What Is Wrong With My Japanese Kerria?

Are there any reddish spots with dark borders on leaves, lesions on stems may have formed?

Are there any small, angular, gray-brown spots with defined darker red-brown margins on leaves?

Are the leaves skeletonized?

Blumeriella kerriae causes Leaf and twig blight in kerria plants. On the leaves, infection shows as reddish spots with dark borders and, if numerous, leaves yellow and fall. Stem cankers are produced as discolored more or less extended darkened areas which may crack open to reveal the black fruiting bodies beneath. Raking and composting of fallen leaves and pruning out any infected twigs are designed to reduce the inoculum. Control can also be achieved with the use of fungicides before symptoms are severe.

These symptoms indicate fungal disease - Septoria leaf spot. Remove and destroy infected plant debris. Don't handle or brush against plants when they are wet. Rotate plantings. Remove weeds growing nearby.

Skeletonized leaves are caused by Japanese beetles, pests that can seriously damage foliage. Handpick adult beetles into a can of soapy water but make sure to wear gloves as Japanese beetles are blister beetles. Apply parasitic nematodes to the soil to limit beetle grub populations. Use pyrethrin powder or neem oil as a last resort.

Mineral deficiencies can cause tip chlorosis or necrosis or cause foliage to discolor, fade, distort, or become spotted, sometimes in a characteristic pattern that can be recognized to identify the cause. When nutrient deficiencies occur, nitrogen and iron are the most commonly seen deficiencies. Apply only the mineral found to be deficient. Excess nutrients, on the other hand, cause symptoms like leaf tip dieback, marginal leaf chlorosis, necrosis (or burn), branch dieback, and pest problems. In this case, you should provide good drainage, and use good practices during fertilization and irrigation.