By Hal Reynolds, Vice President  Desert Rose Society & ARS Consulting Rosarian


Are you being bugged by insects and diseases? 

Fortunately, those of us lucky enough to live in our little corner of this desert paradise are victimized by fewer insects and diseases than people in most other parts of the country. Yes, we do have bugs, and yes, we do have diseases attacking our roses, but far fewer than in other places. We seldom, if ever, see blackspot, downy mildew, crown gall or rust. 

Although we can have powdery mildew, it is not as severe as it is in other places and it is mostly seen in spring before the desert heats up.  We do have aphids, spider mites, leaf cutter bees, thrips and our very own hoplia beetle, but on the other hand we do not have Japanese Beetle, and we seldom, if ever, see rose slug, San Jose scale, midge, cucumber beetle, sawfly, katydid and many other rose pests.

In this article we are covering the most commonly found pests in our area. Overall pest control on roses in our climate is less of a job that in other areas. Two non-insect or disease baddies in parts of our growing area are rabbits and gophers. Most places located in towns are not as bothered by gophers but rabbits can be anywhere. The tiny desert rabbits can be are found anywhere and the big Jack Rabbit is found in the high desert and outlying areas. More versatile in their diet than Bugs Bunny, they do not eat just carrots. If you are wondering “What’s up Doc?” with my munched roses, it could be those “pesky wabbits.” The more pleasant cures for “wabbits” are traps, with relocation and protective fencing. Or you could do as I did one year — just watch them drown in the pool and not offer CPR.


APHIDS: We do have the dreaded aphids (plant lice) and no matter how fastidious and tidy you are you will have these “lice”. They are a fact of life for rose growers. Aphids are small, usually green or black insects that may have wings and are, about 1/8″ long. They suck the plant juices from tender parts of the plant. They excrete honeydew, a sticky substance that attracts ants. They are prolific breeders and multiply rapidly in warm weather.

The question is how can you get rid of them? With a mild infestation you can hand pick them off.  I do this by mashing them between my fingers. There is a YUK!  factor here but not a problem if you wash your hands; it does readily wash off. There is a certain satisfaction in feeling their evil little bodies explode under the powerful force of your mighty digits. Just remember to wash your hands before lunch. If you are too squeamish, or if your infestation is more severe, you might like to try the next earth-friendly way of aphid eradication.

Use your garden hose with a fairly strong stream to wash the little vermin off the plant and onto the ground. Make sure that the water stream is not so strong that it damages the tender growth. Once on the ground they seldom get back on the plants. Aphids have a fast reproduction cycle so you will have to repeat this process every couple of days until the infestation becomes bearable. Aphids hang out under the leaves too so you must be sure you are giving the underside of the leaves a good spraying as well as the tops.

If you have done all the water spraying you can stand and still have an unbearable amount of aphids you may resort to chemical sprays. Start with organic type sprays, such as insecticidal soap, as there is no sense harming the environment if you don’t have to. There are chemical sprays that work, but use them only as a last resort. Check with your local independent nursery for which product is the least harmful to you and the environment. If you are using these chemical sprays, be sure you wear protective clothing, gloves and a proper mask. When you use these chemical solutions you will probably also destroy other insects that kill aphids such as lady bugs, lace wings and aphid wasps.  Some gardeners actually purchase these beneficial insects and release them in their gardens. I find, however, that the effect is short-lived because they soon move on to greener pastures in your neighbor’s buggier garden.


LEAF CUTTER BEES: These honeybee-sized bees are seldom seen but they make perfectly cut semi-circles on the leaf and petal edges. They cut sections out of the rose leaf and petal and use it to line their nests. Now comes the part you really do not want to hear. They are valuable pollinators and need to be protected. Please do not spray for these bees. If you spray for them you will be killing off other beneficial insects and bees. The world is headed for a crisis in the bee populations. We can not afford to lose any more bees.  The world could become a pretty hungry place if we lose all of our bees. Cutter bees are only active for part of the year and, unfortunately, we really should just tolerate them.


SPIDER MITES: The two-spotted spider mite is the most common species found on roses. They are especially prevalent during hot, dry weather and difficult to control if they get established. They feed by sucking sap, primarily from the under side of the leaves and can eventually defoliate your plant. It is important to detect them early.  Early symptoms will be a lightening and speckling of the lower leaves. If you shake the infected foliage over a piece of white paper the spider mites may be seen as small dots. They are so small they are difficult to see on the plant with the naked eye. You will also notice fine webbing and eggs on the underside of the leaves. Old Garden Rose growers be warned: spider mites love the texture of the foliage of Rugosa roses.  A light infestation can be controlled with a forceful spray of water to the underside of the leaves. This can knock them off and spider mites do not like wet places. You will need to repeat this spraying every couple of days for effective control. Insecticidal soaps and oils can be used for the control of spider mites but be sure you spray the lower surfaces and the under side of the leaves. If you find you have to resort to a miticide, check with your local independent nursery for a recommendation for the least harmful yet effective product. Remember to wear protective clothing and masks when spraying chemicals.


HOPLIA BEETLE: This little black beetle about ¼” in size is believed to be a relative of the Japanese  beetle. It spends part of its earlier stages of life in the soil. As of this time there is no approved chemical for the control of this critter. He will appear in the spring when roses start to bloom and is only present for about six weeks. Nasty little creeps like to attack the blossoms of white and very light colored roses and leave them in tatters.  A simple prevention method would be to plant only red and dark colored roses but most of us will not give up our favorite light and pastel beauties for this bug. The approved way to get rid of him is to pick him off, drop him on a flat surface and stomp him to death. The stomping is good exercise and there is that satisfaction that comes with revenge. Otherwise, you could just pick him off and drop him in a container and let him slowly suffocate, and then throw the container in the trash.


CANEBORERS: Caneborers are wasps or bees that nest in the ends of rose canes in the pith of the cane. They can be active from spring through fall. They can be easily spotted by the holes they leave in the ends of cut canes. The borers we find here in the desert do not bore very far into the cane and do not do major damage, but in other parts of the country other borers can do a lethal job on other plants and roses.   You can paint the end of cut canes with waterproof glue to prevent the borers from entering. I do not find this necessary. If I do anything I simply cut the cane below the borer hole and discard it. You will find that they do not go very far down into the cane.


FLOWER THRIPS: Thrips are very active, just barely visible to the naked eye winged insects. They hide in the buds and blooms of roses and damage the petals with their rasping mouthparts. They also seem to prefer lighter colored blooms and do their damage when the blossom is still a bud. This makes it difficult to treat as they hide in the unopened blooms. Orthene has been a good control and the spray will not damage the blooms. Remember to wear protective gear when spraying chemicals.


POWDERY MILDEW: This fungus is one of the most prevalent and serious rose diseases. One of the best preventatives for powdery mildew is to plant powdery mildew resistant varieties of roses. As conditions warm in the spring the dormant fungus becomes active and produces spores which can be blown by the wind to susceptible young growth.  Symptoms are slightly raised blister like areas on the upper leaf surface. Later, all young growth can become distorted and covered with a white powdery substance.

71 degrees and 90% humidity are perfect conditions for spore germination. Temperatures above 90 and free standing water will inhibit germination.  The fungus invades the surface of the plant and feeds on the plant nutrients and grows to produce more fungus and spreads to more plant tissue and produces more fungus to spread to other plants.

Air circulation is important to prevent the spread of the fungus. Closely planted gardens with moderate air movement are ideal for the spread of the disease. The spread of spores usually occurs during daytime when the plants are dryer. Higher humidity at night favors germination and penetration of the fungus. Cool damp nights and warm days favor development of powdery mildew.
Dormant pruning and sanitation of the rose planting area and removal of dead leaves can reduce the chances of re-infection. When roses are rapidly pushing new growth in the spring is the ideal time for powdery mildew to get started.

Fungicidal sprays may be applied at seven to ten day intervals. Fungicides will work best when the disease is just getting started rather than when the disease is well established. There are fungicides that prevent mildew and others that treat the existing mildew and some that claim to work systemically within the plant. Remember that these products have varying degrees of toxicity to you and the environment. Always wear protective gear when spraying. The following applies to anytime you are spraying in the garden. Do not spray when the sun is hot on the plants, when the wind is blowing, or when rain will soon wash your spray off the plant and always wear the appropriate protective gear.

One of the best ways to prevent insects and disease in the rose garden is by good sanitation. Another good practice is spraying water on you roses, as it can wash off aphids, spider mites and other insects. It can also discourage powdery mildew. Although powdery mildew is promoted by high humidity is does not tolerate wet.  In the desert where it is so very dry the roses really like that little refreshing sprits of water when it is so hot. When you go out and splash a little water (more like a good spraying with the hose) on your roses on a hot day you can almost hear them saying “AHHHHHH”!

Having lived in other parts of this country, I can tell you that our insects and diseases are minor compared to other regions. Our roses do not freeze out in the winter, we have a longer bloom seasons, fewer insects and lower humidity helps reduce diseases.  Thus, this little low desert is one of the finest places for rose growers and their pet roses.

  • Facebook Social Icon

Please consider a donation today to help us continue to provide rose information and advice to the Coachella Valley.

(c) 2020 Desert Rose Society   PO Box 11101, Palm Desert, CA 92255