Cooperative Extension San Joaquin County
University of California
Cooperative Extension San Joaquin County

Posts Tagged: pest

Treating landscape pests with oils is safe for people and pets

Horticultural oils can be used to control aphids on roses.
Oils are some of the most useful pesticides available for managing pests on woody ornamentals and fruit trees. They are also widely used on many herbaceous flowers and vegetables. Oils control a range of soft-bodied insects and mites, as well as several foliar diseases including powdery mildew (Table 1). Not only do oils leave no toxic residues, they are safe to use around people, pets, and wildlife; have low impact on beneficial insects; and won't harm honey bees unless applied directly to flowers during the time of day that bees are foraging.

Oils used for managing pests on plants are most often called horticultural oils. Horticultural oils are derived from petroleum sources, and are sometimes called mineral oil, narrow range oil or superior oil. Other oils produced to control pests may be made from plants, such as canola oil, neem oil or cottonseed oil. A number of other plant extract oils have also recently become available on the market. 

How they work

Regardless of their source, the primary way oils kill insects and mites is the same — by suffocation. Insects breathe through structures called spiracles. Oils block spiracles, reducing the availability of oxygen and interfering with various metabolic processes. When applied to insect or mite eggs, oils can penetrate the shells and kill the developing embryo. Oils may also act as a repellent in some cases, especially with some of the plant-based oils, and some such as neem oil have anti-feeding properties. 

Because oils kill by smothering insects, apply the product so it completely covers the target pests. Careful attention must be paid to treat both the underside and topside of leaves, buds, and shoots and all locations where the insects or mites may be located. Spraying during the dormant season, when leaves are off trees or shrubs, is recommended for scales and some other insects, because it is easier to get good coverage on leafless trees. Because oils leave no toxic residues, they won't generally kill insects that move onto plants after treatment.

Usually, immature stages of insects are most susceptible, especially with scale insects, mealybugs and true bugs. Insects that feed within curled leaves, such as leaf-curling aphids, leaf miners, or gall-forming species, are protected from oil sprays and not well controlled. Oils don't control caterpillars, beetles, grasshoppers, and boring insects, with the exception of some caterpillars in the egg stage.

In some cases, oils improve the efficacy of other insecticides. For instance, applications of both codling moth granulosis virus (Cyd-X) and spinosad are more effective against codling moth when 1% oil is added to the spray.

For managing certain foliar diseases such as powdery mildew, oils can act as both a preventive and a curative fungicide, smothering fungal growth and inhibiting spore production. In many cases, the efficacy of oils in reducing powdery mildew is superior to standard synthetic fungicides, especially in reducing existing infections.

Tips to know

All oils now sold as pesticides are highly refined and can be used safely on most plants throughout most of the year, unless plants are drought-stressed. Exceptions include Japanese and red maples, walnuts and smoke tree. Redbud, juniper, cedar, spruce and Douglas-fir are also sometimes injured. Injury usually involves discoloration of leaves or needles. Walnut is very sensitive to oil sprays applied during bud break, and applications aren't recommended during the dormant season because of potential damage to buds and shoots. 

Many plants are sensitive to oil damage when water-stressed, so be sure plants have been adequately irrigated before application. Most oil labels also warn against applying oils when temperatures are below freezing or above 90°F. Oils shouldn't be applied in combination with sulfur, or within 30 days of a sulfur application, because of potential phytotoxicity. As with any pesticide, always check product labels for precautions or other restrictions before applying.

Table 1. Plant Pests Oil Sprays Control.

Dormant-season applications

  • aphid eggs
  • caterpillar eggs on bark (leafrollers, tent caterpillars, and tussock moth)
  • overwintering mites or mite eggs
  • scale insects (nymphs)

Spring and summer—foliar applications

  • adelgids
  • aphids
  • black spot on rose
  • eriophyid mites
  • lacebugs
  • leafhoppers
  • mealybugs
  • powdery mildew
  • psyllids
  • sawflies feeding on foliage
  • scale Insects (nymphs)
  • spider mites
  • thrips
  • whiteflies

This article is from the May 2013 issue of the UC IPM Green Bulletin. This issue of the bulletin also contains these articles:

  • What Can Landscape Managers Do to Help Honey Bees?
  • Pesticide MSDS Format Changes
  • New Active Ingredient Available for Snails, Slugs
  • Visit UC IPM's Web Site for Free Online Training
  • Revised Resources
  • Ask the Expert: bee sting hazards, insecticidal soaps
Posted on Tuesday, June 4, 2013 at 8:50 AM
Tags: aphids (3), IPM (19), pest (4)

Jumping oak galls on valley oaks

This time of year, it is not uncommon to see the valley oak trees (Quercus lobata) with their leaves yellowed and splotchy with numerous small seed like balls on the underside.  These are called Jumping oak galls and they are made by a small Cynipid wasp larva (Neuropterus saltatorius) that is developing inside the gall.  Don’t worry-the wasp doesn’t sting humans.  In fact, you would be lucky to actually see the critter.  While the galls do cause some defoliation, they are not particularly harmful to the trees.  They may cause some serious leaf loss in some years and this year seems to be one of those years.  The adult female wasp, in order to be able to create a gall that contain an egg, must sting the leaf at precisely the right time.  If the leaves are too fully expanded and hardened off, the galls will not form.  That is why you might see one tree with millions of these galls and yet the one nearby might not have any.  Their foliation times may be somewhat different.  There are many types of oak galls including yhose that look like chocolate kisses and some that look like apples, and still others that look like horned or fuzzy balls.  We do not normally recommend any type of control of these insects.  However, some research indicates that if one leaves the infested leaves on the ground, the parasites of these little wasps are not raked away and it may moderate the population over time.  As well, there is more “mulch” on the ground around the trees, which is a good thing.   

One of the fun things to do with the galls as they are beginning to fall off the tree is to just bring them into the house.  As the galls warm, they begin to jump and wiggle around and make a snap crackle and pop noise….

To Learn More….

Posted on Monday, August 3, 2009 at 11:41 AM
Tags: Oaks (4), Pest (4), Quercus (1), Trees (2)
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