Weed control is usually carried out in spring, but farmers may want to consider late summer herbicide applications instead to take advantage of more favourable conditions.
There is a common perception that spring is the best time to apply herbicides to established grassland, but Brent Gibbon, of Nufarm, says achieving the correct timing of application in spring can be tricky for a number of reasons.
He says: “The weather conditions are not always suitable for spraying in April and weeds such as docks may not be actively growing if the weather has been frosty. It is vital that the weed is actively growing to allow the actives in the herbicide to translocate through to the root.”
Mr Gibbon also says timing of spraying in spring can be difficult when trying to factor in a three-week interval between application and cutting for silage ground, and two-week grazing interval in grazing systems.
So instead, grassland farmers may want to consider late August and September as an ‘ideal time’ to control perennial weeds.
Mr Gibbon says: “We are more likely to get favourable conditions at this time of year. Weeds are usually in a leafy, vegetative state following a summer of cutting and/or grazing.
“Weeds are actively growing in warm, moist soil conditions providing an ideal opportunity for the herbicide to be actively taken up and translocated down to the roots.
“Late summer application means there are fewer worries about cutting interval, and there is usually alternative grazing available at this time.”
Despite this, summer weed control is often not on the list of things to do for most grassland farmers.
A recent survey of 200 farmers – a mixture of dairy, and beef and sheep producers – conducted by Nufarm showed summer weed control was a consideration for just one-third of respondents.
Lack of awareness to the benefits of later applications was cited by 50 per cent of the respondents, about 27 per cent had not considered the approach and 16 per cent had not budgeted for it.
Independent grassland consultant Dr George Fisher says: “These producers, while already conscious of the fact they can achieve more from their grass, are unaware August and September are the best months for controlling weeds, especially docks in established grassland including silage leys.
"This season in particular has been conducive not only to grass growth, but also to weed growth.
“Every 1 per cent increase in weed ground cover will results in a 1 per cent decrease in grass growth. So controlling common weeds in a grazing sward with a current 20 per cent dock infestation, for example, could result in improving spring yields from seven tonnes of dry matter per hectare to 8.5t DM/ha.”
Dr Fisher suggests the benefit of utilising this extra grass to replace more expensive bought-in feeds, could provide a five-to-one return on investment.