Alternatives to Methyl Bromide; Integrated Pest Management in Danish Flour Mills

1. Introduction

1.1 Background
1.2 Methyl bromide
1.3 Danish flour mills today
1.4 Stored product pests

1.1 Background

Methyl bromide has been identified as an ozone depleting substance under the Montreal Protocol, and pursuant to the protocol is subject to a freeze in production and consumption from 1995.

In 1993 agreement was reached within the European community to a reduction of 25% from 1998.

A complete ban has been decided upon in Denmark from 1.1.1998 .

Th. E. Hallas from The Danish Institute of Technology together with researchers from the Danish Plant Health Authorities have produced a report for the Nordic Council of Ministers regarding the use of methyl bromide in the Nordic countries and alternatives to its use ( 13 ).
Briefly the conclusion is that in all areas, alternatives which are less harmful to the environment are available, albeit there are certain areas, amongst others the milling industry, which will require special initiatives, to help with the implementation of these alternatives.

Usage of Methyl bromide

About 3.9 tons of Methyl bromide has been used annually by the milling industry in Denmark ( Dec. 1993 ) out of a total consumption of about 33 tons.
The consumption by the milling industry has been much greater in Norway, and Finland, and greatest in Sweden at about 13.7 tons per year. The Nordic report concludes that this can be replaced by IPM, combining alternatives and options which are available today.

The results of this project are expected mainly to benefit the other Nordic countries, as the situation in the milling industry and the situation in general, is similar to Denmark.

1.2 Methyl bromide

Methyl bromide has in the past been an effective and important pest control tool in the milling industry.

It has a number of advantages over other fumigants. It is relatively cheap and easy to produce. It presents no fire hazard. It is effective, leaves no harmful residues and probably the greatest advantage is, that it is quick-acting. The main disadvantage is its acute toxicity.

However due to its ozone depleting properties it has been phased out and is forbidden from 1.1.1998, in Denmark.

Alternatives or alternative methods therefore need to be found. In certain situations alternatives already exist, for example phosphine or hydrocyanic acid.
This paper looks at Integrated Pest Control, IPM, which is a collection of methods and techniques to suppress pests, tailored to suit the specific needs of any food processing plant. Alternative full-site treatments are also looked at. These provide backup in cases where IPM processes break down and infestation levels become unacceptable.

1.3 Danish flour mills today

Starting point

The starting point must be the condition and situation of Danish mills today. Many are situated in older premises which have been built, altered and re-furbished over many years, without any special attention to pests or pest related problems.

Previously, fumigation with methyl bromide was carried out once or twice a year, whenever production and temperature allowed, either on a routine basis or when the infestation levels reached unacceptable levels. In the intervening periods, few resources were available for pest control or preventive measures, apart from ordinary cleaning. In many cases design of the mill did not lend itself to thorough cleaning and disinfestation
In more recent years efforts have been made to reduce the amount of methyl bromide used for preventive pest control.

We believe that with the implementation of a tailored IPM system together with the full support of the responsible management, that full site fumigation can be replaced by other methods or spot treatments.

There will always be some risk of pests being introduced to a factory or of undetected harbourages. However, with regular inspections by competent personnel, coupled with the necessary commitment from all members of staff, these risks can be reduced to a minimum, and fumigations or other full-site treatments only used as a last resort in the case of acute sudden infestation.

1.4 Stored products pests

The pests encountered can be divided into two groups:

1. Stored product pests

2. Casual intruders

Stored product pests

1. Stored product pests can be found in and can complete their life cycle within the product and therefore contaminate the product. The most common stored product pests to be found in the Danish mills are (12 ):

Casual intruders

2. Casual intruders are insects to be found in and around buildings, not necessarily related to stored products, such as spiders, some flies, predatory beetles, wood boring insects and so on .

Stored product pests of the first group present the greatest risk. Mills often provide an environment in which they thrive, an abundant food supply, the right temperature and undisturbed harbourage.

It is important to be able to quickly identify any insects found, to assess the risks and, if necessary, to carry out some form of treatment or corrective action. The presence of particular pests is often a good indicator of where an infestation problem may be found. The presence of slow breeding pests (such as Tenebrio molitor) are indicators of a long standing problem of poor hygiene and pest control in a mill.

Knowledge of the habits of the insects increases the chance of locating them, and of choosing the best measures to limit the spread of the infestation. The wrong choice can result in spreading the problem.

There are many good books available on insects and their identification (see 4 and 5). Professional help can also be obtained from The Danish Pest Infestation Laboratory or from a competent pest control company.