Wednesday, September 30, 2009

Powdery Mildew – The creeping disease - Q&A

Question for James.

How do you assess whether disease pressure is high or low? Why do they call powdery mildew the creeping disease?

Open canopied Shiraz. Note the high level of uV light that can get into the vine canopy.

How do we assess disease pressure?

History – Powdery survives from year to year in your vineyard. Good control last season helps reduce risk for this season coming.

Susceptibility - Verdelho and Chardonnay are the most susceptible varieties to Powdery – while Shiraz is only moderately susceptible. The variety Merlot seems to have low natural susceptibility.

Vigour - High vigour blocks are more at risk than low vigour vineyards. In high vigour vineyards it is difficult to get good protective spray coverage and tend to have dense canopies. When the canopy is extremely dense protection is difficult. Dense canopies cause shade which favours Powdery.

During overcast weather conditions, with high humidity (both favouring Powdery Mildews lifecycle) we say pressure is high.

The best time to control this disease is in the early season by limit the spread of any Powdery mildew flagshoots and stopping any bunch infection during flowering. That is why we call powdery mildew the creeping disease because it creeps around as the canopy closes over.

A rough rule of thumb is start control when shoots are 20- 30cm long, or 2-3 weeks past budburst.

McLaren Vale growers have been having good success by treating each vineyard patch based on its disease risk. They have been using high pressure programmes for blocks with a history of Powdery and low pressure programmes on block where control has been good.

Monday, September 28, 2009

Hail Damage has increased - UPDATE 28/9/2009


A series of hailstorms on Friday night into Saturday morning has severely damaged some vineyards. Check your vineyard for damage. In the worst affected blocks shoots have been snapped in half and some inflorescence damage (as shown below).



There is a lack of definitive information on grapevine recovery responses to hail. It has been several years since McLaren Vale and the Adelaide Hills received damage of this level and growers experiences are limited.

However, you have to best consider how to best manage the vines to maintain yield, both in this season and next season and ensure good canopy structure. Consider the use of foliar fertilisers in your next spray round. Doses of kelp products are also considered beneficial after stress events including hail and frost.

Thursday, September 24, 2009

Low risk of Downy Mildew 10:10:24 - UPDATE 24/9/2009

The region has received heavy rain fall this week – which have been close to producing a 10:10:24 Downy Mildew event. Fortunately night-time minimum temperatures have been below 10oC which slows the disease from starting its life cycle.

We feel there is only a low chance of Downy Mildew because vines do not have a sufficient canopy to host the disease.

A no risk strategy would be to protect your vineyard with your next scheduled spray round using a registered Downy Mildew protectant fungicide. Applied before further rain this protected against the spread of Downy Mildew, which could occur if we have future;

1- (10:10:24) Primary Events or,
2- Secondary events (warm, wet nights - 98% Relative Humidity with some rain before dawn).

Downy Mildew needs unprotected foliage to infect vines. We are entering the high-risk period when shoots are 10-30 cm long in the lead up to flowering. Leaves of any size are susceptible to infection but the larger the amount of unprotected foliage, the higher the risk.

Hail Damage - UPDATE 24/9/2009


Some hail damage has been seen in McLaren Flat. Fortunately most of the district was spared from damage.

Leaf botrytis can develop in vines that have been damaged by earlier hail and wind – as shown above. This can be common in seasons where we have windy and wet weather in spring. Further rain increases leaf botrytis infections, while dry conditions help heal it up. Leaf botrytis is very easy to monitor for because it is easy to see. Many growers worry because of its obvious nature. The good news is unless the leaf botrytis spreads onto the vine stem or inflorescence no crop is lost. Monitor closely for spread.

Thursday, September 17, 2009

2009 Vintage Winegrape Intake.

We have seen the following figures from the Winegrape intake summary for vintage 2009. See all of SA's data here.

The total crush was 33,484 tonnes - a low figure for the region similar to 2007's very low crops.

In general grape prices have fallen with the traditional McLaren Vale varieties Shiraz and Mataro fairing the best.

Reds

Shiraz has slightly fallen by $90-100 to a calculated average of $1432. In dollar terms Shiraz accounted for over half of the income for the districts growers this year ($21,196,971). Demand for Shiraz has helped keep its average price above the lower prices of 2005/06 where the average was below $1400.

Cabernet Sauvignon has fallen to $1136 calculated average, Merlot has fallen to $918. Grenache was calculated at $1212. The 12 tonne of grower supplied Tempranillo was worth $1549, with another 121 tonne being winery grown. Less than 10% of the regions Tempranillo had a price assigned over the weighbridge. This makes it difficult to get a true bearing on the price performance of Tempranillo as a new variety for the region.

Whites

Chardonnay prices have fallen sharply to $778. This following a general trend in Australia where there is a current oversupply.

Sauvignon Blanc, while not considered suited to McLaren Vale attracted an average of $1421.

Earwigs - Identification Photo


Earwig damage is commonly seen in vineyard this week. Some Chardonnay and Merlot blocks have ‘lace’ damage to leaves. Earwigs often hide under the bark in the vine crown, or in the soil and trash around the base of the vine. Be also aware snail damage has been seen this week.

Thursday, September 10, 2009

CropWatch Adelaide Hills

Adelaide Hills Crop Watch 270809

Leaf Botrytis - UPDATE 10/9/2009

Leaf botrytis has developed in vines that were damaged by earlier hail and wind. This is common in seasons where McLaren Vale has windy and wet weather in spring.

Further rain increases leaf botrytis infections while dry conditions will heal it up.

Leaf botrytis is very easy to monitor for but because it is obvious many growers worry about it. The good news is unless the leaf botrytis spreads onto the stems or inflorescence vines recover quickly with warm and dry weather (pictured recovering below in spring 2008).

Wednesday, September 9, 2009

Earwigs - UPDATE 9/9/2009

Earwig damage to developing grapevine shoots (EL-12).
This week some earwig damage has been seen. Interestingly, as in previous years observations, the variety Merlot seems to attract the most serious damage. We are not sure why this is the case but you will often see much more leaves eaten and significant damage in Merlot than other varieties.

Most of the time earwigs do not need to be actively controlled since healthy plants will outgrow small amounts of earwig damage. While the damage can look serious, unless the inflorescence(future bunch)is eaten away, the earwigs are not affecting your crop.

Later in the season earwigs are a predator for Light Brown Apple Moth caterpillars (LBAM).

Thursday, September 3, 2009

What keeps vines dormant? - Q&A

I am curious about why bud burst seems to be happening earlier this season. Many thanks,


John Petters


Happy to help John,


Dormancy is a state of temporary metabolic inactivity or minimal activity. Vines generally go dormant in response to adverse growing conditions. We agree with your observation. Over the last three years bud burst has been seen to be getting earlier and is now occurring in late winter.
Healthy budburst in Shiraz - Sept 2009
We feel there are two reasons this is occurring. The first is warmer than average winter temperatures. The second is water stress after harvest.
Winter bud burst, or early bud burst is considered to be caused by over stressing vines the previous season. This is most commonly seen with weak vines near tree lines. Occasionally whole vineyards show winter bud burst triggered by warm winter weather. It is most common in varieties that experience bud burst at low spring temperatures- Chardonnay and the Pinot family.
Vines are held in dormancy by two forces - endodormancy (true winter dormancy) and ecodormancy (environmentally imposed dormancy). Endodormancy is caused by the vines internal clock – a balance of hormones and internal processes. Ecodormancy is caused by the environmental temperature, eg. when the Spring time weather reaches a certain temperature dormancy lifts and the vine buds burst.
If vines are over stressed after harvest then endodormancy can be weak and the internal balance of the vine unsettled. If the weather after harvest is warm then ecodormancy (environmental) can also be broken and the vine buds will start to develop. Any buds that burst will not grow through winter- they stay at 1-2 cm long until spring begins and normal bud burst occurs. In vineyards that have broken dormancy bud burst, flowering and harvest can be uneven.