Pesticide application practices that save money

Pesticide application strategies significantly affect the amount of pesticides used and the associated costs.

March 1, 2010

Greenhouse managers need to implement practices that reduce production costs without significantly affecting crop quality. This includes practices that reduce pesticide use and associated costs. Recently registered pesticides typically cost more than older products, and the labor for applying pesticides is relatively expensive. Careful and conservative use of pesticides not only lowers production costs, but also prevents potential liability issues, litigation and fines related to pesticide runoff and drift and worker health and safety.
Many preventive practices and nonchemical control measures that are frontline measures for reducing pesticide use can be incorporated into an integrated pest management program. Nevertheless, there are times when pesticides are necessary due to the low damage-threshold levels for ornamental crops.
The manner in which pesticides are applied significantly affects the total amount of pesticides used in a given year. It is therefore important that application strategies, such as selecting effective pesticides and avoiding pesticide resistance, are incorporated into an IPM program to further minimize pesticide use.

Select effective pesticides
Don’t waste money using pesticides that are ineffective in controlling target pests. Consult a cooperative extension agent or pest control adviser for the most recent pest management recommendations. There are also a number of publications and web-based resources that can guide the selection process. For example, for California recommendations, growers can consult the “University of California IPM (UC IPM) Pest Management Guidelines for Floriculture and Ornamental Nurseries” (
Pesticide efficacy can be site-specific, so be sure to check pest monitoring records before and after pesticide applications to evaluate the efficacy of selected materials for the target pests.

Avoid pesticide resistance
Pesticide resistance can occur with the repetitive use of the same chemical to control a particular pest. After a period of time, the chemical no longer effectively controls the pest at the same rate. Higher rates and more frequent applications become necessary until eventually the chemical provides little or no control. Pesticide application strategies that minimize resistance include properly timing pesticide applications, avoiding persistent chemicals, avoiding tank mixes and using appropriate rotation strategies for classes of pesticides, such as pyrethroids, organophosphates and carbamates.
Timing pesticide applications based on monitoring data rather than by the calendar can significantly reduce the frequency of applications. Keep records of insect pests and weeds and do not apply chemicals unless pests are present at threshold levels. Presence of disease pathogens should also be considered. Moreover, environmental monitoring can be used to forecast diseases and to time treatments. When applying pesticides, always start with the lowest recommended rate and use the lowest effective application frequency to reduce pesticide resistance.

Persistent chemicals
Avoid the use of persistent chemicals. An ideal pesticide quickly dissipates so that residuals do not promote the development of resistant insect populations. If a persistent pesticide such as imidicloprid must be used, determine where it can be used in a rotation scheme to provide the control needed with a minimum length of exposure.

Tank mixes
Never combine two pesticides with the same mode of action in a tank mix because this practice can favor the establishment of resistant pest individuals. Most traditional insecticides (organophosphates and carbamates) use a similar mode of action (interfering with the nervous system of the target insect). Long-term use of two-class pesticide mixes should also be avoided, even in situations where the tank mix provides superior pest control, because this may result in a pest population that is resistant to both pesticides.
Occasionally, simultaneous application of two different types of chemicals may be necessary. However, even in this case tank mixes should be avoided and formulations that require different types of application are recommended.
For example, when an insect growth regulator (IGR) and an adulticide are necessary to control whiteflies because all life stages are present, the insect growth regulator could be applied as a spray, and the adulticide, as an aerosol or smoke. This treatment will kill the adults with little residual that might select for resistance buildup in surviving immatures.

Rotate pesticides
A key resistance-management practice is rotating classes of pesticides. However, the rotation strategies for insects differ from the rotation strategies for fungal pathogens. With fungicides, it is suggested that classes be rotated every application. With insecticides, a single chemical class should be used for a single generation of the target pest followed by a rotation to a new class of insecticide that will affect the next generation and any survivors from the first generation.
Longer use of a single chemical class enhances the chance of resistance because the survivors of the first generation and the next will most likely be tolerant to that class. Conversely, if insecticide classes are switched with every application, the same individual insects could be exposed to multiple classes of pesticides, which could encourage the development of multiple-pesticide-resistant pests.
As previously mentioned, pesticides that are effective against the target pest are the materials that should be selected for use. Sometimes, however, only one chemical is effective against a pest and other available products are only marginally effective. In this case, a good strategy to follow is to use the marginally effective materials when pest pressure is less severe and reserve the more effective material for more critical situations.

Spot, direct spraying
Monitoring identifies “spots” in the greenhouse and on plant parts where pests reside that can be flagged. Focusing pesticide applications on these spots rather than spraying an entire crop can substantially reduce pesticide use. Although spot spraying can be more labor intensive, it still results in significant savings for growers due to reduced material costs. In University of California demonstrations, monitoring combined with spot spraying reduced pesticide use by as much as 50 percent.
Directing the spraying toward the part of the plant where the pest resides, also reduces overall pesticide use. For example, if western flower thrips are the target pest, direct the pesticide spray toward the top third of the crop, in the flowers and buds, where the pest is typically found. Conversely, if spider mites are the target pest, direct the spray towards the lower two-thirds of the crop.

Ensure uniform coverage

If a pesticide that is touted to be effective is not working, do not assume there is a pesticide resistance problem. It could be that the pesticide is not actually contacting the targeted pest. Make sure the appropriate nozzle size and spray pressure are being used and that application equipment is properly calibrated. Spray pattern thoroughness can be assessed by placing water-sensitive paper in upper-, mid- and lower-plant canopy locations.
An adjuvant may need to be added to provide more uniform coverage. Most pesticide adjuvants enhance pesticide efficacy by causing the pesticide to spread or stick or penetrate the plant material.
Before using an adjuvant, read the pesticide label to determine if an adjuvant is needed. An adjuvant may have been added by the manufacturer to the pesticide. Furthermore, some manufacturers produce adjuvants that are most compatible with their own products. If an adjuvant is needed, specific information regarding proper usage can be found on the product label.
Julie Newman is environmental horticultural farm adviser, University of California Cooperative Extension, (805) 645-1459;