Plant Health Problems
Diseases caused by Physiological/Environmental Factors:
Bud drop, physiological.
Buds discolor and drop before opening. The cause is physiological, due to some adverse environmental factor related to humidity. Moving from one location to another, too much heat or dry air, or waterlogging or dryness at the roots may contribute to this trouble.
This problem can be minimized by maintaining constant levels of high humidity and uniform moisture levels in the potting mix. It is also helpful to maintain temperatures around 70 F and to avoid high temperatures, especially at night.
Chlorosis, iron deficiency.
This is probably the most common and important problem on gardenia. Leaves appear yellow or chlorotic and have green veins. Growth may occasionally be retarded and highly symptomatic leaves may drop. In most cases, the condition is associated with the unavailability or deficiency of iron in the potting mix.
Chlorosis can be avoided by using a fairly light, slightly acid potting mix. Applications of iron chelates in water may help to increase the availability of iron and cause the leaves to "green-up" within a few weeks after the application.
Fuller rose beetle, Asynonychus godmani.
This weevil sometimes injures gardenia. Roses and many other plants in greenhouses as well as outdoors are sometimes injured by Fuller rose beetle which feeds on the leaves at night and rests in the leaves or in some protected place during the day. This is a brown weevil marked with patches of gray scales on fused wing covers. Only females exist. It varies in length from 1/4" to 3/8" (7-9 mm). The eggs are laid under the edges of bark near the ground or directly on the ground and can be found throughout the season. The white legless grubs live in the soil and chew upon the roots of various plants. At maturity, they measure about 1/2" (10-12 mm). This weevil overwinters as a pupa near the soil surface or as an adult in a protected spot. Adults do the most damage. Control treatments are rarely needed. When the infestation is light, handpicking the insects is a possibility.
Greenhouse orthezia, Orthezia insignis.
This insect is a dark-green or brown scale-like insect that secretes wax as it feeds, leaving behind a long plate of white wax. It damages plants by withdrawing sap. When needed, malathion, which is among the compounds registered for control of this pest in Connecticut, can be applied according to label directions. Imidacloprid, applied as a soil drench, will provide season-long systemic control.
Soft scale, Coccus hesperidum.
These scales are often found on gardenia. This soft scale is very thin, oval, and semi-transparent. It infests many different greenhouse plants including ferns. Any control sprays may need to be repeated if only the crawler stage is controlled. The remedy is to spray with insecticidal soap or horticultural oil, which are among the compounds registered for control of this pest in Connecticut. Imidacloprid, applied as a soil drench, will provide season-long systemic control. Consult the labels for dosage rates and safety precautions.