The winter season can be very hard on rose bushes in a variety of ways. Read on for more information on treating winter damaged roses.
Winter injury to roses can come from strong winter winds whipping around the canes of rose bushes. I like to prune my roses down to about half their height for the winter, excluding the climbers and shrub roses. This pruning is done once there have been a string of very cold days and nights that have convinced the bushes it is time to take their winter nap (aka: dormancy).
The climbers can be tied more securely to their trellises and wrapped with a fine muslin type cloth for winter protection. The shrub roses can be pruned a bit and then also wrapped with the muslin or other fine cloth material for some added protection. This helps hold their canes together so they act more as one unit and, thus, have greater strength to hold up under snow loads and provides better wind resistance.
The damage from winter winds whipping the canes and breaking them can be pruned out in spring. However, if the wind breaks the canes off down into the ground, we can only seal the wound and encourage new cane growth (aka: basal breaks) come spring.
Epsom salt goes a long way to encouraging basal breaks. A half cup (120 mL.) of Epsom salts around all the large rose bushes and ¼ cup (60 mL.) around the miniature rose bushes should do the trick. Water in well early spring.
The best thing to do is prevent winter injury to roses in the first place by providing winter protection for roses.
Mounding rose bushes for winter helps to keep them cold so they do not get any ideas of starting to grow during those strings of warm to hot days while it is still winter time. The flux of temps during the winter can and will confuse the rose bushes, initiating the process of growing. Then the severely cold temps come again and shock the rose, many times leading to its demise.
I use garden soil, gravel, or wood mulch for mounding. I do not use any garden soil that has fertilizer added. Soil with fertilizer can help send the wrong message to the bushes on those warm winter days.
Many winters not only have cold, blustery winds but are also dry, especially for those that do not get much snow. As a result, winter moisture is needed. Forgetting to give the rose bushes a little drink during winter can easily lead to their death or stunt their growth and bloom production in the spring and summer months. We cannot water when it is cold and freezing outside. However, there are usually some strings of days when it is nice enough to do some watering.
The best thing to do is to water as early in the day as possible, usually once the temperature for the day is near its maximum. This gives the water a chance to work its way into the ground and down to the root system, also allowing plenty of time for the plant to take up moisture and put it to good use prior to the cold nighttime temps moving in again. The winds suck the moisture out of the soil, leaving the moisture level dangerously low.
There are fungi that will overwinter on the roses too. A late season spraying with a good fungicide is helpful, and something I have done for years. Banner Maxx is my late-season fungicide of choice, spraying all the plants prior to their winter’s nap. Green Cure is my fungicide of choice the rest of the year, but for this end of season treatment I like the performance I have gotten with Banner Maxx or its generic and less costly counterpart, Honor Guard.
Not treating fungus beforehand allows it to get a head start on attacking the bushes once the shrubs break dormancy and begin their new spring growth. Fungal infections stunt this new growth, leaving plants weak and limiting the bloom production and overall performance of the rose bushes.
If you notice any late season insect activity on your roses, it is not a bad idea to spray them with an insecticide or miticide, depending on the need. Always use the lightest form of insecticide that you can that will still get the job done.
Just as with other things, an ounce of prevention is worth a pound of cure! Put your garden babies to bed properly and they will reward you nicely for it.
Black spot is a common and serious rose disease often reaching epidemic proportions in a season. The disease is caused by the fungus, Diplocarpon rosae. It is most severe after long wet, warm periods in the spring. Symptoms occur on rose leaves as circular, black spots surrounded by a yellow area. Infected leaves often drop from the plant. Infection continues throughout the summer months. The immature wood of first year canes develops raised, purple-red irregular blotches. Plants become stunted and produce fewer, paler flowers. By mid-summer severely infected plants may have lost all of their leaves.
Prevention & Treatment:The spread of black spot can be reduced and future infections minimized by following these cultural practices:
Use fungicide sprays to control black spot effectively, even on resistant varieties. A rigorous fungicide program must be followed during conditions that favor disease development for susceptible cultivars. Select one of the following fungicide sprays, if disease is severe enough to warrant control: chlorothalonil, mancozeb, myclobutanil, propiconazole, or copper fungicides. See Table 1 for examples of products. Apply all chemicals according to directions on the label.
Plant during milder months of spring or fall to avoid heat or cold stress.
Choose a sunny to lightly shaded site with fertile, well-draining soil that stays evenly moist.
Place plants 2 to 5 feet apart depending on the variety, and allow for adequate air circulation to help prevent moisture-borne diseases.
Soak roots in water for at least an hour to hydrate before planting.
Winter damage can occur on many plants. A rapid temperature drop following a mid-winter thaw can cause bark splitting. Dead twigs and branches in the spring may be the result of ice and snow damage from the winter. Injury during the winter or early spring season can be from frost or freeze injury.
Foilage can turn yellow and other off colors from cold.
Some evergreens exhibit yellowing or bronzing of the needles when exposed to winter sun and wind, but return to normal color when growth resumes in the spring. Winter injury may be confused with the early stages of some fungal diseases. Needles turn from bronze to reddish brown or brown, as a result of exposure to cold, dry winter winds.
Freezing and thawing cycles can lead to browning or blighting.
Permanent damage occurs when conditions are severe, prolonged, or when temperatures change suddenly. Tissue death is caused by the removal of water in the needles faster than the plant can replace it through root uptake from frozen water in the soil. Winter scorched needles eventually drop off.
Winter desiccation can cause leaf scorch and winter burn injury.
Leaf scorch symptoms can occur on broadleaved evergreens. Damage is most severe on shallow-rooted plants such as azalea, rhododendron, holly, cherry laurel, boxwood, mountain laurel, or those at their northern limit for winter hardiness (Magnolia grandiflora, Aucuba japonica, Camellia spp. and others). Injury occurs on dry, windy, warm or sunny winter days when the ground is frozen. Plants are unable to move water from frozen soil to replace water lost from the leaves. Leaves curl and droop, then brown from the tips and margins, giving the leaves a scorched appearance. In many cases, damage occurs during the winter months but symptoms appear in the spring as the plant begins to emerge from the winter dormant period and move into the spring growth phase.
Winter burn damage on cherry laurel
Photo: Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org
De-icing salt can accumulate on leaves, causing leaf scorch.
Heavy accumulations of de-icing salts can cause leaf scorch similar to winter damage and may kill buds and branch terminals.
Leaf-scorch from de-icing salt is prevalent in the winter.
Blighted and browning can be caused by warm temperatures in February or March that stimulate buds, flowers or shoots into growth too early. Subsequent spring frost kills young buds and tender new growth, resulting in fewer flowers and later leaf development.
Diagnosis is easy because frozen tissue turns blackish brown. The damaged buds and leaves usually drop off and the remaining bare branches should be pruned out if new growth does not emerge as spring progresses. Blasted or damaged blooms can result from the freezing of flower buds in early spring before or during flowering. Branch dieback and leaf yellowing can be caused by sunscald, root damage, and cold weather following a warm spell.
Ice and snow damage can result in bent or broken limbs from the heavy weight of snow and ice. Gently remove snow from shrubs with an upward movement of a broom. Do not attempt to remove ice from shrubs because ice-laden branches are brittle and more likely to break.
This shows the result of a late freeze on new buds.
Cultural practices that conserve soil moisture, prevent root damage and promote “hardening off” prior to winter will reduce winter damage. Avoid fertilization or pruning in late summer, which stimulates late season growth that does not have time to “harden off” properly and is much more susceptible to winter injury. When watering, soak the soil several inches deep, and then allow to dry between waterings. This encourages deeper rooting. Avoid frequent shallow sprinklings, which encourage surface roots that are easily injured by drought and cold. The use of mulches conserves soil moisture and prevents temperature fluctuations. Mulches also keep the soil cold in early spring, which helps to reduce premature bud break.
Even hardy trees may develop sunscald or frost cracks. Tree bark warmed by the sun in winter can reach a temperature as much as 18 degrees warmer than the air temperature. To cambium layer beneath is damaged. This type of freeze damage is called sunscald.
Frost cracks occur when temperature fluctuations are extreme. Water in the cells of the tree trunk freezes and moves out of the cells, causing the wood to shrink. Tension between the frozen and unfrozen layers of wood is so great that the wood separates, causing a crack. The crack can form suddenly and is often combined with a loud cracking sound. When temperatures warm, the wood absorbs moisture and the crack closes. Frost cracks can reopen and enlarge in subsequent winters and may extend to the center of the tree. Damage to tree trunks in most likely on the south and west sides of the tree where the sun is strongest.
Frost cracks may begin in previously wounded or pruned areas. Proper pruning and avoidance of injury may help to prevent some frost cracks. Tree species prone to frost cracking (those with thin or smooth bark) may benefit from applying white latex paint to the tree trunk. The light color reflects light and helps to reduce temperature fluctuations. The following species are more likely to develop frost cracks: apple, beech, crabapple, elm, goldenrain tree, horse chestnut, linden, London plane, maple, oak, walnut, and willow.
The best prevention of winter injury is to select plants that are hardy in your area. Winter damage can be reduced by locating plants in partially shaded areas protected from winter winds. Place physical barriers about 18 inches away on the windward side of young trees to reduce winter injury. Barriers made from materials such as burlap or plastic can lessen winter wind damage by reducing wind velocity. Maintain adequate soil moisture in the fall to prevent winter desiccation. Inspect plants for winter damage in the spring and prune out affected areas.
Various thrips species feed on roses. Two of the most common are flower thrips (Frankliniella tritici) and western flower thrips (F. occidentalis).
Adult female thrips of both species are tiny, yellowish-brown insects with fringed or feathery wings. At less than 1 /16-inch long, they are barely visible without a magnifying glass. However, blowing lightly into the blooms and leaves causes thrips to move around, making them easier to see.
Thrips (Frankliniella sp.) damage on roses.
Both immature and adult thrips feed by scraping surface cells to suck plant sap. They feed on both leaves and flower petals with the majority of their damage to roses occurring from early to midsummer. Their feeding may result in distorted buds that open only partially or abort prematurely. Feeding on petals may result in petals streaked with silvery-white or brown as well as petals with browning edges. White and light-colored rose blossoms appear to be particularly attractive to thrips. Young leaves may be distorted and flecked with yellow as a result of thrips feeding.
Control: Control of thrips is difficult. Infested rose blossoms should be removed and destroyed. Grass and weeds in the area should be kept mowed or removed when possible. Insecticides are available but timing of sprays is very important. They must be applied before thrips enter unopened buds. In addition, because rose blooms expand rapidly, it is difficult to keep them adequately covered with insecticide. If it becomes absolutely essential to spray an insecticide, the following are available in homeowner size packaging: acephate, bifenthrin, cyfluthrin, lambda cyhalothrin, permethrin, or spinosad. Insecticidal soaps will help control thrips, but thorough coverage is necessary. The soap spray must contact the pest to be effective, and may require three sprays at 5- to 7-day intervals. Soil drenches or granular applications of dinotefuran or imidacloprid will give thrips suppression. See Table 1 for examples of brands and products.
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