Contents

Fungus Diseases ------~ ------3 MOSAIC AND OTHER VIRUSES Iris Severe Mosaic (Yellow or Latent Virus Diseases ------3 Mosaic or Gray Disease) ------17 Nematode Diseases ------3

Bacterial Diseases ------3 MISCELLANEOUS DISEASES AND CONDITIONS

Physiological Diseases ------3 Nematode (Eel worm) ------19

General Control Program ------4 Black Storage Molds ------20

Black Tip ______------21

MAJOR DISEASES Botrytis Blight ------21 Blindness (Three Leaf) 4 Suggestions to the Grower ______5 Gray Bulb Rot ------21 Suggestions to the Forcer ------6 Pythium Root Rot ------21 Summary of Forcing Problems ______7 Rhizoctonia Neck and Bulb Rot ______21 Blasting ------__ 7 Rust ------__ 22 Bacterial Blight ______------8 Sunburn ------2 2 Black Slime (Black Rot) ------9

Blue Mold ------10 Topple ( Sugarstem) ------22

Crown Rot (Southern Wilt) ______11 Other Diseases ------22

Fusarium Basal Rot ------13 Key to Narcissus Diseases ------2 3

Fire (Leaf Spot) ------14

Ink Spot ------16

Much of the information in this bulletin resulted from cooperative research with many individuals, particularly Vernon L. Miller and Neil W. Stuart with the assistance of Worth Vassey. Financial support was provided by the Washington State Bulb Com­ mission, Northwest Bulb Growers Association, and many chemical companies. We are indebted to these and to the following for their review of all or parts of the manuscript: Drs. T. C. Allen, A. A. Brunt, L. W. Moore, D. Price, A. R. Rees, and N. W . Stuart.

Issued by Washington State University Cooperative Extension, J. 0. Young, Director, and the U.S. Department of Agriculture, in furtherance of the Acts of May 8 and June 30, 1914. Extension programs are available to everyone without discrimination. Published June 1979.

2 DISEASES OF BULBOUS IRIS

CHARLES J. GouLD, Plant Pathologist, Emeritus, and RALPH S. BYTHER, Extension Plant Pathologist, Western Washington Research and Extension Center.

The mild, moist climate in western Washing­ like growths within a bulb or diseased plant tissue, ton is ideally suited for bulb production. Wash­ or as hardened lumps of fungus tissue in the soil ington is the leading producer of bulbous iris in where the bulb grew. These masses of weather­ the United States. Millions of bulbs are harvested resisting fungus tissue are usually rounded and annually to be used for the production of cut hard and are called sclerotia. flowers. These flowers are produced by either forcing them in greenhouses or field planting in Virus Diseases coastal areas. Twenty to thirty million are also shipped annually to England and Europe where Virus particles are so small that they can be they are used for early forcing because of their seen only with an electron microscope. When they high quality. Production is confined mostly to gain access to a plant, they usually penetrate into popular greenhouse forcing varieties, particular1 y every part except the seed. Therefore, whenever Ideal, \XT edgewood, and Blue Ribbon. a daughter bulb is taken from a virus-infected Although Washington iris are recognized as plant, it is usually also infected. Certain insects, some of the world's best, they are not without such as aphids, which feed on plant sap, can spread their disease problems. This bulletin describes most some virus diseases. of these problems and outlines control measures that can be used to minimize losses. Nematode Diseases For additional information see Diseases of Nematodes are very small thread-like worms. Bulbs by W. C. Moore, Ministry of Agriculture Many commonly live in the soil without doing and Fish, London 1949 (a revision is in press). any harm, while others attack various plants. The Another reference is Ziekten en Afwijkingen bij bulb nematode and root-lesion nematodes which Bolkewassen, Deel 2: Amaryllidaceae Iridaceae, affect iris are too small to be seen without a micro­ e.a., 1978, Laboratory for Flower Bulb Culture, scope. Nematodes survive from season to season Lisse, Netherlands. It includes iris in addition to as eggs. They also can survive for several years ·certain other bulbs. Information on insects and as worms in bulbs or in infected plant tissue. Any culture is contained in the Handbook on Bulb movement of soil or infected plant parts can be Growing and Forcing, edited by C. J. Gould in responsible for the spread of nematodes. Farm 1957. It is available from Xerox University Mic­ equipment, irrigation, flooding, and planting In­ rofilms, 300 North Zeeb Road, Ann Arbor, fected bulbs are common means of spread. Michigan 48106. 13acterial l)iseases Fungus Diseases Bacteria are simple, microscopic, usually single­ Many important diseases of iris are caused by celled plants that depend upon other plant or fungi. Fungi are small and rather simple plants animal sources for their food. Most are beneficial unable to produce their own food because they and only occasionally do they cause trouble in iris. do not have the green coloring matter ( chloro­ Spread and survival depend on the presence of in­ phyll). Rather than manufacture their own food, fected plants or plant tissues, since the bacteria they feed on living or dead plants and animals, can not survive long in soil. resulting in disease or decay of the tissues they attack. Fungi produce very small seed-like bodies called spores. These microscopic spores can be Physiological Diseases spread by splashing rain, by wind, or carried along All problems which are not caused by para­ with the movement of soil or infected plant debris. sitic organisms are considered in this group. Bulb­ Fungi survive from one season to the next ous iris are quite susceptible to unfavorable weath­ either as dormant spores in the soil, or as thread- er. Frost may injure their leaves, the sun may burn

3 the bulbs, and undesirable temperatures may pre­ kills nematodes, insects, and many fungi, including vent flowers from forming, or ruin them after crown rot and black slime. Therefore a regular they have formed. Because of this, they are cor­ HWF treatment of planting stock is recommend­ reedy considered one of the most difficult of all ed. Certain varieties may be injured by this treat­ bulb crops to grow commercially. ment, thus information on how each variety re­ acts is necessary before large-scale treatment is attempted. A General Control Program Recommendations to control disease and in­ Specific fungicides are not listed in this pub­ sect pests of bulbous crops are revised annually lication because materials recommended constantly on the basis of current research results. These are change. Specific recommendations are contained published by Washington State University as EM in EM 4314, which is revised annually or as need­ 4314 for iris diseases, EM 4313 for narcissus dis­ ed. Suggestions for a general control program are: eases, and EM 4315 for tulip diseases. They are 1. Always plant well-graded stock of known available from your local County Extension Agent disease-free ancestry. Establish a mosaic-free in Washington. and nematode-free foundation stock. 2. Either discard or plant moderately and se­ verely diseased stocks separately. Give these diseased plantings special attention, such as intensive roguing, spraying, etc. Dig and treat them before the major digging commences. Blindness (Three-Leaf) 3. Plant on heavy (silt loam or heavier) well­ Symptoms drained soil on which iris have not previously Blindness is the failure of flowers to develop been grown for 3 or 4 years. A void tighter from normally flowering-sized bulbs. Only three sandy soils. Ridge the rows. leaves are produced instead of the usual five. 4. Spray with a fungicide if leaf spot is a prob­ This condition is sometimes confused with blast­ lem (see EM 4314). ing, in which case buds form but sooner or later 5. Rogue all mosaic-infected plants. Rogue on die (see p. 7 ) . the basis of symptoms on central leaves of new growth ear I y in the season and on flower Importance and Host Range symptoms at the time of blooming. Blindness is found throughout the world. It 6. Remove crown rot-infected plants. Also re­ primarily occurs in forcing greenhouses and is sel­ move the infested soil or sterilize the infested dom seen in the field. It is most prevalent in area. forced bulbs which have been produced the sea­ son before under cool, cloudy conditions, or not 7. Dig nematode-infected stocks 1 or 2 weeks given the proper temperature treatments, or pre­ earlier than normal and treat as recommend­ cooled too early. ed in EM 4314. 8. A void bruising the bulbs in all ,operations. Factors Affecting 9. Store bulbs under dry, well-aerated condi­ Blindness has been attributed to several fac­ tions. tors. Among the most important are the use of 10. Discard all infected and moldy bulbs after small bulbs for early forcing and the improper digging and again before planting. temperature treatments during their storage. Iris bulbs are sensitive to many environmental 11. Heat cure salable st9cks soon after digging. conditions and, therefore, probably no one formula Alternate the use of recommended fungicides, will ever be available to insure their full perform­ whether spraying or dipping. This should help ance under all conditions. Keep this in mind while reduce the likelihood of development of fungicide­ considering the following suggestions. The illustra­ resistant strains of the fungi. tion shows possible treatment sequences that occur The hot water plus formalin (HWF) treat­ from the time of digging until the bulbs are forced ment is an excellent general "cure-all" since it in the greenhouse or planted in the field.

4 Time: Usually 10 to 15 days at 90-95 °F is suf­ ficient. Although there is usually more danger from too little heat curing, excessive heat cur­ ing may cause trouble by stimulating sprouting during the stabilization. treatment ( 65 °F) . Thi$ may result in increased leafiness and reduced root growth and thereby· predispose the iris to blasting and even induce some blindness. Size: Smaller sizes ( 8 ;.1 to 9) need a few more days of heat curing than larger sizes. Other Varieties: Blue Ribbon (Prof. Blaauw) needs at least as much heat curing as Wedge­ wood and possibly more. Three-leaf (left) and normal plants __...... _____...... ______....~ Stabilizing Suggestions to the Grower Temperature: 65 °F is usually optimum, but heat- cured bulbs stored too long at 65 o may sprout Digging before or during the early stages

5 Shipping Length: Bulbs should be treated about 7 to 10 Avoid filling bags and crates too full; this may days, depending on growing conditions of the increase bruising. Include a recorder with each crop. shipment to monitor temperatures. Request ade­ Relative Humidity: The relative humidity should quate air circulation be provided. be maintained between 80-85%. Varieties: End-treatment is more beneficial for Suggestions to the Forcer Blue Ribbon than for \Vedgewood, but it may Handling predispose the bulbs to attack by Penicitlitnn Unpack iris bulbs immediately upon arrival and (blue mold) . air, particularly if they are shipped in cartons. If the bulbs are soft or otherwise appear to have Treatment for Retarded Bulbs been overheated in transit, have them inspected PRECOOLING immediately by a state horticultural inspector or Retarding (at 8 5 oF) tends to maintain grassi­ by the supplier or his representative. ness, so bulbs need some precooling. Precool re­ tarded bulbs at 50 oF for 5 to 6 weeks for late or Treatment for Heat Cured 4 to 5 weeks for very late forcing. PRECOOLING END-TREATING . Pre cool only bulbs that have been heat cured End-treating retarded bulbs may accelerate or retarded. blooming but is usually not necessary and may re­ Temperature: 50°F usually has been the best all­ sult in serious losses from blue mold. However, around temperature for most varieties for pro­ it is occasionally desirable (especially when they duction of early blooms in our experiments. are to be forced under poor light) . Some jobbers prefer 45-48 oF because it prevents FORCING premature sprouting. 40°F may also cause some Planting: Space bulbs at least 2 inches apart in blindness but will include less blasting than rows at least 4 inches apart. The top of the bulb 50°. 45 °F may be best for the variety Blue should be even with soil level. Plant directly Ribbon to reduce sprouting and excessive leaf­ in the bench or, if flats are used, make sure iness. the soil is at least 3 Y2 inches deep. Length: Six weeks is usually best for W edgewood Precooled bulbs: Plant immediately upon arrival. and its sports (Ideal and Dominator) . Eight If outdoor temperatures are ordinarily too high weeks, or seven weeks plus an end-treatment, in earI y fall, be sure to mulch the bench or is recommended for Blue Ribbon and other va­ flats, as exposure to these high temperatures can rieties. Some basal swelling or sprouting should stunt growth. be evident by the end of precooling; if not, the Retarded/precooled bulbs: It is imperative that bulbs are not quite ready, and flowering may these bulbs be planted immediately upon ar­ be delayed. An additional few days of precool­ rival since a delay could stunt their growth. ing will be required. Watering: Keep soils moist at all times. If iris Relative humidity: The relative humidity should roots are allowed to dry, blasting will usually be about 85%. result. END-TREATING (Dry storage after precooling) Soil: Use any mixture that will drain well but still In the United States, end-treating is usually can hold moisture. It should have a pH between not necessary and is often not desirable. The treat­ 5.5 and 7 and soluble salts should not exceed ment results in short leaves and stems. It should 600 ppm. If low in nutrients add a balanced be used only for 1) irises to be forced in areas of fertilizer. known low light intensity in the winter, or 2) for Ventilation: Ventilation should be adequate to irises to be forced under normally cloudy condi­ provide good air movement at all times, particu­ tions for an early market, or 3) for irises that will larly when temperatures rise suddenly in the be forced under lower than recommended temper­ greenhouse. atures. In all instances, the supplier should be Light: Irises require high light intensities. The consulted about the type of application and length temperature should be lowered during periods of end-treating, if it is to be used. of dark and cloudy weather. If irises are to be Temperature: 65 °F is probably optimum tempera­ forced in areas where light is normally low, the ture for end-treating. supplier should be consulted· about possible ap-

6 plication of an end-treatment after precooling. Temperature: The night temperature usually should not exceed 58 to 60°F for top-size bulbs. If possible, keep the difference between day and night temperatures at 5o or less. There is a close correlation between light and temperature, thus temperatures should be reduced during prolonged dark periods. Within limits, early­ forced irises should be pushed hard. Cutting flowers: Cut flowers of W edgewood and its sports in the pencil stage, when about 50% of the colored bud is showing. Store them in water or flower keeping solution at 3 3 to 3 5 o F for no longer than a week. Cut Blue Ribbon after the Bower begins to spread open. Bulb treatments before greenhouse forcing. Miscellaneous Air circulation must be good during all stages of storing and forcing. Maintain adequate moisture when. forcing to produce good growth and to prevent blasting. Leaf length is reduced by precooling and end­ treating. In general, the longer the leaves, the poorer the flowers. Insufficient oxygen eliminated the benefit froin precooling in some of our experiments. Evi­ dently some fresh air should be provided daily in storage rooms . Blasting Because of the many variables involved ( dif­ ferent growing seasons, forcing conditions, va­ rieties, new research results, etc.), we urge that Symptoms you consult your supplier and follow his recom­ FLOWERS. Buds or flowers may be withered mendations for forcing each year's crop. and dead when they appear, or they may wilt and turn brown later. Blasting is primarily a green­ Summary of Forcing Problems house problem but may occur in the field. Iris are most susceptible to blasting about 14 to 15 Blind Plants days before flowering. No flowers and fewer than five leaves. This problem may be caused by: ' · Possible Causes 1 ) Insufficient heat curing, 2) a stabilization Numerous situations may be responsible for temperature lower than 65 °F, 3) precooling too biasing. These include: 1) delay in planting after early, and 4) rotting of roots and bulbs. removal from precooling; 2) insufficient precool­ ing resulting in excessive foliage; 3) excessively Blasted Flowers high forcing temperatures, especially during cloudy Flowers which are withered and dead. Blasted weather; 4) high soil and low air temperatures or flowers may be caused by: both too high; 5) uneven temperatures; poor ven­ 1) Lack of end-treatment where necessary, 2) tilation; 6) too low light, especially in combina­ soil and/or air temperatures too high, 3 ) sudden tion with normal or high concentrations of carbon drastic changes in temperature either up or down, dioxide; 7) plants too close to heating pipes; 8) 4) too little light ( ~ natural or from crowding) , 5 ) allowing soil to dry; 9) under- or over-fertility; inadequate watering, 6) bulb rots, 7) poor root 10) too thick planting; 11 ) disease or insect attack systems, and 8) excessive foliage from ·roo much of bulbs. heat curing, insufficient precooling, or too slow Malformed or distorted flowers most often forcing. occur with high soil temperatures. ------~----~------~~~------~ 7 Control O:>rrection of the above conditions and forc­ ing of only large bulbs during cloudy weather will help to eliminate blasting. Follow forcing pro­ cedure listed under blindness. References FORTANIER, E. ]., and A. ZEVENBERGEN. 1973. Analysis of the effects of temperature and light after planting on bud blasting in Iris hollandica. Neth. ]. Agr. Sci. 21:145-162. GOULD, C. ]., N. W . STUART, and T. SABELIS. 197 4. Suggestions and comments on forcing Washington-grown iris ·in greenhouses in the U.S. Florists Review 154(3396). p 33-34. June 14. KAMERBEEK, G. A., and W. ]. DeMUNK. 1976. A review of ethylene effects in bulbous plants. Scientia Hort. 4: 101-115. KIMURA, Y., and N. W. STUART. 1972. Ex­ ponential nature of heat exposure duration rel­ ative to temperature change in the curing and flowering of bulbous iris. J. Amer. Soc. Hort. Sci. 97 ( 3), p.· 424-427. STUART, N. W., C.]. GOULD, and D. L. GILL. 1955. Effect of temperature and other storage conditions on forcing behavior of easter lilies, bulbous iris, and tulips. Report of the 14th Bacterial blight Inter. Hort. Cong., Wageningen, Netherlands. p. 173-187. Importance and Host Range Bacterial Blight This disease was first observed in Washington and photographed by Dr. G. A. Huber in 1935 Symptoms in a severely infected field of Wedgewood. Only LEAVES. Elongated watersoaked spots or sporadic occurrences were observed until the streaks occur most often near the base of leaves 1960s. Since then it has become increasingly more and stems. These may enlarge rapidly under moist severe, although annually sporadic, perhaps due conditions, become brownish-black, and often to a combination of insufficient rotation coupled cause leaves and stems to turn yellow, collapse, with increased freezing and mechanical injury. Va­ and die. rieties vary in susceptibility. Ideal and Wedgewood FLOWERS. Occasionally flower stems may be are both susceptible. Isolation and inoculation tests affected with symptoms similar to those on leaves. at Western Washington Research and Extension BuLBS. Bulbs will be much smaller than Center have shown that the bacterium was wide­ normal when leaves are severely infected. Infec­ spread in bulb-growing areas and can also cause tions on leaves and stems may extend into the a collapse of Narcissus flower stems held in stor­ bulbs, forming a blackened area within the bulb age. This bacterium appears to be different from where the leaves are attached to the basal plate. Erwinia carotovora, which causes a soft rot of iris Factors Affecting in Holland. Bacterial blight is most severe in warm, moist weather apparently following injury from frost, Control severe freezes, hail, mechanical damage, hot water Dig bulbs and replant in a new location hav­ treatment, or other stress factors. More common ing good air and soil drainage and in the most in dense planting and those left undug for two frost-free location possible. Plant~. thinly as prac­ or more years. ticable.

8 .Causal Agent Importance and Host Range Pseudomonas sp. This fluorescent Pseudo­ Black slime is present in Europe, United States, monas sp. has recently been under investigation and probably wherever bulbs are grown in cool by Dr. Larry W. Moore, Oregon State University, climates. It is particularly severe on hyacinths, Corvallis. tulips, and bulbous iris but at times also on nar­ References cissus, scilla, muscari, fritillaria, ornithogalum, GOULD, C. J. 1950. Diseases of bulbous iris. crocus, and triteleia. Onions were infected in green­ WSU Extension Bulletin 424. p. 14. house tests. It apparently does not survive on weeds in this area. During the 195 Os it was severe in some stocks in Washington. Repeated treat~ Black Slime (Black Rot) ment of bulbs with hot water plus formalin, Symptoms coupled with dusting of bulbs and/or furrow ap­ Infected plants either fail to emerge or emerge, plications with a fungicide, has reduced the disease. turn yellow, wilt, and die. Usually diseased plants occur in clumps. Underground shoots and bulbs Control are covered with a thin gray mass of mold. The In general, the control measures suggested for fleshy scales are at first soft and water-soaked or crown rot are also recommended for this disease dead white. Later the affected parts become an excep~ for the following modifications: intermingled mass of bulb tissue, pockets of white 1. It is not necessary to dig diseased stocks earlier or gray mycelium, and black sclerotial-like layers. than normal. Finally nothing remains but a residue of decayed 2. Discard the smallest bulbs and the debris from bulb fragments and sclerotia. The sclerotia are infested stocks. A majority of the diseased black, irregular, usually rounded when free, but bulbs are small since they contain· most of flattened when between scales, and vary in size the sclerotia. from 1/16 to 1/2 inch or more. The tops of the 3. A 3-4 year rotation should be adequate if bulbs are usually infected first. If infection occurs volunteer bulbs are eliminated. early, bulbs usually decay completely. The most 4. Eliminate fungus in bulbs by treating in hot common symptom in storage is a blackish shrunk­ water plus formaldehyde (see EM 4314). en nose that crumbles easily or black outer scales 5. At planting treat bulbs and/or soil with a surrounding an apparently sound healthy bulb. fungicide (see EM4314).

Factors Affecting Causal Agent Cool weather favors disease development, thus Sclerotinia bulborum (Wakk.) Rehm. Sclero­ it appears in early spring in contrast to Crown Rot, tia white at first, hiter black, smooth and rounded which appears in late spring. Sclerotia in the soil ( Ys- ~") or flattened if between scales, and often from the previous crop are responsible for the fused intt> irregular masses Y2 inch or more wide. survival and sources of the disease. In four west­ Apothecia light brown with asci 140 x 9!1- and ern Washington soils tested, sclerotia of this ascospores 16 x 811-. fungus survived up to 2 years in the absence of the iris host. For this reason 3- to 4-year crop ro­ References tations are recommended. BOEREMA, G. H. 1961. Notes on some unusual fungus-attacks on flower bulbs II. Overdruk uit Black slime Versl. en Meded. Plantenz. k. Dienst No. 136, (Jaarboek 1961) p. 210-217. GOULD, CHARLES ]., and D. M. McLEAN. 1952. Black Rot of Iris, Tulip, and Hyacinth Bulbs. Phytopathology 42 ( 9) p. 5 14. Septem­ ber 1952. GOULD, Charles J., and THOMAS S. RUSSELL. 1965. Soil-borne infection of bulbous iris by Sclerotinia bulborum controlled by bulb and soil treatments with PCNB. Plant Dis. Reporter 49 ( 5) p. 443-446. May 15.

9 Later they will become hard and yellow or brown. Older spots on the sides of bulbs often appear as dead, brown cavities containing masses of blue­ green spores. Such cavities are covered by sunken dead, brown husks that are usually split in the center. Under suitable conditions, the bulb decays leaving nothing but the husk and a little debris. Factors Affecting Infection can start at wireworm punctures or bruised or injured areas, but most infection ap­ parently starts where emerging roots injure the base. The slower the roots emerge (as with pro­ longed precooling or slow forcing in cool green­ houses), the more opportunity there is for the fungus to enter. In general, both low humidity and low temperature delay the healing of the wounds where these roots emerge. Under high humidity and at l7°C these wounds may become resistant to infection within 3 days. Bulbs infected at the side or tip may grow but usually produce inferior plants. The bulbs usually decay completely if the rot begins at the base. Importance and Host Range Penicillium, the fungus that causes blue mold, is also found on many crops throughout the world. In Washington the disease is widespread but us­ ually only of minor importance. Occasionally serious losses have occurred. The varieties Blue Ribbon, Imperator, and Yellow Queen are particu­ larly susceptible but most other types of bulbous iris can also contract the disease. Blue mold infec­ tions are increased when bulbs are dug excessively early or late and on bulbs that have been injured. Injuries by nematodes, insects, sunburning, desic­ cation, hot water plus formalin treatment, bruis­ Blue mold ing, storage in deep masses, or storage under cool, moist, closed conditions aggravate the disease. Susceptibility often increases with prolonged stor­ Blue Mold age, especially under excessively dry or moist con­ Symptoms ditions. Infection can occur from airborne as well LEAVES. Scattered plants fail to emerge; others as soil-borne spores of the fungus. Infections also develop but may be distorted and/or stunted, turn seem to be dependent upon a particular physiolog­ yellow, and die. The base of the stem and leaves ical state of the bulbs, which appears to vary be­ of these plants have a mushy rot with a distinc­ tween varieties, fields, year, etc. tive sour odor. Control RooTs. When infection occurs at the base, few 1. Do not dig excessively early or late. or no roots are formed. Often roots will be limited to one side or portion of the bulb. 2. Avoid bruising bulbs at any time, but par­ BULBS. Symptoms vary depending upon time ticularly when digging. of attack, varieties, etc. Infected fleshy scales are 3. Avoid sunburning, desiccation, etc. first soft and water-soaked, white to greenish-gray. 4. Do not break up clumps until they are well

10 ripened. A void "bleeding" by breaking up during heat curing and stabilizing, it is clumps as soon as the bulbs separate easily. not as critical as during precooling and par­ Do not clean until the basal cap slips off ticularly end treating. The best RH found easily. to date for the latter two stages appears to be about 85% with good but not excessive 6. Cure rapidly by spreading thinly in trays air circulation. Also, if root emergence begins (many growers use screen-bottom trays, but during precooling, either lower the temper­ these must be handled carefully to avoid in­ ature or plant the bulbs. jury) . Stack covered trays in field if the 16. Fohcing bulbs in greenhouses: Both root­ weather is suitable or place in a well-ventil­ emergence and wound-healing are faster at ated room that can be heated if necessary. warm (e.g. 13-16°C, 58-60°F) temperatures Use only enough heat with planting stock to than at cool temperatures; thus, there is less keep the bulbs dry. chance of infection if the bulbs are forced 7. Discard all infected bulbs by burning or as fast as practicable for their size. burying. 8. Fungicide treatments. There is no entirely Causal Agent suitable treatment (see EM 4314) . The ben­ Several species of Penicillium can cause blue zimidazales were very effective until the mold disease. Penicillium corymbiferum Westling, fungu,s developed resistance to them. We sug­ is the most common in W ashingtoa but occasion­ gest several fungicides be alternately used ally P. eye/opium West has also been associated or used as mixtures to· help reduce the pos­ with this disease. See "A Manual of the Penicillia" sibility of this resistance. The timing of ap­ by Raper, H. B., C. William Thorn, and Wilkins plications is crucial. If bulbs are treated be­ for full description. fore shipping, the fungicide has usually worn off by the time of planting. Treating later, References however, is very inconvenient for the forcer. SAALTINK, G. J. 1968. Penicillium corymbie­ ferum entering bulbous iris through wounds. 9. Plant early. If planting must be delayed until . Neth. J. Pl. Path. 74( 1968) p. 85-93. the cool, moist weather begins in the fall, PLATE, HANS-PETER, ROSWITHA SCHNEI­ store under well-ventilated, dry conditions. DER. 1967. Penicillium-faulen an blumenz­ Some heat may be necessary, but too much wiebeln neue beobachtungen in Berliner Gart­ heat is detrimental to large planting stock enbaubetrieben. Mitteilungsblatt des Landes­ since it ·will increase the number of bulbs verbandes Gartenbau und Landwirtschaft Ber­ blooming in the field. Excessive air move­ lin e. V. Jahrgang 18 No. 1. ment is also undesirable since it dries out the bulbs. 10. A void wet soils and poorly drained fields. Crown Rot (Southern Wilt) 11. Disinfect trays and other equipment in the Symptoms hot water plus formalin bath, or spray with LEA YES. Infected plants are yellow, sometimes or dip in formaldehyde. Use 1-2 quarts in 5 stunted, and usually die prematurely. The rotted gallons of water. bases of stems and leaves are soft and fibrous. 12. Control wireworms and other insects. Diseased plants often occur in clumps, since the fungus rapidly spreads under warm, moist condi­ 13. Ship in small containers rather than in large tions. Masses of white thread-like strands form in ones. Do not ship bulbs in closed packages, and around the stem, the bulb, or in cracks of and do not pack bulbs tightly together. soil. This mycelium is usually accompanied by 14. A void desiccation and/or overheating and sclerotia that are white at first and later tan to prevent excessive dampness in the warehouse. reddish-brown. They measure up to ~ inch and Provide good ventilation during cold storage. are rounded and often pock-marked. 15. Bulb storage for forcing: The relative humid­ FLOWERS. Flowers may be blasted as a result ity (RH) is extremely important but the of attack at the stem base. exact amount has not yet been determined. BuLBS. A mass of soil often clings to infected If it is within a reasonable range (70-95%) bulbs. The husk also adheres tightly to the bulb,

11 Crown rot-sclerotia at left it may be partially shredded, and usually has a southeastern United States, but sometimes is ser­ dead, tan appearance. Infected fleshy scales are ious even in cool climates like the Pacific North­ cheesy in consistency at first, later becoming dry, west. The fungus attacks over 1 00 different types sunken, and tan. Sclerotia may develop on or be­ of plants, including many weeds, vegetables, and tween the scales. Infection may occur anywhere ornamentals. The latter include iris, tulips, daffo­ but most often is found at the tip of the bulb. dils, lilies, and hyacinths. All of these may serve Under suitable storage conditions, the infected as carriers of the fungus from infested to healthy area dries up, but under warm, moist conditions fields. The fungus can survive in the soil for many the fungus can spread to adjacent bulbs in the tray. years, probably by growing on volunteer bulbs, Other fungi may invade crown rot-infected bulbs weeds, and other hosts. and alter the symptoms. Crown rot differs in several respects from Control black slime, with which it may be confused. Crown rot appears in warm weather as brown decay of 1. If only a few diseased dumps are present, bulbs and produces reddish-brown sclerotia. Black follow one of these procedures. slime develops in cool weather as a gray or black a. Carefully remove infected plants and soil. decay and forms black sclerotia. Remove all the soil 12 inches from the infected bulbs to a depth of 12 inches. Do Factors Affecting not permit any of this soil or debris to be Since the fungus is a warm temperature para­ scattered when removing plants from the site, it usually does not cause infections until late field. Dust the area with a fungicide (see in the spring. In western Washington the most EM 4314). serious problems on iris have occurred on light, well-aerated soils after heavy rains during warm b. Chloropicrin (tear gas) has been used weather as the plants were maturing (during June successfully by one large grower for ster­ and July). At this time, it may spread rapidly ilizing small infested areas without the along the cracks in soil opened by the expanding necessity of removing plants and soil. In-' bulbs. Crowded and shaded conditions enhance ject this material in the infested area and the disease. The fungus can grow at temperatures around its margin. from 8-40°C with an optimum about 25-35 °C. c. Formaldehyde can be used for small in­ The fungus is rather sensitive to climatic condi­ fested areas in home gardens. (Drench tions. Healthy bulbs have been known to develop loosened soil with Y2 pint commercial from partially diseased bulbs when conditions formaldehyde in 3 gallons of water and were unfavorable for disease development and apply at a rate of Y2 gallon per square favorable for iris growth (grown in heavy, well­ foot.) drained soil in cool seasons) . 2. Dig diseased stock 1-2 weeks earlier than Crown rot is normally not an important dis­ normal. Early digging will help to avoid ease on iris in greenhouses because of the tempera­ spread of the fungus by avoiding warmer tures at which iris are normally forced. In fact, weather. Rapid spread can occur during lightly infested bulbs have been forced expen­ warm, moist weather ~ mentally with satisfactory results. 3. Dry bulbs rapidly in thin layers in open Importance and Host Range trays. Do this outdoors if weather permits or This disease is found world-wide. It is of major in a shed with good air movement and some importance in warm, moist regions, such as the heat if needed. The fungus can spread over

12 bulbs in storage at warm temperature and a um rolfsii Sacc. in iris bulbs. Phytopath, 44 high relative humidity. ( 12) p. 711-713. December. 4. Cull all diseased bulbs. Bury or dump them AYCOCK, ROBERT. 1966. Stem rot and other and the debris from cleaning operations in diseases caused by Sclerotium rolfsii or the a place where crops will not be grown sub­ status of Rolfs' fungus after 70 years. N.C. sequently; Tech. Bul. No. 17 4. August. GOULD, CHARLES ]., and THOMAS S. RUS­ 5. Give infested ·stock the hot water plus for­ SELL. 196 5. Efficiency of various methods of malin ( HWT) treatment recommended for applying PCNB for preventing soil-borne in­ nematode control. If properly done, this will festation of bulbous iris by Sclerotium rolfsii. l kill the fungus in all but some of the largest Pl. Dis. Reptr. 49 ( 2) Feb. 15. infested bulbs ( 10 em. and up) . Either dis­ J CMI Descriptions of Pathogenic Fungi and Bac­ card these larger bulbs or plant them sep­ teria #410-Corticium rolfsii. Eastern Press arately. Since treatments are seldom perfect, Ltd. London. repeat the HWT the following year. 6. Under conditions where the HWT of infested Fusarium Basal Rot stock cannot be used, good but not complete control has often been obtained by dusting Symptoms bulbs with a suitable fungicide (see EM LEAVES. Leaves may not develop from severe­ 4314). ly infected bulbs. When leaves are present they 7. Plow deeply to bury sclerotia and infested are often stunted and yellowed. Young green debris. shoots may be curved and twisted before they turn yellow. 8. Liming has sometimes reduced infection in RooTs. In soil, the fungus first invades the other crops. roots producing sunken brown spots. As the dis­ 9. Plant on dean, heavy, well-drained soil. ease progresses, the infected roots rot, eventually 10. Do not replant on severely infested soil for leading to the infection of the bulbs. at least 3 to 4 years, and preferably longer. BULBS. Infections on the basal plate and The fungus persisted for 10 years in four fleshy scales are at first gray and watersoaked. soil types in western Washington. Later these lesions become light brown or reddish­ 11. If infested soil and/or stocks of bulbs must brown with a fairly definite margin between de­ be used, dust over the bulbs and the open cayed and healthy tissue. The infected area at the furrow with the fungicide recommended in base becomes shrunken. The husks adhere firm! y EM 4314. Certain soil fumigants will also and are sometimes matted with a white or reddish­ elminate this fungus in the soil but if crown tinged mass of the fungus. The rot is rather firm. rot, black slime, and basal rot fungi are ac­ Often, later invasions by Penicillitt,m blue mold cidently reintroduced by planting infested may obscure these symptoms. stock into the fumigated soil, they may spread disastrously before the normal soil Factors Affecting microflora become re-established. Infection increases rapidly in soils above 14°C ( 57 °F) so it is most severe in warm cli­ Causal Agent mates. Sandy soils, southern slopes, and late dig­ ging favor disease development. Usually it is of Corticium rolfsii Curzi (Syn) (Sclerotium only moderate importance in cool climates. Most rolfsii Sacc. and the apparent biotype S. delphinii infection in the Pacific Northwest apparently \ Welch). Sclerotia irregular in shape but usually occurs during harvest when diseased and healthy roughly spherical, somewhat flattened at base, 0.1 bulbs are jumbled together. J to 1.5 em or often larger and coalescing in masses, white at first, changing to brown or to dark Importance and Host Range reddish-brown. Surfaces of the sclerotia are often The disease is found throughout the world and pitted. is occasionally severe in warm climates such as the southeastern United States. It was first described References in the United States at Long Island on both Span­ GOULD, CHARLES ]. 1954. Control of Scleroti- ish and Dutch Iris. Most serious problems occur

13 Basal rot

on yellow varieties but it may also attack others, Causal Agent including W edgewood and Ideal. Other hosts in­ Fusarium oxysporum Schl. 'f. sp. gladioli clude gladiolus, crocus, and freesia. (Mass.) Sny. and Hans. In culture the micl.10- conida are abundant, mostly non-septate, ovoid, Control and measure 7-10 x 3-4p.. Macroconidia are us­ 1. Dig diseased stocks early. Dry rapidly in thin ually scarce, straight to slightly curved, ends point­ layers under well-aerated conditions. ed and curved, typically 3-septate, and average 2. A void bruising when digging, cleaning, and 30 x 4p.. Four- and five-septate spores present but grading. rare. Chlamydospores are abandant, terminal or intercalary, spherical to oval, 7-1 Op., smooth, and 3. Sort and discard all diseased bulbs immedi­ are either single or in short chains. For full de­ ately after digging and again before planting. scription see "The Genus Fusarium" by C. Booth, Burn or bury diseased bulbs. 1971, Commonwealth Mycological Inst., Kew, 4. Treat Fusarium-infected stocks in a fungicide England. Unfortunately, strains of this fungus may solution within 48 hours after digging (see develop (or be selected for) resistance to the EM 4314). Alternate the types of fungicides newer fungicides, such as benomyl. Therefore, it used from one year to another to reduce the is highly important to annually alternate the fun­ likelihood for development of strains of the gicides used for dipping bulbs. fungus resistant to the fungicides. 5. The hot water plus formaldehyde treatment References used for nematodes will also give some con­ APT, W. ]. 1958. Studies on Fusarium diseases trol of Fusarium. However, if a stock is mod­ of bulbous ornamental crops. Dis. Abstr. 19 ( 3) erately or severely infected (above 2% ) it p. 416. (RAM 38:522,1959). should also be dipped in a fungicide either HARRISON, D.]. 1958. A Fusarium rot of bulb­ as soon as the bulbs have cooled or just be­ ous iris. Plant Pathology Vol. 7. p. 16-10. fore planting. The fungus was killed in tests in Israel when bulbs were treated for 30 minutes at 57°C ( 135°F) but this treatment Fire (Leaf Spot) is considered too dangerous for our more Symptoms succulent bulbs. LEAVES. The first symptoms on leaves are 6. Store planting stock at a temperature below small water-soaked spots that soon turn light 15.5 °C ( 60°F) to retard development of the brown in the center. These spots usually enlarge fu~gus. and lengthen up to Y2 inch or more, developing 7. Do not plant until soil temperature is below white or gray centers. They may remain pale or 15.5°C (60°F). Open furrows just before develop reddish-brown borders. The tissue around planting and cover bulbs as soon as possible. and above the spots often turns yellow. Spots may be anywhere on the leaves but are at first most 8. Do not plant in infested soil for 3 or 4 years. numerous near the tips. If these spots are suf­ 9. Plant on heavy, but well-drained soil. Alka­ ficiently large or numerous, the leaves collapse line soils may retard the fungus more than and die prematurely. Under moist conditions a acid soils. thick olive brown mass of spores forms in the 10. Plant diseased stocks separately so they can center of the lesions. Infection does not usually be dug first. become severe until or after flowering.

14 Fire

FLOWERS. Buds and stems may be attacked 3. After digging, destroy as much leaf debris with similar lesions. as possible (deep plowing for example) . BuLBS. Severe leaf infection will reduce the 4. Rake up and destroy old leaves· in home size of the bulbs. plantings. 5. Rotate on a 37 to 4-year basis. Plant as far Factors Affecting away as practical from the previous locations. The disease is favored by mild, moist condi­ 6. Plant in well-drained soil. A void low spots tions. Low areas of fields, areas of poor air move­ and locations with poor air movement. Ridg­ ment, plantings near piles of iris debris or near ing is beneficial. volunteer bulbs are conducive to disease develop­ ment. The disease is also prevalent where iris are 7. Plant as late as practicable to reduce danger not dug annually or on leaves injured during of excessive frost in jury. cultivation. Plants growing under conditions of 8. Plant as thinly as practicable to increase air low calcium nutrition are apparently more suscep­ movement. tible to this disease. Spores can germinate easily 9. Do not plant bulbous iris near rhizomatous over a wide tern perature range-1 0-2 5 ° C ( 50- iris nor in fields containing volunteer iris. 770F) with an optimum near 20°C ( 68°F). 10. Liming at a rate of 1 to 2 tons per acre has These conidia are spread by wind and rain. Over­ been recommended in Canada and England. wintering infected leaf debris is the most import­ ant source of spring inoculum. Causal Agent M ycosphaeretla macrospora ( Kleb.) Jorstad Importance and Host Range (Syn.-Didymellina macrospora, D. iridis, Clado­ Fire is found throughout the world and has sporium iridis, H eterosporium gracile) . Conidia resulted in serious losses. It is generally more are oblong or cylindrical, rounded at the ends, severe on rhizomatous iris than on bulbous iris. echinulate, hyaline at first and later olive brown, There seems to be some varietal resistance, par­ usually 2- to 3- but sometimes 1- to 4-septate and ticularly among the rhizomatous group. Gladiolus, measure 30-80 x 14-20p,. Perithecia are smooth, freesia, hemerocallis, narcissus, and some other globose, dark brown to black, averaging 160 x genera have been reported as occasional hosts. 200p,. The ascospores are hyaline or lightly col­ ored, oval-elliptical or spindle-shaped, two-celled, Control and measure 30-54 x 10-16p,. 1. Keep fields weeded to promote good air movement. References 2. In areas where the disease usually occurs, CMI Descriptions of Pathogenic Fungi and Bac­ begin fungicide applications (see EM 4314) teria # 43 5-Mycosphaeretla macrospora. East­ when leaves are 6-8 inches high. Continue at ern Press Ltd. London. 10-14 day intervals until dry weather occurs. GOULD, C. ]. 1959. Zineb shows promise for In areas of sporadic attack, begin spraying the control of leaf spot of bulbous iris. Plant at the first appearance of the disease. Dis. Reptr. 43 ( 4) p. 491-594.

15 Ink spot

Ink Spot Importance and Host Range Irik spot has been damaging to crops in Europe Symptoms and North America and is probably present world­ LEAVES. The disease begins as small chlorotic wide. Particularly severe outbreaks are reported streaks or spots that soon turn a dark brown. The from southwestern England. It was reported from center of the lesions becomes covered with brown­ British Columbia in 1968 and subsequently was ish-black masses of spores from which the disease found in Washington (unpublished) . Much of gets its name. Ink spot occurs most commonly what has commonly been considered to be fire after flowering and on the oldest leaves, although may well have been ink spot. Originally th~s sometimes young shoots exhibit spots upon emer­ fungus was described as a major pathogen of Irzs gence. Spots may enlarge, fuse, and cause collapse reticulata but now is recognized as a problem on of the leaf. The disease at this stage can be con­ other bulbous iris, including W edgewood. More fused with fire. Ink spot has brownish-black surveys are needed to establish the relative im­ masses of spores, while fire spots are greenish. portance as compared with fire. The disease has The borders of the ink spot lesions may be darker also been reported on T ritonia and Lachenalia. than those of fire. FLOWERS. Stems and flowers may be spotted. Control BuLBS. Dutch-type iris bulbs are not often 1. Keep fields weeded to promote good air affected, but on Iris reticulata the disease appears movement. as irregular inky-black stains on the bulbs and 2. In areas where the disease usually occurs, be­ sometimes as rings on the husks. The stains vary gin fungicide applications (see EM 4314) in size and number. The fleshy scale underneath when leaves are 6-8 inches high. Continue the husk may exhibit small yellow dots or irreg­ at 10- to 14-day intervals until dry weather ular, elongated, sunken black craters with distinct occurs. In areas of sporadic attack, begin raised margins. The fungus is carried on the bulb. spraying at the first appearance of the disease. Infected bulbs sometimes rot, leaving only the husk and a mass of black powder. The fungus can 3. Dig infested stocks early and dry quickly. apparently spread through the soil and attack ad­ 4. Dig bulbs every year. jacent plants. 5. Discard diseased bulbs by burning or bury­ ing them. Factors Affecting 6. After digging, destroy as much leaf debris Disease development is favored by mild and as possible (deep plowing for example) . moist conditions and is most serious in wet seasons. Optimum temperature for fungal growth is 20- 7. Rake up and destroy old leaves in home 25 0C (68-77°F). The fungus apparently survives plantings. primarily on infected bulbs and on diseased debris. 8. The hot water plus formalin treatment has It becomes increasingly severe in stocks left un­ been recommended for killing the fungus in dug for 2 or more years. the bulbs. (See directions under nematodes.)

16 9. Rotate on a 3- to 4-year basis. Plant as far away from previous location as practical. 10. Avoid planting other bulbous iris near Iris reticulata and bearded iris. 11. Plant in well-drained soil. A void low ~pots and locations with poor air movement. Ridg­ ing is beneficial. 12. Plant as late as practicable to reduce danger of excessive frost injury. 13. Plant as thinly as practicable to increase air

Causal Agent Drechslera iridis ( Oud.) Ellis ( Syn.-Mystro­ Virus on W edgewood iris sporium adustum, Bipolaris iridis and Clastero­ sporium iridis) . Conidia are straight, elliptical, or found in bulbous iris. Iris severe mosaic virus broadly fusiform with obtuse ends, smooth, dark ( ISMV) is common and appears to be increasing smokey brown when mature, end cells often pale, in importance. The comments that follow per­ 4-9 pseudoseptate, and measure 45-90 x 16-29p.. tain to it. It is called gray disease in Holland and References yellow latent mosaic in Israel. CMI Descriptions of Pathogenic Fungi and Bac­ teria # 434-Drechslera iridis. Eastern Press Iris Severe Mosaic (Yellow or Ltd. London. PRICE, DAVID. 1971. The effects of "burning­ Latent Mosaic or Gray Disease) over" and fungicidal spraying on iris flower and bulb production and on the incidence of ink Symptoms disease caused by Bipolar-is iridis ( Oud.) Dick. LEAVES AND STEMS. The entire plant may Exper. Hort. #22 p. 25-30. show various degrees of stunting; sometimes PRICE, DAVID. 1973. Ink disease caused by severe stunting occurs. Affected plant tissues may Drechslera iridis. Annual report of Glass House be yellow or have yellowish streaks or patches of Crops Research Inst. p. 115. normal green surrounded by yellow. The most PRICE, D., and A. A. TOMPSETI. 1973. Iris intense symptoms appear on bud sheaths and the flower production. Exper. Hort. #25. p. 133- lower parts of vigorously growing young leaves 135. under cool conditions. As temperature increases STRABY, A. E., and R. A. SHOEMAKER. 1968. and the plants mature, the symptoms become less Bipolaris iridis on iris in British Columbia. Can. noticeable. Reaction of plants to winter injury Plant Dis. Surv. Vol. 48. p. 152. and sometimes drought can be confused with mo­ saic symptoms. These environmental maladies cause a regular pattern of white or pale green flecks or squarish markings, which are usually At least five viruses infect bulbous iris. Two confined to older leaves. In contrast, the mottling (tobacco rattle and tobacco ringspot) are gen­ from mosaic does not usually follow a regular erally unimportant. They are transmitted by nema­ pattern and is most evident on the youngest leaves. todes and usually occur only sporadically. Iris FLOWERS. Dark teardrop markings appear on mild mosaic virus ( IMMV) is spread by aphids diseased flowers of white, blue, and lavender and is widespread but only induces an indistinct varieties, whereas clear feather-like markings ap­ light yellow-green streaking in young leaves and pear on yellow flowers. Bud sheaths may show flower stems. It may produce a more intense bluish-green blotches on a pale green background, mottle in the flower bud sheath and occasionally or less often, yellowish streaks. Not all infected one or more dark spots at the tip of the outer plants show both leaf and flower markings, espe­ petals of dark-flowered varieties. However, it has cially those grown from small bulbs. Mosaic symp­ little effect on flower quality and yield. The aphid­ toms develop more strongly in the greenhouse transmitted narcissus latent virus has also been than outdoors. Cut flowers from greenhouse-

17 grown, severly mosaic-infected plants are poor in quality and do not last long. BuLBS. Infected plantings often produce few­ er and smaller bulbs than normal. Growth from infected small bulbs may only show mild symp­ toms the first year. Factors Affecting In the field, the disease is spread by aphids. An aphid can "pick up" the virus by feeding on an infected plant. When it moves to feed on an adjacent healthy plant, the virus is transmitted into this plant. It is also suspected that aphids can spread this virus when the bulbs are in storage. Mosaic virus on Dutch iris The virus is not spread by picking flowers. Mosaic is more severe in warm climates and under other 3. Dig stock selected by hand, being sure to keep conditions favoring aphid build-up. Increased cliunps intact. Select only the largest clumps, aphid populations can be expected following a and plant them in units with the mother and mild winter. The prevalence of overwintering host daughter bulbs together. These should then plants, presence of weeds, and the type of crop be rogued as a unit, because if one bulb in a and insect control in adjacent fields all can influ­ clump is infected, the others usually are too. ence aphid populations in iris fields. An alternative procedure has been used successfully by a grower in Washington. The Importance and Host Range largest bulbs were selected for planting in a Mosaic is a rna jor problem found throughout mother block. This mother block was rogued the world. It is especially common on many Dutch, intensively for 2 to 3 years, at which time Spanish, and Tingitana types, including the va­ the virus was practically eliminated. The pro­ riety W edgewood. It also has been reported on geny were used to establish the foundation crocus. planting. Using this method, the increase was Control not as fast as with the clump method but much It is not possible to eradicate the virus from hand labor was eliminated. Use only the larg­ diseased bulbs. Thus it is necessary to maintain est bulbs for foundation plantings, since small virus-free bulbs for foundation planting stocks. bulbs are more likely to be infected. After the This may be accomplished by starting with mer­ foundation stock has become established the istem-cultured iris; however, these are not readily daughter bulbs can be used for commercial available. Therefore, the commercial grower must production. rely upon either purchase of healthy stocks or 4. Never plant foundation and mother stocks "cleaning up" his own. Many of the following adjacent to commercial stocks. Keep~ them at recommendations were, developed over 3 5 years least 300 feet from commercial fields of iris ago by F. P. McWhorter. to prevent spread of the virus by aphids. Mosaic cont.rol in iris ·involves a special plant­ 5. Control aphids, especially in foundation stocks, ing program for two reasons: first, diseased plants by regular spraying with an insecticide. Then may not show symptoms the season they are in­ wait at least 24 hours before spraying with a fected; and, second, mildly infected plants are dif­ fungicide. Do not mix the two, unless they are ficult to identify and eliminate. Emphasis must compatible. Begin spraying at first sign of be placed upon establishing and maintaining a aphids in the spring and continue until har­ disease-free foundation stock from which all plant­ vest. Thorough weeding in and around the ing stock can be selected. Here is how to establish field also helps to keep aphid numbers at a a foundation planting: mtntmum. 1. Begin with stock containing less than 10% 6. Rogue the foundation stocks by removing mosaic-infested plants and preferably not over the complete unit (mother and daughter 5%. plants) if virus symptoms are found in any 2. Remove all diseased plants. --- plants of the unit. The largest plants and 18 youngest leaves show the best symptoms early in the season. Symptoms are most easily seen when the sky is slightly overcast. Place rogued plants in a tight container to prevent scatter­ ing of aphids and remove them from the field. Burn or bury the plants. Each crop should be rogued at least three times: early spring, mid­ season, and during the flowering period. 7. Dig mother and foundation stock 1 to 2 weeks Nematode earlier than normal to shorten the period dur­ damage ing which aphids can spread mosaic. 8. Be careful to keep foundation stocks distinct from commercial stocks in the warehouse. Mixing can occur all too easily. 9. Fumigate bulbs or treat with an insecticide if aphids appear on bulbs in storage. Causal Agent Iris Severe Mosaic Virus (ISMV). See Brunt 1974. References BRIERLY, PHILIP, and FRANK P. McWHORT­ ER. 1936. A mosaic disease of iris. J. of Agric. Res. 53. p. 621-635. BRuNT, A. A. 1974. Viruses and virus diseases of iris in Britain. Acta Hort. 47. p. 45-50. Not all the above symptoms are necessarily present in all varieties. The gray discoloration of the basal plate is the most consistent general symptom of nematode infection. This is often the Miscellaneous Diseases only symptom present in English iris. In Wedge­ wood, the dark, sunken crevice around the basal and Conditions plate is more common than are the streaks, while in Imperator, the streaks are quite common. Nematode (Eelworm) Infection varies with the size of the bulbs, Symptoms being most frequent as well as most apparent in LEA YES. Leaves may be lacking or stunted if the larger sizes. The large central bulb of a clump bulb infection is severe. There are no pimples is often the only one that is infected. Since the ( spikkles) such as in nematode-infested daffodil infection progresses during the storage season, leaves. stock that did not exhibit infection when harvested STEMS. Light gray or yellow areas appear on may show symptoms at planting time. stem where it is attached to bulb. Factors Affecting BuLBS. In early stages the outer husk shows Nematode damage is apparently worse in black streaks along the veins; later the husks may cool, moist climates. The nematode apparently become shredded at base. The basal plate becomes does not survive long in fallowed soil. honeycombed and grayish (remove basal cap to check this point) . The outer fleshy scales are Importance and Host Range separated from the basal plate by a dark, sunken The nematode is probably present throughout crevice. Yellow, slate gray, or black streaks appear the world and is particularly serious in Holland on the fleshy scales, usually beginning at the base. and the Pacific Northwest. It is also destructive The streaks are most numerous in outer scales in many other regions and attacks many types of and sometimes fuse and rot the entire scale and iris as well as many other hosts including alfalfa, bulb. Sunken spots with dark margins sometimes tulips, potatoes, sugarbeet, mint, weeds, and even are present near tip of bulb. some fungi.

19 Control least 2 years after all volunteer plants have 1. Harvest infected stocks 7 to 10 days earlier been removed, unless the infested ground is than normal. fumigated first. Removal of all volunteer 2. Bury or burn all diseased bulbs and the trash bulbs will help but unfortunately the nema­ from all cleaning operations. tode may survive on other hosts, so fumiga­ tion may be essential. 3. Treat planting stock, when dormant, in hot 9. A void planting healthy iris on land that gets water plus formaldehyde (see EM 4314). surface drainage from infested soil. Addition of a wetting agent is recommended in England. Treat for 3 hours after bath is 10. Keep healthy and infected, treated, and un­ stabilized at 43.5 °C. Plant immediately or treated stocks definitely marked and separ­ dry and cool promptly by spreading in thin ated in the warehouse. layers in a cool place with good air circula­ 11. Dr. Wm. Haglund (WSU-Mt. Vernon) tion. Determining the optimum date for has recently found that drenching or dusting treatment is still difficult. In the Puyallup one of the new nematocides over the bulbs Valley this usually occurs about the middle in the furrow at time of planting gave excel­ of August in normal years (about a week lent control. See EM 4314 for further details. earlier in Portland area and a week later in As with all new treatments, it would be well the Mount Vernon area) . Many factors in­ to experiment with it first under your own fluence maturity, including precipitation, conditions before using on the entire stock. temperature, and soil type. One possible Hot Water Tanks guide for determining the best time for treat­ Plans for the construction and use of hot ment is to treat a week or two after the basal water tanks are contained in Washington State cap can most easily be slipped off. Treatment College Experiment Station Popular Bulletin No. after the basal plates have begun to swell 184, Hot Water Tanks for Treating Bulbs and has always resulted in injury but too early a Other Materials, by W. D. Courtney, E. P. Breakey, treatment is also injurious. Varieties vary in and Loyd L. Stitt. their susceptibility to hot water injury. Ideal and W edgewood are more resistant than Causal Agent many "Dutch type" varieties. The latter can Ditylenchus destructor Thorne. (See Princi­ only be given 1 ~- to 2~-hour treatment. ples of Nematology by Gerald Thorne, 1961, pp. Repeat annually until the nematode is erad­ 138-148.) icated. References 4. Reports from England indicate that injury COURTNEY, WILBUR D., and CHARLES J. from hot water treatment is lessened by stor­ GOULD. 1951. Tolerance of Wedgewood iris ing the bulbs at 30°C ( 86° F) for a week bulbs to a hot-water-formalin treatment. Phy­ before treatment; however, this may make topath: XLI: 1 p. 40-45. the nematodes more resistant to control. GOODEY, J. B. 1951. The potato tuber nema­ After the 30°C ( 86°F) storage, they pre­ tode, Ditylenchus destructor, Thorne, 1945. The soak the bulbs for 2-3 hours in water plus cause of eelworm disease in bulbous iris. Appl. a wetting agent before using the HWF Bioi. 38 ( 1) p. 79-90. treatment. 5. Treat planting stock regularly every 2 or 3 Black Storage Molds years as an insurance against reinfection. The bulbs are matted together and more or 6. Clean and grade healthy stocks before hand­ less covered with a white to gray mold. Associated ling diseased stocks. with the mold are either very small black bodies 7. Disinfect used trays, cases, tools, etc., by treat­ of the fungus ( Rhizopus sp.) or a covering of a ing with steam; or dipping in hot water at black, sooty mass of spores (Aspergillus sp.). Af­ 85 oC ( 185 °F) or dipping in a solution of fected bulbs usually turn into mummies. Storage 1 quart formaldehyde ( 3 7 % ) to 9 quarts rot appears occasionally in bulbs that have been of water. injured, stored in excessively full trays, kept too 8. Do not plant iris on the same ground for at warm and moist, or overheated during shipping.

20 Black Tip Leaf tips are covered with a black powdery mass of spores. It is widespread in the Pacific Northwest but apparently does not cause any harm since the fungus only attacks foliage that has been frosted or otherwise injured. Removal of debris, rotation, and other proper cultural prac­ tices should keep it to a minimum. Spraying, as for leaf spot, may be of some benefit but is usually unnecessary. Causal agent: Didymellina poecilo­ Botrytis spora MeW. Perithecia similar to D. iridis except blight for size; ascospores 6 x 25 IL; conidia usually two­ celled, 6-9 x 12-38 IL· (McWhorter, F. P. 1937. Didymellina poecilospora, n. sp., A Semipara­ sitic Heterosporium on Bulbous Iris. Phytopath. may aid in cleaning up infested stocks; do notre­ 27 p. 135-136.) plant bulbs in the same area . for 4 years or treat infested soil as described for Crown Rot. Botrytis Blight (Boerema, G. H. 1963. De Veroorzaker van de., Various species of Botrytis (primarily B. cin­ "Kwade-Grondziekte" bij Bloembolgewassen: Rhi- erea Pers.) have occasionally caused a blighting of zoctonia Tuliparum Whetzel & Arthur. Versl. flowers, spotting of leaves, neck, and bulb rots. Plziekt. Dienst No. 1 141. Jaarboek, 179-182, A gray mold usually develops on the aerial parts, and CMI Descriptions of Pathogenic Fungi and followed by formation of small black sclerotia. Bacteria # 407-,Rhizoctonia tuliparum.) The sclerotia also develop on the undergrouncl parts. The neck rot phase has occurred in both Pythium Root Rot field and greenhouse plantings under conditions Leaf tips of diseased plants become yellow. of either excessive humidity or plant injury from These plants may occur singly or there may be freezing. Promoting good air circulation and low small groups. The yellowing continues resulting in humidity and preventing injury as much as pos­ premature dying. The area of diseased plants sible will aid in the control of this disease. usually continues to enlarge. Root tips are infected first but entire roots may be rotted. The problem Gray Bulb Rot is most often found on iris grown in greenhouses but has been serious at times in England and the Infected plants fail to emerge or are stunted Channel Isles. It is also reported from Holland. and often die before flowering. The bulbs are gray, (Humphrys-Jones, D. R. 1975. Root Rot (Pyth­ reddish-gray, or sometimes brown, usually at the ium irregulare Buisman) in Dutch Iris. Pl. Path. tip, and often gray masses of mycelia are present. 24:248.) Dark brown to brownish-black sclerotia up to 1 inch in diameter occur on or in the bulb. The disease develops early in the season on bulbs grow­ Rhizoctonia Neck and Bulb Rot ing in the field or on bulbs being rooted in cool Foliage yellows, wilts, and dies from the soft cellars for forcing. It is considered to be a major light-brown decay of the underground parts. Bulbs problem in Europe, but has been reported only may exhibit dark brown spots, which sometimes occasionally in North America. The fungus also enlarge and completely destroy the bulb. This dis­ attacks tulips, hyacinths, scilla, narcissus, and most ease (caused by Rhi.zoctonia solani Kuehn) occurs other bulbs. It is caused by Rhizoctonia tuliparum, in the Pacific Northwest but is usually of minor Whet & Arth. (Sclerotium tuliparum). importance. Careful culling and rotation should Control recommendations include removal of control it. If the problem persists, a fungicide ap­ diseased plants and surrounding soil; sort and dis­ plication, as for crown rot, should be used. (Son­ card by burning or burying all diseased bulbs after derman, Clarence H., and Neil Allan Maclean. digging and again before planting; the 3-hour hot 1949. Rhizoctonia Neck and Bulb Rot of Iris in water plus formalin treatment (as for nematodes) the Pacific Northwest. Phytopath: 34:174-175).

21 Rust The fungus ( Puccinia iridis Rabh.) produces small oblong or oval, red or dark-brown powdery spots on leaves and stems. The spots are often surrounded by a yellow margin. If such spots are numerous, the leaves and stems die prematurely. It is common and serious in the southeastern United States and in some other areas of the world, but is uncommon in the Pacific Northwest. Va­ rieties differ in resistance. Apparently no control Topple measures have been developed. Rotation and de­ struction of crop residue should help. (Sobers, E. D. 1966. A New Form and Two New Hosts of Puccinia iridis in Florida. Phytopath. 56:804- Other Diseases 806.) Several other diseases affect iris but have either not been identified in the United States or Sunburn. are of minor importance. They are discussed in Moore's book. Included are white root rot Bulb husks acquire a reddish or purplish tint (caused by 1Rosellinia necatrix Prill) and phyto­ when exposed to strong sunlight, especially if it phthora stem and leaf rot, both of which have occurs soon after digging. The outer fleshy scales caused considerable trouble in southwestern Eng­ may be damaged. Sunburned bulbs become ex­ land during winters. A storage disease called cessively dry, thereby losing weight as well as "Pops" has occasionally been serious in North size. Such bulbs are also quite susceptible to at­ Carolina-the fleshy part of the bulb decays, tack by Penicillium and Rhizopus fungi. leaving an empty husk. (Moore, M. A. 1949; Diseases of Bulbs, Ministry of Agric and Fish. Bulletin No. 117, His Majesty's Stationery Office. Topple (Sugarstem) London.) This is primarily a greenhouse problem that results from a calcium deficiency. It begins as a light green water-soaking of the upper flower stalk. An exudation of a viscous liquid sometimes occurs on the affected stalk. The affected tissue shrinks resulting in a toppling of the flower. Top­ ple occurs most often during short days and cloudy skies. This problem in iris resembles that occurring on tulips where a high relative humidity also stim­ ulates topple. Topple has been prevented by incorporating calcium nitrate in the soil before planting or by repeated drenches of calcium nitrate, beginning soon after emergence. Maintain good air circula­ tion in greenhouses and prevent temperatures from going too high. If topple begins, immediately lower the temperature. If it is a commonly occur­ ring problem, mix calcium nitrate in the soil be­ fore planting iris or drench weekly with a 0.06 % solution and place cut flowers for 12 hours in a 1% solution. (Haasis, Frank A. 1953. Topple Disease of Dutch Iris. Plant Disease Reporter, 3 7, p. 558.)

22 Key to Major Iris Diseases

Leaf Symptoms Outer leaves mottled, young inner leaves not mottled ______· ------____ WINTER IN JURY All leaves mottled, most evident on inner leaves ______MosAIC Gray or olive-brown spots with a dark border ______FIRE Black Spots ____------··------··------______INK SPOT Leaves yellow and dying with water-soaked dark green, brown, or greenish-black streaks ______BACTERIAL BLIGHT Leaves yellowed-usually one of the bulb rots ------___SEE BELOW

Flovver Symptoms Discolored streaks in flowers, may be ______MosAIC Flowers lacking from blooming-sized stock ______BLINDNESS Flowers present but prematurely dead or wilted ______BLASTING

Bulb Symptoms Tan sunken areas with brown sclerotia often present ------CROWN RoT Base shruken, often covered by white or pinkish mold ______BASAL RoT Basal plate gray, often surrounded by a dark crevice; dark streaks in husk and fleshy scales ------· ______NEMATODE Soft, cheesey rot, usually at base and covered with blue-green mold ______BLUE MOLD Black rot of fleshy scales with black sclerotia ______BLACK RoT Black irregular patches on husks ------·------______INK SPOT

23