The predicted loss of paraquat/diquat as one of the weed control options is set to disrupt the current standard practice in Australia, along with the potential pressure from Europe on glyphosate and glufosinate seeing longer term restrictions.

This loss of herbicide treatments is an issue of concern for many growers in the WA industry.

Pomewest intends to investigate current weed management practices by WA Pome growers and determine their interest in alternative weed control treatments in this desktop study.

The move away from the bare herbicide strip to a seeded or mulched under-tree line will still require some herbicide treatment to control problematic weeds.

Weeds such as kikuyu are vigorous and disruptive in orchards and can undermine the move away from herbicides.

Meaning the use of integrated weed management is a valuable tool for many pome fruit growers.

Ensuring growers are aware of the herbicides with different modes of action will ensure resistant weeds do not persist.

This investigation has the potential to build onto the PIPS4 regional trial site under-tree treatments by investigating the soil biology activity after weed control treatments.

Soil biology and carbon cycling are becoming more important for measuring soil health and eco-credentials for orchards to maintain market access and social license.

After the desktop investigation a field investigation will follow, that compares different herbicides, mechanical and organic weed control options so the impact can be assessed in a block of single cultivar of apple.

Method:

Approximately 20 per cent of WA pome growers were surveyed on their current weed management approaches, using semi-structured phone interviews and a survey through the Pomewest grower newsletter during the first two weeks of February.

A series of questions were developed to determine the impact of weeds in the treeline of the orchard and the various control options that are being used by growers currently.

The appetite for innovative weed control options was explored with the growers during the interview process.

Results:

There were 15 weeds listed by growers as difficult to control in the orchard under-tree space, with wild radish/turnip, kikuyu followed by fat hen and willowherb named as the most common.

Weeds were present in the orchard from the existing seed bank and growers also identified weed seeds brought into the orchard by carriers such as livestock, cars, people and new tree plantings.

Ninety four percent of those interviewed used chemical management options to control weeds in the treeline, followed by mechanical control options which included slashing, mowing and whipper snipping.

When asked for the chemical options currently in use, common practice was a rotation of herbicides dependent upon the growth stage of the tree and time of the year.

Chemical weed control occurred for most growers 3-4 times during the year.

Most commonly during the season producers rotate between glyphosate and Glufosinate with paraquat/diquat used when conditions were unsuitable for Glufosinate or weed pressure required a heavier response.

Young trees were identified as needing the paraquat/diquat to control weeds if Glufosinate was unable to be used.

The more difficult weeds were controlled using paraquat/diquat or glyphosate. Paraquat/diquat was used by 67 per cent of the sample, who saw its role as critical under certain conditions.

However, 33 per cent of those interviewed did not use the product at all.

For some there was no rotation of mode of action which could increase the incidence of resistance building up if fewer options were available.

Some did identify using selective herbicides that could control broad leaf or grasses.

Integrated weed management strategies included the use of slashing or mowing, along with spot spraying, sowing a cover crop, mow and throw system, and the use of a mulch as a physical weed barrier.

Growers were concerned about the chemical options available in the future, with 78 per cent of respondents reporting concern that fewer options would be available in future.

Following the desktop study of current practices a field investigation will be undertaken to compare the treatments that were highly rated by growers.

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Wednesday, 4th January 2023

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