First Those Fungal Diseases
White, Black or Rusty Spots On Leaves Are From Fungal Diseases.
Black spot, powdery mildew, and rust are the three major disease problems of roses. While mildew is found nationwide, rust and blackspot territories seldom overlap. Correct cultural practices can prevent many disease problems on roses. Plant rose bushes so that there will be a chance for air circulation around each plant to help minimize foliage disease problems. Water before noon; do not let water spatter on to the leaves to prevent fungus.
New Technology As Fungal Disease Preventative
There are now on the market a growing number of products that will help your rose plants become healthier, more drought resistant, and even more insect resistant. What is critical here is that several of these products have proven very effective in preventing the incidence of any of the big three rose fungal diseases.
Fungal control products are generally easy to use and not terribly expensive. If you want to give your rose plants some oomph and prevent fungal disease, check out Adding Soil Microbes and Adding Harpin Protein. Both of these techniques involve applying a foliar spray to your rose bushes every two to three weeks throughout the entire season. For products containing soil microbes go to the file Soil Microbe Products in Yardener's Tool Shed.
Traditional Treatment - In all three cases the traditional treatment was about the same for each disease. As a preventive step, spray vulnerable roses with garden sulfur fungicide as directed on the label during their dormant period in early spring. Check their growing tips and young leaves for signs of fungal disease when temperatures hit the mid 60's and rainfall is sparse. If it appears, prune off the infected parts and begin treatment. Spray healthy leaves and buds with the sulfur fungicide to prevent the spread of the fungus. Continue to remove all the leaves showing disease right away, and prune all branches as soon as a canker is spotted. Strip all leaves from the bushes after the first hard frost, to prevent rust or black spot spores from wintering over from year to year. Anti-transpirant spray products sprayed on healthy foliage show some promise of controlling fungal disease as well. Buy disease resistant bush roses.
Powdery Mildew
It is usually severe only in coastal areas with moderate temperatures, high cloud cover or fog and with minimal rainfall in the summer, such as in the Pacific Coast area. This is a white or gray powdery coating that appears on rose leaves, buds and canes. The disease starts on the young leaves as raised blisterlike areas that cause leaves to curl, exposing the lower surfaces. Infected leaves soon become covered with a grayish-white powder fungus growth. Unopened flower buds may be white with mildew and may not open. Mildew prefers young, succulent growth. The mature tissue on the plant is usually not affected. Powdery mildew usually occurs in periods of cool nights, humid days and no rain.
Rust
Rose rust is mostly confined to western United States. Small orange or yellow pustules (raised spots) appearing on any green portion of a rose bush indicates the presence of rust. Early infections usually occur on the undersides of the leaves and may be inconspicuous. Later, pustules develop on the upper leaf surfaces and stems and are quite visible throughout the summer. Some bushes will (drop)the infected leaves. It occurs during periods of morning dew.
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Black spot
Black spot thrives in moist environments, being most common in the Northeast, Southeast, and in some Mid-western states with warm, moist summer climates. Dark black spots with a surrounding yellow area form on the leaves. The leaves turn yellow-pink and fall off. The young leaves 6 to 14 days old are most susceptible. In severe cases rose bushes can be defoliated by mid-summer. Blackspot prefers rose bushes that produce light colored blooms, such as yellow. Red roses are not as susceptible. Blackspot begins to appear when the air temperature approaches the mid 60's with abundant rain or high humidity. The spots first appear on the leaves, especially young ones, down low to the ground.
Next Those Pesky Insects
Now The Pesky Insects
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Holes in Leaves and Flowers Caused By Japanese Beetles.
Japanese beetles are the number one insect pest of roses in many parts of the United States. Adult beetles are ½-inch long, with shiny metallic green and copper-brown wing covers. Their larvae (grubs) are grayish-white worms, with dark brown heads. Fully-grown grubs are plump, 3/4 to 1 inch long, and lie in the soil in the distinctive arc-shaped resting posture. They emerge from the soil or lawn at the end of June or early July and proceed to eat rose leaves and/or flowers, leaving unsightly holes. They crowd onto rosebuds and devour them before they have an opportunity to open. They also can completely skeletonize leaves.
To control Japanese beetles, adopt two strategies. For the short-term control damage to roses by handpicking the beetles--(drop)or knock them into a jar of soapy water and discard in the trash when they die. If infestations are heavy, spray rose foliage with a pyrethrin/pyrethrum insecticide product as directed on its label. For the long term, spray your lawn with predatory nematodes that will prey on the beetle grubs. Packaged as a powder under several brand names, these microscopic roundworms seek out and kill grubs. Do not use pheromone beetle traps on your property. They are so effective they attract Japanese beetles into your yard where not all are trapped. For more information see the file on Controlling Japanese Beetles
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Leaves Are Curled and Distorted From Aphids.
Aphids are soft-bodied, pear-shaped sucking insects, about the size of the head of a pin. They appear on garden roses in May and June and are common in greenhouses. Most of them are greenish, but pink or reddish broods are often present on roses, especially early in the season. They multiply so rapidly that infested flower buds and stalks become covered with them. They are usually found feeding on the undersides of the leaves. They retard or distort plant growth. Leaves on roses may turn yellow or brown, wilt under bright sunlight, or sometimes curl and pucker. Sometimes a sticky secretion can be seen on the tops of leaves that attract ants. Flowers can become malformed.
For light infestations, spray the undersides of the rose leaves vigorously with water three times, once every other day in the early morning to dislodge the pests. f they persist, spray visible aphids with insecticidal soap according to label instructions. Spray affected foliage and buds with a pyrethrin/pyrethrum insecticide product for longer effectiveness. Do this in the late afternoon or evening to minimize its impact on beneficial insects and bees. For more information see the file on Controlling Aphids
Holes in Leaves and Flowers Due To Various Beetles.
Beetles such as rose chafer beetle, rose leaf beetle, rose curculio, fuller beetle, and goldsmith beetle also attack roses. The best way to control beetles of all kinds on roses is to regularly hand-pick them from the rose bushes and knock them into a pail of soapy water. A spray of insecticidal soap will kill them on contact, however it does not persist on the roses. A pyrethrin/pyrethrum insecticide product, used as directed will persist awhile, but may need to be repeated to catch each new wave of attackers. This requires the same attention that hand-picking does. Control the beetles where they start, as grubs (larvae) in the lawn, by spraying it with predatory nematodes. These microscopic roundworms seek out grubs and kill them.
Canes Girdled, Die Back; Leaves Wilt from Borers.
Several kinds of borers attack rose bushes. Borers are larvae of various insects. They burrow into the insides of canes of hybrid and other roses causing the new succulent growth to droop and to suddenly wilt. They include raspberry cane borer, rose stem sawfly, rose stem girdler. Control borers by pruning affected canes below the infested section in the spring, or whenever you notice wilted canes. To keep the larvae from entering cut canes, insert a flat headed tack in the end or plug the hole with grafting wax, putty, or paraffin. Some gardeners paint the end of a pruned cane with shellac or tree wound paint.
For more information see file on Dealing With Borers
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Leaves And Buds Are Being Chewed By Caterpillars.
Caterpillars such as the rose budworm and the fall webworm sometimes attack rose bushes. Chewed leaves and/or buds, and telltale webs or nests among the foliage indicate the presence of a caterpillar of some kind. Pick off the caterpillars and destroy the infested buds, leaves, and nests. Spray the rose bush foliage weekly with a product containing Bacillus thuringiensis (Bt) while the caterpillars are feeding. They will ingest the bacterium, sicken, stop eating and die in a matter of days. Repeat the Bt sprays after rains and until the caterpillars disappear.
For more information see file on Controlling Caterpillars
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Leaves Discolored and Distorted Due To Leafhoppers.
Rose leafhoppers are blunt-profiled bugs, 1/4 to 1/3 inches long, wedge-shaped, with wings held in a rooflike position above their bodies. They are very active, moving sideways or hopping suddenly when disturbed. Nymphs and adults suck juices from leaves, buds, and stems of the rose. Eggs hatch in May and young insects feed on leaf undersides. Potato leafhoppers are also an occasional rose pest. These pests cause a white stippling effect on rose leaves. The leaves eventually shrivel and (drop)off. Honeydew from the insects' feeding may give foliage a glazed appearance and foster growth of sooty mold.
For chronic leafhopper problems, devise a protective cover for rose bushes made from white, polyspun garden fleece. Put this over the plants in the early spring to prevent access by leafhoppers. If they get to the plant, spray them with insecticidal soap as directed on the product label.
Yet More Pesky Insects
Ragged Holes In Leaves - Slugs and Snails
Slug s are essentially snails without shells. They are usually 1 to 2 inches long (some species grow up to 8 inches). Their coloration may be white, gray, yellow, brown or black. Slugs and snails leave large ragged holes in bush rose leaves and stems from their file-like tongues. They are attracted to moist, well-mulched gardens and acidic soil. Active at night, they hide under boards or leaf litter during the day. Although these pests are always most destructive in shaded gardens and during rainy spells, they may attack bush roses as well. Trap them in a shallow plate baited with beer and set on the soil near the delphiniums. Slugs, attracted to the yeast in the beer, will climb in and drown. Begin trapping within the first three to four weeks after the last frost. The more slugs trapped, the fewer are left to reproduce. For more information see the file on Controlling Slugs
Leaves Discolored and Deformed From Mite Damage
Mites are about 1/50 inch long, about the size of a grain of pepper. They may be yellow, green, red or brown and are always found on the undersides of the leaves. Two-spotted spider mites and the red spider mite stipple and discolor leaves. They spin webs across leaf surfaces and on new growth. As the infestation proceeds, leaves become spotted red, yellow or brown, curl, and (drop)off. Some floribunda roses are so susceptible to mites that they lose their leaves prematurely.
Serious mite infestations can be caused by using certain chemical fungicides sold to control rose fungal diseases. Start control measures as soon as you notice the first stippling on the leaves. Spray infested bushes in the early morning with a forceful water spray to knock mites from leaf undersides. Repeat the water spray daily for three days. If that doesn't do the job, spray the mites with insecticidal soap according to label instructions.
For more information see file on Controlling Mites
Plant Stunted, Leaves Yellowed May Indicate Root Nematodes.
Root knot nematodes are rose pests. Nematodes are not insects, but are slender, unsegmented roundworms. Most are soil-dwellers, less than 1/20 inch long, and are invisible to the unaided eye. Rose bushes infested with nematodes look sickly, wilted, or stunted, with yellowed or bronzed foliage. They decline slowly and die. Root systems are poorly developed, even partially decayed. Roots have knots or galls on them. Effects of nematode activity are most apparent in hot weather, when plants recover poorly from the heat.
If it is available, add lots of compost (especially leaf mold) to the soil around the rose plant to encourage beneficial fungi that attack nematodes. Fertilize the rose with fish emulsion diluted with water, drenching the soil around each affected bush. It repels nematodes. Dig out and remove any rosebushes that have died from nematodes. Remove the soil that surrounds the infected root systems also.
Leaves and Canes Encrusted With Small Bumps Is A Symptom Of Scale.
Scale insects feed on rose bushes underneath protective rounded waxy shells. These shells may be colored either white, yellow, or brown to black, and are about 1/10 to 2/5 inch in diameter. The first sign of a scale attack is often discoloration of the upper leaf surface, followed by leaf drop, reduced growth, and stunted plants. Telltale bumps encrust the canes and leaf stems of rose bushes. Some scale species excrete honeydew, which coats the foliage and encourages ants and sooty mold growth. Rose scale often thickly infests older canes. Heavy infestations can kill a rose bush. Scale outbreaks may be triggered by pesticides used against other pests or by environmental stresses such as too much or too little water. Overuse of nitrogen fertilizer can encourage the growth of scale populations. Avoid this by using a fertilizer with slow-acting nitrogen.
Scrape light infestations of scale off rose plant surfaces with a fingernail or a cotton swab dipped in rubbing alcohol. Spray heavily infested plants with “superior” or light horticultural oil. Cover all leaf, stem and bud surfaces. It will smother the scale insects and their eggs. Repeat the spray when roses begin to bloom in the spring to catch overwintering eggs.
For more information see file on Controlling Scale
Damaged Flowers With Brown Edges May Have Thrips.
Adult thrips are tiny, slender insects, 1/25 inch long, variously colored pale yellow, black or brown. They have four long narrow wings fringed with long hairs and very short legs. Their chief target is the rose bloom, especially the red, white, yellow, and other light colored varieties. Flower thrips and tobacco thrips attack rosebuds and disfigure petals. They attack buds in their early stages, working among the unfurled petals. The buds become deformed and fail to open properly, while the damaged petals turn brown and dry. New growth also may be damaged in the same way.
Since thrips burrow deep between the petals, early identification and control is important. Set out yellow sticky traps about 4 weeks after last frost as early warning devices. As soon as you spot thrips on the trap, spray rose buds with insecticidal soap or a pyrethrin/pyrethrum insecticide product as directed on their labels. Commercially available predatory mites, lacewings, ladybugs and beneficial nematodes are effective backups to the soap spray. Thrips prefer a dry environment, so make sure plants are adequately watered.
For more information see file on Controlling Thrips.
Cultural Problems Are Common
Cultural Problems
Failure to Thrive Is Due To Weather/Moisture Problems.
Blossoms Don't Open Fully Because It Is Too Cool and Damp
Cool nights or dark, damp days can cause balling, a situation in which blooms open halfway and then stop. Cut off these blooms when they start to ball to allow for better growth when weather conditions improve.
Plant Wilts Due To Excessive Heat.
Very hot weather stresses rose bushes. When it is 90°F. or more, they use food faster than their foliage can manufacture from sunlight, water, and nutrients. Do not over prune roses in these conditions. In extremely hot, sunny areas consider fashioning a lath covering over part of the rose garden to give some shade during the hottest part of the day. Move roses in containers to partially shaded locations.
Parts of Plant Are Winter Killed Because Plant Was Winterized Too Late.
Sudden changes in temperature in the fall, before the plant has hardened off for the winter, can be disastrous. Early freezes kill more canes than much colder winter freezes. To discourage new growth that can be destroyed by an early freeze, avoid late summer feedings of nitrogen and hold back on water. If a very early cold spell is expected, cover the rose bush with white, polyspun garden fleece over night to give it some protection.
Rose Bush Does Not Have Uniform Growth In the Spring Due To A Mild Winter.
Sometimes after an unusually mild winter in the North, the branch tips of rose bushes may remain bare. Sometimes the side buds on some canes will fail to grow because they were not chilled enough to induce normal growth. Prune out such canes.
New Roses Slow to Start Possibly Because Plants Have Dried Out.
Do not allow new roses to dry out, either before or after they are planted. Soak new bare root plants 6 to 24 hours before planting. Water generously while planting, and if it is unusually hot, keep the canes moist after planting by shading them with some moist burlap or garden fleece.
Leggy Plants With No Blooms Indicates Not Enough Sun.
If roses do not get 5 to 6 hours of good sun each day they will become leggy and may not produce any blossoms at all. The only solution is to move the plant to a better location.
New Foliage Discolored, Dies From Soil Problems.
If the new foliage on rose bushes dies or is stunted, yellowed and off-color, it may be due to soil problems. Overfertilization leads to excessive salts in the soil. Suspend use of chemical fertilizer for the year. Water the affected bushes heavily twice-- first to put the excessive salts into suspension, then a day later to leach those salts from the soil. Use organic or slow-acting granular fertilizer as recommended. The problem may be that the soil is too alkaline (pH over 7.5). Sprinkle a handful or two of powdered sulfur on the soil around the affected rosebush. Mulch with slightly acidic peat moss (about 3 inches deep) around the plant. Use fertilizers formulated for acid-loving plants until the foliage regains its healthy color.
Some Other Diseases
Growth On Roots May Be Due To Crown Gall.
If a rose bush is not doing very well, and upon close inspection you spot a rough, tumor-like growth near the soil or on the roots, your rose has crown gall. It is a bacterial disease that often gains entry through wounds inadvertently made with cultivating tools. If any galls are present, prune them off and seal the wound with tree paint. Disinfect the knife before reusing it in a solution of hot water and household bleach.
Canes Swell and Are Discolored Because Of Stem Canker.
After a severe winter, stem canker of roses often becomes obvious during the early spring months. Keep a close watch for the appearance of red or brown discolored areas on the rose stems. Swollen and discolored dead areas on rose canes may be the result of infection of the soft tissue just under their surface. Infected canes commonly split open, exposing underlying tissues, and sometimes bleeding a gummy exudate. The disease can progress downward, thus killing major limbs. This is common canker or stem canker that occurs in wounds on canes and in the cut ends of pruned canes, especially if the cut is not made close to a bud. Prompt pruning of the infected cane is the best control. Take care to prevent spreading of the canker disease organisms by dipping the pruning shears in household disinfectant or hot water mixed with household bleach.
Distorted Growth, Excessive Thorns and Witches’ Brooms.
Roses producing distorted growth and branches covered with soft thorns of red or green in color along with leaf clusters known as witches’ broom have contracted Rose Rosette Disease.
