19-03-2013 17:54 PM | Grassland, News, Property News

Wet soils create complex soil pest and disease challenge



Dave Valentine
Dave Valentine
Potato crops could be in greater danger of PCN attack this season, if soil sampling has failed to identify existing populations and impending risk.

Lancashire based potato agronomist, Dave Valentine of CAS Ltd, warned that shallow soil sampling in wet conditions could have underestimated the threat of PCN and Free Living Nematodes (FLN) this season.

In wet soils some testing may not have been getting deep enough to pick up soil pest populations, but when resampled at 20cm or more, he reported the true risk has been revealed.

Valentine also highlighted that FLN will have moved freely through the soil moisture in the exceptionally wet and waterlogged conditions.


"Soil testing works extremely effectively to identify the risk of PCN and FLN and to target appropriate control strategies, but it has to be done well. Inaccurate soil sampling creates a false sense of security," he added.

With the later hatching and more resilient Globodera pallida now by far the dominant PCN species, and with few varietal options for resistance or tolerance, growers have to be aware of the implications in selecting appropriate nematicide treatments, advised Valentine.

Where PCN cysts are located deeper through the soil profile, there is the added issue that triggering of egg hatch by the presence of root hairs will be even later as the crop develops this season.

The season’s prospects and the current soil conditions could make the ability of Nemathorin granules to control later hatching PCN and reduce the effects of FLN and wireworm soil pests more important than ever.

If nematicides have run out of efficacy before the later hatch occurs, PCN populations still could build up rapidly over the remainder of the season, even if physical crop yield is not adversely affected.

As soils begin to warm up, FLN will move back up the profile through soil moisture to attack developing roots, which could have a triple-whammy effect this season.

Initially the concern for the 2013 crop will be the impact of nematodes - both PCN and FLN - feeding on roots, which could be especially serious if planting is in cold, wet soils and growth is slow to get going.

"Secondly, there is the risk of FLN transmitting the Tobacco Rattle Virus that would result in damaging spraing symptoms in tubers at harvest,” advised Valentine.

Furthermore, he alerted growers to the implication of damage caused by feeding nematodes also creating an entry point or weakness for soil borne disease pathogens to attack, with Rhizoctonia (Black Scurf) the key early season threat and the increased risk of Black Dot developing.

"We know that Black Dot is closely correlated to the length of the growing season and the duration that tubers are in the ground; delays in harvesting in the wet conditions over the past autumn and the resulting levels of infection in store have reiterated the issue," he reported.

"In-furrow Amistar treatments have certainly proven extremely effective in delaying the onset of any infection and buying extra time to get a clean crop out of the ground.”

The in-furrow Amistar treatments could also prove particularly effective this year to prevent Rhizoctonia pruning of stems and stolons if crops are slow to get going in the cold wet soils, or from delayed plantings where fast establishment and even emergence will be crucial to counter the effect of a shortened growing season.

Valentine advocated that, where possible, growers hold off planting until soil conditions improve and the crop can grow away faster.

However, he acknowledges that there will be added pressure on time and resources this year as farms struggle to establish spring cereal crops on large tracts of land that wasn’t sown in the autumn; plant your spring arable cropping first, and then concentrate on the potatoes, he advised.

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