ALABAMA A&M AND AUBURN UNIVERSITIES Fire Blight on Fruit Trees and Woody Ornamentals ANR-542 ire blight, caused by the bac- Fterium Erwinia amylovora, is a common and destructive dis- ease of pear, apple, quince, hawthorn, firethorn, cotoneaster, and mountain ash. Many other members of the rose plant family as well as several stone fruits are also susceptible to this disease (Table 1). The host range of the Spur blight on crabapple fire blight pathogen includes cv ‘Mary Potter’. nearly 130 plant species in 40 genera. Badly diseased trees and symptoms are often referred to shrubs are usually disfigured and as blossom blight. The blossom may even be killed by fire blight phase of fire blight affects blight. different host plants to different degrees. Fruit may be infected Symptoms by the bacterium directly through the skin or through the The term fire blight describes stem. Immature fruit are initially Severe fire blight on crabapple the blackened, burned appear- water-soaked, turning brownish- cv ‘Red Jade’. ance of damaged flowers, twigs, black and becoming mummified and foliage. Symptoms appear in as the disease progresses. These Shortly after the blossoms early spring. Blossoms first be- mummies often cling to the trees die, leaves on the same spur or come water-soaked, then wilt, for several months. shoot turn brown on apple and and finally turn brown. These most other hosts or black on Table 1. Plant Genera That Include Fire Blight Susceptible Cultivars. Common Name Scientific Name Common Name Scientific Name Apple, Crabapple Malus Jetbead Rhodotypos Apricot, Cherry, Plum Prunus Kageneckia Kageneckia Avens Geum Loquat Eriobotrya Brambles Rubus Medlar Mespilus Chokeberry Aronia Mountain Ash Sorbus Cinquefoil Potentilla Mountain Avens Dryas Cliff Rose Cowania Ninebark Physocarpus Cotoneaster Cotoneaster Osteomeles Osteomeles Cratnegomespilus Cratnegomespilus Pear Pyrus Creambush Holodiscus Pearlbush Exochorda Dichotomanthes Dichotomanthes Peraphyllum Peraphyllum Docynia Docynia Photinia Photinia False Spirea Sorbaria Quince Cydonia Firethorn Pyracantha Rose Rosa Flowering Quince Chaenomeles Serviceberry Amelanchier Goatsbeard Aruncus Spirea Spiraea Hawthorn Crataegus Stranvaesia Stranvaesia Indian Hawthorn Rhphiolepis Strawberry Fragaria Japanese Rose Kerria Toyon Heteromeles www.aces.edu pear. The stems and midribs of Soft, succulent shoots are very Control diseased leaves often turn black vulnerable to the disease. Mature A control program combining as well. As the twig and leaf apple and pear tissues are much resistant varieties, sound cultural blight phase progresses, leaves more resistant to infection than practices, sanitation, fertilization, die, curl downward, and cling to young tissues. Cultural practices and pesticides is needed to pro- the blighted twigs. Succulent favoring rapid shoot growth in- tect plants from fire blight. Culti- twigs, shoots, and water sprouts crease the plants’ susceptibility to vation and fertilization practices are easily infected. The tips of attack. These practices include se- that produce rank, succulent blighted twigs, shoots, and vere pruning, excessive nitrogen growth increase the possibility sprouts droop, producing the fertilization, and an unbalanced that the disease will develop. Do typical “shepherd’s crook.” fertility program. not cultivate pear and apple or- Leaves may be infected through Warm, moist conditions, par- chards late in the season, and do pores as well as wounds. ticularly during flowering, greatly not severely prune susceptible Cankers form at the base of increase incidence of the disease. cultivars. Regulate plant growth blighted twigs and spurs. The Blight development can occur at and apply fertilizers so that mod- bark surrounding a developing temperatures between 65° and erate shoot growth is maintained. canker first appears water- 95°F, but the 75° to 81°F range is Beginning in late winter to early soaked, then later sunken and most favorable. Temperature ex- spring and continuing through the dry. The surface of bark cover- tremes will slow development of growing season, remove all root ing the canker is usually smooth the disease. In regions with mild sprouts and suckers from trees. and sometimes has a purple winter temperatures, cankers may All diseased tissue (blighted twigs color. Reddish-brown streaks can increase in size during the fall and branches) should be re- be seen in the sapwood under and winter on trees with a sou- moved as soon as possible to the discolored, sunken bark. therly exposure. Rain is critical to slow the spread of the disease. Amber-colored discharge can the spread and development of Prune diseased wood about 12 to often be seen near blighted tis- the disease. Fire blight outbreaks 14 inches below visible cankers sues of the plant at any stage of are encouraged by warm, cloudy during the growing season, and 6 infection. weather following a rain. A to 8 inches below cankers in the humid environment promotes fall or winter months. Clean your Characteristics bacterial growth and spread. tools with a solution of isopropyl Other weather events like frost, alcohol or other disinfectant after The fire blight pathogen, high winds, and hail create Erwinia amylovora, is a rod- each cut to avoid spreading the wounds through which the bacte- bacteria. shaped bacterium that overwinters ria can enter the plant. in tissues around the edge of The first chemicals used for cankers on large branches and the control of fire blight were limbs. A gummy, amber-colored copper fungicides like copper hy- discharge oozes from cankers dur- droxide (Kocide 101 at 2 to 4 ing warm, humid weather. The pounds per 100 gallons of water discharge, which contains bacte- between silver-tip and green tip ria, is dispersed by insects or on apple and pear) and copper splashing rain to blossoms, leaves, sulfate (Tri-Basic Copper Sulfate and shoots (see drawing on next at 1⁄2 pound per 100 gallons of page). Dried bacterial discharge water on pear only). Recommen- often forms strands which are car- ded spray schedules are listed on ried by wind. the product labels. These com- pounds provide effective control Susceptibility to fire blight Typical ‘Shepherds Crook’ often depends on: (1) cultivar charac- under light to moderate disease seen at the end of fire blight- pressure but can cause fruit rus- teristics, (2) maturity of tissue, damaged shoots. The brown color and (3) weather conditions. Pear of the blighted leaves indicates that seting on some apple and pear flowers are invaded very rapidly this blighted shoot is on apple or varieties. Copper fungicides that through nectaries and pistils, crabapple. are cleared for fire blight control which are ideal sites for growth on woody ornamentals may be of the bacteria. Apple flowers phytotoxic to crabapple and are usually invaded through stig- some other plants. mas and anthers. Copper hydroxide (Kocide 2000 T/N/O at 0.75 pounds per 100 gallons of water or 1.5 2 Disease Cycle of Fire Blight Blossom and leaf blight Bacteria enter Bees carry bacteria uncuticularized to blossoms flowering parts Bacteria Primary splashed Secondary Cycle to blossoms cycles and twigs Blighting of twigs and limbs Insects pick up ooze Bacteria oozing from from edge of holdover infected cortex canker Canker at base Bacterial cells of diseased shoot teaspoons per gallon) and cop- Spray (0.5 teaspoon per gallon per sulfate pentahydrate (Phyton of water) are recommended 27 at 20 to 40 fluid ounces per every 4 to 5 days during the 100 gallons of water) will give bloom period. Begin spraying some protecation from fire blight just before the center flower in on woody ornamentals. See the the cluster opens and continue comments for streptomycin sul- applications through petal fall. fate for instructions on optimum For best results, make applica- application timing for the control tions in the late afternoon or of fire blight. Kocide 2000 will early evening because strepto- damage the foliage of crabapple mycin breaks down in sunlight. but is safe to use on Indian Aphids, leafhoppers, flies, hawthorn, loquat, hawthorn, and ants play a major role in photinia, pyracantha, and flow- spreading the bacteria from ering pear. Refer to the label of cankers to blooms and new each fungicide for additional growth in the spring. These in- directions on product use. sects should be monitored and The antibiotic streptomycin controlled with insecticides if (Agrimycin 17) will give better necessary before bloom occurs. control under higher disease The surface of this perennial fire Bees do not feed on bacterial pressure than the copper com- blight canker on the main trunk of ooze but will spread the disease pounds, and does not cause fruit pear is cracked and dry. Note the from infected to noninfected russeting. When using these dead branch stub in the center of blossoms during pollination. products, start spraying as soon the canker. Insecticides used during bloom as bloom begins because strep- will kill the bees, but pollination tomycin is ineffective against fire will also be prevented, greatly blight once infection occurs. reducing fruit set. Protective sprays of Agrimycin Many popular trees and 17 at 100 ppm (8 ounces of for- shrubs are resistant to fire blight. mulated product per 100 gallons Establishment of disease-resistant of water or 1 tablespoon per 21⁄2 plants is an inexpensive, easy, gallons of water) or Fireblight 3 and effective means of control- Resistant firethorn cultivars ling fire blight without the need include Pyracantha coccinea cv. for chemical treatments. Some Sensation, P. koidzumii cv. Santa shrubs and small trees resistant Cruz Prostrata, and hybrids San to fire blight are listed in Table Jose and Shawnee. The firethorn 2. Refer to Table 3 for reaction cultivars Apache, Fire Cascade, of some apple and pear varieties Mohane, Navaho, Pueblo, to fire blight. Rutgers, Shawnee, and Titon are The reaction of selected resistant to both fire blight and crabapple and flowering pear scab. Cotoneaster selections re- Note the reddish-brown discol- cultivars to fire blight is listed in sistant to fire blight include C.