With the recent re-registration of soil fumigants, it is easy to forget the basics of soil fumigation and why it may be needed for pest control. Soil fumigation is a type of chemical control strategy used to reduce the incidence of soil-borne pests. It can be used alone or in conjunction with other methods such as cultural, mechanical, or physical as part of an Integrated Pest Management (IPM) program. There are several types of soil fumigants. Some are considered broad spectrum and kill most everything they come in contact with, while others are more pest specific. Some common pests controlled by fumigants include nematodes, fungi, bacteria, weeds, and weed seeds. Fumigants are most often used in the production of higher value crops due to cost. They have the potential to increase yield and plant quality. This ultimately translates to higher profitability for the producer.
Soil fumigants begin as liquids or solids and when released into the soil become gases. They can be applied as liquefied gases, volatile liquids or granules. However, most growers are familiar with liquid fumigants. When fumigants are applied to the soil, they volatilize into a gaseous state and spread through the air pores in the soil. Depending on a particular fumigant’s chemical properties it may volatilize quickly or more slowly than others. Due to volatility, fumigants must be incorporated or sealed into the soil during or immediately following application. In order to kill soil-borne pests, fumigants must come in contact with the pest and must reach a lethal concentration. The lethal concentration is expressed as Fumigant Dose: Σt=1 (Concentration x Time). As with any pesticide, the lethal dose is not just the concentration of the pesticide, but the amount of time in which pests are exposed. Obtaining this lethal dose is needed to kill problem pests and is the objective of all fumigant programs.
Soil fumigation was first discovered in the 1940s when it was noticed that plant production and quality increased when the soil was treated. In the early 1950s we saw the development of the first fumigants produced for use in commercial agriculture including (DD) 1,3-dichloropropene, (EDB) ethylene dibromide and Vorlex. Since this time safer, more effective fumigants continue to be developed.
Fumigant application equipment has also improved dramatically over the years. The first fumigants were contained in 55 gallon drums and were applied via gravity flow lines to the soil through tractor pulled chisels or shanks. Now, most fumigants are contained in pressurized cylinders and can be applied through various methods on flat ground or raised beds using chisels or shanks or through drip irrigation. Fumigants can now be sealed using plastic mulch technology or rolling devices.
Types Of Pests Controlled And Fumigant Uses