Diseases and Pests of Roses in zones one to four:

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The roses listed in our ‘Rose Listing are those which are winter-hardy for the colder climates. These fall into three groups though these may be all classified as “Shrub Roses.” We are establishing a rose garden which contains Explorer, Parkland and other shrub roses and have found all in this group to survive in our Zone 2A (Ag-Canada zone Map) garden. Insects that attack roses will be dealt with first and then we’ll look at some of the diseases that affect rose bushes.

Rose Curculio:

A reddish coloured weevil, which when present in the rose garden, will pierce the rose buds and cause the buds to dry up without opening. Sometimes, if the damage is minimal, the buds will open but will have holes in the petals. The adult Rose Curculio is about 8 mm long, bright red in colour with a black under surface, black head and long black snout or beak. The control of this insect may be difficult but hand picking the adult and removing any of the damaged buds will decrease the infestation the following year. Destroy all materials collected by burning.

Rose Midge:

This tiny fly-like insect lays eggs in the terminal growth of young rose shoots and buds, and the developing larvae cause the buds to abort. For early detection look for bud formation in the growth point of the first shoots if midge is present the bud will have been removed and only the bud stem remains. (In some cases the bud, in early stages of development, may have been only partly severed and be still be partially attached). In severe cases flowering will be eliminated. Drenching the soil with diazinon in May and spraying of plants periodically will reduce infestations. Because of their small size, midge adults and larvae are rarely seen. Rose midge is not common, but may occur in certain localities.

Leafcutter Bees:

These insects may cut uniform circles in rose foliage. It has been reported that the bees will not use leaves coated with spray residue.

The Rose Gall Wasp:

This wasp attacks certain shrub roses, particularly rugosa hybrids, causing large brown or grey swellings on the stems. Adults hatch out of the galls in April. Chemical controls have been ineffective, so pruning out galls in autumn or very early spring is the only recommended control. Galls should be destroyed and not left in the vicinity of the bushes.

Red Spider Mites:

Mites are not insects but really spiders. These spiders will damage the rose plants by sucking on the underside of the leaves. Cobwebs on the underside of the leaves or covering the whole shoot (sometimes even around all the canes) will be an indication that these mites are present. Red spider mites thrive in hot dry weather.

Thrips:

This insect is about 1 mm long and can be seen by shaking the rose leaf over a white cloth and then using a magnifying glass to see the insect. Many insects are produced each growing season. Thrips damage the rose flower by probing and sucking the juice from the petals leaving tiny translucent spots on the rose petals.

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