Blight is off to an early start.

Every year the disease we call Late Blight is around and waiting to destroy our crops of potato and tomato.  And every year, the arrival and reproduction of the pathogen, Phytophthora infestans, is different.  Last year we didn't see much disease until very late in the season but we had a very mild winter.  This means that unharvested tubers lying on or just under the soil surface were not frosted and some of these must have carried a latent infection of blight. Some of these infected tubers will grow on as volunteers in the next crop or in a ditch or discard pile and in a small percentage of these the blight will grow into the sprout and produce spores on the leaves and stems. Similarly, latent infection on seed tubers can give rise to an outbreak of the disease.

That's how blight gets started each year. The first sample, from a dump, was noted on 9th May.  This is quite a bit earlier than usual.  The weather in May and in early June favoured blight reproduction and spread - that is, minimum temperatures above 10C and high humidity or rainfall. As a service to potato growers, the Potato Council Ltd has a web site that records when blight has been detected in postcode areas throughout GB.  This depends on potato professionals (Blight Scouts) sending leaves or stems from suspected outbreaks to FERA for confirmation. Amateurs (Monitors) are also encouraged to  register and receive prepaid mailing envelops and instructions. Dots are placed on the map so that the risk of blight arriving on healthy crops can be assessed.  Conducive weather (Smith periods) AND a confirmed outbreak in your area means that you  must watch your crop carefully for the first signs of the tale-tale brown/black spots on leaves and stems that indicate blight. That is when the commercial grower will protect his crop with fungicide and apply it at weekly intervals to prevent any infection. In dry conditions, the weekly applications are usually discontinued or extended.

Of course growers of our Sarpo varieties do not need to use fungicide.  But if you are growing a Sarpo cultivar with moderate resistance on a large scale you might consider less frequent application of preventive fungicide particularly in a wet season.

A measure of the earliness of blight this year is that 88 samples of blighted foliage were sent in by the end of June whereas you need to go back to 2006 or 2007 to find anything approaching this number.  In 2006, 60 blight outbreaks were detected and 56 in 2007 (which later became a blight meltdown year).
Our trials at Henfaes have remained healthy so far in spite of severe blight outbreaks on the allotments at Llanfairfechan a few miles to the east. Early attacks are devastating as the whole plant may lose all foliage before any tubers have formed = CROP FAILURE.

Allotment gardens are often places where blight develops.This is because lots of susceptible varieties are grown, few if any are sprayed against blight and hygiene in not always up to scratch e.g. dumps of old tubers and volunteers on neglected plots. So 2014 has the makings of a meltdown year again but it all depends on the weather during July and August.  We just might escape.

Open Day at Henfaes in Mid June - no blight in sight - yet.

This plant was infected soon after emergence. Latent infection of the seed tuber is a strong possibility here.