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Rose Pests and Diseases In Utah
And How To Deal With Them

Fortunately, Utah's geographical isolation and semi-arid climate have helped limit the pests and diseases that affect our roses. In this section you will find a LIST OF MAJOR PEST AND DISEASES of roses in Utah. The TREATMENT and remidies will be listed in IPM (Integrated Pest Management) order, which starts from the simplist least harmful to the more stringent measures.

Powdery Mildew:
Powdery mildew becomes a problem when we have warm days followed by cool humid nights. The optimum temperature for germination is 71F and the minimum is 42F. Usually germination does not take place over 90F. Spores remain viable at a humidity of 80%. They will die in 48 hours at 70F and 24 hours at 90F. Germination does not take place over 90F. Therefore, in Utah mildew is a spring and fall problem.

1). The easiest way to prevent powdery mildew is to provide good air circulation for your roses. Also the planting of a monoculture will reduce the probability of any disease.

2). The spores are mobile in early afternoon. Therefore, rose growers who have the time to wash the leaves with water between 6:00 pm and dusk have obtained good powdery mildew protection.

3). If mildew is a persistent problem in your yard you can use a preventative spray. Fuginex a Class I (danger) fungicide has been effectively used by rosarians for several years.

4). If you suffer an outbreak of powdery mildew Immunox (the active ingredient is Systhane) can be used.

Blackspot is seldom seem in Utah because it is most pernicious in conditions of high humidity. For infection to occur the leaf must be wet for over seven hours. Spore germination requires 9-18 hours at 70-80F. Blackspot is more of a summer problem because it requires hot days and warm nights under humid conditions.

1). Because blackspot infestations require several hpurs of highly humid conditions it can be prevented by watering in the early morning. This will give the leaves ample time to dry out.

2). If blackspot is a frequent problem in your yard, you can strip the lower leaves from the plant. infestations begin in the lower older leaves.

3). If blackspot occurs it can be treated with daconil a Class III (caution) fungicide or Fungigard Class II (warning) fungicide with Daconil as the active ingredient. General Fungus Information: Neither Powdery Mildew nor Blackspot will kill your roses, but a severe infection could weaken your roses to such an extent that they may not survive winter. Most other fungi are not a problem in Utah. Should such a fungal problem occur check the Consulting Rosarian heading to find assistance.

Aphids are soft bodied green, brown, or black sucking insects. They are bound on the tender young growth at the top of the young shoots.

1). The aphids can be smashed using your fingers or washed from the plant surface using a heavy stream of water.

2). Insect controls can be obtained from specialty sources. These insects feed on the aphids and in sufficient number can control aphid populations.

3). The aphids can be sprayed with organic (insecticidal soap or horticultural oil) sprays. These sprays work by suffocating the aphids.

4). The aphids can be sprayed with a chemical insecticide Malathion (class III, Caution) or Orthene (Class III, warning).

Thrips: Thrips are nearly microscopic long bodied insects. They cause the petals of the rose to brown and if severely infected not to open. They damage the capillary feeding system in the petals by rasping against the petals. Thrips seem to prefer pastel colored roses.

1). Try to remove alternate sites, i.e. dandelions, iris, etc. The thrips will infect these sites and then move to roses.

2). Insectiside control requires a systemic insecticide (Orthene, Class III (warning)).

Spider Mites:
Spider Mites: Spider mites are related to spiders and not insects. They become a problem in hot dry weather and a major infestation can kill your roses. Spider mites suck the juices from the leaves and tender part of arose bush. Early symptoms will be drying of the leaves at the bottom of the plant (this is where the infestation begins). If you rub the leaves between your fingers the bottom of the leaf will fill gritty. If the leaf is shaken over a piece of paper, you will see small brown spots that move. If the infestation becomes sever you will notice webbing. If an infestation becomes severe and is not treated spider mites may even kill the bush.

1). If spider mite infestation occurs repeatedly it can be slowed or prevented by stripping the bottom leaves from your rose plants.

2). The major culprit in rose infestation is the two spotted spider mite. Predator mites may be purchased from specialty sources.

3). The spider mites may be washed off by spraying the bottom of tyhe leaves with water.

4). The spider mites may be controled or eliminated by using an ascaricide. A commonly available pesticide is Isotox a combination insecticide (Ortene) and ascaricide (Vendex).

General Pest Information: Most other pests are rarely a problem in Utah. Should such a pest problem occur check the Consulting Rosarian heading to find assistance.

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