With grass selective herbicide applications not far around the corner, I thought it would be a good time to look at the features of the Group A herbicide clethodim. Herbicides are grouped by the way they kill plants and Group A herbicides work by inhibiting an initial enzyme in the synthesis of fatty acids, acetyl co-enzyme A carboxylase (ACCase). This herbicide group includes both ‘fops’ such as Smart Quizalofop and ‘dims’ such as Smart Clethodim.
ACCase activity is highest at the base of young growing leaves and at the crown region. The herbicide must reach this area of the plant to be effective. This is also where herbicide symptoms are first visible. It is during rapid growth that ACCase is most active and therefore when the herbicide will be most effective. When growth is slowed by dry conditions, frost, or plants are more mature the herbicide’s performance is reduced.
Clethodim with the correct adjuvant (Smart Accel or Smart Up) penetrates the cuticle and enters the leaves of the plant very readily. However, once inside the leaf the ‘dims’ are translocated quite slowly which is why good coverage is important to get the herbicide near areas of the plant where it will be most active. Grass architecture is also beneficial as droplets tend to run down the leaves putting the herbicide where it is most effective.
Clethodim has poor water solubility which causes its slow movement within plants, which in turn means symptoms from the herbicide are slow to appear. Both root and shoot growth is inhibited after application which is why affected grasses can easily be pulled from the soil and leaves can be pulled from the crown.
When sprayed on broadleaf plants, clethodim does not inhibit ACCase in the same way it does with grasses, giving it high selectivity and virtually no crop effect. It is only active as a foliar spray and is not taken up from the soil solution, therefore there is no residual activity. Clethodim is not volatile and degradation in the soil occurs by soil micro-organisms. Herbicide breakdown in soil occurs rapidly which reduces leaching.
Choosing a quality adjuvant such as Smart Accel or Smart Up is critical for ‘dim’ efficacy, this is in part because ‘dim’ herbicides degrade quickly in sunlight. A quality adjuvant has been designed to increase the speed of uptake, helping penetrate the leaf cuticle and with resistance increasing quickly in grasses (e.g. ryegrass) this becomes more important. Clethodim is formulated as an emulsifiable concentrate (EC) containing organic solvents to make it mix with water. When you open a container, it is the organic solvent you smell not the herbicide.
In summary, to get the best from Smart Clethodim ensure a good coverage of the herbicide, use one of our Smart oils and spray grass weeds when small and actively growing.
The Smart Agro