MIDSUMMER
ROSE GARDEN CARE (July-August)
by
Albert Ford, Editor, MRS Newsletter
Quick Links:| Spraying| Discoloration Of Leaves | Watering |
By the middle of June in Maryland, the Spring
Rose Shows have been held and most remontant roses are into their second
cycle of bloom. Toward the latter part of June average daily temperatures
reach summer levels. By July, roses begin to experience unusual stress.
Stress from the sun, from reduced moisture, from the depletion of early
spring fertilizers and from fungus and insect invaders.
If the gardener has followed the earlier
suggestions in this series concerning a regular spray program, a second
major fertilizing around the middle of June, and the roses have received
rainfall or have been watered at least an average of one-inch per week,
the rose bushes should be in good condition to meet the environmental
challenges of July and August, the Stress Months. Some additional activities
will assure continued health and flower production.
Despite spraying regularly, should Blackspot appear on lower leaves, pull them off and discard together with fallen spotted or yellowed leaflets. To leave this condition unattended simply invites the spreading of the spores of Blackspot to other areas of the plant or to other rose bushes in the garden. Splashes from rain or overhead watering transport the spores to unaffected plant areas. Spores may be airborne also from fallen leaves and transmitted by air movement.
Continue to use a wetting agent (mild dishwashing liquid) in your spray formula and to add white vinegar as a catalyst. Remember to be cautious with the use of Phaltan or systemic foliar feeding in hot weather to reduce the risk of leaf burn and further stress to the plant. To prevent leaf burn spraying is recommended in early morning or in early evening. Incidentally, July and August are not good months to experiment with new chemicals. As previously mentioned, caution should be exercised when using any chemicals. Follow the manufacturer's recommendations carefully and exactly.
Insects and other pests which may be encountered in the rose garden will include aphids, cucumber beetle, leaf-cutting bee, leaf hopper, rose budworm, rose midge, rose slug and thrip. There may be others, but those mentioned are not uncommon in this area. The drawings below together with the notes on each will help you identify them. Orthene or Isotox, both Ortho products, may be used to control them, with the possible exception of the cucumber beetle. Both products can be combined with Funginex.
Most gardeners know what Aphids look like and how to treat them. Infestations may be washed off with a strong spray of water to which a teaspoon of dishwashing soap has been added to a gallon of water. Safer Insecticidal Soap For Roses and Flowers is also effective. Aphids are easy to get rid of, but prompt action is necessary to prevent distortion of new growth and buds. This pest was written about in detail in the March-April, 1988, issue of the Newsletter.
The cucumber beetle may be the 12 spotted type, which is most common in this area, or may show stripes of alternating colors. The spots are black and contrast sharply against its greenish-yellow background. It has a black head and its body length is about 1/4 inch. The damage it does is generally confined to the open petals of buds and flowers but can be severe if unchecked. Hand-picking of this insect is arduous because it often hides between petals and at the least threat takes flight. Both varieties, however, can be controlled with Malathion 50, Sevin or Rotenone wettable powder. It is necessary to spray the buds and flowers only. The cucumber beetle was discussed in greater detail in the May-June, 1988, issue of the Newsletter.
Damage to rose foliage as a result of leaf-cutting bees is unmistakable. The outer edge of a leaflet has been sculpted out smoothly by a talented and meticulous shiny black, blue or purple bee for the purpose of obtaining nest building material. The damage is small circles or ovals on the leaf margins. What a sight it would be to see one of these sculptors at work. It is not recommended that chemicals be used to destroy the bees since they are pollinators of crops. Unsightly leaves can be pruned out; however, since the bee generally returns to the same or adjacent leaflets for additional material, it is better to ignore the minimal damage caused by this insect.
The gardener need contend with the leaf hopper twice during the course of the rose growing season, in the spring and again in late summer and fall. The adult is 1/8 to 1/4 inch long, its body is wedge- shaped, creamy white to light yellow in color. It gets its name from its tremendous hopping power when disturbed. The adult feeds from the underside of leaves by puncturing the foliage and sucking out the content of leaf cells, leaving irregular but conspicuous patterns and tiny yellow specks. It may also cause yellowing and curling of leaves. Eggs deposited in leaf veins and petioles in July produce a second generation which defaces foliage in late summer and fall. Adults may be controlled with Malathion 50, Diazinon or Orthene.
This insect is a very small larva of a fly, about 1/2 inch long and white in color. Its presence is evidenced by a sudden blackened, "burned- to-a-crisp" appearance of flower buds, leaf buds and tips of vigorous new shoots where the larva feed. A bent neck of the rosebud is also characteristic. The affected parts should be pruned away immediately and destroyed. A systemic insecticide, like Orthene, should be sprayed on the plant and the surrounding ground or mulch where the larva pupate. Prompt action is necessary because otherwise a new generation of the rose midge will develop in two to three weeks.
The rose slug is the larvae of the Rose Sawfly or the sawfly wasp and is light yellowish-green with a dark brown head; It is soft-bodied with a tapered form, and is up to 1/2 inch in length. The larvae feeds on the underside of leaves which can become skeletonized. They do not feed on buds or flowers. Some species have shiny bodies and others, like the Bristly Rose Slug, are covered with hair. An insecticide like Orthene or Cygon 2E should be sprayed on the plant giving particular attention to the underside of the leaves.
The usual symptom of the damage done by this insect is the detection of a hole in the side of an unopened bud. Should we remove the bud and cut it open the chances are one would find a yellow or green, soft-bodied, caterpillar, which is the larvae stage of certain moths and butterflies. Damage may occur also on leaves and stems. Detectable budworms may be 1/2 to 1 inch in length and also may be dark brown or black in color. Most budworms can be controlled with Orthene or if their number is limited--which is usually the case--they can be hand-picked and destroyed. Some recommend spraying with Bacillus thuringiensis (Ask for Bt), a bacterium fatal to caterpillars but harmless to plants and animals.
Spider Mites appear on the underside of rose foliage as tiny specks detectable only by placing apiece of paper under the damaged foliage and tapping the foliage with a finger. Some of the tiny spiders will drop to the paper and their movement is then detectable. Uncontrolled infestation are evident by webbing of leaves and leaf axils and a graying and curling of the leaflets. Unless prompt action is taken, spider-mites can completely defoliate a plant. Some such plants may recover; however, others may be killed. This insect is more prevalent in the southern states, yet the plants in this area are not immune, particularly those we try to carry through the winter inside where the temperature and humidity is favorable for their growth. On first noticing this insect's presence a strong stream of water should be directed to the underside of the leaves and repeated every three days for three or more times. If caught early, this water treatment seems to work. Advanced infestations on miniatures grown inside have not responded to water or to miticides which I have tried. In Texas the rose gardeners have reportedly had good success with Avid, a relatively new product on the market.
The first evidence of the presence of thrips is flecked petals and deformed flowers, especially on white varieties. Adult thrips are very active, tiny, slender, brownish-yellow, winged insects. Damage is inflicted by nymphs (tiny, white and wingless insects) and adults thrips sucking the plant sap through holes rasped primarily in tender young tissue of leaves and buds. An infected bloom will show evidence of several rows of tiny holes in the outer petals. Robbed of nutrients, the bloom does not open or is considerably disfigured. Since egg laying occurs in buds and new upper foliage, such parts should be removed and destroyed. Preventative spraying of buds and top growth with Malathion, Diazinon or Orthene can prevent damage occurring prior to a rose show. This can be done by misting the buds and blooms with Orthene and water in a discarded but clearly marked Windex spray bottle or other suitable applicator. Spraying for infestations should include the ground or mulch since the nymph of the thrip moves down the canes to pupate in the ground, after which the adult emerges to repeat the process. The egg to adult cycle takes about two weeks.
In the above instance, the discoloration is a uniform yellowing and is usually confined to the lower part of canes close to the ground. These leaves are older and have outlived their usefulness and their loss should not be cause for concern. Should the yellowing of lower leaves be more widespread with all canes involved and the yellowing extends well above ground level, a deficiency of magnesium may be the cause. This condition can be corrected by the application of magnesium sulfate or Epsom Salts. Try two tablespoons to a large bush worked into the soil and watered in. Repeat this procedure after three months if the condition persists.
General yellowing of newer upper leaves may result from an iron deficiency. The leaves may also be light green and the veins will remain dark green. The effect is a change in coloration between the veins. The cure for iron deficiency is iron chelate available at most nurseries. If the soil is alkaline, with a pH of 7.0 or more, sulfur should be used to bring the pH into the slightly acid range for the iron chelate to be most effective. The amount of sulfur will depend on the difference between the observed pH and 6.5, a good target pH for roses.
Should the leaves appear smaller than usual for the variety and the coloration is pale green to yellow and sometimes accompanied by red spots, nitrogen deficiency may be the culprit. If these symptoms are accompanied by stunted and weak canes, few basal breaks and a drying of the leaves followed by early leaf fall a classic case of nitrogen deficiency exists. To correct the condition the addition of nitrogen in the form of urea, ammonium sulfate, ammonium nitrate, or a soluble fertilizer with at least 10% nitrogen in recommended. Should the yellowing be confined to the leaf tips and outer edges, a potassium deficiency may be the cause and can be corrected with a good balanced fertilizer like 10-10-10.
A condition of early yellowing of veins and midribs followed by browning of leaves and a general sickly plant can result from an oxygen deficiency and chlorosis caused by wet, soggy soil where drainage is poor. If this condition persists, drainage need be improved by raising the rose beds and putting stones in the bottom of the bed. Compacted soil may give rise to the same symptoms, in which case cultivation or loosening the mulch and soil will be beneficial.
On this general subject, problems can arise by having too much fertilizer in the soil. The symptoms are a curling, crinkling and drying out of the foliage. If you have reason to believe this has happened to your plant or plants it is advisable to water heavily to leach out the surplus fertilizer and to use additional care in the setting of a new fertilizer schedule. Vegetative centers occur occasionally in a number of varieties. I have seen them often on Cecile Brunner and once or twice on Double Delight. Sometimes vegetative centers can form as a result also of too much fertilizer.
The discoloration of leaves is not a cause for panic, for it may be a natural occurrence or it may call for some action from the gardener. If it is a widespread condition or you have a question about discoloration in leaves or plant health and are unsure of the cause, contact a Consulting Rosarian for assistance. Their names and phone numbers can be found on the cover page of this Newsletter.
updated October 6, 2004