Chemical management methods

Pesticides used to control downy mildew fall into two categories;

  • pre-infection - preventative, and
  • post-infection - curative

Preventative sprays are applied just prior to a predicted infection period with spray programs commencing when shoot length are about 10cm. These sprays help reduce the chance of zoospores germinating.

Chemicals including Copper oxychloride – Headland Inorganic and Mancozeb – Karamate will be used. These have a low resistance risk but are easily washed off by rain and new growth is not protected. Frequent applications during risk periods will be necessary. Copper should be avoided close to flowering to avoid the risk of coulure. Copper is phytotoxic in cold weather and should not be applied too early in the season.

Excellent spray penetration is vital to achieve maximum protection with applications timed just before forecast risk periods. Where there is a risk of the ground being too wet after a rain event to allow access or where careful monitoring is not possible a regular programme of preventative spraying every 10-14 days should be undertaken. Close to flowering this may be
increased to every 5-7 days if weather conditions require.

Curative sprays are applied after a contamination event and are systemic. Careful monitoring is essential to avoid the rapid establishment of the disease. In years or regions with low disease pressure the use of curative pesticides will mean fewer applications and less expense.

Chemicals including Fosetyl aluminum – Aliette 80 WG and Metalaxyl-M – SL 567A/Syngenta may be combined in a curative spray programme. Phosphorous acid – ProPyt is also cost effective and is said to stimulate vines Natural defences.

Curative sprays should be applied within a few days of the infection event and preferably before the appearance of oil spots. Once the disease is established it may take a number of spray applications to control. Bag tests should be undertaken after each spray application to monitor effectiveness. Systemic sprays are translocated to the shoot tips before spreading to the rest of the vine. It is important not to trim vines soon after an application of much of the benefit will be lost. New growth will also be protected.