Managing blight in high risk conditions – August 2009
Stephen Bell, CoLouise Cooke and George Little, Agri-Food and Biosciences Institute (AFBI), Newforge Lane and College of Agriculture, Food and Rural Enterprise, (CAFRE) Greenmount Campus.
July’s high rainfall and humidity has produced conditions very favourable for the spread of blight in potato crops and infection has been reported in all areas. Frequent fungicide applications are needed to maintain protection and this is difficult in the current unsettled, showery weather. Many maincrops were late planted as a result of wet weather in May and the continuing strong top growth in these crops is particularly vulnerable to blight. Continue to monitor all crops closely for signs of blight and follow the advice given below to help manage blight in infected crops.
Managing localised patches of blight:
- Localised patches of severe infection (10 or more spots per plant) should be destroyed using diquat tank-mixed with Shirlan. It is better to lose a small area in order to protect the rest of the field. The remainder of the crop should be treated as outlined below.
Managing crops where blight is present as low level spotting, most plants unaffected:
- Use a translaminar product such as Infinito, Invader, Revus or Curzate M. Translaminar products offer some kickback properties against blight at the very early stages of infection. Blight symptoms take a minimum of 4-5 days to appear after infection so new lesions will be seen for some time after treatment.
Managing crops where blight is over 1 percent (more than10 spots per plant):
- Once blight is much over 1 percent, fungicides will have little effect in checking spread unless the weather turns hot and dry. The longer the crop is allowed to grow on, the greater the risk of tuber blight, so burn off as early as possible. After desiccation, maintain protection with products such as Shirlan or Ranman until the haulm is dead to prevent the crop acting as an infection source. Wait at least three weeks after haulm death before lifting.
Managing blight infections at the end of the season:
- Where there is a high risk of blight, it is worth adding a blight fungicide to the desiccant (check labels for approved tank mixes) and applying further sprays of products such as Shirlan or Ranman as long as any green haulm remains.
Potato Blight Warnings can be checked via the Blightline 24 hour telephone service on (028) 9038 2372 and via DARD Blight-Net on the DARD Rural NI Internet site at www.ruralni.gov.uk. Growers also can contact Stephen Bell on 028 9442 6766 to sign up for SMS messages of blight risk.
Before using any agrochemical, always read product labels and consult your buyer protocols.
