Pesticide Reduction at Kew Botanic Gardens

The Royal Botanic Gardens at Kew has a mission to ensure better management of the environment by increasing knowledge and understanding of the plant kingdom—the basis of life on Earth. This is achieved through world-wide research into plants and the ecosystem, publication, access to all knowledge so gained for the world’s scientific community, and through the display and interpretation to the public of the collections at Kew in London and Wakehurst Place in Sussex. David Buffin has explored these ideals with Fiona Dennis of Kew to see how they relate to the practical implementation of integrated pest management using, in particular, biological control and the reduction in pesticide use.

In recent years, there has been a move towards greater emphasis on biological control at Kew, according to Fiona Dennis, Senior Botanical Horticulturist in the Herbaceous Section. Biological control programmes are now in their fourth year at Kew, and ninth year in the non-public experimental Jodrell Glass areas. The implementation of biological control has been centralised in order to minimise duplication and standardise practices and purchases of biological control agents.

Environmental commitment 
As part of Kew’s corporate strategic plan there is a commitment to develop an ‘environmentally sympathetic charter’. The charter would include a commitment to  the existing audits on energy use, health and safety, noise and toxic waste, and to continue developing projects on biological control, water conservation and waste recycling. There is a strategy to undertake experiments and to support scientific study on the efficacy agents introduced into the glass houses. “As far as possible, Kew does not use chemical pest control and when it is used, we select only those with the least persistent active ingredient.”  There may  also be some occupational health and safety benefits from using these products.  Biological control will be used as a primary method in all public display glass houses and nurseries.  Guidelines are currently under review.

Examples of biological control

• In the non-public research glass houses Chinese painted quail were introduced to control grubs. They were found to be more interested in weed seeds and have also become a biological weed control agent. This highlights the fact that  Kew has the capacity to be experimental and innovative, with results which benefit commercial horticultural operations by the publication of findings.

• In the temperate glass houses, black tea thrips are a major pest causing severe damage to plants.  Biological control agents Amblyseius and Orius have been used with little effect to date. The reasons for this are still to be determined and this is undergoing continual review. The most effective method to reduce infestation proved to be cultural control, including pruning out large colonies of affected areas.  On the other hand, broad mite was successfully controlled by Amblyseius. Sticky traps are used to monitor pests—attracted by their bright yellow colour. One potential problem here occurs if the predators also come to a sticky end.

• Companion planting has been adopted. The plant Convulvulus tricolor has been found to attract hover flies. These in turn attack aphids. The aphids can spread debilitating viruses to plants. By placing the Convulvulus tricolor above a  plant susceptible to aphids, the attracted hover flies will help to control them.

• In the Princess of Wales Conservatory brown lizards have been introduced, unknown to, and (because of  their shy nature) generally unseen by, the public, to pick off insect pests which attack the precious plant collection. Frogs and toads may be introduced in the future to carry out similar tasks.

Cockroaches
Cockroaches are a problem at Kew, although being nocturnal they are not often seen by the public. They thrive in the warmth of glass houses and attack leaf and root tips and flowers. There is also a public health concern as they can harbour diseases.  The main form of control remains chemical. Sticky traps to capture cockroaches have been tried, but the synthetic pyrethroid cypermethrin remains their most effective control tool. Research into the identification and life cycles of cockroaches is being undertaken to determine if the pest can be eradicated using an integrated pest management control system.

Training in IPM and biological control 
A pilot training programme began in 1993. Integrated pest management and biological control are knowledge-based systems. Information and monitoring are essential for success. Factors such as pest/predator biology including life-cycle analysis, periods of greatest activity and environmental requirements such as temperature and moisture, are key. The diversity of the plants grown is such that the interactions can give surprising results and these pose many challenges to horticulturists at Kew. Continual observations are needed to monitor the pests to determine their relationships with specific plant groups. This may include plants which have in-built physiological deterrents which need further research input. All relevant staff are required to:

• have the skill to identify accurately the pests and their predators; 

• know what appropriate remedial action should be taken when faced with a pest  problem;

• design a biological programme for the year stating when likely biological control agents will be required and how much would be required.

Mark Flanagan and Andrew Jackson of Wakehurst Place putting down one of the hundreds of PLANTEX tree mats used around new tree plantings. Photo: PLANTEX

‘Plantex’ reduces herbicide use
Plantex is widely used at Kew for non-chemical weed control. It is a porous fabric made of polyurethane that allows air and water to permeate through  to the soil whilst preventing weed growth.  It is light, easy to lay, and when covered with mulch will last for over 15 years (without a cover it would last five years) . It is now specified and used by many local authorities, architects, landscapers, utility and amenity companies.
    After a successful five-year trial Plantex has become one of the first products to receive a full commercial endorsement from Kew, running for three years from 1993.  The original trial started in 1988 at Wakehurst Place, Kew’s estate in Sussex.  Mark Flanagan, Deputy Curator, had the task of replacing trees lost during the heavy storms of 1987. He felt it was an ideal time to start a long term assessment of the use of mulch mats around new tree plantings. The aim was to reduce weed competition and help retain moisture in the ground. Water conservation is important at Kew because of the poor water retentive properties and a free draining soil. It would be in keeping with the reduction in the need for irrigation as part of Kew’s environmental strategy. The initial assessment for six months, using several different products, resulted in Plantex being chosen for the full five year evaluation. During this time the use of the product was extended to include the gardens at Kew under the supervision of Tony Kirkham, Supervisor of the North Arboretum. “Considering the rarity of our trees, and the effort required to obtain them, the use of Plantex has certainly reduced any losses we might have expected” he said.
    According to the manufacturers, Du Pont, chemical herbicides can generally be avoided when using Plantex around tree bases. It is still necessary to use glyphosate, which is applied with a controlled droplet applicator to further reduce quantities sprayed. Tony Kirkham confirmed chemical use has been reduced:  “Before, we would be using five applications of glyphosate a year for weed control around young trees. Now, two or less are required.”  These are sprayed around the perimeter of Plantex and suppress annual weed growth, which may germinate on the top mulch.

[This article first appeared in Pesticides News No. 24, June 1994, pages 6-7]