Rose of sharon leaf

Yellowing Rose Of Sharon Leaves – Why Rose Of Sharon Has Yellow Leaves

Rose of Sharon is a hardy plant that usually grows in difficult growing conditions with very little maintenance. However, even the toughest plants can run into trouble from time to time. If you notice your rose of Sharon has yellow leaves, you’re understandably perplexed about what has befallen this trusty late summer bloomer. Read on to learn a few of the most common reasons for rose of Sharon leaves turning yellow.

What Causes Yellow Leaves on Rose of Sharon?

Poorly drained soil is one of the primary reasons for rose of Sharon leaves turning yellow. The moisture can’t drain effectively and soggy soil suffocates the roots, which causes drying and yellowing rose of Sharon leaves. You may need to move the shrub to a more suitable location. Otherwise, improve drainage by digging a generous quantity of compost or bark mulch into the soil.

Similarly, overwatering may be the culprit when leaves turn yellow on rose of Sharon (especially when overwatering is compounded by poorly drained soil). Allow the top 2 to 3 inches of soil to dry, and then water deeply enough to soak the roots. Don’t water again until the top of the soil is dry. Watering in the morning is best, as watering late in the day doesn’t allow sufficient time for the leaves to dry, which may invite mildew and other moisture-related diseases.

Rose of Sharon is relatively pest resistant, but pests such as aphids and whiteflies may be a problem. Both suck the juices from the plant, which can cause discoloration and yellowing rose of Sharon. These and other sap-sucking pests are usually easily controlled by regular applications of insecticidal soap or horticultural oil. Remember that a healthy tree, properly watered and fertilized, is more resistant to infestation.

Chlorosis is a common condition that frequently causes yellowing of shrubs. The problem, caused by insufficient iron in the soil, is usually ameliorated by applying iron chelate according to label directions.

Inadequate fertilization, especially lack of nitrogen, may be the cause for rose of Sharon leaves turning yellow. However, don’t overdo, as too much fertilizer can scorch the foliage and cause yellowing. Excessive fertilizer can also burn the roots and damage the plant. Apply fertilizer only to moist soil, and then water well to distribute the substance evenly.

By George Weigel/The Patriot-News

Q: I have a rose-of-sharon tree that is several years old and about 6 feet tall. Every year, it gets lots of buds, but only about half end up opening up. The rest dry up and fall off. Is this some kind of disease or bug? Is there something I can do for the tree to produce more flowers?

A: A few things can cause buds to drop like this. My leading guess would be drought stress.

This species (Hibiscus syriacus) survives drought well, but one coping mechanism it has is dropping some of its prolific flowers to conserve energy and moisture. The drop often happens when we get a good rain following a dry spell – conditions most of us had after that sudden heat wave in early June. The antidote is keeping the soil consistently moist, i.e. giving it a good weekly soaking when it gets really hot and dry.

Bugs can also abort flower buds. Aphids would be a likely culprit on rose-of-sharon, but you’d be able to see these crawling around and excreting a black, sticky substance all over the leaves near the flower buds. If you see signs of that, just hose them off with a stiff blast of water for a few days until they give up.

A third and less likely possibility would a fungal disease called botrytis. There are chemical fungicide sprays to control that, but they have to go on early in the disease. I’d try the rain/watering angle first and also check for aphids.

I personally would rather sacrifice half of the flowers each year rather than get into spraying if neither of the first two ideas helps.

Rose of Sharon Disease

tahiti hibiscus image by Xavier MARCHANT from Fotolia.com

Rose of Sharon is scientifically known as hibiscus syriacus and more commonly as althea or althaea. It needs little care and only regular watering to thrive. Rose of Sharon is resistant to most diseases but can still contract a few, primarily fungus diseases. Good planting and maintenance practices will prevent most of the diseases from affecting the Rose of Sharon.

Leaf Spot

Leaf spot is a fungus that can affect a wide variety of plants, including Rose of Sharon bushes. Circular or patchy brown or black spots often with a yellowish edge appear on leaves first. Next, the leaves begin to fall from the bush. Left untreated, the loss of leaves can kill the bush. Remove and destroy any leaves with spots. Also remove and destroy any leaves that have fallen around the base of the bush. Treat the bush with foliar fungicides to prevent the spread of the fungus to the rest of the bush.

Powdery Mildew

Though it causes very little damage to most plants, powdery mildew is an unsightly fungal disease that affects Rose of Sharon bushes. It appears as grayish or white spots on the leaves, stems buds and flowers. It can cause leaves to curl and drop and cause buds to become deformed. The fungus overwinters in plant tissue and releases spores in the spring. Most often it can be left untreated. If the disease returns year after year, it may need to be treated by moving plants to a sunny, dry location and removing all dead debris from around the plant. Treat with a fungicide at the first sighting of spots in the spring to be effective.

Botrytis Blight

Botrytis blight, also known as gray mold, attacks the unopened buds of the Rose of Sharon bush. The foliage looks fine and buds form in the usual way but give the appearance of rotting from the inside out. Botrytis blight is a fungus. All buds should be removed from the bush. Any fallen leaves or buds should also be removed and destroyed as the fungus overwinters in the debris. Treat the bush with foliar fungicides to prevent the spread of the fungus to the rest of the bush.

Cotton Root Rot

Cotton root rot is prevalent in alkaline soils like those found in Texas. In some areas the disease is called Texas root rot. Leaves and branches will wilt and die but remain attached to the plant. The disease is diagnosed by examining the roots of the affected plant at a 10X magnification to identify light brown strands or webs. The fungus invades the soil and the bush should be transplanted to a container using sterilized potting soil. Soil treatment must be done by a licensed applicator at one- to two-year intervals. Only plant specimens that are resistant to cotton root rot in affected soil.

Canker

Canker is inverted blisters that form on the bark of shrubs and trees. Fungi cause cankers on the trunks and branches. At some point during the growing season, the cankers will ooze sap. Leaves may turn yellow and drop on established wood while new shoots may not develop leaves at all. Left untreated for several years, canker can kill the bush. Once canker is discovered, the affected limb should be cut off. If the outbreak is on the main trunk, the tree may need to be replaced as there is no treatment for canker. The best prevention is to follow good care management.

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