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Forewarned Is Forearmed For Potato Pests

28 September 2019

The warm wet end to the summer has further fuelled the risk of tuber blight and it is more important than ever to maintain effective fungicide protection until the haulm is completely dead.  SRUC trials over many years, together with practical experience, have repeatedly shown that tuber infection can occur even when foliar blight severity is low.  The risk of tuber infection is enhanced in wet soils.  Strains of blight with reduced sensitivity to fluazinam have been confirmed in Scotland and so fluazinam-based products should not be used for tuber blight control at the end of the season because of the risk of selecting for less sensitive blight (i.e. genotype 37_A2) thus creating a high risk of inadequate future control of foliar and tuber blight.

It is a building concern to the potato industry, particularly the seed industry, how much land in Scotland is now infested with potato cysts nematodes.  It is never too early to start planning for next year’s crop and sampling fields when the soil is moist gives the most accurate estimate of nematode populations.  The populations of potato cyst nematode being found in ware land, in particular, have increased dramatically over the last 10 years and in some cases are unmanageable, requiring a 15-year break from potatoes to reduce populations to manageable levels.  Free-living nematodes which transmit tobacco rattle virus, leading to spraing also cause significant feeding damage and reductions in yield.  Sampling for potato cyst nematodes and free-living nematodes can be done at any time after the previous crop has been harvested, but for free-living nematodes ideally, sample a few days after there has been some rainfall.  In dry periods the nematodes retreat down the soil profile and will not show up representatively in soil samples.  Where nematodes of either sort are detected then rotational choices can be made to avoid infected fields and the use of nematicides minimized.  Care should also be taken not to move soil accidentally from contaminated fields into clean fields which means extra care should be taken with harvest machinery etc.

Andy Evans and Fiona Burnett for the Farm Advisory Service.

Find out more about potato pests & diseases here.

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