Here is a valuable article from the latest E-weed newsletter by Sally Peltzer and Alex Douglas, DAFWA.

Despite the rain in September in many areas of WA and southern Australia, there are still dry conditions in many regions.

It is tempting to stop any harvest weed management in the dry years. “There doesn’t seem to be many seeds on those annual ryegrass plants”, I can hear you say. That’s where you may be wrong.

 Research by AHRI has shown that annual ryegrass seed numbers can still be relatively high in poor seasons (Table 1). These can carry over to the following year and reduce yields. Note the comparative ryegrass seed yields for the two seasons. Not much of a yield penalty for ryegrass in a drought year when compared with wheat.

 Table 1: Wheat yield and annual ryegrass seeds produced over 2 years.

Year	Wheat yield	Annual ryegrass
	(t/ha)	(plants/m2)	(seed/m2)
2011	4.0	19	12,000
2012	0.6	29	7,000

Cut your crop lower in a dry year to catch more ryegrass seeds.

In a good year with a big crop, there will be less light penetration and the annual ryegrass tillers will be upright and easier to catch. In a low-yielding year with a light crop and an open canopy, the ryegrass tillers will be also shorter. The work done by AHRI showed that at 40cm harvest height in 2011 (high yielding crop) collected about 60 per cent ryegrass seed at crop maturity compared to about two per cent in 2012 (low yielding crop).

 The more seeds dropped in one year, the less crop yield in the following year.

To illustrate the difference in cutting height in a dry year, The Weed Seed Wizard has simulated wheat yields in 2013 after 7,000 annual ryegrass seeds/m² were set in 2012. If the crop was cut at 10 cm, only 1250 ryegrass seeds/m² are returned to the seedbank with a resulting 400 kg/ha of wheat yield loss the next season. This compares to a yield loss of 1.4 t/ha when the crop is cut at 40 cm and most of the ryegrass seeds are dropped.

Fig. 1 Effect of weed seed management strategy on crop yield and
weed seed numbers modelled with the Weed Seed Wizard.

Also in dry years where wheat yield is low, it is possible to burn narrow windrows in wheat.  For wheat crops of 2 to 2.5 t/ha or less it is possible to burn just the windrows. Cutting low is imperative to keep the fire in the windrow.

A Great Southern (WA) vigneron, who was worried about his under-vine weed control, contacted me in early September. Sally Peltzer, DAFWA, and I paid him a visit to discuss the potential problem and to collect samples for testing.

For the past 20 years the vigneron had regularly used paraquat (L) under the vines rotated with glyphosate (M) and the occasional Basta® (N) application. As can be seen in the image the paraquat applied two weeks earlier has had little effect on the annual ryegrass.

Live samples were sent to Plant Science Consulting in South Australia to conduct Quicktests® to determine herbicide resistance status before the grass had set seed.

The results are back and yes the annual ryegrass is resistant to paraquat with a low level of glyphosate resistance in some plants. Seed will be harvested from test survivors for more detailed testing in 2014.

I am now discussing best management strategies now and the future with the vigneron.

This highlights the fact that rotating herbicide modes-of-action delays resistance and doesn’t prevent it. To prevent/manage herbicide resistance multiple tactics must be used in the ONE season to PREVENT SEED SET of any survivors.

Those vineyard managers and broadacre farmers rotating modes-of-action need to have a rethink of their weed management strategies.

The Australian Pesticides and Veterinary Medicines Authority (APVMA) has cancelled 11 high volatile ester (HVE) products, retailed as ester 800, as part of the agency's ongoing review of 2,4-D (2,4-dichlorophenoxyacetic acid).

The products have been widely used in broadacre agriculture and sugarcane. The decision means:

• supply of cancelled 2,4-D HVE active constituent has ceased (effective as of 21 August 2013)
• supply of cancelled product manufactured prior to 21 August 2013 has ceased from Saturday, 31 August 2013
• products already purchased can be used up until 31 August 2014, under the same permit instructions (PER14329) that currently apply
• this permit restricts use to ‘winter only’ under strict conditions
• use of the existing products after 31 August 2014 will be illegal.

The decision follows the APVMA’s July report Annex to the APVMA's Preliminary Review Findings (Environment) Part 1: 2,4-D Esters Volume 1: Review Summary and advice to selected 2,4-D HVE registrants and approval holders of the intention to cancel selected registrations and approvals on the basis of unacceptable environmental risks.

Update on 2013-10-21 08:27 by Andrew Storrie

My post about the cancellation of all high volatility 2,4-D products has an error.

High volatlity 2,4-D ester will still be registered in Western Australia ONLY for the control of broadleafed weeds in wheat and barley, and in fallow situations before direct drilling or sowing of cereals, grain legumes, canola and pastures.

This is a winter use pattern ONLY.

Also DO NOT apply within 2km of potentially sensitive or susceptible aquatic areas, townsites or non-target vegetation. The latter includes commercial seedling and plant nurseries, horticultural crops, grapevines, tomato crops, intensive agricultural operations and wildflower processing crops, national parks, nature reserves, areas and aquaculture operations.

Following a wine tasting foray to Denmark, Western Australia last weekend I thought it timely to flag the issue of glyphosate resistance in vineyards.

While Sally and I were sampling the delectable products of this prize-winning winery I turned my attention out the window to the vineyard.  Yes, old habits die hard. What caught my eye were the beautiful healthy annual ryegrass plants scattered along the under-vine strip that is normally kept weed free (See image below).

Glyphosate resistant annual ryegrass getting a root-hold in the vineyardThis is typical of the early stages of the development of glyphosate resistance where an over-reliance on glyphosate for weed control allows naturally resistant individual plants to multiply and eventually dominate if management isn’t changed.

Currently twenty two separate populations of glyphosate resistant ryegrass have been confirmed in South Australian and Western Australian in vineyards (http://www.glyphosateresistance.org.au/register_summary.html).

This is likely to be the ‘tip-of-the-iceberg’ and vineyard managers need to take action immediately to prevent these glyphosate resistant plants from producing fertile seed. A range of post emergent herbicides with different modes-of-action are registered for use in vineyards and can be used NOW to kill the existing plants. These herbicides include amitrole (Group Q), Alliance® (Groups Q + L), glufosinate (Group N), paraquat (Group L), Spray.Seed® (Group L) and Fusilade® (Group A).

An integrated weed management program then needs to be developed for the management of herbicide resistance in our fantastic vineyards.