsted. That would cause next to no damage to the brassicas, but plays a vital role for subsequent potato crops.

"These nematodes maintain a specific fungus in the soil which is parasitic on both potato and brassica female cyst nematodes. Hence the brassica crops maintain this beneficial fungal population between potato crops."

Three distinct species of parasitic fungi have been identified, says Dr Crump. Two colonise the root of the host plants and infect the nematode feeding on the root. The other simply attacks the exterior of the feeding female.

Once cysts have hardened, the resting state is immune to attack until the next host crop is planted, he adds. Without the brassica crops and associated nematodes, there would be no food source for the fungi between potato crops.

All three types of fungi have been identified in Jersey where early potato crops are grown annually on some land.

For UK maincrops such continuous cropping is not an option due to other disease limitations, but closer rotations without nematicide are a real opportunity with biological pcn control. "A one in three rotation would be brilliant for growers," he observes.

Of the three strains of parasitic fungi, verticillium, paecilomyces, and acremonium species, verticillium shows the most promise for commercial growers. "It has the advantage of chlamydospores – a resting state which can be used dry to inoculate tubers. The other two would require some form of wet culture medium," he says.

A seed-treatment or planter applied granule would ensure fungal inoculation of the soil and roots when and where it matters most.

"The roots we need to target are the first thick main roots. These can host loads of females hence it makes sense to apply the inoculum round the seed tuber," he stresses.

Dr Crump is confident that such techniques have a commercial application. "This generates a lot of interest but most commercial people dont really believe in bio-control. However, I am totally confident that this could work in the right situations."

Small niche markets such as organic or garden potatoes may be the first to pioneer the technique, but large-scale applications could follow.

Besides the environmental aspect of reducing nematicide use, the cost of such treatments should be competitive too he reckons. "I would like to think it would be less than a nematicide," he says.

For Mr Walker, the natural phenomenon is saving him nematicides, and bringing more land into potato production.

"We have almost doubled our potato acreage in the last three years, which would put pressure on the rotation. But we are putting in more brassicas to try and bring the pcn numbers down and it seems to be working," he says.

BOX

NO NEMATICIDE PCN CONTROL

Chemical free PCN control

Fungal pathogen attacks PCN

Other nematode host crops required

Fungal inoculum seed treatment?

Brussels sprouts to control potato cyst nematodes? Lincolnshire Field Products manager David Walker is doing just that on potato ground near Spalding. IACR-Rothamsted researchers found nematode parasitic fungi were responsible for the falling pcn phenomenon.

BIOPCNCONTROL

&#8226 Chemical free PCN control

&#8226 Fungal pathogen attacks PCN

&#8226 Other nematode host crops required

&#8226 Fungal inoculum seed treatment?

Bio-control of potato cyst nematode is a real possibility, says IACR-Rothamsted nematologist Dave Crump. Parasitic fungi applied as a seed dressing or granule could end nematicide use for some growers, he reckons.