SCEPTREplus: Improving weed control in cucurbits (courgettes)

• Trial code: SP13
• Title: Improving weed control in cucurbits (courgettes)
• Crop: Field vegetables – Cucurbita (courgette)
• Target: General broadleaf weeds and grasses

Conclusions and Take Home Message

• Wing-P or Stomp Aqua applied inter-row in a tank-mix with Gamit 36 CS gave improved weed control compared to the current standard, was crop safe, and gave equivalent yields to the current standard.
• An application for an EAMU for Wing-P for inter-row use in courgettes has been submitted.
• AHDB9987 applied in a tank mix with Gamit 36 CS post-planting shows promise in controlling weeds in courgettes with no phytotoxic effects in this trial.
• AHDB9995 and Bonalan pre-planting followed by Gamit 36 CS were safe to the courgettes, but gave poor weed control of the weed species on site. Tank-mixing or being included in sequence with other products could improve the range of weed species controlled. Further work is needed to investigate possible safe product combinations.
• Further studies should also be repeated on the newer products Bonalan and AHDB9987

Introduction

There are currently very few herbicide options for weed control for cucurbit growers with only three residual herbicides approved under EAMU for use on the crop; isoxaben, propyzamide and, most recently, clomazone which gained approval in 2015 to improve control of groundsel. Diquat is also approved for inter-row application to control emerged weeds after planting, but it only offers temporary suppression and often needs to be repeated. This limited range of herbicides leaves gaps in the weed control spectrum, and growers experience problems with a wide range of weeds. In particular; polygonum weeds, black nightshade, black bindweed, sowthistle, and a number of grass weeds including annual meadow grass, volunteer cereals (especially barley), wild oat, black-grass and brome are problematic for growers. As well as competing with the crop for nutrients and water, these weeds also hinder pickers reducing harvest efficiency. Black plastic mulch is commonly used in courgette crops for weed control in the row and occasionally in some pumpkin crops. This is because the crops are very sensitive to herbicides, including those currently approved. For some growers, it is therefore common practice to apply authorised herbicides via hooded tractor-mounted spray applicators to shield the crop foliage. However, problems with weed between rows are still experienced as there are weaknesses in the spectrum of weeds controlled by the few currently authorised herbicides. Further options are therefore required inter-row as well as over the row.

Results

All treatments except AHDB9995 significantly reduced the mean percentage weed cover (p <0.001). Of the experimental treatments the greatest weed control (>90% reduction on 22 August pre-harvest) was achieved by five treatments; AHDB9987 tank-mixed with Flexidor or Flexidor + Gamit 36 CS; Stomp Aqua + Gamit 36 CS + AHDB9947 in a tank-mix pre-planting, Bonalan pre-planting followed by Flexidor + Gamit 36 CS, and Wing-P pre-planting followed by AHDB9987. However, these and many other treatments were not crop safe to the courgettes despite giving effective weed control (Table 1).

Six treatments combined acceptable crop safety, or close to acceptable crop safety with reasonably effective weed control; the standard Flexidor + Gamit 36 CS, Bonalan or Wing-P applied at a reduced rate pre-planting followed by Gamit 36 CS post-planting, Wing-P or Stomp Aqua applied at reduced rates inter-row with Gamit 36 CS post-planting, and AHDB9987 in a tank-mix with Gamit 36 CS applied post-planting.

All treatments with the exception of the lower rate of AHDB9995 gave higher yields than the untreated control, in those that were assessed. Three treatments gave significantly greater yields than the untreated control, these were the commercial standard, Flexidor + Gamit 36 CS, and the two inter-row treatments; Stomp Aqua + Gamit 36 CS and Wing-P + Gamit 36 CS.

Despite giving poor weed control in this trial AHDB9995 should not be overlooked for further work as it gives useful control of annual meadow grass, black-bindweed, black-grass, knotgrass, pale persicaria and wild oat which have been reported as problematic by growers. The weed species present in this trial would not have been well controlled by AHDB9995, as the main species were fat-hen and barnyard grass which are only moderately susceptible to this herbicide. Therefore further work is required with AHDB9995 to find suitable tank-mix partners to cover a wider weed spectrum.

The standard treatments performed as expected and were comparable to commercial practice. There were no issues with mixing or application of any products. No wetters were used.