As an Extension Educator with the UF/IFAS Extension, clients told me many times that the applied pesticides do not work against the targeted pest anymore. In most cases the pesticide applicators blame pesticide failures on the manufacturer. I agree that pesticides can fail but, in most cases, failures occur because of applicators error or lack of best management practices. Pesticides often fail due to the build-up of pesticide resistance. Pesticides resistance occur when the same pesticide or group of pesticides use repeatedly on the same pest, without rotating mode of action.
Mode of action describes how the target site of the pesticides; example, some insecticides target the cell wall while another may affect the nervous system. Rotating pesticide that will disrupt one bodily function to another will be more effective than using the same pesticide each time. To reduce pesticide resistance, it is a good practice to mix pesticide that are not in the same group. Every pesticide label has a group/class on it, before mixing chemical, read label to ensure both labels do have the same number. You can always mix chemicals unless the label state otherwise. Restrict the number of applications and/or total amount per season and apply only when necessary. Always maintain manufacturers recommended application rate; reducing the rate below label recommendations can result in reduced pest control and encourage development of pest resistance.
It is important to note that, loss of effectiveness of a pesticide is not necessarily proof of resistance, low performance can cause from: breakdown of the pesticide by soil micro-organisms, high pH of spray water, poor pesticide application procedures. Also, pest not properly identified can be a challenge, weather favors disease in the case of too much rain. Other factors that affect poor pesticide effectiveness include timeliness of application, planted less resistant variety, Inadequate pest control program, and too-few applications. Choosing the right pesticide is also important and it is also necessary to gain basic knowledge of the target pest. Finally, avoid applying pesticides outdoor if rain is in forecast within the next 12 hours.
For more information on pesticides and other horticulture topics, contact Grantly Ricketts with the UF/IFAS extension in St. Lucie County at firstname.lastname@example.org or at 772-462-2847.