How to Manage Pests

Interactive Tools and Models: Dormant Spray Alternatives

The practices included as alternatives to the OP and oil dormant spray are considered to be those which are most viable and do not include all possibilities. Except for alternate year OP and oil dormant spraying (alternative #3), all of these alternatives have been the subject of University of California research and sufficient data exist to substantiate their viability. Viable, for our purposes, refers to practices which, when compared to conventional OP and oil dormant sprays, offer acceptable levels of pest control efficacy, while reducing the risk of aquatic toxicity.

Note that these alternatives can also be variously combined to fit the needs of individual growers and pest situations. As an example, alternative #3 is essentially a combination of alternatives #1 and #2 and intuitively should be viable. Many of the other alternatives are very similar as well, but they are presented separately to emphasize the key element differentiating the particular alternative from the others.

Alternative 1. Conventional dormant OP and oil spray

It has long been recognized that the best time to use an OP insecticide (diazinon, chlorpyrifos, methidathion, phosmet, and others) and oil mixture for treating peach twig borer, San Jose scale, and aphids on almonds and a variety of stone fruits is during the orchard dormancy period. Beneficial arthropods are less affected during the dormant period and certain other pests can also be controlled at that time. There is also better coverage of the bark for control of the overwintering larvae, scale, and eggs and less conflict with other cultural practices. Further, because there is no crop on the tree, no residue will be deposited on the fruit.

Because of the concern for pesticide runoff into waterways following OP and oil dormant sprays, their use should always be associated with Best Management Practices (BMPs). There are a number if possible BMPs, each of which has highly variable costs that depend on the specific orchard situation. The costs of BMPs are not included in the calculator because of this degree of variability.

This alternative includes only the dormant spray, and assumes that other insecticides or miticides may well be applied during the season. These other sprays should not be included in the calculator when considering the costs of the other alternatives.

Alternative 2. No dormant treatment

It may be possible to skip OP and oil dormant sprays in some years with adequate monitoring of peach twig borer and San Jose scale abundance. This is quite possible if the orchard has not had a recent history of peach twig borer or scale problems. Skipping the dormant spray will be less of a risk in almonds than other tree crops. If the crop being grown is plums or prunes, aphids can present a problem and skipping a dormant spray without applying an in-season spray is only advisable if there is no recent history of aphid problems. Additional in- season control measures will likely be needed for fresh-fruit production.

If no dormant spray is applied, monitor for peach twig borer larvae associated with blooms or emerging shoots, as well as twig strikes resulting from feeding by the emerging larvae. If larvae are observed associated with blooms or emerging shoots, Bacillus thuringiensis (Bt) can be applied during bloom as mentioned later. Once strikes are observed, it is probably too late for bloom time Bt sprays to be effective. If several twig strikes are seen on each tree by mid-April, in-season sprays should be applied for peach twig borer control timed to pheromone trap catches and the phenology model for peach twig borer. The degree-day calculator on this Web site and the microcomputer program, DDU, can be used to generate degree-days for use with the phenology model.

More detailed information on timing in-season sprays as well as how to identify twig strikes is provided in the UC Pest Management Guidelines for almond, peach, nectarine, plum, and prune available on this Web site and through county UC Cooperative Extension offices, as well as in the UC publications Integrated Pest Management for Almonds, second edition, and Integrated Pest Management for Stone Fruits.

If an OP and oil dormant spray is not applied, also monitor for San Jose scale in all tree crops, and for the presence of aphids in prunes and plums during the spring. Orchards can be monitored for San Jose scale during the dormant season by inspecting prunings from the treetops, twigs with attached leaves, and loose bark on older trees for the presence of scales. Pheromone traps for male scale, or double-sided sticky tape for crawlers, are used to monitor scale development in the spring, and can be used with a phenology model to time in season sprays. Due to the damage potential of San Jose scale, particularly to stone fruits, annual oil sprays during the dormant or delayed dormant period should be considered to maintain populations at low levels if it is found chronically in an orchard.

Dormant oil sprays without an insecticide can also control the eggs of European red mite and brown mite. In dry winters when trees have not received adequate watering, the higher rates of oil may be phytotoxic. Monitoring and control guidelines are described in the UC Pest Management Guidelines for plum and prune, and in the UC publication Integrated Pest Management for Stone Fruits.

Alternative 3. Alternate-year dormant application

In concept, alternate-year application of conventional dormant pesticides should reduce potential environmental risks by one- half, assuming a mechanism were developed to restrict applications in a given year to half of the orchards on which a dormant spray might be applied. Also,alternate-year applications should maintain populations of insect pests at densities lower than would be anticipated in the absence of any dormant sprays.

In years when conventional pesticides are not applied in the dormant season, monitoring and in-season sprays can be used as described for alternative #2, or one of the other options substituted. When in-season sprays are the alternative chosen, the assumption is made that the same choice of product will be made in both years. As is the case in all of the alternatives, a good monitoring program is necessary to determine both the need for a treatment and the most effective control measure to use.

Alternate-year organophosphate and oil dormant sprays have only been tested in one study on prunes. In that six-year study, alternate-year dormant applications appeared to provide control of San Jose scale and peach twig borer for more than one year, but aphids were not present. No study has been conducted to demonstrate if this concept can reduce levels of overall aquatic contamination sufficiently to fall below established regulatory toxicity standards.

Alternative 4. Bloomtime Bt sprays for peach twig borer

Overwintering peach twig borer larvae can be killed during bloom with well-timed treatments of Bacillus thuringiensis (Bt), a microbial pesticide. This treatment is very selective and therefore not considered harmful to parasites or predators of the pest species, or to the aquatic indicator species. However, because of its selectivity, Bt will not kill other pests like San Jose scale that are normally controlled by the dormant spray.

Thousands of acres of California orchards now use this approach. In many almond and prune orchards, the bloomtime Bt sprays may provide satisfactory peach twig borer control without further in-season treatments, but additional treatments will probably be necessary in peach and nectarine orchards. Guidelines for using Bt at bloom are available in the UC Pest Management Guidelines for almond, peach, nectarine, plum, and prune.

The primary difference between this alternative and alternative #5 is the timing of the application that targets overwintering peach twig borer, and the product being applied.

If this approach is used, dormant prunings should be examined to determine if scale populations require treatment. Peach twig borer shoot strikes should also be monitored in each generation, as well as the presence of larvae as fruit start to ripen. If monitoring indicates that any of the pest species require additional control measures, they can be applied during the season. Oil sprays alone applied during the dormant season will provide control of European red mite, brown mite, and low populations of San Jose scale, but will have minimal impact on overwintering peach twig borer larvae. Additional in-season control measures may well be needed for fresh fruit production.

Alternative 5. Spinosad as a dormant spray

Spinosad (Success) is a newly registered pesticide considered by the EPA to possess reduced risk relative to the OPs. This pesticide has been shown to control peach twig borer as effectively as OPs when used as a dormant spray. However, like Bt it does not control scales or aphids, so these pests must be carefully monitored.

The primary difference between this alternative and alternative #4 is the timing of the application that targets overwintering peach twig borer, and the product being applied. The difference between this alternative and alternative #6 is the relative selectivity of spinosad.

If this approach is used, dormant prunings should be examined to determine if scale populations require treatment. Peach twig borer shoot strikes should also be monitored in each generation, as well as the presence of larvae as fruit start to ripen. If monitoring indicates that any of the pest species require additional control measures, they can be applied during the season. Oil sprays alone applied during the dormant season will provide control of European red mite, brown mite, and low populations of San Jose scale, but will have minimal impact on overwintering peach twig borer larvae. Additional in-season control measures may well be needed for fresh fruit production.

Alternative 6. Conventional non-OP pesticides

Pesticides belonging to chemical classes other than OPs, including pyrethroids (permethrin and esfenvalerate) and carbamates (carbaryl), have been used for control of peach twig borer in the delayed-dormant or dormant season. Specific label restrictions preclude the use of certain of these products on some crops and sites, so it is necessary to examine the label carefully to see if a given product may be applied to a specific crop.

The pyrethroids are not as effective as the OP and oil spray in controlling scales during the dormant season, and another approach should be considered if moderate to high scale populations are present in orchards. Pyrethroid use has been increasing during the 1990s with a corresponding decrease in the amount of OPs applied. Residues of the pyrethroid insecticides permethrin and esfenvalerate persist on bark and may impact naturally occurring predator mites for extended periods of time after dormant season and in-season applications. Mite outbreaks that result from the use of pyrethroids may require additional miticides, over and above those which may normally be applied, for their control.

While the pyrethroids remain effective for control of peach twig borers in most areas, greatly increased tolerance of the peach twig borer to pyrethroids has been identified in the Sacramento Valley, raising the possibility of resistance. In general, insects become resistant to pyrethroids more rapidly than for the other classes of pesticides registered for this use.

Some registered products have not become widely used in the dormant season because of possible effects on nontarget organisms or because of label restrictions. For example, carbaryl cannot be used in orchards where honeybees are present, and endosulfan use is restricted near water or wetlands. As with all pesticides, labels must be checked carefully to determine the legality of a specific use.

All of the conventional non-OP insecticides can affect nontarget organisms in water, but the potential for their offsite movement from runoff has not been well studied. If any conventional pesticides are applied as dormant sprays, they should be applied so as to prevent their movement into surface waters.

Alternative 7. Pheromone mating disruption with Bt bloom sprays

Mating disruption with sex pheromones is a relatively new method for control of peach twig borer. It has been shown to be effective against peach twig borer in almond, peach, and nectarine orchards, but some of the details of application and effective rates of specific products are not completely worked out.

Mating disruption is most effective in orchards with lower endemic moth populations and orchards that are not close to other, untreated, peach twig borer hosts which can be sources of mated females. It is also most effective when used on an areawide basis, that is all growers in an area adopting this practice. Other factors that reduce efficacy of mating disruption include small orchard size, uneven terrain, reduced pheromone application rates and improper treatment timing.

Costs of the material and its application are high relative to pesticide treatments, and this has been a limiting factor to more widespread use. The cost of this approach can be reduced in peaches and nectarines when it is applied coincident with mating disruption for the oriental fruit moth.

Pheromone mating disruption must not be considered a stand-alone system. It is selective for the target pest, so monitoring for other orchard pests as well as peach twig borer is necessary. Pheromone mating disruption is most effective when peach twig borer densities are low to moderate, so it might be necessary to apply an additional control measure prior to its use. Because it is considered nontoxic, using pheromone mating disruption in combination with Bt bloom sprays can provide excellent control. The difference between this alternative and alternative #8 is the timing of the application that targets overwintering peach twig borer, and the product being applied.

If this approach is used, dormant prunings should be examined to determine if scale populations require treatment. Peach twig borer shoot strikes should also be monitored in each generation, as well as the presence of larvae as fruit start to ripen. If monitoring indicates that any of the pest species require additional control measures, they can be applied during the season. Oil sprays alone applied during the dormant season will provide control of European red mite, brown mite, and low populations of San Jose scale, but will have minimal impact on overwintering peach twig borer larvae.

Alternative 8. Pheromone mating disruption with other alternatives

Mating disruption with sex pheromones is a relatively new method for control of peach twig borer. It has been shown to be effective against peach twig borer in almond, peach, and nectarine orchards, but some of the details of application and effective rates of specific products are not completely worked out.

Mating disruption is most effective in orchards with lower endemic moth populations and orchards that are not close to other, untreated, peach twig borer hosts which can be sources of mated females. It is also most effective when used on an areawide basis, that is all growers in an area adopting this practice. Other factors that reduce efficacy of mating disruption include small orchard size, uneven terrain, reduced pheromone application rates and improper treatment timing.

Costs of the material and its application are high relative to pesticide treatments, and this has been a limiting factor to more widespread use. The cost of this approach can be reduced in peaches and nectarines when it is applied coincident with mating disruption for the oriental fruit moth.

Pheromone mating disruption must not be considered a stand-alone system. It is selective for the target pest, so monitoring for other orchard pests as well as peach twig borer is necessary. Pheromone mating disruption is most effective when peach twig borer densities are low to moderate, so it might be necessary to apply an additional control measure prior to its use if monitoring indicates that populations are moderate to high. Spinosad and oil or a conventional non-OP insecticide applied with oil during the dormant season can be used to reduce overwintering peach twig borer populations. The difference between this alternative and alternative #7 is the timing of the application that targets overwintering peach twig borer, and the product being applied.

If this approach is used, dormant prunings should be examined to determine if scale populations require treatment. Peach twig borer shoot strikes should also be monitored in each generation, as well as the presence of larvae as fruit start to ripen. If monitoring indicates that any of the pest species require additional control measures, they can be applied during the season. Oil sprays alone applied during the dormant season will provide control of European red mite, brown mite and low populations of San Jose scale, but will have minimal impact on overwintering peach twig borer larvae.