2019 trials summary – IWMPRAISE UK

In the UK a number of trials for IWMPRAISE have taken place over the 2019 reporting season; ranging from the potential of shallow row cultivations to replace glyphosate ahead of spring cropping, to mechanical and chemical control strategies in vineyards. Summaries can be found in the 2020 booklet and in individual trial reports (http://www.iwm-uk.co.uk/iwmpraise-results-and-publications/), but a brief outline is presented below.

Trials investigating the effects of cultivation, drilling date or herbicide treatment in narrow row crops (Work Package 3 – Annual Narrow Row Crops)

Several trials, based at NIAB Cambridge, have looked at the single or interactive effects of low impact cultivation, drilling date or herbicide treatments on the control of black-grass (Alopecurus myosuroides) and other grass weed species. In general, drilling date proved to be the most significant factor, and the experiments found positive effects of delayed drilling on grass weed control. This is particularly apparent for black-grass in Spring Barley and Oat crops, as the plants are out-competed by vigorous crop growth. However, delayed drilling may also be associated with a yield penalty and reduced herbicide efficacy.

Drilling date is a vital cultural control technique for black-grass as it establishes a crop after the major germination period. Work in Italian ryegrass (Lolium multiflorum) demonstrates that similar effects can be achieved in this troublesome grass weed, although there is significant interaction with cultivation. For black-grass, many growers are already using spring cropping to reduce the burden of weed in the crop. These growers are beginning to move the drilling date of their spring crops forward (Jan/Feb) to maximise yield; however work in the 2019 season shows that this can have a detrimental effect. Waiting until March in the UK is necessary to balance a strong competitive crop, whilst reducing the emergence of black-grass seedlings.

The success of cultivation controls is highly context-dependent. Shallow cultivation (for sustainable practice and lower soil disturbance) can be a tool to help reduce black-grass burden in the autumn; however, this effect is reduced in the spring or without additional herbicide treatment, and may partially depend on soil conditions. In combination with delayed drilling, ploughing can also achieve high levels of control for ryegrass, but with concomitant increases in soil disturbance. Cultivation is an important consideration for grass weed management, and often is a compromised between the benefits that come with low disturbance establishment and actually reducing grass weed populations to a manageable level.

In general, the benefits of pre-and post-emergence herbicides are additive, with proportional improvements in control with additional actives or applications in most circumstances. However, the benefit of herbicide is mostly derived at earlier sowings, when weed germination is highest, and similar results can be achieved by delaying sowing.

Thus integrated weed management in narrow row crops is a complex multifaceted question, and is a compromise between competing demands for cultivation, drilling date and yield. Delaying drilling dates, in particular, may be a key future strategy for IWM.

Integrated weed management in vineyards (Work Package 6 – Woody Perennial Crops)

In conjunction with Clemens GmBH and Cotswold seeds, vineyard trials were established in 2018 in NIAB EMR (East Malling, Kent) assessing mechanical and chemical control methods. In 2019, three weeding solutions were assessed (herbicide vs blade vs serrated disk). Early results showed no differences between control strategies on the vegetative growth of vines, and weed competition only became problematic in the late growth season. However, non-treated controls showed significantly reduced growth rates, most likely due to competition by weeds for water and nutrients. In the coming season, the population dynamics of weed populations in response to control methods will be determined, as will cover-crop sustainability.  

Effects of cultivation and rotations on weed control

As part of IWMPRAISE, we have been investigating the effects of varied cultivation controls on weed populations. To do this we have used the long-term Sustainability Trial for Arable Rotations Trial (STAR) in Suffolk, with Annual Plough, Shallow non-inversion and deep non-inversion as treatments. Using ground sheets to protect the weed populations from herbicide, we will hopefully detect some differences as they emerge through the year.