Vineyard Profile
The most extensive damage occurred in a 2.2 hectare block of five year old Semillon vines. These vines were pruned to between 16 and 18 buds per metre on 3.6 m row spacings. A cropping level of 6.4t/ha (2.3kg/m) was achieved in 2003 with a block yield of 14 tonnes. The target yield for 2004 was 8.3t/ha (3.0kg/m) with a potential block yield of 18 tonnes. This yield target allowed for the removal of bunches from low capacity shoots of less than 50 cm in length.

Spray Damage
On October 16, 2003 the herbicide Oxfluorfen was inadvertently added, at a concentration of 0.1%, to a tank mix of Wettable sulphur before being sprayed over the vineyard at a water rate of 400L/Ha. The sulphur was mixed at label rates and there was no risk of leaf burn with ambient temperature at less than 25 degrees C. Vine shoots were at E-L stage 12, with 5-6 leaves unfolded and clearly visible inflorescences.

Oxyfluorofen is generally applied as a pre-emergent barrier herbicide which binds to the soil particles and kills weeds as they emerge. Oxyfluorofen can also be included as a ‘spike’ with systemic and contact herbicides to increase the spectrum of weeds controlled.

Upon establishing the nature of the spraying accident, the vineyard was monitored for symptoms of herbicide damage. Within 4 hours of application a brown/black speckling was evident on leaf surfaces (Fig. 1, top leaf). Leaf symptoms progressed from an oily brown discolouration (Figures 2 & 3) through to severe defoliation within 14 hours.

Post Damage Treatments
An ERA Farming treatment program was specifically formulated to detoxify the vines and promote strong regrowth from the secondary buds. The primary goal at this point was to generate enough shoot length to provide pruning wood for the following season. Had treatments not been applied the vines may have taken several years to recover. Macronutrients, trace elements and soluble carbon sources were administered to the vines via foliar sprays and drip irrigation. Irrigation was scheduled to deliver 16 litres of water per vine each day until harvest. This irrigation rate was considered appropriate due to the nature of the site which was previously mined for gravel and the top soil removed.

The following treatments commenced within 24 hours of defoliation.

Week One

• A foliar spray incorporating 4L/Ha of ERA Crop Minder , 4L/Ha of ERA Generate and 500g/Ha of Powdered Kelp was applied in 300L/Ha of water.
• A second foliar spray of compost tea solution was applied at a rate of 50L/Ha.

Week Two

• A 10L/Ha application of ERA Generate was drip fed (fertigated) to the vines.
• The Generate application was followed 24 hours later with a fertigation of 100g/Ha of Powdered Kelp, 20L/Ha of N-Hib (liquid) Calcium and 50L/Ha of compost tea solution.
• A third fertigation combining 3L/Ha of Molasses with 20L/Ha of N-Hib Calcium was applied 24 hours later.

Week Three
Three weeks following the initial damage secondary buds began to swell, signalling a start to the recovery process.

• Weekly fertigation of Ammonium nitrate (15kg/Ha) commenced as soon as green shoot tips were visible. N-Hib Calcium (20L/Ha) was included with the Ammonium nitrate applications on a fortnightly basis.

Nutrient applications ceased at E-L stage 17, prior to flowering.

Why This Programme?
The treatments were centred on the four mineral elements directly related to vegetative growth in plants. These elements are calcium, potassium, phosphorus and nitrate nitrogen. All the products listed above contain varying amounts of these elements.

After the vines defoliated the requirement for vegetative growth was of major importance, so fertigations and foliar sprays focused heavily on these elements. The other factor that is critical to the recovery of plant growth in this situation is to provide the hormones required for cell extension and growth. The best way to supply these hormones is through the application of powdered kelp and compost tea.

The nitrogen programme was commenced when the secondary buds appeared and vine recovery was imminent. To have started a nitrogen fertigation programme prior to this point could have been a waste of money and too much nitrogen too quickly before the detoxification was complete could also have applied extra stress to the vines.

Of primary concern throughout the vine recovery process was the activity of soil organisms. Soil organisms can influence nutrient uptake when activated by the correct food sources. One method of returning micro-organisms to the topsoil is to apply a compost tea solution. Compost tea is a concentrated inoculum of beneficial micro-organisms which are cultured in an aerated nutrient broth. The broth or tea contains a suspension of mature, biologically tested compost which acts as the inoculum for the tea. During the brewing process humates leach from the compost into solution. Humates, which are also found in deposits of brown coal, contain organic acids which improve soil structural bonds and increase nutrient uptake levels in plants. The compost tea also contains soluble nutrients, growth promoting substances and microbial metabolites. Molasses is generally included as a bacterial food source. Fulvic acid and humic acids are fungal food sources. This programme was aimed at stimulating fungal activity more than bacterial activity.

Recovery to Harvest
Secondary growth showed no residual effects of the herbicide damage (Figure 4). New shoots emerged with normal leaf pigmentation and up to two inflorescences per shoot. The greatest concern, however, was whether the vine phenology would advance at a normal rate following the herbicide shock. It would not have been surprising to have observed poor shoot extension and sterile inflorescences as the regrowth progressed.

Although shoot lengths were variable after the secondary bud-burst, vine growth stages appeared to unfold with regularity. The period from flowering to harvest spanned 16 weeks, the time line we would expect in a normal growing season for Semillon. With secondary budburst occurring 3-4 weeks after the herbicide damage, the flowering period shifted from early November to early December. The harvest date was correspondingly delayed, occurring one month later than in 2003.

The crop was harvested on April 1, 2004. The block yield amounted to 11.45 tonnes from 2.2 hectares, compared to 14 tonnes in 2003. The 2004 block yield of 5.2t/Ha was markedly lower than the predicted 8.3 tonnes/Ha. However, the recovery of the vines following severe defoliation demonstrated an effective treatment programme for herbicide damage of this nature.

After ripening to target maturity (12.5 – 13.0 Beo) the grapes showed no fermentation problems. Surprisingly, the resulting wine, free of any residues, was highly commended in a prestigious Western Australian wine show.