Alternaria leaf spot on scheffleras (Brassaia actinophylla) was very common when I worked at the University of Florida. Individual spots coalesce into large necrotic areas and leaf drop can occur. In many cases, these older cultivars have been supplanted by newer cultivars (see Figure 3, below). Alternaria Leaf Spot This disease is caused by the fungus Alternaria cucumerina and causes small, circular, tan spots to appear on the leaves, which later enlarge to 1½ inches or more in diameter. In a number of plants, such as zinnia, the infection originates in contaminated seed. These individuals are today’s movers and shakers who are already setting the pace for tomorrow. 75 Applewood Drive, Suite A ‘Tropicana Rose’, ‘Tropicana Bright Eye’, ‘Tropicana Blush’ and ‘Paraso’ had consistently lower levels of Alternaria leaf spot than the others. On petunia, the disease is characterized by small spots that are initially water-soaked. This species has a very wide host range, including antirrhinum, asclepias, calathea, callistephus, chrysanthemum, clarkia, dahlia, ficus, hedera, helianthus, hibiscus, oenothera, pelargonium and petunia. Learn how to manage this disease. Prevention is the best method for controlling leaf blight of cucurbits. 1,2). Get one year of Greenhouse Product News in both print and digital editions for free. Definite concentric rings and margins appear that give the area a “bull’s eye” appearance. For example, helianthus (sunflower) is attacked by A. alternata, A. helianthis, A. helianthinficiens and A. zinniae. Common on tomato and potato plants, early blight is caused by the fungus Alternaria solani and occurs throughout the United States.Symptoms first appear on the lower, older leaves as small brown spots with concentric rings that form a “bull’s eye” pattern. Early blight can be caused by two different closely related fungi, Alternaria tomatophila and Alternaria solani. Certain fungicides are effective in controlling cucurbit alternaria leaf spot. Lesion centers may fall out, giving the leaf spots a shot-hole appearance. This class of fungicides does not control Alternaria (or any closely related fungus) and should not be used for this purpose. Make no more than 2 sequential applications before switching to a fungicide with a different mode of action. Initial symptoms are small black spots about 1mm in diameter. Although Alternaria diseases are quite common on many ornamentals, they have not received much attention in recent years. Spots caused by both fungi are small, ranging from the size of … The disease is caused by A. panax and is characterized by large (up to 2-inch) black spots on schefflera but also attacks aralia, dizygotheca, panax and polyscias. Spread of Alternaria diseases from one type of flower to another can occur with some species (like A. alternata) so control measures must focus on all susceptible plants. Plants were sprayed three times on a 10-day interval, with inoculation four days after the second application. Under their field conditions marigolds are very susceptible to Alternaria leaf spot. In the early 1990s this disease was very common but is less so these days. These lesions develop into characteristic 'target-spots', 5mm to 15mm in diameter, with light and dark concentric rings. As this trial clearly shows, strobilurins are very effective, while phosphonates are ineffective. The spots turn black as the fungus produces spores. light brown spots on the upper sides of older leaves on cucurbit plants. Bacterial Slow Wilt or Stunt: Wilting, twisting, curling and stunting of lower leaves and side shoots followed by death of lower leaves. This disease was first found in Florida but has been reported in other states (especially in the South). Alternaria Leaf Spot on Geraniums. Primarily, removing diseased plants upon detection and at the end of the season will deter further development and spread. The late spring and summer seasons bring warmth and humidity to California’s almond orchards. Alternaria leaf spot on alstroemeria is most common in cut flower production. Eventually, infected foliage drops from the plant, which can cause the fruit to become damaged by wind, sunscald or ripen prematurely. In contrast, tests with either vinca cultivars or rainbow pinks did demonstrate a number of cultivars with significant resistant to Alternaria leaf spot (see Figures 2 and 3, page 40). Strobilurins can be very effective but occasionally not as good as the zinnia graph shows. Many trials have been completed in the past few years on Alternaria leaf spots on ornamentals, including marigold, zinnia, impatiens, dusty miller and poinsettia (see Figure 4, left). In spring, new plants can be infected by contact with infected garden surfaces and the splashing of rain or watering. IVIA factsheets, Instituto valenciano de investigaciones agrarias, Spain, 2015, Spanish language External factsheets Spanish Alternaria blotch is most likely to occur on Delicious strains and should not be confused with Marssonina blotch, frogeye leaf spot, captan spot, or Golden Delicious necrotic leaf blotch. They generally move by splashing water or by very strong winds. Leaf spots sometimes develop a target-like pattern of rings. are dark brown to black and appear in felt-like black masses on leaf and petal spots when conditions are ideal. Leaf spot develops most rapidly in June and July, and trees can be almost completely defoliated … The Alternaria genus contains over 250 known species, including Alternaria alternata (by far the most common species), Alternaria tenuissima, Alternaria infectoria, Alternaria chartarum, Alternaria stemphyloides, Alternaria geophilia, and Alternaria dianthicola.All these species are isolated from infections. This fungus can over winter in garden debris. This disease is most often found on landscape Geranium spp. Alternaria alternata: Causes leaf spots, blights, and rots on over 380 plant types. One such disease that thrives in the warmth of midsummer that follows wet spring weather is alternaria leaf spot on cucurbits. Howard F. Schwartz, Colorado State University, Bugwood.org, Watermelon Alternaria Leaf Spot Control – Treating Leaf Blight Of Watermelon Crops, Diseases Of Pumpkins: Learn About Pumpkin Diseases And Treatments, Alternaria Leaf Spot: How To Treat Alternaria In The Garden, Holiday Garden Baskets: How To Make Christmas Hanging Baskets, Planting A Giving Garden: Food Bank Garden Ideas, Giving To Food Deserts – How To Donate To Food Deserts, Easter Flower Ideas: Growing Flowers For Easter Décor, Winter Grass Control – Tips For Managing Winter Grass, Marshmallow Peep Control – How To Get Rid Of Peeps In The Garden, What Is Tomato Leaf Mold – Managing Tomatoes With Leaf Mold, Recipes From The Garden: Pressure Cooking Root Vegetables, Gratitude For The Garden – Being Grateful For Each Growing Season, 7 Reasons To Do Your Garden Shopping Locally, Thankful Beyond Words – What Represents Gratefulness In My Garden. 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