Soil Tests Suggest Cyst Nematode Levels Are Increasing

June 2012

Researchers report increasing levels of beet cyst nematodes (BCN) in soils tested last year and are starting to pick up clear differences in levels of tolerance to the pest in recommended varieties.

According to Broom’s Barn, crop protection leader, Mark Stevens, the pest which can cause 30-40% yield loss through direct damage to the root could be being favoured by a larger area of oilseed rape in the rotation which is also a host of BCN.

His advice is for growers to be increasingly vigilant during the summer months and not to confuse symptoms of rhizomania with those of the nematode.† “Seen from June onwards, beet cyst nematode damage to the roots leads to wilting of crops similar to that seen in rhizomania.† The key visual difference is the appearance of lemon shaped cysts on the lateral roots,” he said.

Last year, Broom’s Barn undertook joint research with British Sugar and NIAB TAG to undertake BBRO funded work into the ability of tolerant varieties to resist BCN.

Taking soils with different known levels of the pest, Broom’s Barn grew varieties known to offer some level of tolerance to the pest side by side in one tonne boxes to check their ability to resist attack and to minimise build up of nematode populations in soils.

These included commercially available varieties Annouschka KWS and Sentinel and seven other RL entries compared alongside susceptible variety Bullfinch.

Dr Stevens reported that first year work showed that under high levels of the pest - >88 eggs/g of soil - KWS Annouschka had a 13% loss of root yield, compared to Sentinel at 25% which was just 4% ahead of the susceptible variety Bullfinch.†

In terms of overall root yield under high levels of infestation, KWS Annouschka was 9t/ha ahead of Bullfinch, whereas Sentinel was 14t/ha behind the KWS variety.

Perhaps more significantly in the long term, Annouschka KWS appeared better able at reducing BCN population build up in infected soils. ††Here, the research team measured the numbers of BCN eggs in the soil before and after the tolerant varieties had been grown – to give a final population: initial population index or pf/pi.

In essence, growing a non tolerant variety such as Bullfinch serves as a host for the pest and population levels in the soil rise – in this trial the pf/pi indicated they were 6.6 times higher after harvest.† In comparison, Annouschka KWS had a pf/pi of 1.3, showing a slight population increase, whereas Sentinel’s score of 5.9 suggested that the variety is less effective at reducing pest levels in the longer term.

Dr Stevens pointed out that it was a different story under lower levels of infestation.† Here, both KWS Annouschka and Sentinel produced similar yield responses to the pest, indicating that both can cope with low levels of the pest.

“Those who think they have a problem should have soils tested – these analyses can be turned round quickly – and if they test positive for BCN they should discuss their options with their British Sugar fieldsman,” he advises.

Dutch BCN Risks

Bram Hanse of the Dutch Institute of Sugar Research (IRS) painted a similar picture of rising BCN levels in Holland.† From a study of groups of farmers producing either high or moderate yields, he said that management levels were the key to differences in crop performance.

Of these, poor pest and disease control the most significant contributing factor to yield differences between the best and the worst growers and appeared more important than soil conditions or the influence of weeds or sowing date.

He pointed out that 70% of all beet fields surveyed had beet cyst nematode infestations, but 55% of these growers didn’t realise they had a problem and only 2% of the farmers surveyed were doing anything about it.

Since the survey – carried out in 2006-2008 – more growers had adopted BCN tolerant varieties in order to reduce yield loss in their crops, recognising that the right varieties were important to improving crop performance.