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« Tips on Scarifying a Lawn | Main | Late Summer Lawn Weed Control »

Garden Weed Control Advice

Hand Pressure Sprayer Hecht 4500 With the recent wet weather, the weeds are having a bit of a field day out in the garden, growing like the clappers with not that many days rain free in order to weed spray them!

A couple of friends recently came up with the same comment following their attempts at weed control in their gardens.  They had both applied a branded total weed killer on their gravel and pathways and remarked after a few days following application that "The weeds have not gone yet."

When I asked of them "When did you apply the control product?" they said only a few days ago to which I replied "You are expecting too much, please be patient."  Their observations on the speed of the mode of action of single active ingredient or a blend of active ingredients is rather common so a little bit of advice may be required in choice of product for the time of year follows.

There are total weed killers and selective weed killers and some total weed killers can also be selective just to confuse you.  Total weed killers kill everything and selective weed killers are selective in what they kill unlike totals.  Lawn weed killers are selective which is why if correctly applied, the weeds die and the lawn grasses do not.  If you applied a total weed killer to your lawn, this would kill the weeds and turf grasses so unless this is your intention, do not apply total weed killers to your lawn!

Selective weed killers should be applied in the normal growing season as the control active ingredient rely on the normal plant growing process to get the ingredients in and around the plant system and down to the roots to ultimately kill the weed.

Total weed killers can come with many different modes of action and as a result are applied at varying times throughout the year.  There are three main classifications of total weed killers - Contact, Systemic and Residual. 

Contact weed killers, those containing the active ingredient of Diquat also written as Diquat dibromide, will kill the weed upon contact by quickly turning the weed foliage black.  You may remember the total weed killer Paraquat doing a similar task.  Apply Contact weed killers in the growing season when weeds are present.  Diquat may be joined in a control product by a Systemic weed killer such as Diflufenican or Glyphosate also written as Glyphosate diammonium.  Glyphosate stops the plant producing chlorophyll and treated weed grasses will turn a pink colour a week or so following application before total death. Weeds will take a bit longer to fully die.  Apply Systemic weed killers in the growing season so as early as March to end of November but ideally April to September when what you want to kill is actively growing.  Systemic weed killers will kill what is there at the time and a repeat application may be required some 3 months following the first application to keep the area weed free.

The last group of total weed killers are Residual weed killers, applied usually to cold soils in the non-growing season as a blanket spray (all over) to prevent weed growth in the usual growing season occurring.  The active ingredients are held in the soil for a few months and form a proactive barrier killing germinating weeds and grasses before they mature.  Active ingredients will include Diflufenican, Oxidaizon.   Residual weed killers often have some Glyphosate in the mix to pick up on any green vegetation present in the area at the time of the application.  Gardeners make the mistake of only applying Residual weed killers in the growing season months of April to September when ideally they work better going forward if applied in November to March when soils are traditionally much colder.  The active ingredients naturally break down in drier and warmer soils into harmless elements.  It is an odd concept weed killing a gravel driveway when there are no weeds present but give it a go and this winter apply your weed killer containing the active ingredient of Diflufenican or Oxidaizon and you will visibly note a vast reduction of weeds coming through in the spring.

A typical weed control programme for gravel & non crop areas:
 
Jan/Feb - Apply Residual Weed Killer as blanket spray (all over) to cold soils to form a residual barrier in the soil to prevent pre germinated weeds and grasses.  Even if weeds are not present.
 
May/June - Apply Systemic Glyphosate based product as blanket spray or spot spray to provide translocated weed control to weeds and grasses.  Repeat after 6 weeks if control not achieved of tougher weeds like Ground Elder and Brambles/Nettles
 
August/Sept/October - Apply Systemic Glyphosate based product as blanket spray or spot spray to provide translocated weed control to weeds and grasses
 
Repeat annually. The important one is the Jan/Feb residual barrier spray

Need to see where you have sprayed?

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