Keep disease guard up as flowering approaches – Vineyard – Rob Saunders, Chris Cooper

As Rob Saunders and Chris Cooper from Hutchinsons explain.

The dry spring may have reduced early risks from wet weather fungal diseases but other threats remain and conditions can change quickly, so it is essential growers maintain their guard.

Phomopsis is still a priority early in the season, and is best managed by protecting clusters as soon as they are visible at the 3-5 inch shoot growth stage. Mancozeb-based products are preferred, but kresoxim-methyl has also shown worthwhile efficacy.

Mancozeb is a good “dual purpose” option as it is also effective against Downy mildew, although at the time of writing, this risk is relatively low due to dry conditions.

Instead, Powdery mildew has been more of a threat. It is a “compound interest” disease, which means it can build quickly from a low base, so preventative control is essential. The disease is very difficult to tackle curatively and flowers are particularly sensitive to infection, which can lead to micro cracks in developing berries, increasing susceptibility to botrytis.

Varieties vary in Powdery mildew tolerance, with hybrids more resilient than Champagne varieties, which account for around half of UK vines.

We saw in 2019 how quickly the weather can change, when the dry April/May was followed by a wet June, then hot July, resulting in immense leaf growth as vines were flowering. Excess foliage, combined with warm, wetter conditions will increase risks from Phomopsis, Downy mildew and Botrytis, which must be prepared for.

Botrytis usually infects plants through wounds, flowers or ripening fruit and remains the focus of most disease control programmes as flowering begins. It is best controlled with a robust, threespray strategy starting at early flowering, then mid-flowering and a final spray at late-flower.

Risk is greatest in damp, warm conditions, but is heightened by thick canopies or large amounts of under-storey weed growth, which holds moisture close to vines.

Downy mildew equally needs moisture for infection to occur, with mancozeb being the preferred option early in the season.

Managing vegetation beneath vines helps mitigate disease risk, but remember there are limits on total glyphosate use over the season, so plan applications carefully and integrate with mechanical weeding or mulches where appropriate.

An example programme may be to apply 1.5kg/ha of Roundup Powermax for the first cleanup, followed by another 1kg/ha with carfentrazoneethyl later. Carfentrazone-ethyl is also useful for burning-off suckers, rather than doing so mechanically or by hand.

Finally, consider applying a biostimulant during flowering; options among the seaweed extracts are either Maxicrop to improve leaf function or Kelpak to promote set by enhancing pollen activity, but they should not be mixed with each other, so instead consider Cultigrow, which appears to do both.

We are also starting to evaluate the Vineus range from Lallemand, particularly Pinot Pro Flowering. Based on amino acids and yeast, it is used to promote set in Pinot (and Chardonnay), reducing millerandage.

May is also the time to put out pheromone monitoring traps for Light Brown Apple Moth (LBAM) and Spotted Winged Drosophila (SWD).

LBAM risk is generally greatest along southern English coastal counties and presents the greatest threat at two key timings. The first generation of caterpillars emerge in late spring and can cause significant yield losses by feeding on primary inflorescences, while the second generation later in the year feeds on grape bunches, reducing yield and quality, and increasing botrytis risk.

There is a good range of products to control LBAM, for both conventional (e.g. indoxacarb) and organic systems, however discuss product choice with your local Hutchinsons advisor, as restrictions can apply and some options may be better reserved for SWD control later in the season.