According to Teagasc, pre-emergence herbicides have been shown to be more effective in controlling problem grass weeds such as Bromes, Blackgrass and Annual Meadow Grass.
Fortunately, Teagasc has said there are choices, so growers should select a mix that will control the main weeds encountered in each field.
It is unlikely that the same mix will cover all the weeds in all fields, so specific knowledge of the predominant weeds is vital for pre-emergence herbicides to work efficiently.
Products
Products such as pendimethalin – found in a number of herbicide brands, prosulfocarb (Defy/Roxy), flufenacet (Firebird/Navigate) – give best results when applied early.
This is especially so where Annual Meadow Grass is a problem. Chlorotoluron (Tower) can be used early post-emergence.
The active ingredient, diflufenican, (Stride/Diflanil/Sempra) can be used to improve the control of Charlock, Chickweed and Speedwells.
Firebird MET will help to control Groundsel as well as many other broadleaf and grass weeds.
Tri-allate (Avadex) will improve control of Blackgrass and Italian ryegrass, while Zypar will improve control of Fumitory, Poppy and volunteer beans.
Many of the active ingredients will appear in mixes, so growers should choose products that will control as many weeds as possible.
Farmers should also target the most problematic weeds first and the less important ones can be tidied up later.
Oilseed rape
Meanwhile, seed sales figures suggest that there has been an increase in the area of oilseed rape planted again in 2022, with much of it planted early and in ideal conditions.
Even in dry conditions, establishment seems good, although there have been reported cases of slug and pigeon damage.
Growers should try to get on top these early so that canopies will be big enough to reduce grazing later in the season and hopefully, fertiliser costs.
Phoma will be the main target of autumn fungicide applications; however, varieties differ in their susceptibility, so growers should follow the threshold guidelines for the control of the disease – 10% of plants affected.
In addition, fungicide timing needs to effective against both phoma and light leaf spot (LLS).
The choice of fungicide will often come down to whether or not the crop needs a growth regulator effect or not.
Backward or thin crops will not need a growth regulator, so an application of a half-rate prothioconazole (Proline) should be adequate.
In early sown crops where a regulator is probably needed, options include metconazole-based products (Sirena, Plexeo) or tebuconazole-based products (Prosaro, Jade, Pontoon, Protendo), again at half the recommended rates.