You don’t have to be a collector to appreciate the wide range of color and form found in the dahlia family. Slugs, snails and cutworms produce topical damage that is visually obvious and reduces plant health and attractiveness. Sign up to get all the latest gardening tips! A soil-borne fungus, it is a common contributor to seed rot and pre-emergent … Sclerotinia minor only infects stems or leaves in close contact with the soil. Slugs and snails may be controlled with diatomaceous earth or slug baits. Sign up for our newsletter. As if there weren’t enough dahlia pests and diseases, the tubers are very susceptible to freezes, which makes the plants a challenge, but a worthy one, to northern gardeners. Watch for common dahlia problems and nip them in the bud quickly for continued blooms and healthy plants. These exciting and diverse blooms are fairly easy to grow, but there are a few problems with dahlia that may limit their production and even their health. 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Knowing what to watch for is half the battle in keeping your prized plants healthy and beautiful. More sinister complications can arise in your dahlias which can sometimes kill the plant permanently. The culprits are usually caterpillars or some form of larvae. Pythium’s white cobwebby growth (mycelium) can often be seen on dew-covered grass in early morning. Horticultural soaps and blasts of water can minimize their presence. Fusarium can infect dahlia roots and tubers, even ... Signs. Plants eventually wilt and collapse. Infected dahlia tubers will break down, soften and ultimately rot. In addition to the caterpillars and larvae, sucking insects are probably going to be the biggest issue with the most widespread offenders being: Although these are relatively tiny pests, their habit of sucking sap from the plant can diminish its health, cause stunting and distorted plant parts and even transmit disease. Rot will often proceed up the stem eventually causing the plant to yellow and die. These may include: Numerous insect pests find dahlias delicious. Tuber rot in dahlias is caused by a species of fungus, Fusarium, commonly found in soil. Once infection takes place, water-soaked brown necrotic areas develop. Look for a white ring in the... Mosaic virus – Mosaic virus dwarfs plants and distorts leaves. Start with healthy tubers first. Find more gardening information on Gardening Know How: Keep up to date with all that's happening in and around the garden. Two species of Sclerotinia spp. Tuber Rot on a Dahlia. Healthy, chubby tubers are crucial to big bountiful dahlias. Causes. Those amazing flowers known as dahlias are no exception. It is common to find new leaves completely chewed, lacy and barely still there. Dahlia pests and diseases are usually confined to sucking insects and fungal problems but a few diseases can actually kill the tubers. Avoid overhead watering and use a horticultural fungicide. Fungal issues such as powdery mildew are another universal complaint. These may include: Stem rot – Stem rot occurs when dahlias are growing in heavy, poorly drained, wet soil. You will have little chance of huge bunches of flowers if your tubers are scrawny, moldy or rotting. The first signs of trouble in your plants is often just as they sprout and develop leaves. Hand picking may be the solution to beating these types of problems with dahlia. Hunt at night with a flashlight and use the “squish” method of pest control for cutworms. By: Bonnie L. Grant, Certified Urban Agriculturist. Among the most common dahlia diseases are those caused by fungi, such as powdery mildew and gray mold. You must destroy the plant, as there is no cure. Phytophthora (spp) – rot is related to Pythium and as one of the fungi in the oomycete class, has similar symptoms and treatments as Pythium. Several types of borer are also dahlia flower pests. Systemic fertilizers may offer some protection if applied early in the season. These feed on leaf tissue and make Swiss cheese of the foliage, diminishing the plant’s ability to intake solar energy. can cause disease on dahlias. Dahlia flower pests tend to reflect the sap drinking forms but can also encompass leaf eaters such as a wide array of caterpillars and larvae.