July 29, 1994
Bacterial canker of tomato has been diagnosed recently in the Plant Disease Clinic. The disease is caused by the bacterium, Clavibacter michiganensis subsp. michiganensis. The disease can be devastating to tomato production, however, the disease appears sporadically from year to year and may be more severe in dry years.
Crabapple and apple leaves showing symptoms of cedar-apple rust have been arriving in the Plant Disease Clinic. This disease is easy to recognize. Initially the rust fungus causes small yellow spots on the upper surfaces of leaves. These spots enlarge and turn bright yellow-orange. They are commonly 1/4 inch in diameter. As the disease progresses, raised tubular structures are formed on the lower surface of the leaves, directly under the spots. Spores are released from these structures and travel to a nearby susceptible red cedar or juniper host.
The geranium, Pelargonium xhortorum, is widely grown in flower beds, containers, and hanging baskets. A wide variety of flower and foliage colors are available. From the true orange flower of 'Orange Appeal' to the fluorescent shade of 'Orbit Violet' there is surely a color to coordinate with any landscape plan. Flowers are packed densely on umbels rising above the plant foliage. Flowers may be single, double, or semi-double. In past years, most varieties were grown vegetatively from cuttings. Today, many varieties are available from seed.
Turfgrass management in late summer and early fall is extremely important. Proper practices can help maintain a vigorous lawn or revive a declining lawn. These practices include mowing, fertilization, dethatching, aeration, weed control, and seeding.
The newsletter two weeks ago discussed both the strawberry root weevil (SRW) and the imported longhorned weevil (ILHW). See page 109.
ILHW has finished the adult stage now in most areas and is no longer a problem. The SRW, on the other hand, is still emerging and the number of calls and samples is increasing.
The yellownecked caterpillar is a common site on crab apple, pin oak and birch trees. Other fruit and shade trees may be infested also. This insect is named for the large yellow dot that appears behind the head (where the neck would be, if caterpillars had necks) of mature larvae. Small caterpillars do not have the characteristic yellow spot though a light colored area may be visible. Small larvae are purplish, with slender white lengthwise stripes. Very small larvae feed in a cluster but as they grow they disperse throughout the entire tree.
Yellowjacket wasps, like the hornets and paper wasps, live in colonies that increase in size throughout the summer. Finding and eliminating wasp nests around the house and in the landscape now prevents potentially bigger problems in the fall. Yellowjacket stings are quite painful, but the wasps are usually not aggressive except when disturbed at the nest.