Common problems here in the desert

Symptom: The edges of the blooms are brown. Roses looked deformed when they open.
Diagnosis: Thrips. These are tiny tan bugs that suck the moisture out of the petals. They get into the bud when the color first begins to show. They like light colored roses the best (white, pink, yellow).
Organic control: Don’t plant light-colored roses.
Chemical control: To control the damage, fill a small spray bottle with insecticide and spray the buds every few days as they begin to open. Recommended insecticides are Bayer Rose & Flower Insect Killer, Ortho Isotox Insect Killer or Ortho Orthenex Garden Rose Insect & Disease Control.

Symptom: Tiny green bugs.
Diagnosis: Aphids. These bugs like to feed on the new growth and buds; they flourish when the weather is cool.
Organic control: The best control is to wash your roses off every 1-2 days with a sharp stream of water.
Chemical control: Insecticide (see recommended insecticides above, under ‘Thrips’).

Symptom: Sticky substance on leaves.
Diagnosis: Aphids. See above.

Symptom: Gray powder on leaves.
Diagnosis: Powdery Mildew. This fungus is caused by spores and generally forms when daytime temperatures are in the 80’s and the nighttime temperatures are in the 50’s.
Organic control: It is much easier to prevent than to treat mildew once it gets stared. The best prevention is to wash off your roses with a hose daily, preferably in the morning.
Chemical control: If you prefer, you can use an fungicide such as Ortho Orthenex Garden Rose Insect & Disease Control or Green Light FungAway.

Symptom: Black Spots on leaves.
Diagnosis: In Arizona, most likely Anthracnose, but possibly Black Spot.
Control: Treatment is the same for both – spray weekly with a fungicide such as Ortho Orthenex Garden Rose Insect & Disease Control Green Light FungAway.

Symptom: Leaves and blooms are droopy.
Diagnosis: Not enough water or watering is too shallow.
Solutions: Always be sure you are deep watering to a depth of 18 to 24 inches. You should flood the beds if you water by hand. If you are using drip irrigation, you should have a minimum of 2, preferably 3 or 4 emitters per rose bush. Roses in pots (especially clay pots) typically need to be watered more often than roses planted in the ground. You don’t want the soil to be soggy, but you also don’t want it to get totally dry between waterings.

Another possibility is that you have grubs eating your rose’s roots, or tree-root competition for water and nutrients.

Symptom: Leaves are dull or feel sandy and are falling off in the summer.
Diagnosis: Spider mites. If you look closely, you will see tiny webs in the leaf axils.
Organic control: The best control is to spray the undersides of your leaves with a sharp spray of water every couple of days. Morning is the best time to do this.
Chemical control: A miticide can be used, but since spider mites reproduce so quickly, the miticide needs to be reapplied frequently as new generations hatch.

Symptom: Holes on the tops of pruned canes.
Diagnosis: Cane borers. These are bugs that “drill” holes into the canes to lay their eggs.
Control: Best prevention is to seal your canes with carpenter’s glue after pruning your roses or cutting blooms from canes pencil-size or larger..

Symptom: Circles or half-circles cut out of leaves.
Diagnosis: Leaf Cutter Bees. These are tiny bees that are cutting pieces of leaves to line their nests for their eggs.
Control: There is no known prevention. Pesticides will not work because the bees are not eating the leaves; they are also very beneficial insects because they are such energetic pollinators.