Wednesday, February 24, 2010

How salinity builds up over the irrigation season

Salinity builds up in the plant root zone during the irrigation season. This occurs in the rootzone of grapevines (above) and also Olives, Almonds, Strawberries, indeed any irrigated crop.

Above: Water and salts come into the vineyard with your irrigation water. Water is taken into the vine, pushed up the trunk and respired out of the leaves. Salts build up in the soil. Without rainfall leaching it has no where to go. The vine works hard to exclude taking up salt (certain vine rootstocks are very efficient at doing this) but unfortunately once the salt levels in the rootzone build it takes it up into the plant.

If heavy winter rain doesn’t fall, leaching and drainage will not occur and soil salinity may quickly increase to unsustainable levels. More symptoms of salt would be expected to be seen and a reduction in the quality and yield of the fruit is expected.

Recent research has shown that if you need to apply irrigation to leach the salts that have built up in your soil this is best applied during winter when the soil is full. Any extra water from irrigation is pushed down into the soil.

In the aftermath of this season dealing with the salinity that has built up in the soil is a major issue. If good winter rains do not flush the salt through the soil, irrigators may have to flush the soil with a winter irrigation.

Consider a soil test, and seek specialized advice.
Shiraz is nearly ready to pick. I have always found it is an 'ugly' grape. In the last week before picking it often loses 10-15% of its weight and begins to shrivel up like a raison. In this photo (above) you can just see the first signs of shrivel.

The fruit in question is 14.5 Be with a TA of 5.1. It is sheduled to be picked on Friday.

The weather in the last month has been ideal for ripening, the vine canopies are still in good condition. They are healthy and better still the grapes are in good condition too. They have noticibly thick skins which are ideal for red winemaking.

Note the 'weeds' under the vines. This Shiraz vineyard is running by organic principles and doesn't use herbicide (below). This vineyard is 'knifed' during winter and spring to keep the weeds down.

Tuesday, February 23, 2010

Grape Vine Weevil Damage

Look out for vine weevil damage. In these picture they have eaten through the bunch racchus and weaken the structure of the bunch. The weevils themselves are medium sized about 7mm long and grey-brown in colour. They have a bulbous abdomen. The adult weevils are flightless and they are active during the night.

Tuesday, February 16, 2010

Sooty Mould (and Powdery Mildew) - ID Photo

Sooty moulds are fungi which cover plant leaves, stems and twigs in a black sticky substance. In the picture below, Powdery Mildew has damaged the fruit which has broken apart the berry skin. The berry skin has leaked sugar which has caused an outbreak of Sooty Mould.

Sooty Mould and Powdery Mildew on Sauvignon Blanc.
In most cases Sooty Mould in grape bunches is caused by Mealy Bug, which produce 'honeydew' when they feed on the ripening grape berry. There are several means of treating Sooty Mould. In simple terms, they all boil down to controlling the Mealy bug secreting the honeydew on the plant. Without honeydew the Sooty Mould does not develop.

Secondary Crop.

Green bunches on lateral shoots within vine canopies are an issue for winemaking in terms of affecting the baume and ripe flavour profile of your fruit at harvest.

If blocks are sampled correctly you can also expect them to reduce your sampling results. Look at your vineyard for secondary bunches on laterals, or areas of green berries over one third in a bunch.

If your vineyard has a significant amount of green fruit it may require fruit thinning to assist in the evenness of ripening and presentation to winemakers.

Wednesday, February 3, 2010

The underground water supply in McLaren Vale explained.

Underground water is McLaren Vale largest water resource. It is also the most heavily used.

The McLaren Vale Prescribed Wells Area (PWA, or wells area), formerly known as the Willunga Basin, is the term used to describe the water that is held underground. It is estimated that the safe yield of underground water for the McLaren Vale PWA is 6,560 megalitres (ML) per year.

Since water usage records started in 1992/93, the annual metered groundwater use in the McLaren Vale PWA has ranged from 3,713ML (1992/93) to 8,924ML (1994/95).

Since 1997/98 there has been a steady decrease in the amount of groundwater used in the McLaren Vale wells area. In recent years, groundwater usage has averaged around 4,500ML per year.

All of the water resources of the McLaren Vale wine region are part of a larger water system and they interact with one another. The table below shows the major flow transfers in the Onkaparinga Catchment, based on current water use. It highlights how these major water resources interact with each other and how an increase or decrease in one can affect another.

Underground water within the McLaren Vale can be drawn in varying quality and quantity from four aquifers – Quaternary sediments, Port Willunga Formation, Maslin Sands and Fractured basement rock. In many locations all four of these aquifers can be accessed at different depths, with the aquifers being separated vertically by different layers of rock. The schematic diagram of McLaren Vale Prescribed Well Area groundwater system (below) shows this.

Quaternary- This aquifer occurs mainly south of Pedler Creek, and as smaller perched aquifers in gullies and along the edges of the basin where bedrock outcrops. Quaternary aquifer is generally not used for vineyard irrigation. It is shallow and of poor quality.

The Port Willunga Formation- is the most utilised underground water resource in McLaren Vale, which is estimated to account for around 64% of all metered water usage in the McLaren Vale wells area. It can be accessed throughout the floor of the Willunga Basin. Salinity ranges from 350 mg/l at the northeastern extent of the formation and adjacent to the Willunga Fault to approximately 1000 mg/l around South Road and then increases to greater than 2500 mg/l at the coast.

The Maslin Sands aquifer is estimated to account for around 20% of all metered underground water usage in the McLaren Vale wells area. Like the Port Willunga formation aquifer, recharge is via direct rainfall infiltration, recharge from streams and inflow from surrounding fractured rocks.
Underground water salinity in the Maslin Sands aquifer varies from less than 500 mg/l to more than 50000 mg/l at the coast.

Groundwater from the Fractured basement rock aquifer is believed to account for around 16% of all metered underground water usage in McLaren Vale. This water source is accessed by the deepest bores in the district, generally sunk over 100 meters into the ground.