Rhubarb: Evaluation of herbicides for problem weeds - 2015

Project Summary:

Efficient and cost effective weed control is important in rhubarb as with other crops to prevent yield loss as a result of competition for water and nutrients and to enable efficient harvesting without impedance by weed growth.
Rhubarb production is increasing year on year, with marketed yields rising by 1000 tonnes a year, every year for the last three years. Multiples therefore have an increasing interest in this crop with a potential 10 month season. In recent years, rhubarb crown size and yield is decreasing in both forced and green pull crops, and growers believe that this is as a consequence of increased competition from weeds amongst other influencing factors. Therefore, effective weed management in rhubarb is set to become more important to allow supply to keep up with this increased demand. In addition, the strict requirements of retailers’ quality protocols for clean produce free of dirt and contamination mean that cultivations carried out for weed control can occasionally lead to unintentional mud splash. Further effective herbicides may reduce the frequency of these operations and aid the grower in avoiding such issues.
The majority of rhubarb herbicide programmes are currently based on pendimethalin propyzamide and clomazone, and these do not provide complete enough weed spectrum efficacy and persistence (See appendix for detail on weeds controlled by current herbicides). Work carried out in HDC project SF 129 gave useful information for growers on the efficacy and crop safety of clomazone which gained an EAMU while the experiment was being carried out and increased the weed spectrum controlled, but there are still gaps to fill. Mesotrione and metribuzin tested in the same project also showed useful activity, with the latter showing some control of Himalayan balsam and therefore it would be useful to revisit these products as well as test some newer materials with a view to gaining EAMUs. This would be particularly timely with the introduction of the Sustainable Use Directive and the recent change in the EU to the assessment of plant protection products by hazard in addition to risk based criteria which has placed some residual herbicides under threat. The recent Endocrine Disruptor review and the review of implications for the industry carried out by HDC, highlights the future status and availability of pendimethalin and propyzamide is therefore at best uncertain.
Consultation with rhubarb growers in Yorkshire, the Midlands, East Anglia and the South has confirmed support for work to identify alternative herbicides from amongst currently available products - or those likely to become so - which provide a good spectrum of weed control, with a high priority for ‘problem weeds’ such as Himalayan balsam (Impatiens glandulifera) and perennials e.g. docks and thistles, and potential replacements for products being lost. A literature search has shown there is virtually no specific information available to rhubarb growers on the control of Himalayan balsam.
Although there is an EAMU for glyphosate, the short dormant season of the crop gives few windows for treatment and since the loss of dichlobenil, perennial weed infestations are on the increase.
Growers should benefit from this work by having a wider choice of herbicides in order to maintain effective weed control in plantations, which would otherwise be difficult as a result of increasing restrictions on or loss of current herbicides. The project will also add useful information on weed control of the more unusual weeds that may trouble growers, as these are seldom listed on product labels and agrochemical company websites. Furthermore, information gained on weed species controlled may give guidance in other perennial sectors such as asparagus, and field grown ornamentals.

Benefits to industry:

Aims and objectives:

Aims:

The aim of this project is to evaluate a selection of newer herbicides for crop safety and efficacy against a range of problem weeds in rhubarb plantations, compared with industry standards.

Objectives:

• To identify and evaluate the weed control efficacy of a number of new residual herbicides against crop standard treatments
• To evaluate the weed control efficacy of a range of contact herbicide treatments for perennial weed control
• To evaluate the crop safety of both the contact and residual herbicides applied by assessing phytotoxicity
• Publicise the results to the industry through an HDC news article and a presentation at an appropriate grower event.