Australian wine is well known for its quality and reliability and the Australian wine industry are world leaders in innovation and quality control. The maintenance of its reputation increases pressure on the vineyard managers to stay well within the allowed limits for the use of pesticides. As such weed control in vineyards becomes relatively complicated with a limited range of herbicides being used.

Current management strategies have led to increasing levels of herbicide resistance and incidence of hard-to-kill-weeds.

Glyphosate resistant annual ryegrass in vine row

Adding to the limited number of herbicides that are acceptable, under-vine spraying is often left until spring when weeds are large with healthy root systems. Good spray coverage then becomes difficult. Adding issues with sprayer setup then leads to highly variable weed control.

Another complication with wine grape production is the encroachment of suburbia as towns expand and get closer to areas of agricultural production. Residential developments in wine growing areas are also popular, with a mandatory golf course attached. This increases the pressure on Vineyard managers to reduce the risks of pesticides going where they should not.

Close proximity of houses limits vine management options

To put all this in perspective wine grape growers have their fungicide applications well sorted which is understandable because fungal disease has the greatest effect on grape yield and fruit quality in wine grapes. Weeds on the other hand have a much smaller effect on the production of high-quality grapes.

Important factors in high levels of weed control are understanding how different herbicide modes of action work which then determines how they need to be applied to optimise their effectiveness. The questions we need to ask are:

• What kind of target are we aiming at?

• What kind of droplets are most appropriate to hit this target?

• What does the product do once it deposits on the target?

Source: Syngenta

Table 1 the number of spray droplets per square centimetre and per cent area coverage for different pesticide types.

The per cent area coverage is most easily measured using water sensitive paper and the SnapCard® app.

To check what pesticides can be used in wine grape production get the Australian Wine research Institute “Agrochemicals registered for use in Australian viticulture” or commonly known as “the dog book” which is also available as app. https://www.awri.com.au/industry_support/viticulture/agrochemicals/agrochemical_booklet/

 Knockdown herbicides that are permitted for use in wine grape production are listed in Table 2. This table shows the behaviours of the different herbicide modes of action. Glyphosate is highly translocated and therefore very forgiving in application technique whereas paraquat is the opposite. Products like paraquat that are translocated need much higher levels of coverage therefore product rate and application volume are critical for high levels of weed control.

Seedling grasses smaller than 3 leaf make a challenging target so it is important to keep the application volume up to ensure there are enough droplets to hit the target.

Table 2 Knockdown / Non-selective herbicides

A small number of selective herbicides are allowed and often used in the inter row area. Most of these herbicides are poorly translocated and also need good coverage to be effective.

Table 3 Selective herbicides

Soil active (residual) herbicides (Table 4) have a set of characteristics which must be understood the get optimum weed control. For example they work poorly if the soil is dry. Sufficient soil moisture is needed to allow the weeds to absorb the herbicide from the soil water. Also due they work poorly or not at all on emerged plants so need to be applied to bare ground or tank-mixed with a compatible knockdown herbicide. Some managers tend to minimise the use of residuals for these reasons and because there is often a lot of dead plant material under the vine row which will intercept the herbicide.

Table 4 Soil active herbicides

Lower levels of trash under the vines opens options for using soil active herbicides

Because of the limited number of herbicides available for use in vineyards and the increase in herbicide resistance it is essential for vineyard managers to understand the characteristics of these herbicides when developing their weed management plans.

As part of the 20^th Australian Weeds Conference Agronomy Field Tour in September 2016, the tour participants tested their ability to recognise herbicide damage symptoms across a range of crops and pasture species with the trial funded by Department of Agriculture & Food WA and Royalties for Regions™. To make it not too difficult, the guinea pigs (sorry, particpants) pre-downloaded the new GRDC Ute Guide herbicide Injury app to assist them in their quest. To sharpen their wits we also made it into a competition with extravagant prizes to be had. 

Herbicide injury demonstration at Muresk InstituteAfter saying I would never ever go on another Conference field tour, I had to put my money where my mouth was when Sally Peltzer and I were approached early in 2016 to organise the agronomy tour for the Weeds Conference to be held in Perth, WA.

We had to make the day interesting so decided to base it at or close to the Muresk Institute, just outside Northam, Western Australia. This is an easy 1.5 hour bus trip from Perth.

So back to the issue of herbicide injury of crops. We know herbicide damage is caused by herbicide drift, poor sprayer hygiene, adding the wrong product or spraying the wrong paddock. So how can growers and their advisers know what which herbicides are causing the problem? They can:

• pinpoint the herbicide and therefore hopefully decipher how it happened
• estimate a level of potential yield loss
• determine harvest or grazing withholding periods that could affect marketing of produce through exceeding maximum residue levels

GRDC has recently released an app to enable growers and agronomists more easily identify which herbicides are damaging the crop. Sally and I decided to establish a herbicide injury demonstration to test the Agronomy tour participants’ brains, as well as evaluate the app.

The treatments in Table 1 were sprayed across 18 crop and pasture types 15 days before the field day. No tank-mixes were used as this would have “muddied the water”.

Table 1. Herbicides and rates used in the demonstration.

Trade name	Active Ingredient	MOA Group	Rate
MCPA LVE	MCPA ester	I	1 L/ha
Amitole® T	amitrole	Q	5 L/ha
Verdict® + Uptake™	haloxyfop	A	100 mL/ha
Ally®	metsulfuron methyl	B	5 g/ha
UAN	urea + ammonium nitrate		50 L/ha
Atrazine + Uptake	atrazine	C	1.1 kg/ha
Brodal®	diflufenican	F	200 mL/ha
Hammer®	carfentrazone-ethyl	G	40 mL/ha
Glyphosate	glyphosate	M	0.5 L/ha
Gramoxone®	paraquat (200 g/L)	L	500 mL/ha

So how did the competition go?

There were 8 ‘stations’ for the contest and we split the participants into groups of 3 or 4.  We wanted the modes of action causing crop damage at the 8 stations and those in the “herbicide business” also had to name the actual herbicide to help level the playing field.

As can be seen from the photos the groups were busy competing.

Various groups busy trying to identify the 8 herbicide modes of action

What this exercise highlighted was how difficult it can be to identify the herbicide causing crop damage. It is important to not just look at the crop, but the weeds and other species and observe how they are reacting. Knowing the time elapsed since herbicide application also makes a huge difference in assessing the symptoms as symptoms change with time and dose. For example with cool low light intensity conditions paraquat (Group L) damage to cereals can look like a number of other herbicides during the first 2 weeks before desiccation has properly commenced. Even some of the 'herbicide experts' were fooled.

 Catherine Borger, DAFWA, with Kerry Harrington, NZ, and two international visitors.

Besides the fun, some great feedback has also been supplied to the GRDC to improve the Herbicide Injury app.

Rest of the day

After the herbicide injury competition Peter Vella and Dave Rogers from Hardi Australia discussed how modern spray technology, as used on their Saritor 5500, improves spray efficiency and efficacy through lighter booms and accurate height control .

The group fascinated by the high tech Hardi Saritor 5500.

Next we inspected the exhibition model of the iHSD – integrated Harrington Seed Destructor – with Devon Gilmour, McIntosh & Son, along with Ray Harrington, the inventor.

 Inventor and farmer Ray Harrington explaining how the iHSD kills weed seeds.

After lunch Andrew Guzzomi, University of Western Australia, demonstrated his selective cultivating tine. The tines are activated when the sensors detect a weed, digging it out. This shows lots of promise for low density fallow weed control.

Andrew Guzzomi explaining the complicated path to developing a new concept in tillage.Then it was back on the bus to head out to Andrew Boultbee’s farm nearby to look at his approach to harvest seed management with chaff dumps. Andrew has a number of approaches to dealing with the dumps. He sows through them and may or may not burn them depending on the season and amount of rain received. Everyone was fascinated by Andrew’s adaptation of the dump and burn approach.

Farmer Andrew Boultbee explaining how he manages weed seed production in cereal crops.

After that it was back to Perth via York.

We are pleased to say that the feedback was all positive from the day and a great deal of thanks goes to:

• Peter Vella and Dave Rogers at Hardi Australia
• Devon Gilmour at McIntosh & Son
• Ray Harrington
• Andrew Boultbee
• Andrew Guzzomi, UWA
• the staff at Muresk Institute, Northam, Western Australia
• Bridget & the team from Kalyx Australia

There has been rain and that means it’s weeds and spraying time. This time of year also lends itself to extremely risky spray conditions. Beautiful autumn weather is when surface temperature inversions are most common. For more information on inversions read my previous blogs here and here.

Strong inversion conditions March 2016. Image: AGRONOMORemember that all pesticides drift, it is just that some, such as Group I herbicides like 2,4-D, have a recognisable odour and produce unique symptoms on sensitive vegetation.

So what is the problem with off-target movement of pesticide? The most obvious agricultural issue is damage to sensitive crops. For example in the 2007-08 cotton growing season it was estimated that 10 per cent of the Australian cotton crop has some level of herbicide damage costing $5 million.

The second agricultural issue is pesticide residues. Organic farmers certainly don’t want anyone else’s pesticides. Drift is a particular problem when a crop is getting close to harvest. Signing a vendor declaration that you haven’t used certain pesticides gets complicated when the purchaser tests the product and it is ‘contaminated’.

Some of our major trading partners also have zero tolerance for certain pesticides. Ship loads of grain have been turned around and sent back for such breeches. The wine grape industry is particularly aware of the potential effects of unwanted residues on their markets.

Contamination of the natural and human environments is also a major concern.

Sensitive areas

Other than showing a duty of care, reading and following the label, using buffer zones and using best practice application, we need to be aware of sensitive areas in the vicinity of the farm when spraying. Talk to your neighbours and find out what crops they will have in, particularly in paddocks along the boundary. Be aware of state restrictions on pesticide use and spraying.

Some Australian states have restrictions on spraying in or near ‘sensitive’ areas. Western Australia has listed most Group I herbicides as ‘Scheduled’ meaning they cannot be used within certain distances of sensitive crops and high volatile 2,4-D ester is banned within 5 km of a commercially sensitive crop (vineyards or tomatoes), within 19 km of the Geraldton post office and within the Swan Valley, or within 10 km of the Kununurra Post Office. High volatile ester is not registered any other state or territory.

Victoria has nine designated areas where the type of pesticide and its application is regulated.

Agricultural Chemical Control areas in Victoria. Source: Agriculture VictoriaThe cotton industry has led the way with on online mapping with 95% of cotton crops mapped.  There is no excuse to say you didn’t know there is cotton nearby.

Cotton field awareness map for the western Riverina. Source: Cotton Australia & Cotton CRDCWestern Australia also has a voluntary system of registering your pesticide sensitive crop with the Department of Agriculture & Food WA.

DAFWA sensitive areas map 2015The map highlights organic farms, vineyards, tree crops, vegetable, bee hives and aquaculture sites. Being voluntary not all WA sensitive crops are mapped and a quick comparison with Google Earth will show additional vineyards and orchards. Another problem is that most broadacre farmers I have spoken with are unaware that this map of sensitive crops exits.  This is ironic because much of the potential drift affecting these sensitive crops could come from cropping country.

When it is spray time, do some planning, look at the weather forecast and for any potential risks, talk to your neighbours, use the right gear and get that pesticide where it is meant to be.

In the past we were always told to worry about strong winds when spraying. We now know that low wind conditions can be as bad or worse. New and reviewed herbicide labels since 2008 state that you must not spray during a surface temperature inversion.

What is a surface temperature inversion?

At sunset the ground loses heat and under low wind conditions air close to the ground cools while air above it is warmer. The air doesn’t mix and is described as being stable. Air temperature increases with height compared with during the day when air temperature most often decreases with height.

When this occurs close to the ground it is called a surface temperature inversion.

Typical inversion profiles during night and day. In an inversion the air warms to the top of the inversion. Source: G Tepper

In a surface temperature inversion the point where the temperature stops increasing and begins to decrease is the top of the inversion layer. This is usually the top level of suspended particles such as dust, smoke and small spray droplets or vapour.

Note that these inversions can act as a barrier to regional winds which go over the top of the inversion preventing mixing of the air. This means that inversions can co-exist with higher wind speeds such as greater than 20 kph.

About 30 minutes after sunrise smoke from wood heaters not mixing and moving parallel to the ground due to a surface temperature inversion. Image: AGRONOMO

What is the big deal with surface temperature inversions?

In November-December 2015 large areas of sensitive crops in NSW and Queensland have been damaged by spray drift, largely through spraying during inversion conditions. See the APVMA press release http://apvma.gov.au/node/19546 saying they won’t take action at this point. Hmm.

Because inversions prevent the mixing of air, any suspended fine droplets and particles, including spray, can move off in any direction to be deposited up to 20 km away once the inversion breaks the next day.

Cold air drainage within the inversion will cause fine droplets and particles to accumulate in the low parts of the landscape.

Remember that spray drift creates a number of major issues including crop damage, damage to sensitive vegetation and contamination of water and produce. Have you signed a declaration saying that you haven’t applied certain chemicals? You might not have, however contamination could have occurred via drift and you could be paying the price through rejection of your product.

Visual clues to indicate the existence of an inversion

• Formation of mist or fog
• Smoke of dust hanging in the air and moving horizontally
• Flattening of clouds as evening approaches

 As evening sets in fluffy (cumulus) clouds flattening is a sign of impending inversion formation. Don't mix another spray tank! Image:AGRONOMO

Rules of thumb – Conditions necessary for inversions to form Source: National Working Party on Pesticide Application  

• A reduction in wind speed to below 11 kph is necessary for all seasons.
• In summer, a fall of at least 4°C from maximum temperature recorded on the day promotes an inversion an hour after sunset.
• In winter, a fall of at least 2°C from the maximum temperature recorded on the day promote an inversion even an hour before sunset.
• If the difference between the observed maximum temperature and forecast minimum temperature is 10°C or more then there is a 90% risk of inversion conditions at sunrise.

Research funded by the GRDC is currently being conducted by Graeme Tepper and Warwick Grace to predict the formation of surface temperature inversions and assign risks for night spraying. The research is well advanced in Western Australia and will be continued in more complex terrain (i.e. not WA) over the next 12 months. Yes, WA is pretty flat.

Nufarm Spraywise Decisions™  and Syngenta’s Weather forecast are tools you should all be using for planning your spray program.