Chemical weed control in ornamental crops

New, commercially available, herbicide active ingredients are now a very rare occurrence, not only for horticultural crops but across agriculture in general. New herbicide products do come to the market, but these are combinations of other available active ingredients. As a sector which relies heavily on Extension of Authorisation for Minor Use (EAMUs) for new product generation, this has a serious impact in terms of the available chemical weed control options.

The various work programmes funded by AHDB have assessed numerous herbicides for efficacy and safety on a range of crops to supplement current control programmes. However, in the future as further products are withdrawn from the market different approaches are going to be needed.

In field-grown crops, precision application of herbicides is starting to come of age where products are targeted specifically to the weeds or where different herbicides are used within the crop relative to those applied outside the rows. This allows for the use of potentially more effective herbicides which may be less crop safe and cannot be used over the crop. With container-grown crops, physical methods of weed control via mulches or ‘pot-toppers’ will have to be combined with chemical options to generate season-long weed control programmes.

Specific outcomes from a number of recent AHDB funded projects for hardy nursery stock, cut flower crops and narcissus are summarised below (note - always undertake small scale trials on new herbicide products first before widespread commercial use):

Project HNS 198 ‘Improving weed control in hardy nursery stock’ has been the driving force in terms of identifying new chemical weed control options for both container- and field-grown crops over the last five years. The project has identified a number of new products such as Centurion Max (clethodim), Defy (prosulfocarb), Sencorex Flow (metribuzin) and Sunfire (flufenacet) which can be used in current herbicide programmes for both container- and field-grown crops to expand the available options for weed control. Sencorex Flow has shown promise in trials on field-grown budded roses and trees and may have potential as a dormant treatment in container-grown crops. Centurion Max and Sunfire can be used in programmes or tank mixes over container-grown crops to improve grass weed control.

As part of the Cut Flower Centre (PO BOF 002b) and SCEPTREPlus programme (CP 165) recent and ongoing work has targeted chemical weed control options in China aster, gladioli, larkspur, peony and sweet william. Earlier trials showed that Stomp Aqua (pendimethalin) and Gamit 36 CS worked well as a pre- or post-planting treatment on transplanted China aster. In terms of gladioli, pre-crop emergence applications of Sencorex Flow; Springbok (dimethenamid-p + metazachlor); Sunfire and Wing P (dimethenamid-p + pendimethalin) have proven safe and effective. With larkspur a coded product followed by Defy worked well pre-drilling and tank mixes of Dual Gold and Gamit 36 CS; and Stomp Aqua and Gamit 36 CS worked post-drilling. The trials on peony and sweet william are still ongoing.

Over the past few years, work in the SCEPTREplus programme has focused on weed control in narcissus post-cropping and during the dormant period. During the post-cropping period tank mixes of Kerb Flo (propyzamide) and Stomp Aqua; Butryflow (bromoxynil) and Stomp Aqua; Wing-P and Centium 360 CS (clomazone) (plus the first and second tank mixes with a coded product) have all worked well. During dormancy, tank mixes of Sencorex Flow and Stomp Aqua; Stomp Aqua and Praxim (metobromuron); and Sencorex Flow, Stomp Aqua and Centium 360 CS have all performed well.