Post Harvest Disease - Does it matter in your vineyard?

Late season powdery mildew on a vine leaf.
There is much debate about whether vineyards should be sprayed after harvest Latest research would indicate that these sprays are often not needed.

Powdery mildew - Grape growers become concerned about high levels of Powdery mildew on their leaves (above).

1/ You might reduce the spread of powdery mildew in the canopy.

However, where disease has already developed, further increases in levels of powdery after–harvest generally make little difference to leaf and vine health.

2/ You might aim to reduce the amount of disease for next season.

Unfortunately spraying after picking has little effect on the chances of Powdery mildew next year.

Most buds that survive to next season are susceptible to powdery only in early growing season, so spraying now will not affect levels of winter-carryover in the buds. Also, the fruiting bodies of powdery, called cleistothecia, are somewhat like apples on a tree, they ripen in late summer and autumn. Since cleistothecia have already matured in most vineyards by now, post-harvest sprays are too late and do nothing to reduce their numbers.

Spraying for Rust Mite after harvest is also not recommended.

The Rust Mite bronzing to leaves you see are not doing any damage to your vine leaves and they function normally.

If you have bronzing on your leaves (above), record this as it is the threshold for rust mite spray next spring. Spraying in spring 2012 is recommended if uniform, moderate to high bronzing is obvious in your vineyard now (March 2012).

A spring spray aims to re-set the rust mite population down to a level where predatory mites can then maintain effective control. However, this approach does have some toxicity to predators therefore, using it when it is not needed can damage predators unnecessarily!