Things that trouble roses
Roses grow exceptionally well in the Mediterranean climate of south west, Western Australia. However, as is the case with other plants, maintaining the health of roses makes them less susceptible to disease and better able to withstand insect attack. On this page we look at some of the pests, diseases and physiological problems that affect roses.
Reducing problems- When buying new stock from reputable growers, ask them to recommend cultivars that are more resistant to certain diseases and physiological problems. Roses need at least six hours of sunshine each day and should be sited in a bed away from invasive tree roots. Roses are heavy feeders and must be planted into soil improved massively with soil improver or compost. Soils must be free draining and sandy soils should have a clay additive worked into the top 30cm of soil. Feed regularly with a complete fertiliser once established. Humidity encourages fungal disease, as does poor air circulation. Do not position roses too closely together, avoid overhead watering, and prune to maintain an open structure. Fortunately, in most parts of Western Australia the climate is generally dry, resulting in good conditions for growing roses.
Herbicide Over Spray- Roses are particularly susceptible to drift from Glyphosate, so care is needed when tackling nearby weeds. The safest method is to paint the herbicide onto the weeds with a brush, rather than use a spray which can easily drift. Glyphosate damage results in bleached, distorted foliage that is almost white. Plants will grow out of it in time.
Physiological problems- Physiological problems are often related to climatic conditions. Bull-heads are short, squat blooms triggered by low temperatures. Sometimes, leafy Calyces develop, or leaves are seen emerging from the centre of a bloom. This is also climate related. Some rose varieties are more prone to physiological problems.
Reducing problems- When buying new stock from reputable growers, ask them to recommend cultivars that are more resistant to certain diseases and physiological problems. Roses need at least six hours of sunshine each day and should be sited in a bed away from invasive tree roots. Roses are heavy feeders and must be planted into soil improved massively with soil improver or compost. Soils must be free draining and sandy soils should have a clay additive worked into the top 30cm of soil. Feed regularly with a complete fertiliser once established. Humidity encourages fungal disease, as does poor air circulation. Do not position roses too closely together, avoid overhead watering, and prune to maintain an open structure. Fortunately, in most parts of Western Australia the climate is generally dry, resulting in good conditions for growing roses.
Herbicide Over Spray- Roses are particularly susceptible to drift from Glyphosate, so care is needed when tackling nearby weeds. The safest method is to paint the herbicide onto the weeds with a brush, rather than use a spray which can easily drift. Glyphosate damage results in bleached, distorted foliage that is almost white. Plants will grow out of it in time.
Physiological problems- Physiological problems are often related to climatic conditions. Bull-heads are short, squat blooms triggered by low temperatures. Sometimes, leafy Calyces develop, or leaves are seen emerging from the centre of a bloom. This is also climate related. Some rose varieties are more prone to physiological problems.
Fungal Problems
Black Spot
Black spot, one of the most common diseases of roses, is caused by the fungus Diplocarpon Rosae. Infection results in irregular black spots with fringed margins developing on leaves and young stems. Affected leaves turn yellow and drop prematurely and if defoliation is severe stem die back can occur. Spores are spread by wind and water-splash. To control black spot remove and destroy all diseased material. When new growth occurs spray bushes with Mancozeb, Myclobutanil or Triforine. Organic controls include sprays containing bicarbonate of soda (potassium bicarbonate).
Black spot, one of the most common diseases of roses, is caused by the fungus Diplocarpon Rosae. Infection results in irregular black spots with fringed margins developing on leaves and young stems. Affected leaves turn yellow and drop prematurely and if defoliation is severe stem die back can occur. Spores are spread by wind and water-splash. To control black spot remove and destroy all diseased material. When new growth occurs spray bushes with Mancozeb, Myclobutanil or Triforine. Organic controls include sprays containing bicarbonate of soda (potassium bicarbonate).
Powdery Mildew
The fungus Sphaerotheca pannosa causes the disease Powdery Mildew on roses. New growth is most susceptible. Leaves, stems, and flower buds develop a pale grey powdery coating, leaf edges may scorch and curl inwards, and buds may be deformed. The fungus can overwinter in infected buds. The disease spreads by wind-borne spores. To control powdery mildew, remove and destroy diseased material. During the growing season spray bushes with Mancozeb, Lime Sulphur, Tebuconazole, Myclobutanil or Triforine. Organic sprays contain bicarbonate of soda (potassium bicarbonate). Make your own spray by mixing one part full cream milk with ten parts water and spray at the first sign of the disease.
The fungus Sphaerotheca pannosa causes the disease Powdery Mildew on roses. New growth is most susceptible. Leaves, stems, and flower buds develop a pale grey powdery coating, leaf edges may scorch and curl inwards, and buds may be deformed. The fungus can overwinter in infected buds. The disease spreads by wind-borne spores. To control powdery mildew, remove and destroy diseased material. During the growing season spray bushes with Mancozeb, Lime Sulphur, Tebuconazole, Myclobutanil or Triforine. Organic sprays contain bicarbonate of soda (potassium bicarbonate). Make your own spray by mixing one part full cream milk with ten parts water and spray at the first sign of the disease.
Rose Mosaic
A complex of viruses causes mosaic, which can appear on leaves in a number of different formats, for example, narrow yellow bands along the veins, yellow mottling which spreads and merges, or broad bands of pale green or creamy white tissue. Sometimes the plant’s vigour is reduced, but generally mosaic is not a serious problem. There is no remedy.
A complex of viruses causes mosaic, which can appear on leaves in a number of different formats, for example, narrow yellow bands along the veins, yellow mottling which spreads and merges, or broad bands of pale green or creamy white tissue. Sometimes the plant’s vigour is reduced, but generally mosaic is not a serious problem. There is no remedy.
Cane Canker caused by Botrytis
Apart from Botrytis, two of the commonest fungi to cause cane canker are Coniothyrium and Botryosphaeria species. These diseases are more commonly seen on plants stressed through poor management practices such as inadequate nutrition or irrigation. Water-borne spores enter mainly through pruning wounds or other injuries. The disease can affect any part of the stem, initially producing yellow or red spots on the bark. These enlarge into brown cankers with dark margins, and the bark cracks and becomes sunken. Tiny black fruiting structures are sometimes seen. Canker can encircle the stem or travel down it, killing the plant. To treat canker, prune stems back to healthy buds and destroy diseased material. After pruning apply Mancozeb to protect wounds from infection.
Apart from Botrytis, two of the commonest fungi to cause cane canker are Coniothyrium and Botryosphaeria species. These diseases are more commonly seen on plants stressed through poor management practices such as inadequate nutrition or irrigation. Water-borne spores enter mainly through pruning wounds or other injuries. The disease can affect any part of the stem, initially producing yellow or red spots on the bark. These enlarge into brown cankers with dark margins, and the bark cracks and becomes sunken. Tiny black fruiting structures are sometimes seen. Canker can encircle the stem or travel down it, killing the plant. To treat canker, prune stems back to healthy buds and destroy diseased material. After pruning apply Mancozeb to protect wounds from infection.
Phytophthora and Pythium Root Rot
Roses affected by root rots wilt and may eventually die. The root ball may be water-soaked and brown and none or few new white roots may be seen. Phytophthora root rot may be caused by more than one species of the pathogen. Common sources of Phytophthora cinnamomi (jarrah die back) are infected soil or irrigation water that has been in contact with the soil, for example, dam water. Other species of Phytophthora may be imported in potting mixes. There is no cure for infected plants, but the disease may be suppressed with the use of phosphorous acid. Pythium affects plants in a similar manner but is more often a sign that the plants are being stressed in some other way, for example, by high salinity, low pH, or water logging.
Roses affected by root rots wilt and may eventually die. The root ball may be water-soaked and brown and none or few new white roots may be seen. Phytophthora root rot may be caused by more than one species of the pathogen. Common sources of Phytophthora cinnamomi (jarrah die back) are infected soil or irrigation water that has been in contact with the soil, for example, dam water. Other species of Phytophthora may be imported in potting mixes. There is no cure for infected plants, but the disease may be suppressed with the use of phosphorous acid. Pythium affects plants in a similar manner but is more often a sign that the plants are being stressed in some other way, for example, by high salinity, low pH, or water logging.
Rust
Most rusts are host-specific. The fungus Phragmidium mucronatum that causes rust on roses does not infect any other plants. In spring and early summer, orange powdery pustules develop on the undersides of leaves. Upper leaf surfaces become speckled yellow. These leaves drop prematurely. In late summer, black or brown spore masses appear with the orange pustules — these are the Teliospores that can overwinter. The fungus spreads rapidly and can cause severe defoliation. The spores are spread by wind. To control rose rust remove and destroy diseased material. When new growth occurs, spray bushes with, Mancozeb, Myclobutanil or Triforine. An organic spray for rust is Lime Sulphur or bicarbonate of soda.
Most rusts are host-specific. The fungus Phragmidium mucronatum that causes rust on roses does not infect any other plants. In spring and early summer, orange powdery pustules develop on the undersides of leaves. Upper leaf surfaces become speckled yellow. These leaves drop prematurely. In late summer, black or brown spore masses appear with the orange pustules — these are the Teliospores that can overwinter. The fungus spreads rapidly and can cause severe defoliation. The spores are spread by wind. To control rose rust remove and destroy diseased material. When new growth occurs, spray bushes with, Mancozeb, Myclobutanil or Triforine. An organic spray for rust is Lime Sulphur or bicarbonate of soda.
Gall
Crown galls on roots. The bacterium Agrobacterium tumefaciens causes crown gall. The galls that develop on stems or just under the soil surface are round and rough textured. Young galls are soft and white or pale green — older ones are dark and woody. Affected plants lose vigour and may become stunted, with poor leaves and fewer flowers. The bacterium is spread on garden tools. Treat the soil with products containing beneficial bacteria Agrobacterium radiobacter, strain K1026. This works best as a preventative and is not a cure.
Crown galls on roots. The bacterium Agrobacterium tumefaciens causes crown gall. The galls that develop on stems or just under the soil surface are round and rough textured. Young galls are soft and white or pale green — older ones are dark and woody. Affected plants lose vigour and may become stunted, with poor leaves and fewer flowers. The bacterium is spread on garden tools. Treat the soil with products containing beneficial bacteria Agrobacterium radiobacter, strain K1026. This works best as a preventative and is not a cure.
Nematodes
Nematodes of the genus Meloidogyne attack the roots of a wide range of plants including roses. The damaged root system develops root knots which causes low growth, wilting, and yellowing leaves. Nematodes are spread by introducing infested plants or soil to your garden, and also can be carried on garden tools. To reduce nematode numbers improve the soil with organic matter and plant a crop of marigolds. Roses grafted onto Fortuniana rootstock are resistant to nematodes.
Nematodes of the genus Meloidogyne attack the roots of a wide range of plants including roses. The damaged root system develops root knots which causes low growth, wilting, and yellowing leaves. Nematodes are spread by introducing infested plants or soil to your garden, and also can be carried on garden tools. To reduce nematode numbers improve the soil with organic matter and plant a crop of marigolds. Roses grafted onto Fortuniana rootstock are resistant to nematodes.
Problem Pests
Aphids
Aphids are sap-sucking insects that extract nutrients from the plant, particularly in spring. This activity can result in distorted leaves, drooping buds, stunted growth, and poor flowers. Aphids secrete honeydew, on which sooty mould may develop, further spoiling the plant’s appearance. Small populations can be removed by hosing at high pressure, but this needs to be repeated every two or three days. If gardeners can wait two weeks without spraying any chemicals, beneficial insects like ladybirds and lacewings will build to sufficient numbers to prey on the aphids and reduce numbers. Spray big infestations with Imidacloprid, Acetamiprid, Maldison, Pyrethrins, or white oil. Chilli and/or garlic sprays are also effective and the garlic acts as a repellent to further aphid attack. This treatment will need to be repeated.
Aphids are sap-sucking insects that extract nutrients from the plant, particularly in spring. This activity can result in distorted leaves, drooping buds, stunted growth, and poor flowers. Aphids secrete honeydew, on which sooty mould may develop, further spoiling the plant’s appearance. Small populations can be removed by hosing at high pressure, but this needs to be repeated every two or three days. If gardeners can wait two weeks without spraying any chemicals, beneficial insects like ladybirds and lacewings will build to sufficient numbers to prey on the aphids and reduce numbers. Spray big infestations with Imidacloprid, Acetamiprid, Maldison, Pyrethrins, or white oil. Chilli and/or garlic sprays are also effective and the garlic acts as a repellent to further aphid attack. This treatment will need to be repeated.
Two Spotted Mites
Mites are sap-sucking arachnids that can cause yellowing or bronzing of leaves. If the population is large, leaf drop occurs and the health of the plant is reduced. Two-spotted mite, also known as red spider mite, is the most serious pest mite. Although mites are so tiny that they are difficult to see, the fine webbing that they build across leaves and between leaves and stems betrays their presence. Mites can infest your roses at a rapid rate and left untreated can devastate them quickly. To help reduce their numbers you can spray water beneath the rose leaves, however if you have an infestation you will need other approache. One of the the best ways we have found to attack this problem, is the use of Wettable Sulphur mixed with a wetting spreader, like Searles Spredmax. In extreme cases where mites have built up an imunity, is to use a commercial grade miticide such as Omite.
Mites are sap-sucking arachnids that can cause yellowing or bronzing of leaves. If the population is large, leaf drop occurs and the health of the plant is reduced. Two-spotted mite, also known as red spider mite, is the most serious pest mite. Although mites are so tiny that they are difficult to see, the fine webbing that they build across leaves and between leaves and stems betrays their presence. Mites can infest your roses at a rapid rate and left untreated can devastate them quickly. To help reduce their numbers you can spray water beneath the rose leaves, however if you have an infestation you will need other approache. One of the the best ways we have found to attack this problem, is the use of Wettable Sulphur mixed with a wetting spreader, like Searles Spredmax. In extreme cases where mites have built up an imunity, is to use a commercial grade miticide such as Omite.
Leaf Cutter Bee
Telltale signs of a leaf-cutter bee. Female leaf-cutter bees (Megachile spp) cut semi-circular holes in leaves and use the segments to line their nests. The damage is minimal and harmless. No control is necessary.
Telltale signs of a leaf-cutter bee. Female leaf-cutter bees (Megachile spp) cut semi-circular holes in leaves and use the segments to line their nests. The damage is minimal and harmless. No control is necessary.
Thrips
Thrips are sap-sucking insects that can cause deformities in flowers, leaves, stems, and shoots. The insects are difficult to see because they are small and hide deep in the flower or on the undersides of the leaves, which become silvery on the upper surface. Thrips are most active during spring, summer and autumn. To check for infestations tap flowers over a sheet of white paper and examine the black, torpedo-shaped 'specks' beneath a magnifying glass. Small populations may not do enough damage to warrant chemical control. For large infestations, which can seriously weaken the plant, spray with Imidacloprid, Acetamiprid or Pyrethrins. Horticultural soap is an organic control but it is often difficult to kill the pests when they are hidden deep within the flower petals.
Thrips are sap-sucking insects that can cause deformities in flowers, leaves, stems, and shoots. The insects are difficult to see because they are small and hide deep in the flower or on the undersides of the leaves, which become silvery on the upper surface. Thrips are most active during spring, summer and autumn. To check for infestations tap flowers over a sheet of white paper and examine the black, torpedo-shaped 'specks' beneath a magnifying glass. Small populations may not do enough damage to warrant chemical control. For large infestations, which can seriously weaken the plant, spray with Imidacloprid, Acetamiprid or Pyrethrins. Horticultural soap is an organic control but it is often difficult to kill the pests when they are hidden deep within the flower petals.
Scale insects
Scale are sap-sucking insects with a waxy or armoured cover which they use to protect themselves. Scales found on roses include cottony-cushion scale, red scale and rose scale and include ‘soft’ and ‘armoured’ varieties. In soft scales, some scale insects hatch from eggs, while others are born live. Juvenile scales are known as crawlers. They disperse to favourable sites, settle down and start feeding. The juveniles then become sedentary, and start building their protective scale covers. The females of most species remain under the covers for their entire life, while the male insects live under the covers until maturity, when they emerge as winged adults. Scale is usually found on canes at the base of the plant but can cover higher stems. For minor infestations the scale insects can be rubbed off the rose canes using a damp cloth. Alternately smother the scale by spraying with a horticultural oil or spray with a potassium soap which works by blocking the breathing pores and dissolving the scale's outer covering so it dehydrates and dies.
Scale are sap-sucking insects with a waxy or armoured cover which they use to protect themselves. Scales found on roses include cottony-cushion scale, red scale and rose scale and include ‘soft’ and ‘armoured’ varieties. In soft scales, some scale insects hatch from eggs, while others are born live. Juvenile scales are known as crawlers. They disperse to favourable sites, settle down and start feeding. The juveniles then become sedentary, and start building their protective scale covers. The females of most species remain under the covers for their entire life, while the male insects live under the covers until maturity, when they emerge as winged adults. Scale is usually found on canes at the base of the plant but can cover higher stems. For minor infestations the scale insects can be rubbed off the rose canes using a damp cloth. Alternately smother the scale by spraying with a horticultural oil or spray with a potassium soap which works by blocking the breathing pores and dissolving the scale's outer covering so it dehydrates and dies.
Mealy Bug
Members of the Psuedococcidae family of scale insects, mealy bugs are about an eighth of an inch long and have a white powdery appearance. Mealy bugs feed on plant sap and generally position themselves under leaves and at stem joints, while they attack the plant with piercing mouths known as Stylets. This penetrative feeding style damages the plant by draining its sap and transmits bacterial and fungal infections. Heavy infestations can kill a plant. Mealy bugs are soft-bodied creatures, but they secrete a powdery wax layer over themselves. This protective layer gives them their name, as it makes them look as though they’ve been coated in meal or flour. It is also what makes it so difficult to kill mealy bugs. The first rule of successfully ridding plants of mealy bugs is to catch them early. It’s far easier to kill one or two bugs than to eradicate a full-blown infestation. Inspecting your plants regularly is essential for early detection. For larger infestations, try spraying with a mixture of dish washing liquid and water. Use equal parts of each and stir to mix rather than shaking to avoid excess foam. Spray all infected areas. The soap coats the mealy bugs and effectively suffocates them. It also breaks down their protective waxy layer. Made from a mix of mild detergent and Pyrethroids, insecticidal soaps are applied to the plant, its pot, and the immediate surrounding area. You can also mix insecticidal soap and horticultural oil together as an alternative approach to killing mealy bugs – use 1 teaspoon soap, ½ teaspoon horticultural oil and 1 litre of water and apply with a spray bottle.
Members of the Psuedococcidae family of scale insects, mealy bugs are about an eighth of an inch long and have a white powdery appearance. Mealy bugs feed on plant sap and generally position themselves under leaves and at stem joints, while they attack the plant with piercing mouths known as Stylets. This penetrative feeding style damages the plant by draining its sap and transmits bacterial and fungal infections. Heavy infestations can kill a plant. Mealy bugs are soft-bodied creatures, but they secrete a powdery wax layer over themselves. This protective layer gives them their name, as it makes them look as though they’ve been coated in meal or flour. It is also what makes it so difficult to kill mealy bugs. The first rule of successfully ridding plants of mealy bugs is to catch them early. It’s far easier to kill one or two bugs than to eradicate a full-blown infestation. Inspecting your plants regularly is essential for early detection. For larger infestations, try spraying with a mixture of dish washing liquid and water. Use equal parts of each and stir to mix rather than shaking to avoid excess foam. Spray all infected areas. The soap coats the mealy bugs and effectively suffocates them. It also breaks down their protective waxy layer. Made from a mix of mild detergent and Pyrethroids, insecticidal soaps are applied to the plant, its pot, and the immediate surrounding area. You can also mix insecticidal soap and horticultural oil together as an alternative approach to killing mealy bugs – use 1 teaspoon soap, ½ teaspoon horticultural oil and 1 litre of water and apply with a spray bottle.
Leaf Hopper
Many species of Leaf Hoppers exist in home gardens throughout North America. Both adults and nymphs feed by puncturing the undersides of leaves and sucking out plant juices. Their toxic saliva causes spotting (white specks), yellowing, leaf curling, stunting and distortion of plants. They are also responsible for transmitting the organisms causing virus diseases in plants. Common host plants include beans, lettuce, beets, potato, grapes, roses and many others. Leaf Hopper adults (1/4 inch long) are slender, wedge-shaped insects that fly or disperse rapidly when disturbed. Depending on species they may be green, brown or yellow in color and often have colorful markings. Nymphs do not have wings and are generally lighter in color than adults. Both adults and nymphs run sideways and are good jumpers. Control of the various Leaf Hoppers depends upon monitoring their development. Sprays should be applied before adults appear, sprays applied after adults are present are less likely to be effective. There are different ways to control leaf Hoppers, you can treat with insecticidal soap to keep pest populations under control. Thorough coverage of both upper and lower infested leaves is necessary for effective control. To improve the effectiveness of insecticidal soap, mix 1 tablespoon of Isopropyl alcohol to 1 quart of the spray. It helps the soap penetrate the insects’ outer shell.
Also there are many pesticides are labeled to treat Leaf Hoppers, look for pesticides containing Diazinon, Disulfoton, Endosulfan, Imidacloprid, Lambda-Cyhalothrin, Malathion, Neem Oil, Permethtrin, Phenothrin or Pyrethrins. Some of these pesticides are available in systemic formulas, meaning the plants take the poison in. Systemic pesticides are often most effective against Leaf Hoppers. Read package labels carefully to ensure the product is safe to use on roses.
Many species of Leaf Hoppers exist in home gardens throughout North America. Both adults and nymphs feed by puncturing the undersides of leaves and sucking out plant juices. Their toxic saliva causes spotting (white specks), yellowing, leaf curling, stunting and distortion of plants. They are also responsible for transmitting the organisms causing virus diseases in plants. Common host plants include beans, lettuce, beets, potato, grapes, roses and many others. Leaf Hopper adults (1/4 inch long) are slender, wedge-shaped insects that fly or disperse rapidly when disturbed. Depending on species they may be green, brown or yellow in color and often have colorful markings. Nymphs do not have wings and are generally lighter in color than adults. Both adults and nymphs run sideways and are good jumpers. Control of the various Leaf Hoppers depends upon monitoring their development. Sprays should be applied before adults appear, sprays applied after adults are present are less likely to be effective. There are different ways to control leaf Hoppers, you can treat with insecticidal soap to keep pest populations under control. Thorough coverage of both upper and lower infested leaves is necessary for effective control. To improve the effectiveness of insecticidal soap, mix 1 tablespoon of Isopropyl alcohol to 1 quart of the spray. It helps the soap penetrate the insects’ outer shell.
Also there are many pesticides are labeled to treat Leaf Hoppers, look for pesticides containing Diazinon, Disulfoton, Endosulfan, Imidacloprid, Lambda-Cyhalothrin, Malathion, Neem Oil, Permethtrin, Phenothrin or Pyrethrins. Some of these pesticides are available in systemic formulas, meaning the plants take the poison in. Systemic pesticides are often most effective against Leaf Hoppers. Read package labels carefully to ensure the product is safe to use on roses.