Useful potato blight information for 2016

Is this warning earlier this year due to good weather?

AFBI warnings are released based on recent weather conditions, as determined by data from weather stations across Northern Ireland.  Blight develops during warm, wet conditions, and ideal conditions have been formally defined as Smith Periods. A Smith Period is defined as at least two consecutive days in which the minimum temperature is 10°C or above and on each day the relative humidity is greater than 90% for at least 11 hours.

Blight sporulating on a potato leaf
Blight sporulating on a potato leaf
This year there has been a very warm start to the summer, but this has been coupled with dry weather, which is not conducive to late blight. However, in the past number of days, warm, wet conditions have arisen. This has led to an earlier warning compared with last year, when conditions were more consistently cooler and drier early in the season.

Although 2015 was a low disease year in Northern Ireland, and therefore sources of late blight would likely have been low, a wet and warm winter would have created ideal weather conditions for the spread of this disease. Therefore, it is important to be vigilant in regards to fungicide spray applications and timings.

Recommended types of fungicides to use and application times?

It is recommended that farmers start protecting their crops from blight whenever the first blight warning is issued or when plants meet within the drills, whichever is earlier. It is also recommended that blight fungicides are applied at the intervals recommended for high risk conditions during sustained periods of warm, wet weather. Fungicide timing and coverage are critical, as, no matter how good the product, nothing makes up for a late start, stretched intervals or areas left unprotected. It is good practice to use a range of fungicides with different modes of action and not to rely on any one active ingredient for more than half of the programme. This makes best use of their different types of activity and reduces the risk of selecting for blight strains resistant to any one fungicide. Once blight has got a foot-hold in the crop, it is almost impossible to eradicate it.

Reports of any resistant strains this season so far or last season?

There have been no reports of late blight so far this season. Last season was an extremely low disease year, with only six outbreaks confirmed in Northern Ireland. However, genotypic analysis of this very small number of samples from 2015 indicates that a mixture of blight genotypes continues to exist in blight populations in Northern Ireland. These include the older A1 types, which seem to be well-suited to conditions here, as well as the aggressive A2 mating-type genotype known as Blue 13, which is resistant to phenylamide fungicides. Also found was Pink 6, a genotype that favours warmer weather and is frequently found in Great Britain, but has been found rarely in Ireland.

Due to the very small number of samples available from 2015, it is not possible to draw conclusions on any shifts that might be happening in blight populations in N. Ireland. However, there is no indication that new resistance against currently recommended fungicides has developed within strains of late blight in Northern Ireland to date.