Dealing with Downy Mildew Post Flowering

January 10, 2012

A Happy and Prosperous New Year to you and a successful vintage.

With the weather conditions the way they are, we thought it might be helpful to share some thoughts on managing Downy Mildew in your vineyard ...

Downy Mildew

The wet weather that has beset the country lately is perfect Downy Mildew weather. This disease has surfaced already in Auckland and can be expected to put in an appearance as far south as Marlborough and Nelson any day soon.

Downy can ravage the young leaves in the canopy quicker than any other disease as it has a very short life cycle. Three to five days is all it needs from infection to sporulation, so it’s essential to monitor for those tell tale oil spots and act immediately infection is seen.

If you see oil spots but are still not sure, pick some infected leaves, put them in a sealed plastic bag in the hot water cupboard overnight. In the morning look at the undersides of the leaves. If there is a whitish grey ‘down’ where the oil spots were the previous day you have an active Downy infection.

Last year many growers used phosphorous acid products for Downy control with great effect. Unfortunately this product can no longer be applied to grapes if you are a SWNZ grower, as it doesn’t have registration for grapes, the residue situation is unclear and the Phosphorous it contains is not in a form available as fertiliser.

So what can you do if you suddenly find yourself with a Downy outbreak at this time of the year?

Below we have prepared a table of products that can be used post flowering for Downy control. We have also listed the PHI’s for ‘Nil Residue’ and ‘All Markets’. The ‘All Markets’ PHI is the minimum interval required to ensure the product can enter every market currently listed in the NZ Winegrowers Spray Schedule. Do note our observation in the Notes column.

Remember this is not a list of all products that control Downy. It is a list of products with PHIs suitable for use post flowering.

Product Nil Residue PHI All Markets PHI Notes
Chlorothalonil Products 28 28 Also controls Black Spot. Some russetting possible on sensitive varieties.
Captan Products 28 28 Suitable for low disease pressure. Also controls Black Spot.
Copper Products Not Known 0 Check label claim exists for Downy. Most copper products are very effective against this disease and also active against Black Spot. Copper products may strip aroma/flavour from grapes. To overcome this when we use copper products in our vineyards we switch off the nozzles facing the fruit zone as Downy does not infect mature leaves.
Mancozeb Products Don’t use See notes Highly effective against Downy but the PHI for Ontario is Pre Capfall. For all other markets the PHI is 14 days so consult with your winery before using. So OK to use for all markets except Ontario.
Folio Gold/Max Don’t use 30 Some russetting possible on sensitive varieties.
Gem 28 28 Appears to give good control. Adjuvant necessary.
MicroPlus 0 0 Biological. Not recommended for medium to high disease pressure.
Phaltan 21 21 Old but broad spectrum effective fungicide that may be hard to find.
Terace 7 7 Good coverage essential. Works as a knockdown with no persistence in the canopy.

In our organic vineyards we use organic copper products in tank mix with Protector as an adjuvant. In the exceptionally wet 2010-11 season we were able to maintain very good control of Downy Mildew with this combination right through to harvest.

We sincerely hope you won’t be needing this advice this season and we will post this on our website for your future reference ...just in case.

At http://www.mistyvalley.co.nz/catalogue/ you will find our current list of available vines. There are a few lines already sold out, so do let us know your replacement or new block requirements as soon as possible to avoid disappointment next spring.

Kind regards
Donna Goricki and Rex Sunde
www.mistyvalley.co.nz
Phone: 09 8367466/ 0800 444 614
Rex mobile: 027 4980183
Donna mobile: 021 849839