Ask the ISU Extension Garden Experts: Oak Wilt, Germinating Gourd Seeds and Starting Tomato Seeds

How can I determine if my oak tree has oak wilt?  Oak wilt is a serious disease that can infect many oak species. It is caused by the fungus Ceratocystis fagacearum. Red and pin oaks are very susceptible to the oak wilt fungus and can die within four to six weeks. White and bur oaks are moderately resistant to the disease. Trees can be infected by the fungus through root grafts or by sap-feeding beetles that carry spores to newly wounded trees. When a tree is infected it tries to protect itself by producing gummy material called tyloses which clog the water conducting vessels. Water is prevented from moving to the canopy and leaves begin to wilt. Leaves of infected oaks wilt, turn brown at the edges and fall off. The outermost ring of sapwood sometimes turns brown and appears as streaks when the bark is peeled or as a ring when the branch is cut in cross-section. 

Diagnosing oak wilt can be difficult. Other factors, such as construction injury, drought stress and insect borers, can produce symptoms that resemble those of oak wilt. The best way to determine if a tree has oak wilt is to submit a plant sample to a laboratory for diagnosis. A sample submitted for diagnosis should consist of several branches that are one-half to one inch in diameter and six to 12 inches long. If possible, collect the material from several different branches that are exhibiting symptoms. The sampled branches should have freshly wilted leaves, but must be alive, as the fungus cannot be isolated from dead wood. Samples should be kept cool and dry prior to shipment. It is also helpful to include a few partially discolored leaves. In Iowa, samples can be submitted through your Iowa State University Extension county office or mailed directly to the ISU Plant and Insect Diagnostic Laboratory, 327 Bessey Hall, Iowa State University, Ames, Iowa 50011. There is a fee for this service. Additional information on submitting plant samples can be found at the clinic Web site at www.plantpath.iastate.edu/pdc. 

Are gourd seeds difficult to germinate?  Gourd seeds have hard seedcoats. To hasten germination, soak gourd seeds in water overnight or up to 24 hours. Gourd seeds also can be nicked along their edge with a file or other device. 

Gourd seeds are typically planted outdoors after the danger of frost is past. Gourds also can be started indoors. When starting gourds indoors, sow seeds in peat pots about three to four weeks before their intended outdoor planting date. Gourd seedlings should be planted outdoors after the danger of frost is past. Harden or acclimate the seedlings outdoors for a few days prior to planting. 

When should I sow tomato seeds indoors?  Tomato seedlings grow rather quickly. Ideal transplants are short, stocky plants. Sow tomato seeds indoors five to six weeks before the intended outdoor planting date. Plant seedlings in the garden after the danger of frost is past. Gardeners in southern Iowa can plant tomatoes outdoors in late April, while those in northern counties should wait until mid-May. 

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