Prepared by Carl Dibley of Classic Roses, Rotorua

There is nothing quite like the joy and pleasure a healthy bed of roses gives. Most roses are more robust than most people give them credit for. Here are few guidelines to help.

All Roses respond to a good start in life. This includes:

• good feeding;
• disease control (spraying or other means); and
• pruning.

Good Feeding

Roses love organic manure. If you have good compost, dig it into the ground before planting. Blood and Bone is also beneficial. Never put artificial fertiliser in the hole around the roots of newly planted roses as this can burn the tender young roots. It can be used later in the season if needed. In most districts a good dressing of lime is needed in the winter. If your soil is low in magnesium, Dolomite is a good idea, put this on your roses in winter as well. Mulch your roses in spring as it helps to conserve moisture in summer. A light side dressing of a balanced N.P.K. fertiliser before each flush of flowers also helps keep your roses healthy. Remember healthy growing roses are the best defence against disease.

Spraying

Good garden hygiene is very important. After winter pruning, clean up all the dead leaves and prunings and burn them, or put them out with your rubbish. Do not put them in your compost as the leaves may be carrying fungus spores which could spread back to your garden when you use the compost. Spray your roses and the ground around them with a good copper spray, then spray 3 or 4 days later with winter oil. Do not mix them. You can use copper based sprays up until October, or in warmer districts, in mid September. After this, you can alternate Bravo with Shield or Guild or similar spays. You can also use companion planting to aid disease control.

Diseases

The following diseases are common for roses.

Downy Mildew

• What it looks like: Downy Mildew looks like, and can be confused with, Black Spot. The spots are brown and have irregular and defined edges. The rest of the leaf soon turns yellow and falls off. In bad cases of the disease, dark lesions form on the young stems and they die back.
• What it does to the rose: It weakens the plant which makes it more susceptible to other diseases.
• When most likely to occur: Early Spring in the first growth if the weather is cool and wet as it quite often is at that time of the year.
• Controlling the disease: Once it is established Downy Mildew is hard to control. Therefore, prevention is best. Copper-based sprays during Winter are the best protection. In Spring I find Bravo or Manzate are very good and they also help to control Black Spot and Powdery Mildew.

Black Spot

• What it looks like: As I mentioned above, Black Spot and Downy Mildew have a similar apperance. If you look at the shape of the spots, Black Spot is darker in colour, is circular in shape and the edge of the spot is fuzzy.
• What it does to the rose: First it is unsightly as it progresses the leaves drop off. Second, the plant is weakened by the disease.
• When most likely to occur: This disease only attacks if the leaves have been wet for several hours during daylight. Generally it takes water and light for the spores to germinate.
• Controlling the disease: In the earlier part of the season, the same control as for Downy Mildew. Later in the Spring, Guild or Shield can be used. Like most diseases, prevention is better than trying to cure it.

Powdery Mildew

• What it looks like: Look out for white dusting on new tender growth and buds.
• What it does to the rose: It is very unsightly and can deform the buds and they can drop off. As well as this, the new shoots can be stunted and die.
• When most likely to occur: Powdery Mildew seems to like the dryer weather especially when warm days are followed by cool nights.
• Controlling the disease: The same control as for Black Spot. Once again, prevention is better than cure.

Rust

• What it looks like: Look out for raised orange spots on the underside of the leaves. These spots turn dark brown as they get older. Little white spots also show up on the top side of the leaves.
• What it does to the rose: If left untreated, the leaves will go a straw colour and drop off. In time Rust can kill the plant.
• When most likely to occur: Like Powdery Mildew, Rust seems to revel in warm dry weather where the days are warm and the nights are cool.
• Controlling the disease: Try to remove the diseased leaves and burn them. Do not put them on your compost as as this could spread it back to your garden. Manzate or Bravo are probably the best sprays to use.

Here I would like to point out that rose breeders are releasing new varieties that are relatively trouble free. I find that if you can start the season with clean roses, the task of keeping them clean is so much easier for the rest of the year.

Insects

Another problem that rears it's ugly head from time to time is those pesky insects, namely aphids, caterpillars, mites, scales and thrips. I feel with these, treatment is necessary only if you can see the problem.

Aphids

• What to look for: Those little green sucking insects that cluster on the buds and the new green tips of the roses.
• How they affect the rose: Aphids can spread some virus diseases that look unsightly and can deform the buds. The honey dew aphids excrete causes a problem called Sooty Mould. It does not hurt the plant but does look unsightly.
• How to treat them: If not too many aphids, digit control (squeeze them with your fingers) works well. Check to see if you have any friendly predator insects (ladybirds and small wasps). Take a close look at the aphids. If you see some very fat almost black ones then you can be sure you have a small friendly wasp which has layed an egg in the aphid which in time will kill it. Also look for hover flies as they devour aphid. This is where companion planting comes in handy to encourage your friendly insects. Remember if you use a spray, most will also kill your friendly insects. This includes sprays such as Super Shield, Pyrethram and Maldersen. But sometimes you will find that spraying is the only answer.
  

Caterpillars

• What to look for: Look for chewed buds or leaves stuck together.
• How they affect the rose: They chew the new growth and flower buds.
• How to treat them: If not a big problem, again digit control is good. B.T (Bacillus Thuringiensis) is a safe spray to use as it only kills caterpillars.

Mites or Red Spider Mites

• What to look for: The leaves look lighter green with a silvery appearance. Look on the underside of the leaves (you may need a magnifying glass) and you will see small red or brown insects. The brown mites have two black spots. They are spider-like insects, generally in great numbers.
• How they affect the rose: As you can guess, they suck the sap from the leaves and affect the chlorophyll so the plant becomes starved.
• How to treat them: The best time to control mites is after Winter pruning. Use Winter spraying oil making sure you cover all the stems and crown. During Summer, there are predator insect that will hopefully kick in and help control them or you can use a proprietary spray.

Scale insects

• What to look for: If you have them, scale insects will show up as small white raised spots on the stems of the rose. If left, they can also spread onto the leaves.
• How they affect the rose: Because they suck the sap from the plant, a bad infestation can weaken your roses.
• How to treat them: If you have a bad infestation after Winter pruning, spray with Lime Sulphur. Follow this a week later with the same Winter oil spray which will also control mites. During Summer, if you find small pockets of infestation, I find mixing a bit of Winter spraying oil (double strength) with water and painting it on the infected stems with a brush.

Thrips

• What to look for: This can be another troublesome insect in a hot dry Summer. They affect buds and flowers. Look out for the first sign is browning of the edges of the petals and for flowers not opening properly. If you open the petals with your fingers you will see minute brown or black elongated insects.
• How they affect the rose: The flowers don't open properly and are disfigured.
• How to treat them: If the thrips become too troublesome, a spray of Target can help, especially the new buds. Try spraying in the evening as the spray can sometimes burn the tender growth in the heat of the day.

Pruning

Winter

My first word on pruning is hygiene. It is important to keep your pruning gear clean at all times. Before you start pruning, sterilise your gear and keep it clean. Wait for a fine day. Remember to use a prune dressing on larger cuts.

• Bush and shrub roses: Take out any dead or weak wood, try to keep 4 to 6 of the newer canes. Cut them back short for show blooms, longer for garden display. Remove the older canes back to the crown. Roses are very forgiving plants, if you make a mistake they soon bounce back.
• Climbers: Take out the old and spent canes, tie down up to 6 aside of the one year old canes or the best of the older canes. Cut out the rest.
• Ramblers: Most ramblers can be pruned straight after Summer flowering. Take out all the old flowering canes to as low as possible, leave all the young shoots coming from lower down. If they are good hip varieties, leave pruning until winter.
  

Summer

Remove spent blooms by cutting off at the first true leaf or a little lower on tall branches (notice that the top leaves have only 3 lobes compared to 5 of a true leaf). For multi headed blooms, remove individual blooms until head has finished then treat as above. Also remove any wood that has died back and is diseased or weak.