Leaf Spot Treatments for Gardenias

Bacterial Leaf Spot

• Bacterial leaf spot first causes small, water-soaked spots to appear on young gardenia leaves. As the round spots grow larger, the light yellow center turns red-brown with an outer yellow halo. These spots often merge to form big, irregularly-shaped areas of damaged tissue. Severe infections can cause your gardenias to defoliate. According to the University of Rhode Island, the only course of action is to remove the diseased plant tissue and discard or burn it immediately to avoid spreading the infection. You can prevent bacterial leaf spot by not using overhead watering methods or letting your gardenias sit out in the rain. Use only sterilized pots and soil to prevent spreading leaf spot disease.

Cercospora Leaf Spot

• Cercospora leaf spot disease is caused by a fungus and looks similar to bacterial leaf spot. Symptoms of Cercospora leaf spot include small brown spots of damaged plant tissue surrounded by yellow halos. Severe infections often cause premature leaf drop. The University of Rhode Island recommends treating Cercospora leaf spot with a foliar fungicide appropriate for gardenia plants. Follow the directions on the manufacturer's label to apply the fungicide properly. Help prevent this disease by avoiding overhead watering methods and spacing your gardenias far enough apart to promote ample air circulation.

Rhizoctonia Leaf Spot

• Rhizoctonia leaf spot is a fungal disease that causes brown or tan spots to form on gardenia leaves. These spots reach up to 1/4-inch in diameter and first appear on older leaves before spreading upward. Over-watering and overcrowding promote the spread of this leaf spot disease. Treatment involves pruning out the affected foliage and destroying it immediately to avoid spreading the infection. Prevention includes pruning out dense plant tissue to promote better air circulation and keep water from lingering on the gardenia leaves.

Myrothecium Roridum Leaf Spot

• According to the University of Florida, Myrothecium roridum leaf spot typically shows up only on wounded, stressed or broken gardenia leaves. The infected spots look watery and typically contain concentric rings of white and black fungal fruiting bodies. High levels of humidity and warm temperatures promote the spread of this disease. Prevent this infection by handling gardenia foliage carefully to prevent breakage. Keep the leaves as dry as possible by avoiding overhead irrigation. Prune out affected foliage and dispose of the diseased material immediately. Treat this leaf spot disease by applying a fungicide appropriate for gardenia plants. Follow the instructions on the product's label and thoroughly douse all plant tissue, including the stem, the leaves and the crown.

Considerations

• Healthy gardenia plants are far less likely to contract any type of leaf spot disease. Gardenias prefer full sun locations when kept indoors and partially shady locations if sited outdoors. Gardenias prefer loose, organic, evenly moist soils with good drainage. They also need humidity, but you should avoid misting the leaves since that promotes the growth of leaf spot disease. Regularly inspect your gardenias for tissue-damaging insects, particularly spider mites, aphids, scale and thrips.