Residual weed control in amenity areas
After many years of 'one size fits all' residual weed control, using dichlobenil granules, everything changes this year for the management of weeds in amenity areas. Casoron, and its variants, has now gone. This popular product has been extensively used in many different situations including ornamental shrubs, fence lines, around tree bases and street furniture and even cemetery headstones, not to mention aquatic weed control. Not any longer!
Many larger users have relied on just two herbicides, dichlobenil and glyphosate, simply buying and using these in large volumes without needing to think much about the job in hand or needing advice on how to use the products effectively. Winter applied dichlobenil has provided residual protection for many months and dealt with smaller seedling weeds. Glyphosate has been used to clean up and deal with deep-rooted perennials, 'spot' treating the problems that dichlobenil did not control.
From now on, a choice of alternative products is available, but this will require planning, expert advice on how, when and where to use them, and a change in operating methods.
The overall application of a granule that drops to the ground through shrubs without causing them problems has gone, so spray application by knapsack sprayer, CDA or ULV lances will become much more necessary.
Some herbicides, such as glyphosate, are highly systemic so, in circumstances where work in or under shrubs is more necessary, glufosinate ammonium (Finale) may be a better and safer choice. Older residuals like propyzamide (Kerb) can be used, perhaps in tank mix with other products such as isoxaben, metazachlor, oxadiazon (Ronstar liquid) or glufosinate ammonium (Finale).
Choices will depend on whether treatment is to existing clean ground, the weed spectrum present - which could include difficult weeds such as couch grass (Elymus Repens) - and the soil type.
In that respect, the fashion of applying large amounts of bark mulch to shrub beds can be a problem. Many residual herbicides simply won't work in organic soils or on organic matter. If residual control is limited or fails, then there are specialist products such as Panarex (quizalofop-P-tefuryl) that are highly selective and can deal with couch grasses during the growing season by foliar application. Product mixes are a minefield, so an on site meeting with your BASIS advisor will be beneficial.
Tidying up in season can be done with glufosinate ammonium (Finale), glyphosate, where safe to do so, or Pistol (glyphosate plus DFF). In the latter case Pistol can be used very effectively on fence lines, around mowing obstacles, gravestones and gravel or porous pathways, but its use in shrubs should be spot treatment rather than blanket treatment.
There are companies now promoting similar products to Pistol (glyphosate plus alternative residuals) as an 'alternative' to Casoron (dichlobenil). Tread carefully! If 'blanket' applied, or over applied, great damage to sensitive shrub species can occur and, in any case, the use of systemic glyphosate in that context is inevitably going to carry risk if spraying around and under shrubs.
The message is clear. There are alternatives to Casoron, but please seek expert advice from experienced BASIS qualified advisors or Amenity Assured Contractors.
The goalposts for registered products and approved uses keep being moved by the regulators, so up to the minute advice is essential. Also, be prepared to change working methods and timings of shrub weed control, as the old routines will have to change. One size no longer fits all!