UNIVERSITY OF ILLINOIS EXTENSION HOME, YARD ARDEN PEST College of Agricultural, Consumer and Environmental Sciences, University ofG Illinois at Urbana-Champaign &Illinois Natural History Survey, Champaign NEWSLETTER No. 2 • April 20, 2005 cankers. Copper compounds are usually applied PLANT DISEASES before green tip (when the tips of green leaves begin Watch for Fire Blight to emerge from buds). Copper products may include Fire blight is a bacterial disease that causes concern Camelot, Champion, Chipco Aliette, Junction, Kocide, to growers with apples, pears, crabapples, and orna- Magellan, Nu-Cop, Phyton 27, and others. Antibiot- mental Callery pears. You might also see infection on ics are used in commercial fruit-production areas to other rosaceous hosts, such as cotoneaster, hawthorn, prevent fi re blight. Sprays are made during bloom, quince, fi rethorn, and mountain-ash. Fire blight is specifi cally when no more than 10% of the blooms are caused by a bacterium (Erwinia amylovora), and the open on the tree. There are few antibiotics available or bulk of the infection occurs during fl owering when recommended for ornamental plants. It is best to rely temperatures are warm (mean daily temperature of at on nonchemical management practices to control fi re least 60°F) and conditions are wet. The causal bac- blight on ornamental plants. terium may spread by wind, water, equipment, and A few other helpful management tips include avoid- animals. Rain or insects may move the bacterium from ing high-nitrogen fertilizers that promote lush suscep- cankers and bark to open blossoms, vigorous shoot tible growth, removing water sprouts when they are tips, and leaves. As long as warm, wet conditions small, and removing nearby neglected pear and apple continue during bloom, the bacterium can continue trees. (Nancy Pataky) to infect. Management practices focus on controlling the bacterium during fl owering. The bacterium is also Steps in Diagnosing a Plant Problem known to cause infection directly through wounds Many of you feel very comfortable trying to diagnose made during a hailstorm. a plant problem, readily separating the noninfectious Look for water-soaked or wilted new growth that from the infectious causes or quickly distinguishing quickly turns brown to black and remains attached to insect injury or site stress. Still, I know from telephone the stem. Also, dark cankers may develop in the wood, inquiries that others are uncomfortable making such especially on edible and ornamental (Callery) pears. diagnoses and have requested some help. Here are Because the bacterium originates on old cankers some step-by-step suggestions on how to go about and bark infection, removal of branches killed by fi re diagnosing a plant problem. blight is extremely helpful in disease control. This Above all else, do not let anyone rush you into a di- should be done when the tree is dormant or after the agnosis. “On-the spot” diagnoses and partial informa- infection, when weather is hot and dry. Disinfecting tion are the most direct route to a misdiagnosis! This pruning equipment is an important step is reducing may cause unnecessary expense, concern, and delay in disease spread. Use 10% household bleach or similar getting to the actual cause of the problem. disinfectant between cuts. Step 1. Identify the plant species. In fact, knowing If you are thinking of planting new trees, do a bit of the cultivar or hybrid may also come in handy. If you searching for resistant varieties. It will be well worth know the host, you can eliminate many problems that your search. Among the ornamental Callery pears, wonʼt occur on that host, and you can start looking in ʻAristocratʼ and ʻAutumn Blazeʼ have good resistance reference books, on Web sites, or in fi les for problems reports. Also refer to the University of Illinois Report that might occur on that host. For instance, sudden on Plant Disease on fi re blight at http://www.ag.uiuc. stem tip necrosis and death on crabapples could be the edu/~vista/horticul.htm. result of fi re blight infection, but that disease will not Pesticides may be used for fi re blight prevention. occur on redbud. A dormant (early-season) application of copper may Step 2. Determine what is wrong. This may seem be of some benefi t to kill bacteria as it oozes from obvious, but sometimes drooping foliage, variegated 2 No. 2 • April 20, 2005 leaves, or bark splitting is normal for a species. Some- often associated with site stress, so donʼt be too quick times the yellowing of leaves is a problem, while to blame only this disease. We have seen cases where other times it is a cultivar quality. spider mites, root rot, and even weed trimmer injury of Step 3. Dig out the facts. This is probably the the trunk were the major problem, but Rhizosphaera most important part of the diagnostic process. Details was present and was the only problem addressed. on symptom expression are much more useful that There may be more than one problem on a plant. Rhi- generalizations such as “my plant is dying.” The pres- zosphaera often accompanies other problems. ence of fruiting bodies, mushrooms, conks, bacterial The disease is Rhizosphaera needle cast; and the ooze, insects, insect parts, insect trails, odd growth, cause is a fungus, Rhizosphaera kalkhoffi i. Blue or information on anything abnormal can help the spruce is most often infected, while Norway spruces diag nosis. Critical information includes a description are resistant. Infection is favored by wet weather, but of the pattern of the problem over the entire planting symptoms do not often show for 12 to 18 months after and a description of the pattern of the problem on one initial infection. Rhizosphaera needle cast may cause affected plant. For instance, the problem might occur severe defoliation of spruce, a species that does not only along one side of the property and only on one refoliate readily. A few years of infection may cause a side of all plant species. Such a description would very unsightly and weakened spruce. Fungicides are strongly suggest a wind or weather stress or possibly often recommended for control, but such fungicides a chemical drift. As another example, only a few of are preventives, meaning that you apply the fungicide the pines are affected, and they have suddenly turned before new infection occurs in a given year. The usual brown over the entire tree. This might involve a root series of events is the positive identifi cation of Rhizos- problem or possibly pine wilt. Finally, it is helpful to phaera in year 1, followed by use of a fungicide in the know how things have changed on the site just before spring of year 2. It may be necessary to use cultural the problem was manifested. Often this information controls, as well as fungicide sprays, for several suc- leads us to investigate cultural problems, construction cessive years until the disease is under control. Two injury, weather stress, or the like. sprays are recommended for control of this fungus–one Investigate conditions around the plants, weather, when the bud caps have fallen off and another about chemicals, and any other facts that might have a bear- 2 or 3 weeks later. Chemical options for commercial ing on symptom development. growers include Camelot, Chlorostar, Daconil, Echo, Step 4. Consult references. There are textbooks Kocide, Manicure, Protect T/O, Spectro, and Two- that list problems by host; books on insect problems, Some. Home growers can choose a labeled chloro- diseases, chemical injury, nutritional problems, and thalonil product, such as Dragon Daconil or Ortho the like. There are university fact sheets, Web sites, Daconil. Tables at the end of disease chapters in the and advice from specialists. Start with a general plant pest management handbooks list the active ingredient problem reference that lists many problems for each and mobility of chemicals mentioned. Company names host. Extension offi ces have many useful references to are also listed. Pick a product that works best for you, get you started. but read and follow label directions carefully. Refer to Step 5. Determine probable cause(s). At this the Home, Yard, and Garden Pest Guide or the 2005 point, you might want to ask for diagnostic help if you Commercial Landscape and Turfgrass Pest Manage- are uncertain. There is always the University of Illi- ment Handbook. nois Plant Clinic! Check out the Plant Clinic services Remember, there are many other noninfectious at http://plantclinic.cropsci.uiuc.edu/. Most Illinois problems that can mimic this disease. A few possi- Extension unit offi ces also have Master Gardeners bilities include an imbalance in soil pH, poor fertil- who have been trained to help in plant problem diag- ity, fertilizer or chemical burn, root injury, root rot, nosis. The Master Gardener Web site is http://www. drought stress, and spider mite infestations. To confi rm extension.uiuc.edu/mg/. (Nancy Pataky) the presence of the pathogen, look for fruiting bod- ies (pyc ni dia) on the discolored needles. It might be Rhizosphaera Needle Cast of Spruce necessary to place some affected needles in a moisture Rhizosphaera needle cast of spruce is seen frequently chamber (plastic bag with moist toweling) overnight to in Illinois. This fungal disease causes one-year-old encourage growth of fruiting bodies. Look for pin- needles to turn purplish brown before they drop. The head-sized black structures poking out of the needle newest growth remains green and healthy. The pattern through stomates. A hand lens is usually required to on the tree is usually scattered hot spots, giving areas observe these structures, which occur in rows. They of thinned foliage scattered in the tree.