this means "to rid of infesting insects, vermin, etc." according to the New Shorter Oxford dictionary

It is alleged, in the case of one introduction, that inspections undertaken on entry to Australia did not include searches for this pest 'because it was not known to be in the country of origin'. In another case it is alleged that the consignee, when told that a consignment had to be disinfested with methyl bromide, persuaded the inspector to use another treatment less injurious to the plant 'because methyl bromide damages the plants'. It appears that there has been a failure to communicate to the inspectorate the precise location details of some rapidly dispersing insect pests that are known to pose a quarantine risk to Australia; and a lack of rigour in the application of prescribed quarantine disinfestation treatments.
http://www.science.org.au/academy/media/aqis3.htm

In the United States, irradiation has been approved for use on foods since 1963 for the control of insects in wheat and wheat flour and since 1964 for the prevention of sprouting in potatoes. In February 1984, the FDA issued a proposal to permit the use of irradiation to inhibit the growth and maturation of fresh fruits and fresh vegetables, to disinfest food of insects, and to disinfect spices of microorganisms. The FDA reported that foods radiated up to 1kGy are wholesome and safe for human consumption, even in cases where the irradiated foods represent a large portion of the diet. In turn, low dose radiation was approved for fruits and vegetables to control maturation. (It is important to note that the 1kGy that the FDA allows is significantly less than the level of 10kGy deemed safe by international experts.)
http://www.aboutproduce.com/faq/irradiation.html