Alfalfa is attacked by many fungi, bacteria, viruses and nematodes which USDA estimates reduces hay yields by 24% annually in the U.S. Even greater losses occur in Kentucky. However, it is the diseases of the root and crown which cause the greatest damage because they limit the number of years a stand can remain productive

Nesmith, William C.

English

University of Kentucky

====---~-------~==~~---~-=-=~-~--~--------------....... 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. - 22 -References Hagemann, R. W., C. F. Ehlig, M. J. Rubber R w Re and L. S. Willardson. 1978 Effect of Ir~ig~ti;n fyrnoso cies on alfalfa seed yield.· c l'f · . equen-17-18. October. a i ornia Agriculture, 32(10): Jones, L: G. and C. R. Pomeroy. 1962. Effect of f . . , row ~pacin? and clipping on alfalfa seed producti ertili~er fornia Agriculture, 16(2):8-10. February. on. Cali-Kolar, J. J. and P. J. Torell. 1970. Row plantin alfalfa seed production. Idaho current Informat;ong for No. 122. March. ~ Series Ma:ble, _v. L. 19?1· Producing alfalfa seed in Cal'f . University of California Division of Agricultural Si.ornia. Leaflet 2383. May. ciences ;~dersen, M. W., G. E. Bohart, V. L. Marble and E c Ostermeyer. 1972. Alfalfa Science and Technol;gy. graph No. 15. American Society of Agronomy Ch 'Mono-Seed Production Practices, pages 689-719. . apter 32, Pedersen, M. W.'. et al. 1959. Cultural practices for al !!r~~~d production. Utah Experiment station Bulletin 408 ~al Stan?er, _ward and R. w. Thorp. 1974. Honeybees in alfalfa pollination. California Agricultural Experiment Station AXT-228. May. Yamada, H., D. W. Henderson, R. J. Miller and R M H 1973 I · t · · · oover . · rr7ga i?n wat~r management for alfalfa seed roduc: tion. California Agriculture 27(12)·6-7 D b p Sh 1 ' · · ecem er ees er, Robert and E. A. Yeary. 1982. Alfalfa se~d prodhuction cost analysis work sheet. Fresno County mimeo gr~. -Sheesley, Robert, L. Stromberg, R. Coviello and D. May. 1982. What shall I plant in 1982?. Fresno County mimeograph - 23 -CURRENT DISEASE PROBLEMS IN ALFALFA Dr. William C. Nesmith Extension Plant Pathologist University of Kentucky fa is attacked by many fungi, bacteria, viruses and which USDA estimates reduces hay yields by 24% annually Even greater losses occur in Kentucky. However, it ~ases of the root and crown which cause the greatest 'cause they limit the number of years a stand can remain y alfalfa stand has its share of diseases and few plants ld are without some disease. Actually, most plants ized by several pathogens at the same time. Which path-ates at any one period depends primarily on plant vigor, re, moisture and stand management. Thus, the extent of - stand from disease should be reducible through proper However, growers have few tools to reduce these dis-er they start causing major damage. Instead, the dis-t be kept in check by using preventative tools like crop 'proper cutting intervals, using disease tolerant var-d good site selection. There are no chemicals cleared ut those stands which have serious disease problems . ow is a discussion of a few of the most important dis-'rrently occurring in Kentucky with a few remarks on some cimportant elsewhere in the U.S. Spring Black Stem ang the past few years, Spring black stem has become a hificant disease of alfalfa in Kentucky. Typically, it ring the cool, wet periods of Spring and Fall causing ~gular black spots on the leaves, petioles, and stems. s turn yellow and drop. Stem lesions are dark green at ut turn black with time. Stems may become girdled by sions and die. ensive defoliation has been associated with this disease cky during the last two seasons. We find the pathogen Spring black stem to also be associated with diseased d suspect that the disease plays a major role in finish-~lants_that have been weakened by other pathogens. ,in California have shown that this pathogen is associated crown year around and moves to the stem and leaves cool, humid periods. present, about all we can recommend to reduce the impact disease is: ' !I', ! ! i,! i .. !· :i - 24 -1) Early cutting of.t~e stand to reduce leaf loss. Thi also reduces humidity and allows drying of the c s O b t. . d. rown ur o serva ions in icate greatest damage occurs t · b?th.h':'y quality a~d ?rowns w~en cutting is delaye~ s 7gnifican~ly. Thi~ is especially common in Kentuck w7th the first cutting because growers are involved y with other crops and forget their forages. Plus h k · h . , poor ay ma ing weat er frequently prevails at that time of year; yet such weather greatly favors this disease. 2) Varieties which perform well in Kentucky tests at Princeton and Lexington differ little in their suscep~ tibility to Spring black stem. 3) Foliar fungicides show some promise for use against this disease, but none are labelled to date. 4) Avoid poor quality seed because this pathogen is car-ried on the trash with the seed. Instead, use certifi seed produced in dry climates. Rhizoctonia Root and Crown Rot Rhizo?tonia is common to all soils in Kentucky and becomes a p7oblem in our.alfa~fa sta~ds during hot, humid periods, es-pecially when soil moisture is also high. We saw very little damage from this disease during the drought year of 1980 but it accounted for major damage during the wet years of 1979 ~nd 1981' The disease appears in patches within a stand and a range o plant symptoms may appear on a variety of different plants with' the same areas. Some plants appear scalded while others appear stunted. Above ground the disease appears on the buds crowns and stems causing water soaked rot that turns black with time.' Leaves appear matted together. Alfalfa roots have circular to elliptical lesions associated with the points of lateral root g7owth from the tap root. These lesions are yellow to brown at first, but become black with time. This may be our most difficult alfalfa disease to manage irr Kentucky, because so few tools are available to control it. No resistant varieties are available for our area. About all we ca do at present is watch the stands, especially during hot, humid weath~r, and.cut early if the disease is active above ground. The disease is favored by excessive nitrogen, so avoid additions of manure to alfalfa, especially during hot, humid weather. Southern Anthracnose Southern anthracnose is a warm weather disease that led to serious damage to alfalfa stands in 1980 because the fungus en-tered the crows causing heavy damage to the crowns. Spread of - 25 -the crowns occurs when water from dew or rain to· · h d · 1 a se and spores are spread tote ~rowns uring e re e · 1 .. ntly during these dry periods p ants were un-ppare , . . a t' ist the advancing infections an en ire crowns wer~ s Many stands t~roughout Kentucky were damaged heavily at that time. 11 anthracnose is more common as a stem canker ab ythe presence of bleached, bent, dead, young shoots . .· y nd the fields. Close observation of these diseas-;~~~~d reveal a diamond-shaped ·1esion with. smfall. pepper-: s inside the lesion. However, the crown in ections are · a by sudden death of many of the stems from a crown ize . d t t . d .lesions in the crown appearing as a ry ro, s aine , ·with blue to black specks of the fungus. As the ·'&vance into the root, the tissue turns brick red. Stems •from such crowns are usually dead and appear to have ''ched except for being blue-black at the base. Such 'brittle and easily break from the crown. management t?ols ex~st fo7 t~is di~ease in that el;cel-Stance is available in varieties which are performing entucky tests. Arc, Classi?, Olympic, S':'ran':'c-AR, an.d are varieties with good resistance to this disease that tming well in University tests. A new race of this . owever, has appeared in some areas of the U.S. for which ieties do not resist. But that race has not yet been in Kentucky. Rotation to crops other than clover or or two to three years, greatly reduces the fungus in the However, inoculum is moving into our fields probably by pastures. We strongly suggest that growers use.re-arieties to manage southern anthracnose, a maJor disease Kentucky stands. Phytophthora Root Rot phthora root rot is a disease associated with wet, ·rained, and poorly managed alfalfa stands. Al though .al agent is common in our soils, we seldom find it serious problems on good managed alfalfa sites. How-~ce the fungus is common to our soils, the potential ge exists during unusually wet seasons and poorly drained otherwise good alfalfa fields. sis a disease of the root system where the pathogen the tap root causing reddish brown lesions that later wn and girdle the root. Affected plants turn yellow .. ear stunted and they die from drought stress, cold or occasionally even from the above ground attacks by thogen. Ytophthora root rot can be controlled in Kentucky by using ltural practices and resistant varieties where it has i,! i .. !· :i - 24 -1) Early cutting of.t~e stand to reduce leaf loss. Thi also reduces humidity and allows drying of the c s O b t. . d. rown ur o serva ions in icate greatest damage occurs t · b?th.h':'y quality a~d ?rowns w~en cutting is delaye~ s 7gnifican~ly. Thi~ is especially common in Kentuck w7th the first cutting because growers are involved y with other crops and forget their forages. Plus h k · h . , poor ay ma ing weat er frequently prevails at that time of year; yet such weather greatly favors this disease. 2) Varieties which perform well in Kentucky tests at Princeton and Lexington differ little in their suscep~ tibility to Spring black stem. 3) Foliar fungicides show some promise for use against this disease, but none are labelled to date. 4) Avoid poor quality seed because this pathogen is car-ried on the trash with the seed. Instead, use certifi seed produced in dry climates. Rhizoctonia Root and Crown Rot Rhizo?tonia is common to all soils in Kentucky and becomes a p7oblem in our.alfa~fa sta~ds during hot, humid periods, es-pecially when soil moisture is also high. We saw very little damage from this disease during the drought year of 1980 but it accounted for major damage during the wet years of 1979 ~nd 1981' The disease appears in patches within a stand and a range o plant symptoms may appear on a variety of different plants with' the same areas. Some plants appear scalded while others appear stunted. Above ground the disease appears on the buds crowns and stems causing water soaked rot that turns black with time.' Leaves appear matted together. Alfalfa roots have circular to elliptical lesions associated with the points of lateral root g7owth from the tap root. These lesions are yellow to brown at first, but become black with time. This may be our most difficult alfalfa disease to manage irr Kentucky, because so few tools are available to control it. No resistant varieties are available for our area. About all we ca do at present is watch the stands, especially during hot, humid weath~r, and.cut early if the disease is active above ground. The disease is favored by excessive nitrogen, so avoid additions of manure to alfalfa, especially during hot, humid weather. Southern Anthracnose Southern anthracnose is a warm weather disease that led to serious damage to alfalfa stands in 1980 because the fungus en-tered the crows causing heavy damage to the crowns. Spread of - 25 -the crowns occurs when water from dew or rain to· · h d · 1 a se and spores are spread tote ~rowns uring e re e · 1 .. ntly during these dry periods p ants were un-ppare , . . a t' ist the advancing infections an en ire crowns wer~ s Many stands t~roughout Kentucky were damaged heavily at that time. 11 anthracnose is more common as a stem canker ab ythe presence of bleached, bent, dead, young shoots . .· y nd the fields. Close observation of these diseas-;~~~~d reveal a diamond-shaped ·1esion with. smfall. pepper-: s inside the lesion. However, the crown in ections are · a by sudden death of many of the stems from a crown ize . d t t . d .lesions in the crown appearing as a ry ro, s aine , ·with blue to black specks of the fungus. As the ·'&vance into the root, the tissue turns brick red. Stems •from such crowns are usually dead and appear to have ''ched except for being blue-black at the base. Such 'brittle and easily break from the crown. management t?ols ex~st fo7 t~is di~ease in that el;cel-Stance is available in varieties which are performing entucky tests. Arc, Classi?, Olympic, S':'ran':'c-AR, an.d are varieties with good resistance to this disease that tming well in University tests. A new race of this . owever, has appeared in some areas of the U.S. for which ieties do not resist. But that race has not yet been in Kentucky. Rotation to crops other than clover or or two to three years, greatly reduces the fungus in the However, inoculum is moving into our fields probably by pastures. We strongly suggest that growers use.re-arieties to manage southern anthracnose, a maJor disease Kentucky stands. Phytophthora Root Rot phthora root rot is a disease associated with wet, ·rained, and poorly managed alfalfa stands. Al though .al agent is common in our soils, we seldom find it serious problems on good managed alfalfa sites. How-~ce the fungus is common to our soils, the potential ge exists during unusually wet seasons and poorly drained otherwise good alfalfa fields. sis a disease of the root system where the pathogen the tap root causing reddish brown lesions that later wn and girdle the root. Affected plants turn yellow .. ear stunted and they die from drought stress, cold or occasionally even from the above ground attacks by thogen. Ytophthora root rot can be controlled in Kentucky by using ltural practices and resistant varieties where it has ===-c-c -=--=--=--=··--=-= ---=-:...=cc:--==---------- -=====~-.:::::=----·-·------------ 26 -app7 ared previously. The resistant variet res7stant variety that has yielded well . YK Apollo, is the o Resistant varieties should be consideredl~f !~tucky tests. rot has been.a problem in the particular fieldy~o~hthora root ever, no variety has juvenile resistance to . ei~g used. H cultur~l practices must be applied even witht~1s_d1sease. So ~o avoid ~eav~ losses from this disease duringe~tstant varieti iod. Avoid fields that are poorly drained e seeding per ~orary wet ~i tes on otherwise well drained :~~l~e aware of tem; 11~ f1el<:1s w7th compaction layers should greatly s:d ?eep plowi' ing this disease. ai in control,;; Verticillium Wilt To date, Verticillium wilt has been found onl · north of Kentucky especially O 1 . Yin areas Northern Iowa, and Oregon Thi'ns ~ in7 no~th of Pennsylvania d' · is primarily a 1 isease so many feel it is unlikel th t 't coo season blem in Kentucky. However the di;easa hi can become a pro-to be seed-borne, so we sh~uld be watc~fu~s f~ec7~t~y been foun-f~ngus could adapt since our climate is col r l ecause the disease to operate during Spring and Fall ~on~~~~gh for the - 27 -NO-TILL ESTABLISHMENT OF ALFALFA Harlan E. White, Extension Agronomist-Forages Dale D. Wolf, Associate Professor of Agronomy VPI and State University Blacksburg, VA concept has been widely accepted in Virginia fo1 s.oybean production. However, alfalfa is still commonly _ed by plowing and tilling the ~oil into a fine seedbed. many tons of productive topsoil is eroded by rainfall repared seedbeds. The resulting gullies remain in the or the life of the stand to damage equipment and "rat-eth" of the operator. advantages of establishing alfalfa without tillage me to mind. Moisture in the seedbed is conserved for e new seedlings instead of being lost to the atmosphere :l:;3.ge. Time is saved during seeding because of the re-b_er of trips across the field. Fuel conservation also ,~rom fewer trips that require less power. arch at Virginia Tech, as well as at other universities, lished several "musts" for establishing no-till alfalfa: 'Living competition must be eliminated. ~lant debris tall enough to shade the soil surface must be removed. ,Protection must be provided against a wide spectrum -,' of insects. v'Seed must be placed in the soil and no deeper than one inch. Soil fertility and pH must be adequate. ination of plant competition is dependent primarily upon The general "recipe" being followed in Virginia is: Apply 2,4-D if broadleaf plants are present. After 10-14 days apply Paraquat. After another 10-14 days apply Paraquat again. Seed 15 lb of alfalfa seed plus 15 lb of lOG granular Furadan per acre. -------------------------------------------------'~re are many variations of this general guideline, depend-the particular situation. For example, 2,4-D may not be 7f broadleaf weeds are not present. It may also be appli-l~r than indicated, such as in fall prior to spring seed-• in the spring prior to summer seeding. The rate of t may vary from 1 to 4 pts. per application, depending on 'i 

Current Disease Problems in Alfalfa

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Current Disease Problems in Alfalfa

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