- Dormant season oil sprays
- Dormant season copper sprays
- Dormant season urea sprays
Dormant Oil Sprays: The first pest control applications in tree fruit usually consist of oil and copper sprays. These are long standing standard recommendations that are not without special considerations. Oil is generally recommended at rates of 2%, or 2 gals. per 100 gallons of water for dormant applications. Traditionally this has translated to 4 gallons of oil per acre for stone fruit based on a dilute volume of 200 gallons per acre: the amount generally considered to cover a mature peach tree to the point of drip. For pome fruit the recommendation has been 6 gallons of oil per acre based on a dilute volume of 300 gallons per acre: the amount generally considered to cover a mature semi dwarf apple to the point of drip. The use limitations and application rates vary by product and growth stage so be sure to read and adhere to the product label.
Oil acts by suffocating overwintering scale insects and mite eggs as they begin to respire in the spring. Since fruit tree architecture includes many cracks and crevices as well limbs and twigs that exponentially increase surface area, coverage to the point of drip is key. Coverage has always been challenging and is increasingly so in recent years as weather extremes have increasingly been the norm. Since a single female san jose scale can produce up to 400 crawlers per generation it’s important to try to get as close to 100% coverage of the scaffold and trunk surface area as possible. It’s worth mentioning that opening up canopies with proper pruning can go a long way toward accomplishing that goal.
Dormant oil can be safely applied up to the pink stages of peach, apple and pear. Delayed dormant applications applied for mite suppression should provide good control of scale and suppress early season aphids. Multiple applications are often recommended in apple and may be beneficial where both scale and mites are a concern in peaches. Since conditions are seldom optimal for good coverage in the spring, multiple applications also help to get closer to the goal of 100% coverage. Where multiple applications are made the rate is generally dropped the closer an application is made to bloom. So a split application in apples for example might consist of a 2% application up to ½” green, and a 1% application up to tight cluster. An application of 0.5% at pink is an option that may provide additional insurance. Growers that have been having difficulty controlling scab may consider control programs that shift to materials like captan in pre-bloom or bloom sprays. This type of program would not be compatible with split oil applications since captan applied within 10-14 days of an oil application can injure fruit trees. Refer to the product label for crop specific safety precautions.
One sees many recommendations for mixing materials efficacious for scale such as Lorsban (chlopyrifos) or insect growth regulators (Centaur; Esteem) with delayed dormant oil applications. The general consensus seems to be that the addition of scale insecticides to oil do not significantly improve control over oil applied alone. The key takeaway is no matter what products are applied for scale and mite control, coverage to the point of drip is the most important consideration. Chorpyrifos formulations may also increase the risk of oil phytoxicity from cold temperatures. Combinations are useful however for other pre-bloom pest control decisions. Chlorpyrifos and Esteem also control rosy apple aphid, however in recent years we’ve observed poor control from Chlorpyrifos applied with oil at green tip due either to resistance or more likely, poor timing. Read the chlorpyrifos product label for use restrictions. Esteem applied at 1/4″ to 1/2″ green either alone or with oil will control rosy apple aphids. Sivanto Prime and Closer are recent additions to the insecticide toolbox that have excellent ratings for Rosy Aphids and efficacy against scale. Based on the ratings in our production guide, Sivanto is the better scale material. Recent tests performed by Dr. Neilsen’s lab indicate that both Sivanto Prime and Centaur when applied alone pre-bloom are comparable to dormant oil for scale control. Closer has not been evaluated for control of overwintering scale so it should be saved for summer use.
On pears dormant petroleum oil applications are a standard practice for early season pear psylla control. Unlike applications made for scale control and mite suppression, oil acts less as an insecticide and more as a method of exclusion since pear psylla adults tend not to lay eggs on oily surfaces. Therefore oil needs to be applied as early as weather and soil conditions permit. Usually the first applications are made in southern counties from mid to late March when ovposition begins.
These applications are useful throughout early bud stages and are generally long lasting; about 2 -3 weeks. In the dormant or delayed dormant stages apply a 2 % solution of oil (2 gals/100 or 6 gals/acre), or two applications of 1% through the green bud stage (when buds are swollen and green tissue is present). Adjust rates downward for later stages: 1% (1 gal/100) from swollen bud through green bud, or 2 applications of 0.5% (0.5 gals/100) from green bud through white bud (flower parts are visible). During the delayed dormant stages the addition of a pyrethroid or a insect growth regulator such as Centaur or Esteem may improve control. Centaur has been observed to provide excellent control of summer generations of psylla nymphs when applied to early instars. Sivanto Prime combined with oil in the delayed dormant timing is an also an option. Surround, a clay product, may also be applied with oil at a rate of 25-50#/ acre in the delayed dormant stages. Surround applications without oil can be applied through bloom to disrupt the entire oviposition period and has shown to provide good control of the first generation nymphs. Surround alone is also useful when temperatures are too cold to safely apply dormant oil.
Dormant season copper Sprays: Coppers are early season fungicides recommended for early season scab control and fire blight suppression in apples and pears. Coppers, Ziram, and Bravo (Chlorothalonil) are also used for peach leaf curl control, and should be applied before or at bud swell. Many different copper formulations are available and it’s often difficult to decide which one is best, and is also labeled for the crop and season of application. See the links here, and here for detailed discussions about the different forms of copper and their use for disease control.
Care must be taken when applying copper to prevent unintended consequences. Copper phytoxicity takes the form of leaf damage on stone fruit and leaf and fruit injury on pome fruit. We recommend season-long copper applications at very low rates in peach for bacterial spot suppression. But significant phytoxicity can occur from tank mixes, especially when applied after a long period of overcast weather, and/or the spray water ph is less than 6. Therefore it’s recommended to have some ph strips and buffer on hand to test the finished spray mixture and adjust the ph to lessen acidity if necessary. On apples and pears, coppers should not be applied much past green tip unless fruit finish is not a concern. Copper ions present after half inch green can cause russet, especially on sensitive varieties. The risk of fruit injury is increased in years with little rainfall between bud break and pink, because more copper will be present when the fruit is fully exposed.
Dormant season urea sprays: One final early spring chore is to get a jump on apple scab in orchards that have high inoculum from the previous season. Here orchard sanitation using urea and/or by shredding leaves is of benefit. Last season’s leaves carry the overwintering inoculum of the fungus. Urea works in two ways to reduce this season’s inoculum: it helps organisms in the ground cover decompose the leaves quickly; it also suppresses the development of 
spores so that they are not released. Chopping the leaf litter with a flail mower will accomplish the same end, and if combined with a fall or early spring urea application will greatly reduce overwintering inoculum. This is useful for getting the upper hand on primary scab control and for resistance management.
Urea is applied at rate of 40# per acre in 100 gallons of water per acre. This can be applied with an airblast sprayer with the nozzles directed at the ground cover. It is best done after leaf drop in fall but can still be applied in the spring before bud break or as late as green tip. Applications made after bud break should be done with a boom sprayer since urea drifting onto green tissue may make it more susceptible to phytotoxicity from copper or oil sprays.
