Tuesday, December 9, 2008

When do you stop spraying for disease? Q&A


Hi DJ's,

At what time of the season should you stop spraying for powdery mildew? What about Apple Moth?

Thanks,

Ryan J

At the time of writing this answer vineyards are at EL-30-31, nearing Berries Peasize.

In vineyards targeted at "A Grade," that have shoots that have stopped, open bunches and sunlight in the bunch zone, Powdery Mildew has not been seen and the risks of it developing are slight. Open canopies and small berries also cause conditions that limit botrytis.

In can be difficult to talk in general terms, but having a good clean block now, means you are looking at a clean harvest and can consider stopping your protective sprays.

Powdery Mildew on green berries.
For those with actively growing blocks don’t sit back and think dry weather means you are totally safe.  

 Assess your vineyards risk. Vineyards with a large canopy and a history of poor disease control are likely to have some disease- in spite of dry weather.

Levels of powdery mildew are lower than in the last few years but don’t get caught out – warm, overcast weather does suit the disease.

Monitor your vineyard before the Christmas break. Check 50-100 bunches and leaves for any signs like the photos shown.

Powdery Mildew- is a dry disease. It doesn’t need any rain to spread. While hot summer day time temperatures (plus 32-34oC) don’t suit the disease night time temperatures in the mid 20’soC do. While the heat of the day may last 5-6 hours temperatures in the morning, evening and night suit the disease. While a quarter of the day doesn’t suit the disease the remaining three quarters of the time it does well.

There is Powdery in sheltered canopies around the district. Be particularly careful where you have seen Powdery in previous seasons. Look at your 50 bunches around this area.

Downy Mildew- all fruit is now immune, although vines can defoliate if levels build up enough, however the risk of this is almost nil.

Downy is totally reliant on rain to affect vines (and other crops). No rain = no downy.

Some rain is forecast this but at this stage it is likely to only be 10 -20mm over three days and not conducive to either a 10:10:24 Primary Event.

Botrytis- Needs rain or moisture to spread. Any botrytis present in your vineyard now is ‘dormant’ inside your berries or present in small amounts on any flower caps or dead plant material trapped inside bunches as they close. No rain before harvest = no botrytis.

LBAM- Some fresh LBAM egg masses have been seen. Levels vary from vineyard to vineyard. Now that berries have grown past peasize (EL 31), only the biological insecticide BT’s- Delfin, Dipel etc can be used.

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