Roundup Best Practice: Growth Stage

Perennials

The optimum time for treatment of perennial broad-leaved weeds e.g. docks or thistles is from flowering, but before the plant dies back, usually July to October. This is when the natural flow of sugars is downwards to the root sink, which ensures maximum translocation and efficacy of Roundup.

Perennial grass weeds must have full emergence of healthy green leaf. Common couch for example becomes susceptible at the onset of tillering and new rhizome growth, which usually occurs when plants have 10-15 cm of new growth.

Where perennials are a major problem before planting in the spring, treat pre-planting and then follow up pre-harvest or in the stubble before the following crop.

Annuals

Annual grasses and broad-leaved weeds should have at least 5 cm of leaf or two expanded true leaves. Very small plants may not have the leaf area to easily target with the spray and absorb the herbicide.

Timing for Annual grass control

Annual grasses – growth phases to avoid

The stem extension phase describes the growth stage when assimilates are pushing upwards very strongly to produce flower heads and translocation of glyphosate down to the roots is against the direction of that flow. Poor uptake from applications at this time can lead to variable control. When sprayed at this stage the usual effect is an initial good kill followed by re-growth from those tillers that were at stem extension. The re-growth typically goes on to produce more flowering stems and requires a further treatment to stop viable seed production. This phenomenon has been particularly noted in the pre-cut treatment of grassland, it is not related to product, dose rate or formulation.