Larvae feeding on the shell produce chemicals that change it into an incubating gall. The appearance of each gall is specific to the kind and number of larvae it shelters. The larvae remain small until the gall approaches its full size, when their growth rate increases as they consume its nutritious inner tissues.
Oak Tree Leaf Identification Has Never Been Easier Than This
Research into exactly how the entire process works is ongoing. Oak leaves with red gall clusters are probably hosting one of three cynipid species. Clusters of red, fuzz-covered caterpillarlike structures on leaf backs shelter crystalline gall wasp Andricus crystallinus larvae. Cynipid leaf galls seldom damage oaks seriously enough to require treatment.
Pruning heavily infested leaves may improve the appearance of small trees, but isn't practical on large ones.
Oak Leaf Blister is Common Now
The best way to protect your oaks from gall damage is to maintain their vigor. The California Oak Mortality Task Force recommends spring feeding stressed trees with 2 to 4 pounds of actual nitrogen per 1, feet of root zone from a slow-release, granular high-nitrogen fertilizer. A fertilizer with an "N" number of 20 contains 20 percent nitrogen, so scattering 20 pounds of it evenly over the outer two-thirds of the root zone and watering it into the soil provides 4 pounds of actual nitrogen.
In Mediterranean-climate regions, watering the outer two-thirds of and established oak's root zone to a depth of 1 or 2 feet in spring alleviates the effects of unusually dry winters.
Crochet Oak Leaves – IN THE YARN GARDEN
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Home Guides Garden Pest Control. Cynipid Wasps More than species of cynipid wasps use oak trees as egg-laying sites. Life Cycle Leaf-feeding cynipid wasps' survival depends on the adults emerging from their galls to lay eggs just as the oaks' new spring foliage is emerging.
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Red Galls Oak leaves with red gall clusters are probably hosting one of three cynipid species. The oak wilt fungus invades the water-conducting tubes of oak trees, eventually causing leaves to wilt and die.
All oaks are susceptible to the disease, but oaks in the red oak group, such a red, pin and shingle oaks are more susceptible than oaks in the white oak group, such as white, bur and swamp oaks. Trees in the red oak group typically die within a few months of infection. Infected bur oak trees may survive a number of years with the disease, and white oak trees may survive for 20 years or more with the disease.
Oak wilt causes loss of leaves and death of branches. Anthracnose, on the other hand, can cause defoliation, but new leaves typically emerge as time progresses. Anthracnose is most commonly observed on lower branches in the spring, especially if extended wet conditions occur, whereas oak wilt symptoms may appear throughout the tree. Symptoms of leaf loss and branch death related to oak wilt are most often observed as conditions become hot during the late spring and summer months. In contrast, the seriousness of anthracnose tends to lessen as the summer progresses.
Diagnosing oak wilt can be difficult. Other factors, such as construction injury, drought stress, advanced tree age and borer activity can contribute to dieback of branches and can be confused for diseases caused by fungi.
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A close look at a sample in a laboratory can be helpful. Anthracnose can be diagnosed by using a microscope to look for specific fungal structures on the underside of leaf tissue.
Oak wilt is diagnosed by culturing branch segments from affected areas in the trees. Samples should be collected for several different symptomatic branches. Place the samples in a plastic bag and ship in a sturdy container. They should be kept cool and shipped as quickly as possible. Include detailed background information about the tree and the surrounding site conditions.
Pictures or digital images are very helpful in diagnosing oak problems, but are not a substitute for a good sample of affected tissue. Paula Flynn, Plant Pathology, , pflynn iastate. You are here Home. Sick Oak Leaves — Serious or Superficial? Contacts : Paula Flynn, Plant Pathology, , pflynn iastate. Yard and Garden. Anthracnose , lesions , leaves , fungi.