If you’ve followed Rainbow Gardens on our social media channels, or these blogs for any amount of time, you’ve probably noticed us telling you to avoid “wipe out” sprays for pest and disease control, and how we even try to encourage you not to spray for problems before they have presented themselves. We often share organic gardening habits that can help you avoid the problems in the first place. Today we are sharing that sometimes there is a place for sprays, and that time is now. Preventative spraying with horticultural and dormant oils can be extremely beneficial at this time of year to prevent a long and tedious battle against some serious pests, like scale, that tend to plague certain types of plants. Preventative spraying is a powerful tool when used correctly and it can actually help limit the amount of spraying you would end up having to do if you don’t implement it now. Let’s take a closer look at horticultural and dormant oil and their benefits.

Horticultural and Dormant Oils for Scale Prevention:

What are horticultural and dormant oils and why do you use them?  Horticultural or dormant oils (the terms are used interchangeably)  are pest and disease control products that, at this time of year are used to kill off the eggs of pests, like scale, which overwinter on susceptible plants. These pests would otherwise be difficult to control or eradicate if not for prevention. Dormant oil acts as a physical pest control and coats the eggs and pests, attacking the respiratory system and basically smothering them. Sorry for the graphic imagery, but who likes scale anyways?

Scale that needs to be treated with horticultural and dormant oils,

What do you use it on? Deciduous trees, fruit and nut trees that are currently dormant and not in bloom, evergreens that are susceptible like: euonymus, photinia, bay laurels, hollies, boxwoods.

When and how do you apply horticultural and dormant oil? The best time to apply horticultural and dormant oil in San Antonio is during the winter, when your deciduous and fruit trees are dormant and not in bloom. On deciduous trees, treating at this time of the year allows for the most concentrated application of the oil as it will not cause damage to foliage (because there is none) and also allows for the least harm to beneficial pollinators (since they arrive when there are blooms). When the foliage is off the trees, the spray is able to go directly to the limbs where the scale resides. Don’t delay your spray because the warmth of spring arrives quickly and brings with it new foliage growth and flowers. 

Susceptible evergreens (like those listed above) can be treated as well, just follow the label for concentration formulas. Early morning applications are generally advised when the sun isn’t at its most direct. This is to prevent any burning or damage of foliage. You will also need to make sure you are getting through the evergreen foliage and into the nooks and crannies of the limbs. 


Dormant Oil spray on shelves at nursery.

Important notes when it comes to applying these oils. Some horticultural oils labels state that they can be applied year round, and that may be so, but you still have to be mindful of the temperatures (no higher than 70° and no lower than 40°) and the pollinators. Try not to apply when a freeze is predicted within 3-4 days of spraying. Usually you only have to apply this dormant oil once as an effective method to essentially smother the pests, and successfully stop them from being a nuisance throughout the rest of the year. This of course will depend on how correctly the product has been applied. 

Always read labels thoroughly! This link provides the label for Bonide All Seasons Horticultural and Dormant Oil. The link is just for an example to show you how much information is provided on the backs of your products. Labels MUST be followed in order to use the product correctly and safely. We carry other horticultural and dormant oils in the nurseries as well.

Last note is to take precaution with any annuals that may be planted near the trees or shrubs you are planning to spray. Cover them with some type of drop cloth so that they do not receive any overspray. That’s it. If you want to save yourself from fighting the sap-sucking damage (sometimes irreversible) that scale insects can inflict, you might want to think about doing some preventative spraying soon. Hope this helps!

~The Happy Gardener, Lisa Mulroy