Diseases Of Hibiscus

Phytophthora

This group of fungi is responsible for the wilt disease related to soils that become arid during the summer and are damp during the winter. This soil-borne plant disease has the potential to destroy several ornamental shrubs, counting hibiscus. It is quite difficult to keep away from the conditions that are conducive for phytophthora, as the plants affected by this fungi group usually never recover. However, this problem is rare when hibiscus is provided with sufficient compost and grown in soils having excellent drainage.

"Collar rot"

This condition is evident in the form of a discoloration at the root joint, which turns brownish and usually greasy. Collar rot is more prevalent in places where the winter months are cool as well as damp and especially when the soil drainage system is not adequate. This condition can be treated by removing the entire stem as well as bark and by applying a coat of Bordeaux paste with a paint brush. In addition, clear the ground adjoining the plant completely and spray a potent garlic solution in the area. As sclerotina rot damages the stems close to the ground level, you should apply a potent garlic solution or an infusion prepared from chamomile on a regular basis to overcome the problem. It is not advisable to plant a new hibiscus in the same place where you had a plant earlier and that died due to rot. However, in some cases it may be necessary to do so and if this is the case with you too, you should first enhance the site. Begin with removing the dead plant and burning it. Subsequently, excavate the entire area further than the root depth and spread of the previous plant's roots and dump the infected soil in a distant, but unimportant area, for instance to elevate a portion of your yard or plug a hole or crack in the driveway. According to some gardeners, it is best to light a fire and spread the flames all over the infected site with a view to killing all the pathogens and then refill the place. When this is done, start refilling the site. In order to ensure proper drainage, first place a stratum of pumice combined with gravel over some coarse materials like small stones and sand. Finally fill the hollow using new topsoil. In order to ensure that the new plant is not infected by pathogens, use a disinfected potting mix. Apart from the various types of soil diseases, the foliage can also be affected by different fungal diseases. Among these, you should be careful about leaf spot and initiate immediate measures if you notice this happening. It has often been found that plants grown in pots or containers are somewhat more vulnerable to fungal diseases compared to those grown in open ground, particularly when the potted plants are not placed in a well ventilated area. Presence of dark spots or deep brown spots on hibiscus leaves is an indication that they are inhabited by pathogens and these microbes are full of live during damp weather conditions. If you find that a leaf does not have isolated dark spots, but has been discoloured, you should known that that particular leaf has been infected heavily. Such infected leaves will drop on the ground depleting the shrub of its green leaves. This problem can be solved effectively by applying any good fungicidal spray like Bordeaux. You can purchase liquid Bordeaux from retailers selling gardening products. Alternatively, you may also prepare an effective fungicidal at home by blending calcium hydroxide - Ca(OH)2 - and copper sulfate (CuSO4). These two chemicals in less diluted form along with skim-milk powder are used to prepare Bordeaux paste. Skim-milk powder is used to make the paste gluey. Generally speaking, applying good compost and mulching the hibiscus are the most excellent means to prevent root rot. In addition, sprinkling dolomite on all over the area around the plant may also prove to be effective. Moreover, you can prepare a common spray for preventing various fungal infections. Prepare a "weak" infusion or tea from comfrey, nettles, horseradish or yarrow and apply it on the affected areas. Applying a diluted liquid of seaweed steeped in fresh water is even four times more beneficial. This liquid serves as an excellent foliar fertilizer, a fungicide, an insect repellent, and to promote resistance against frosts. In addition, the seaweed that is left behind can be used to mulch the plants or turned into compost.

Solutions to other problems

Sparse foliage: Often hibiscus plants are affected by sparse foliage. This is in addition to problems like infestation by insects and general undernourishment. To avoid this problem, ensure that you provide your hibiscus plants with utmost sunlight.
Crinkled leaves: A creased or wrinkled leaf is another problem with hibiscus. To avoid this problem you need to check if there is any leaf hopper or aphid on the underside of the leaf. In fact, aphids can form large colonies underneath the leaves and they have the potential to draw out the life sap from the leaves even before you notice the problem. However, if you notice any infestation by aphids, remove the leaves immediately together with the pests. In case of severe infestation, spray herbal pesticides.
Deformed and sickly foliage: In case your hibiscus is regularly exposed to systemic insecticides, the plants will become sick quickly and may also die eventually, as the chemicals in the insecticide go into the plant and poison it. In fact, hibiscus cannot endure systemic chemicals like maldison. Feeding the plants properly and watering them regularly will help them to overcome this problem.
Yellow leaves: Don't panic if you find yellow leaves at the base of the stem or the lower branches of your hibiscus, as this may occur as a natural process with the trees shedding their old foliage. However, it is an altogether different issue if the leaves on branches higher up on the tree start turning yellow, particularly at their growing tips. When this occurs, it indicates that the plant may be suffering from a deficiency of iron or magnesium. You can add these vital minerals to the soil to overcome the problem. On the other hand, such discoloration of the leaves may also indicate that the plants are being fed and watered excessively. It also denotes that the plants might have been provided with too many chemical fertilizers. Therefore, discontinue with both. In addition, yellowing of the leaves is also an indication of them being exposed to systemic or chemical insecticides.
Yellow leaves with green veins: If you find the leaves of your hibiscus turning yellow while their veins are still green, be sure that the plants are suffering from insufficiency of iron. In such situations, you need to provide the plants with a nourishing compost and manure with some amount of seaweed or kelp meal. Often gardeners are advised iron chelate, particularly to help the plants overcome the deficiency. Use this by lightly digging up the soil at the plant's base and avoid packing it firmly around the stem. In addition, you can also mulch the plant away from the stem's base, as this is also helpful in overcoming the problem.
Other leaf discoloration: Apart from becoming yellow, hibiscus leaves may also suffer from other types of discoloration. This problem can be overcome by light feeding and watering the plants. If the windburn is persistent and continues for a long period it indicates that the windy climatic condition may not be appropriate for your hibiscus hybrids. You can overcome this problem if you replace the hibiscus hybrids with coastal species that can endure strong winds. Sometimes salt toxicity is also attributed to the leaf margins turning brown. Water the plants generously to get rid of this problem. On the other hand, potassium deficiency may cause the leaves to turn brownish at their tips or become purple along the edges. In addition, brittle leaves are also an indication of potassium deficiency.
Frost damage: Hibiscus growers should shelter their plants from frosts, because if they are damaged by frost they can do nothing to help the plant recover. If the damage is severe, it is unlikely that the hibiscus will recover. On the other hand, if the damage is somewhat light, the hibiscus will fight back itself to produce fresh growth during spring. In case your region is prone to frosting during winter, it is advisable that you grow your hibiscus in pots so that you can take them indoors or other places for shelter during this period.
Weeds: Weeds are detrimental for the growth of hibiscus, as they compete with the plant for nutrients. Therefore, it is essential to get rid of all weeds in the vicinity of hibiscus. Bear in mind that the hibiscus' feeding roots are in the layer close to the soil surface and they rely on the same layer of the soil for food that is encroached by weeds. The simplest means to get rid of weeds in the vicinity of your hibiscus is to clear the soil prior to mulching the area. In fact, mulching will deter weeds.
Lawn encroachment: If you are growing your hibiscus in your lawn, it is essential to keep an area of about 1 square meter (3 square feet) clear of any growth that has the potential to compete with hibiscus. Mulching the plant will put off the grass from encroaching the hibiscus.
Lichen: You may often find green, gray, or silver lichens established on old and mature hibiscus trees. While they are unlikely to disturb the plant, they may be a problem for the gardener. In order to damage the plant, lichens need to cover and choke the entire shrub. To get rid of the growth of lichen, just remove it using a brush. Alternatively, you may also use a Bordeaux paste during the winter.
Ants: There are several ant species that are considered to be beneficial predators for hibiscus gardens. These specific ants invade hibiscus only if the plants have something to feed them. However, there may be occasions when an ant gets drawn to the plants nectar. In general, ants climb a hibiscus for the honeydew expelled by mealy bugs or aphids. Eliminating aphids will help to deal with the ants too. It is important to mention here that presence of moisture deters ants, while the number of ants may be more in arid places. In addition, you may use pyrethrum spray to get rid of ants. Alternatively, you may also use Vaseline to band the hibiscus trunk's base to put off ants from climbing up the tree.
Poor flowering: Often even healthy plants may produce very few flowers. It may occur from excessive shade or due to feeding the plants with too much nitrogenous substance even when grown in proper sunlight. Such excessive feeding encourages leaf growth at the cost of producing flowers. In addition, it can also be attributed to bud damage.
Buds but no flowers: Sometimes you will notice that your hibiscus produces buds, but they do not blossom. In fact, this happens when the buds are invaded by beetles and borers, who enter the buds even before they can open. In such cases, the soil will provide you with evidence of the problem. This problem can only be dealt with by getting rid of all the buds, from the bush - counting the branch tips, as well as those lying on the ground below. Burn these affected buds and follow up by spraying insecticidals. In fact, this will only help to lessen the problem, but not solve the problem permanently. In addition, bud drop can also be attributed to absence of watering the plants when the weather is warm and sunny. Therefore, you should never allow your prized hibiscus plants to dry.
Flowers appear late in the season: At times, your favourite hibiscus may bloom late. Often this can be attributed to the sun and temperature. It is possible that the plant is not receiving enough sunlight and warmth. In other words, the temperature may not be favourable. So site the plant in the sun.
Blooms change color: The hibiscus hybrids that are available these days are a fall-out of intensive hybridizing undertaken over several years by crossing one plant variety/ species with another and, sometimes, even backcrossing them to get the sought after properties. Therefore, even after these hybridized plants have been crossbred several times, sometimes they show the dominant attributes of their parent plants or earlier ancestors. Therefore, your hibiscus may sometimes produce flowers having hues of their earlier form. Occasionally these plants may also revert from ruffled to being unruffled, double to single, or change from windmill single to just plain single. It has been found that this occurs most frequently when the plants bloom out of season. However, you may expect the flowers to have their actual colors and forms during summer and the fall.

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