Last week I walked through the world of weeds. This week is about waving them goodbye, the chemical way. Next week I’ll look non-chemical cheerio’s.
Chemical products for killing weeds are known as Herbicides.
There are 4 main types, grouped together in relation to how they work:
- Contact
- Translocated/Systemic
- Residual
- Hormonal/Selective
Contact weedkillers
Contact weedkillers kill/damage whatever they touch in terms of a plant’s top growth. This makes them effective against Annual weeds. However as they neutralize when they hit the soil they have no effect on the roots. This means Perennial weeds with their stored root reserves will survive underground and regrow.
Although sold by brand names, a common chemical associated with this type of weedkiller is Diquat.
Translocated/Systemic weedkillers
Translocated/Systemic weedkillers enter through a plants’ leaves and are carried by its sap around the plant and down to the roots.
This method and the fact the weedkiller reaches the roots means it can be used against Perennial weeds.
An even more effective way to eradicate Perennial weeds however is with the combination of constant weeding vigilance over a growing season and a Translocated finale.
Perennial weeds are more difficult to eradicate than annual weeds because of their storage system of underground roots. This store is depleted each time they send up a shoot but with the expectation of replenishment when the plant puts on green, leafy growth enabling it to send nutrients back down to the roots.
By removing perennial weed shoots; not allowing them to grow, the root system is left running on empty, getting weaker each time it sends up another shoot.
By repeating this process through the growing season and then at the end allowing the plant to crop once with leaf (though not to flower) and then using a Translocated weedkiller to travel through the leaf growth back to the much weakened roots the impact on the plant, although it may take up to 2 weeks to show, will be much greater.
Chemical associated with this kind of weedkiller would be Glyphosate.
Residual
Residual weedkillers enter the plant from the soil through their roots. The product is also then held in the soil where it continues to be active preventing the germination of further weeds.
This active period can last up to 12 months and so Residual weedkillers are only suitable for use where plants are not intended to be grown i.e hard standing and paved areas etc.
A chemical for a residual weedkiller would be Diuron.
Hormonal/Selective weedkiller
This is often used in a lawn situation where two different types of plant, one wanted one not, are growing in close proximity.
Unwanted plants are daisies, dandelions and clovers’ broad leaved plants known for their ‘rosette habit’.
This habit allows for the application of weedkiller which will sit on and be absorbed by broad leaved plants but which will run down and off thin grass spikes.
Referred to as hormonal as they interfere and upset the hormonal system of the plant, causing it to grow very fast, producing long stems but not producing chlorophyll, first weakening and then killiing the plant.
2,4-D is a selective weedkiller.
The chemical components of weedkiller are subject to change as they are either banned, withdrawn or not licensed. There are also different products and strengths avaliable to the licensened professional user as opposed to the home gardener.
This article contain further technical information.
