Q: I have a 4-inch diameter Wisconsin weeping willow that has three baseball-size swellings on the trunk about 4 inches from the ground. Are these harmless deformities, or something I should be concerned about?
A: Many shrubs and trees, especially those in the rose family but also almond, apricot, cherry, cypress, euonymus, hibiscus, lilac, peach, raspberry, viburnum, walnut and willow trees are susceptible to a fascinating bacterial disease called crown gall. The crown of a plant is the section of trunk next to the soil, and a gall is a tumorlike growth on a plant stem.
The bacterium lives in the soil and enters the plant through a wound. It multiplies within the plant for a while and then transfers its tumor-inducing genetic material into the host-plants cells, where it is maintained as though it were part of the host plant's genetic material. Afterward, since the bacterium isn't necessary for the tumor, the bacterium cells within the plant die off.
The resulting gall can range in size, from hardly visible to over a foot in diameter. The cells within the gall are not organized into the typical food- and water-conducting tissues of the plant, so the growth of the plant above the galls can be disrupted and weakened. And since this gall is typically at the bottom of the plant, the plant is usually of no future value. The gall often becomes infected with other bacteria and fungi that cause more health problems. However, some plants last for years with only cosmetic damage. And some galls occur on the plant roots, so they are not visible until the slow-growing and sick-looking plant is dug up. If your willow appears healthy, you can leave it until it starts to weaken.
Because of the bacterium's ability to transfer its DNA into other plants and cause abnormal function, this bacterium is useful in the genetic engineering of plants. I won't describe the complicated procedures, but it has resulted in some interesting plants.
Tomatoes can release an enzyme called polygalacturonase that degrades the pectin in the fruit. By transferring a gene that inhibits the tomato plant from releasing polygalacturonase, the fruit can be left on the plant longer to accumulate more flavor, which will give the fruit a better taste.
Some varieties of cotton, soybean and canola crops have new genes that cause them to be more immune to the effects of herbicides that contain the weedkiller glyphosate. The herbicide can be sprayed on the crops and weeds at the same time, but only the weeds will die.
Q: Toward the end of the summer, our red-twig dogwood bush got a severe fungus. What do you recommend to prevent this from happening, and what product should be sprayed?
A: Dogwood shrubs and trees are both susceptible to many fungal diseases that attack the stems, trunks and leaves. In the fall and winter, remove all fallen leaves from around the plants. Cut out all dead and dying wood. The shrubs can be cut completely down to the ground, but you lose one of the few reasons to plant red-twig dogwoods: the color red in the winter landscape.
Next spring, begin spraying the plant with a fungicide as the new growth begins to come out, and do so as long as the spring weather stays wet and cool. Often, the infection occurs in the spring but the visible signs do not show up until there is more stressful weather in summer or fall.
Dogwood trees do not like to be flooded, so if they are in low areas where the trunk could get waterlogged, they should be moved to higher ground. Do not pile lots of mulch around the stems of any trees or shrubs, but especially the dogwoods.
Email questions to Jeff Rugg at firstname.lastname@example.org. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.