HAVE YOU SEEN THIS IN YOUR ROSE GARDEN THIS SPRING?
Every Spring we receive a number of questions about unusual occurrences gardeners report finding in their gardens. Some can be a problem and will require intervention on the part of the gardener and others are just natural occurrences that will go away once the weather warms up and the bushes have a chance to grow.
The new growth sprouting on some rose bushes that is very red or burgundy colored is a phenomenon often reported at this time of the year. Gardeners worry that this is some sort of nutrient deficiency and wonder what they should do to correct the problem.
Red Foliage is not a disease or deficiency but just the way some roses produce their new growth in Spring. As the leaves mature, they will turn a good shade of acceptable green. Interestingly the bushes producing red new foliage are more often than not red flowering roses.
Instead of producing flower buds at the tips, a few to many new shoots have no flower buds at all. Blind Shoots is a problem most often reported in spring. Its cause is thought to be caused by low light levels and cool weather common to our Spring weather.
This issue can be easily corrected by simply pruning back the Blind Shoots to a lower bud just above a five leaflet leaf and the next shoot will produce a flower bud.
Most often seen in Spring, Proliferation seems to affect certain rose cultivars year after year but can been seen from almost any rose. Proliferation is not a disease but caused when the apical cells are multiplying so fast that they do not stop dividing when a flower is produced, but they keep on dividing and produce a cluster of new buds in the center of the earlier flower. If the condition bothers you, simply prune off the affected flowers and the next flower produced by that stem should be normal.
Again most often seen in cool moist Springs, Balling seems to affect certain rose cultivars more than others. ‘Tropicana’ and ‘Montezuma’ are roses that come to mind when someone complains of this problem. Balling seems to affect very double flowered roses in cool wet weather, where the petals stick together and the flowers fail to open properly. If left on the bush too long, flowers will turn brown and fuzzy grey, a condition caused by the common fungus Botrytis. Again, the solution to the problem is to deadhead the affected blooms and new flowers should be normal. If Balling is a problem seen often enough, the solution might be to remove (prune with the shovel) the offending bushes and plant roses that do not have the problem!
Flowers fail to open normally and just sit on the bush turning fuzzy grey. Botrytis Blight is caused by the common fungus Botrytis cinerea and is most often seen in the cool moist weather of our Southern California Springs.
Optimal conditions for Botrytis Blight are temperatures in the range of 59° with high humidity and moisture. Once again, the best solution for the problem is to remove (deadhead) offending flowers early and new growth should be normal once the environmental conditions improve.
Mature rose canes start turning black and dying. Sometimes called Canker, this problem is caused by any number of common funguses and other agents. Often the Dieback will progress down an infected cane and the whole cane and in worst cases the whole plant will die.
Dieback can become a major problem if the affected canes are not pruned back into healthy green tissue early. Improper pruning practices can help the problem become established in the garden. Never leave stubs when pruning. Always prune within a 1/4” of a healthy bud and do not leave stubs jutting above the targeted bud. Such stubs will start to die back and often the entire cane will die if the problem is not pruned out early enough. The only remedy is to prune back affected canes to healthy green tissue or remove entirely.
Always a problem locally in cool moist springs, Aphids can overwhelm a gardener in a few days if corrective measures are not taken early in the infestation. Sometimes called Green Fly, Aphids are always born female and hungry. A sucking insect, they insert their needle-like feeding parts into the cell of a plant and feed on the sugars produced by photosynthesis. Large infestations of Aphids will produce black sticky covering on lower leaves. This is caused by a fungus feeding on the sugars not consumed by the Aphids.
Many gardeners reach for their chemical sprays the moment they see an Aphid. Aphids are only a problem in our cool weather; once we start warming up, they burn off and go away. Using your hands to rub off a few aphids on a stem or flower bud will help. In larger infestations, a firm stream of water will wash most Aphids off the bush. If the aphids keep coming back, you might have an ant problem. Ants are known to “farm” aphids, harvesting the sugars these insects expel. In that case cleaning up the ant problem will help to limit the aphid population on your roses. If you feel you must use a chemical intervention, consult your county Agricultural Advisor or a local nursery for their recommendations.
Rose Mosaic Virus (RMV)
Some rose leaves have different patterns of yellow and green in blotches, spots, or flame-like patterns. Caused by a number of viruses, RMV is not a problem that can be corrected once observed on a plant.
RMV is not thought to spread from rose to rose as do other plant viruses by contact or infected tools. RMV can only be spread during propagation by using infected cuttings or by grafting a healthy shoot onto an infected rootstock. RMV will not kill a plant outright but will weaken the plant and the infected bush will produced smaller numbers of flowers over time.
The only way to get rid of RMS in the garden is to remove (prune with a shovel) infected plants and then demand healthy plants from your nursery or supplier.
Gardeners often report strange brown papery looking egg cases in the garden. Do not remove these egg cases as they protect the eggs of a most desirable good insect, the Praying Mantis. Praying Mantises eat aphids and any number of harmful bugs and are worth twice their weight in gold! Lucky is the gardener who finds multiple Praying Mantis egg cases in the garden!
If you see rose leaves, stems, and buds covered by a white cottony-looking growth, you have Powdery Mildew. Roses are most susceptible to Powdery Mildew in the cool, moist weather of our Springs and Fall. This fungus will attack one rose and leave another alone. If you grow roses in Southern California you can expect to see some Powdery Mildew on your rose bushes from first growth (March) up until the 4th of July when our day temperatures are hot enough that the fungus can no longer grow. We often see some Powdery Mildew again in our cool, moist Falls.
Optimum conditions for Powdery Mildew are temperatures around 68° F. and near 100% humidity--in other words, Spring. Planting roses with enough space between shrubs to encourage air movement and full sun will help prevent some of those conditions favorable to the problem. Also high rates of Nitrogen fertilizers will produce soft, succulent new growth which will also be more susceptible to the fungus and Aphids. The other best recommendation I could give is to try to select Powdery Mildew-resistant roses. If you must use something to control the problem, try one of the fungicidal soaps on the market. One home remedy often used is to make your own spray solution out of baking soda, vinegar, and either a horticultural oil or good old Canola cooking oil. For each one gallon of spray, mix in 1 tablespoon each of the baking soda, vinegar, and canola oil. Do not apply any spray containing oil on a day that will go above 80° or you will burn the foliage and the bush will drop all its leaves! If you must use a commercial fungicide, then again the best advice is to check with your county Agricultural Advisor or a nursery.
Seeing red pustules on the underside of rose leaves? That is Rose Rust and is usually more of a problem in our Fall weather. For some reason we are seeing some Rust in the garden earlier than usual. Rust is another problem caused by a fungus; there are nine species of the rust fungus Phargmidium that attack roses. Spores that are carried by the wind spread funguses and when conditions are optimal, they infest our roses. Wet leaves for two hours or more and temperatures between 64° and 70° are enough to get Rust established on our roses.
If the infestation is light simply pick off the infected leaves and dispose in the trash. Again, planting with full sun and spacing bushes so that they are not crowded will help but if a particular bush seems to be infested year after year then prune with the shovel and dispose of your ‘Typhoid Mary’! The home remedy mentioned under Powdery Mildew will help, but again, if you must resort to chemicals then check with your Agricultural Advisor or a nursery for their recommendations.
Leaves show small black spots that converge and form larger roundish black lesions that are caused by the Blackspot fungus Marssonia rosae. Normally not a problem in dry Southern California, we do see the problem in wet, humid weather. Blackspot is a major problem of the South, East, Northwestern, and Mid-Western regions of the US with summer rain and high humidity. Those of us lucky to live in the warm dry Southwest with no summer rain seldom see Blackspot in our gardens.
If just a few leaves are showing symptoms pick them off and dispose in the trash. Blackspot will not be a problem for us in the hot dry days of summer. If you must spray, try the home remedy mentioned under Powdery Mildew. If you decide to use a chemical intervention then consult your county Agricultural Advisor or a nursery.
Often this time of the year gardeners will see foamy, disgusting-looking masses on the stems and leaves of soft herbaceous plants. The nymphs of the appropriately named Spittlebug cause this. Once winter is over and Spittlebug eggs have hatched, the newly emerged nymphs begin feeding and produce the frothy spittle masses to protect themselves from predators. Even a bug will not eat a Spittlebug so protected!
Not usually seen on roses, an infestation of Spittlebugs can be cleaned up with a strong spray of water washing away the foamy spittle masses.
Less often seen in gardens or understood Downy Mildew (Peronospora sparsa), does not look like the more common fungus Powdery Mildew. Only a problem in cool, humid weather, Downy Mildew is commonly seen on the canes and stems of infested roses. Symptoms appear as purple to black lesions on the canes but can be seen on leaves as well. Some rose cultivars seem to be more susceptible to infestations of Downy Mildew and should be pruned with the shovel and removed from the garden.
If Downy Mildew is suspected then you should check with your county Agricultural Advisor for their recommendations.
Nearly every gardener worth his soil will recognize a Lady Bug! One of the “good guys,” Lady Bug nymphs and adults are aphid-eating machines. Every gardener should encourage Lady Bugs to take up residence in their gardens. Today, a gardener can purchase Lady Bugs from their local nursery or via the internet. Nymphs are sure to stay in your garden because they have not developed wings yet but adult Lady Bugs are most often seen for sale. When releasing adult Lady Bugs around your garden wait until the evening just at dark as they will not be so likely to fly away. Also place small shallow trays of water around your garden as the Lady Bugs will be thirsty and a cool drink will encourage them to stay and dine a while longer in your garden.