What is it Sorghum ergot is a disease caused by a fung - PDF document

by a fungus (infects the ovaries of sorghumflowers and often converts theminto a white, fungal massexternal symptom of infection isthe abundant exudation frominfected flowers of an amber-col-ored, sticky fluid, or Òhoneydew,Ówhich often drips onto the leavescontained within the honeydew,and when these germinate theysurface of the honeydew, giving it awhite-scum to powdery appear-ance. Wind rapidly spreads thesesecondary spores over long dis-tances. The fungus also can bespread by seed contaminated withsphacelia or honeydew. Under cer-tain conditions, produces very durable, compactWhere is it? Sorghum ergot has existed in Africafor many decades. It appeared inproduction areas in the Americas.It was first detected in the UnitedStates in Texas in 1997. During thefrom the Lower Rio Grande Valleyto the High Plains of Texas, andinto Kansas, Nebraska, NewMexico and Georgia. How Are DifferentTypes of Sorghumized ovaries. Once fertilized, anovary becomes resistant to infec-tance is highly effective. Any condi-tion that prevents or delays fertil-ties caused by cool temperaturesare most severely affected by ergot. Because of their high self fertility,grain sorghum hybrids should sus-tain very little damage from ergot,except where cool temperaturescan predispose the flower to infec-tion. Cool temperatures (averagedaily minimum below 55 degreesF) occurring 3 to 4 weeks beforeflowering inhibit pollen develop-occurring at flowering to 5 daysthereafter can delay fertilization byslowing pollen tube growth. There-fore, grain sorghum maturing dur-summer months. Male-sterile sorghum (female ÒAÓline) used in hybrid seed produc-a delay in pollination, since thefemale flower receives pollen froma different plant. Poor pollinationcaused by cool temperaturesgrain sorghum hybrids. Highfavor ergot infection. Foragesorghums vary in their levels of fer-tility. Some forage sorghums, espe-cially sterile hybrids, are very sus-ceptible to ergot because they oftentillering provides a succession ofsorghum flowers that can be con-ducive to the rapid and prolongedpathogen and likely serves as anoverwintering source of ergotinoculum in south Texas. 6-98 Sorghum ErgotNew Disease Threat to the Sorghum Industry *Extension Plant Pathologists, The TexasA&M University System. Newly formed honeydew drippingfrom an infected panicle. Joseph Krausz and Thomas Isakeit* w is it a Threatto Texas?Each flower infected with ergotrepresents a direct loss of one seed.Additional losses occur because thestickiness of infected panicles inter-feres with the harvest of healthyseed and favors the growth ofsaprophytic fungi, which can affectseed quality. A high incidence ofergot in sorghum forages also can-eydew that can interfere with har-vest by ÒgummingÓ the equipment. Seed production fields are very sus-ceptible to this disease. Texas pro-duces approximately 90 percent ofthe hybrid sorghum seed planted inthe United States and 45 percent oforld supply. To protect thisseed supply, seed production fieldsmay need to be treated with afungicide and additional pollinatorws may need to be planted.These measures will add to the costybrid seed production. Evidence to date suggests that C.africana, the sorghum ergot fungusin the United States, has little or notoxicity to livestock, especially atthe low quantities that might beconsumed if good disease manage-ment practices are employed.However, the presence of ergot ongrain sorghum may result in regula-tory restrictions on grain shipment.What to Do?The following practices can mini-mize the development of ergot andlimit its impact: 1.Time planting to avoid lowevening temperatures (below 55degrees F) during the period 3to 4 weeks prior to floweringand from flowering to 5 daysthereafter. The former inducespollen sterility and the latterws pollen tube growth. Bothsubject the flower ovary to therisk of infection.2.When planting inergot-free areas, useseed treatment fungi-cides such as captan,thiram or Maxim¨.Where the disease isalready present, or ifthe seed has beenstored for 3 or moremonths prior to-ments are of muchergot management. 3.After harvest, disk the fields toprevent sorghum ratoon andsorghum volunteer develop-ment. The ergot fungus canolunteer plants notkilled by winter freezes. 4.Manage Johnsongrass withinand around the borders of thefield.5.Harvest forage sorghums priorto heading. 6.In hybrid sorghum seed produc-tion, use an approved fungicideaccording to the label. Also usee pollen man-agement practices. It is not nec-essary to use fungicides for rams of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in coop-eration with the United States Department of Agriculture.Edward A.Hiler, Interim Director, Texas Agricultural Extension Service, The Texas A&M University System.5MÐRevisionPP Produced by Agricultural Communications, The Texas A&M University System ore information on sorghum ergot can be foundon the internet at:(http://www.cgiar.org/icrisat)(http://www.ars.grin.gov/ars/SoAtlantic/Mayaguez/sorghumnews.html)(http://www.agr.state.tx.us/comm/pr112.htm)(http://cygnus.tamu.edu)(http://primera.tamu.edu.pubs/ERGOT.HTM) White secondary sporulation of the ergot fungus on the surface ofhoneydew. White secondary sporulation on honeydewthat dripped onto leaves.