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Weekend potato blight warning

Potato crops can be attacked by a number of pests and diseases but by far the most common is potato blight. Met Éireann has issued a Blight warning for 14 counties for this weekend with some opportunities for spraying this evening. Eamonn Dempsey, Teagasc Advisor, Tralee has guidance here

Met Éireann Blight warning


See https://www.met.ie/warnings/today 

Potatoes are an excellent source of Starch and Vitamin C, resulting in it forming an important part of a stable Irish diet. When we mention potato blight, we are reminded of when blight destroyed the potato crops between 1845 and 1852 and the devastating consequences of this disease on  our population.

Potato Blight defences

Today thanks to advances in fungicides, improved varieties, better disease forecasting, we are able to prevent blight. However it requires excellent crop management as there is still no means of eradicating an outbreak in a crop.

The first defence against any potential disease in getting crop nutrition right. Potatoes can grow very well below PH of 6.0, but it is necessary to maintain the soil at a PH suitable for other crops in the rotation.

Lime should not be applied within the 2 years preceding a potato crop because of the increased risk of common scab.

Fertiliser applications should be based on a recent soil test report, this report will allow you to apply the recommended rates of N, P and K based on the fields P and K index. Raising the level of N application up to a certain point, increases tuber yields. Higher applications delay the development of tubers and the foliage in these plants with excessive nitrogen is very susceptible to blight.

More about Blight

Blight is caused by an airborne fungus called Phytophthora Infestans. The spores germinate in humid weather, when the temperature is greater than 10 degrees celcius. The first signs of blight are yellow spots that turn black on the leaves. The fungus produces more spores on the infected leaves of the plant and these spores can be washed down into the soil by rain where they will then infect and rot the tubers.

The Meterological Service issues blight warnings when weather conditions are ideal for the spread of blight. It is up to the grower to implement a blight control strategy for the different growth stages and select the correct product for application e.g. Dithane in May/Early June (Early Season). As the crop progresses during June move to more systemic fungicides which will give better protection of new growth. Products like Infinito, Zorvec + partner product will give good cover at this time. When blight warnings are issued crops should be sprayed every 7 to 10 days depending on broken weather, severity of blight and continue until the crop is Dessicated (Burned Off) and harvested. However be vigilant and don’t rely soley on blight warnings to make decisions on timings of fungicide.

  • Watch out for awkward corners, areas around poles, sharp bends etc. that are difficult to spray where less than the ideal amount of fungicide is being applied. Where possible reverse the sprayer into the corners before you start spraying, otherwise these areas can act as entry points for the fungus to get into the crop.
  • The fungus survives the winter on blighted tubers, therefore make every effort to ensure that all tubers are picked at harvest time and that volunteer potato plants are not allowed to grow the following year.
  • Destroy all potato dumps i.e. Areas where potatoes have been disgarded after grading by applying Glyphosphate or Diquat based products and make sure that only blight free tubers are sown.

A good blight programme which prevents infections from happening in the first place is the best strategy.

Listen to The Tillage Edge podcast on Blight Control in potatoes below

For more reading on this topic check out this article by Shay Phelan, Teagasc Crops Specialist Fight against Blight

Teagasc Advisors are regular contributors to Teagasc Daily while The Teagasc Tillage Crop Specialists issue an article on a topic of interest to Tillage farmers every Thursday here on Teagasc Daily