Contents

Fungus Diseases __ ·------______3 Blackleg ______·------. ------_ . __ __ 19 Diseases _------______3 Botrytis Measles ______------·------19 Nematode Diseases ______----··-··-- __ 3 Fluorine _____ ------·------______------______19 Bacterial Diseases ------4 Fusarium Blight ------·--- __ _ 19 Physiological Diseases ______4 Miscellaneous N em a toes ------___ 19 Rhizoctonia Blight ______------··------19 MAJOR D ISEASES Basal Rot ______4 Rust and Smuts ______------_ 20 Black Slime (Black Rot) ______6 Sativa ------______2 0 Skin Disease (La Reine) ______20 Blue Mold ------______. ____ 7 Smoulder ______----· ______2 0 Botrytis Blight (Fire) --··------7 and Stem Nematode (Eelworm) ______10 Sooty ------·------·------___ _ 20

Crown Rot (Southern Wilt) ______11 PHYSIOLOGICAL PROBLEMS Foot Rot (Root Rot, Shoo trot, Shanking) _ __ 12 Blind, Blasted, or Deformed Flowers ______20 Gray Bulb· Rot (Bad Soil) ______12 Blueing of Bulbs ( Blawgroeien) ______20 Pythium Root Rot and Soft Rot ______13 Bud Necrosis (Core Rot or Kernrot) ______20 Topple (Sugarstem or Wet Stem) ______14 Ethylene Damage ______-··------______21 Frost Injury ______------·----. 21 V IRUS DISEASES Heat Damage ______21 Major Virus Diseases of - Table ______16 Breaking (Mosaic) ______16 Gun1mosis ------______21 Nutrient Deficiencies _ ------21 Yellow Pox ______------______18 Mechanical Damage ------__ __ 22 MISCELLANEOUS DISEASES Hard Base ------__ __ 2 2 Anthracnose ______19 KEY to Major Tulip Diseases ______23

Many of the recommendations in this bulletin are based upon cooperative research with other colleagues, particularly Mr. Vern Miller and Dr. Neil Stuart. We express our gratitude to them and to Mr. Worth Vassey and Mrs. Evelyn Morris for their research assistance; to Drs. Tom Allen, Alan Brunt, Gary Chas­ tagner, William Haglund, ]. ]. Hesling, David Price, Alen Rees, and Willis Wheeler for reviewing the manuscript; and to the Washington State Bulb Commission and the Northwest Bulb Growers Associa­ tion for their support in the research and publication of this bulletin.

Issued by W ashington State University Cooperative Extension, ]. 0 . Young, Director, and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 20, 1914. Extension programs are available to all persons without discrimination. Issued August 1979.

2 DISEASES OF TULIPS

CHARLES J. GouLD, Plant Pathologist, Emeritus, and RALPH S. B);'THER, Extension Plant Pathologist, Western Washington Research and Extension Center, Puyallup

In general, botrytis blight (fire) is the one able from Xerox University Microfilms, 300 N. serious disease of tulips that consistently occurs Zeeb Road, Ann Arbor, Michigan 48106) . in the Pacific Northwest. It is also the most ser­ ious in other growing areas of the world. Our climate is extremely favorable for the develop­ Diseases ment of this fungus disease. Other diseases that may cause trouble at times include crown rot, Many important diseases of tulips are caused basal rot, blue mold, and tulip break. by fungi. Fungi are small and rather simple plants The most threatening disease to the tulip in­ unable to produce their own food because they dustry is the bulb or stem nematode. It is not do not have the green coloring matter ( chloro­ known to be present here, but we urge growers phyll). Rather than manufacture their own food, to keep a sharp lookout. It is more destructive they feed on living or dead plants and animals than the race attacking daffodils, and it spreads resulting in disease or decay of the tissues they -easily. It is almost impossible to eradicate since attack. tulip bulbs cannot tolerate the full hot water Fungi produce very small seed-like bodies treatment. called spores. These microscopic spores can be spread by splashing rain or wind or carried along A key to the rna jor diseases is provided. In with the movement of soil or infected plant addition, there are many diseases listed as minor debris. Fungi survive from one season to the next, that are occasionally serious, so do not overlook either as dormant spores in the soil or as thread- . them when diagnosing a problem. If in doubt, like growths within a bulb or diseased plant take samples to a local expert who may be able tissue or as hardened lumps of tissue in the soil to help you. where the bulb grew. These masses of weather­ The controls listed are for commercial pro­ resisting fungus tissue are usually rounded, hard, duction. Disease Control Recommendations for and are called sclerotia. Tulips, EM 4315, is updated annually to identify currently registered for disease control. When chemical applications are recommended, Virus Diseases the hobbyist will probably find it necessary to spray as often as the commercial grower to obtain Virus particles are so small that they cannot adequate control. In general it is a good practice be seen with an ordinary light microscope but re­ to eliminate all abnormal plants or bulbs as soon quire the use of an electron microscope. When as noticed and change planting locations at least they gain access to a plant, they usually penetrate evety other year. into every part except the seed. Therefore, when­ ever a "daughter" bulb is taken from a virus-in­ The authors have drawn heavily upon the fected plant, it is usually also infected. Certain following publications and readers are referred insects, such as , which feed on plant sap to them for additional information. can spread some virus diseases. MOORE, W. C. 1949. Diseases of bulbs. Min. Ag. and Fish. Bul. 117, London. (A re­ vision is in press.) Nematode Diseases REES, A. R. 1972. The growth of bulbs. Nematodes are very small thread-like worms. Academic Press. Many commonly live in the soil without doing General culture, forcing, etc. are covered in any harm, while others attack various plants. The more detail in the Handbook on Bulb Growing bulb nematode and root lesion nematodes, which and Forcing, edited by C. J. Gould, 1957 (avail- affect tulips, are too small to be seen without a

3 microscope. Nematodes survive from season to season as eggs. They also can survive for several years in bulbs or in infected plant tissue. Any movement of soil or infected plant parts can be responsible for the spread of nematodes. Farm equipment, irrigation, flooding, and planting in­ fected bulbs are common ways of spread.

Bacterial Diseases Basal rot Bacteria are simple, microscopic, usually single­ the base. The roots are a dull gray. Small, gray, celled plants which depend upon other plant or slightly sunken spots with a dark edge appear animal sources for their food. Most are beneficial first on the bulbs. These may enlarge rapidly with and only occasionally do they cause trouble in a soft, dull white, gray to brown decay that has tulips. Spread and survival are dependent on the a sour odor. Later these tissues shrink, become presence of infected plants or plant tissues since firm, and often have felty masses of white or pink the bacteria are not able to survive for any period mold (mycelium) and powdery masses of spores of time in soil. in or under the husk. Often the infection is ring­ like with concentric rings of darker zones. The Physiological Diseases initial symptoms are often small and easily over­ looked. Symptoms increase during storage and All problems that are not caused by para­ usually the bulb continues to decay and is con­ sitic organisms are considered in this group. verted to a granular mass. Often this process is Tulips are quite susceptible to unfavorable weath­ aided by mites. Gum may be exuded during the er. Frost may injure their , the sun may early stages. burn the bulbs, and undesirable temperatures may prevent flowers from forming, or ruin them after Factors Affecting they have formed. The fungus grows well at warm temperatures but is more capable of spreading through the relatively cool soils in the Pacific Northwest than either of the strains attacking or . Although infection can occur at temperatures as Basal Rot low as 7°C ( 46°F), it increases rapidly above l5°C (58°F). Particularly favorable infection Symptoms periods commonly occur during the last two to LEAVES. Plants in the field may fail to emerge three weeks before harvest. The fungus produces from diseased bulbs or emerge and later become abundant spores at 20-34 °C ( 68-93 oF) when stunted with leaves turning red, wilting, and dying the humidtty is high. These spores can cause prematurely. In the greenhouse a rapid attack at infection within 24 hours. In a dry condition such warm temperatures may cause leaves to rapidly spores have survived for over eight months in turn yellow, wilt, and die. dust, boxes, etc., and for over eight years in dried FLOWERS. Flowers may be blasted, deformed, bulbs. The fungus can also survive in the soil for or lacking because of the decay of the bulb or in­ several years, particularly in warm climates. fection on the lower part of the stem. Similar More disease occurs in the warmer light sandy flower symptoms can appear on plants arising soils than in heavier ones. A warm, wet spring from "nondiseased" bulbs which have been in can be disastrous. The fungus can spread through storage with infected bulbs. In storage, basal rot­ the soil up to 6 em ( 2 Y2 in.) per year. Cultiva­ infected bulbs produce ethylene gas, which af­ tion and movement of soil within and between fects the other bulbs and results in these flower fields can account for a more rapid spread of the symptoms. disease. BuLBS. Symptoms vary depending upon the The diseased bulbs often produce ethylene, time of attack, temperature, etc. Infection may oc­ which weakens adjacent bulbs or plants and cur anywhere on the bulb but is most often on makes them more susceptible to attack. Ethylene

4 can also cause gummosis, death of buds, flower bud blasting, stunting of roots and stems, and leaf abnormalities (see under Physiological) . Ap­ parently the tulip Fusarium produces more ethy­ lene than others do. The outer immature white scales contain tulapine (a-methylene butyrolactone) , which re­ tards invasion by Fusarium. Ethylene inhibits formation of tulapine, which also naturally dis­ appears as the bulb matures, increasing its sus­ ceptibility. In the Pacific Northwest most infec­ tion apparently occurs just before or during har­ vesting. We found that the earlier we dug tulips, the less the disease developed. Sometimes the fun­ gus infects bulbs but the lesions do not enlarge. These infections are easily overlooked and can serve as a source for later outbreaks. More infection usually occurs on forced bulbs when they are precooled at 5 °C ( 41 °F) for 9-12 weeks and then forced at 16.5 oC ( 61 °F). Symp­ toms (premature yellowing and dying) may ap­ pear within 2-3 weeks in the greenhouse. Similar bulbs forced at 12 °C (54°F) may be slightly infected but still produce a marketable flower. In culture the fungus grows very slowly at 10°C (50°F), best at 25-30° (77-86°F), and practical­ ly ceases at 40°C (104°F). Heavy nitrogen fertilization may increase sus­ ceptibility.

Importance and Host Range The disease occurs throughout the world and probably is the second most important disease of tulips. The Fusarium attacking the tulip is pri­ marily confined to tulips and does not usually attack iris and narcissus, so rotation with these crops is satisfactory. Strains of the fungus exist and some are resistant to some of the fungicides such as benomyl. Tulip varieties vary in suscepti­ bility-many of the Darwin hybrid group (such as Apeldoorn) are particularly susceptible.

Causal Agent Fusarium oxysporum 'Schl. f. sp. tulipae Apt. Cultures white to peach with a purple tinge. Abundant microconidia ( 5-12 x 2.2-3.5/L) are borne on simple phialides arising laterally on hyphae or from short sparsely branched conidio­ phores. The thin-walled, 3-5 septate, fusoid­ subulate pointed ends, 30-60 x 3.5f.L, macroconi­ dia are borne on more elaborately branched coni­ diophores or on the surface of Tubercularia-like sporodochia. The only known major host is tulip.

5 Black Slime (Black Rot) Symptoms LEAVES. Leaves on infected plants turn red­ dish, wilt, and die, usually before flowering. Often groups of plants are affected. FLOWERS. The underground stems are partial­ ly or entirely rotted and blackish on the outside, gray internally, and sometimes have black scler­ otia adhering. BULBS. Infection first appears as irregularly Black slime shaped, soft black spots in the outer scale. The top of the bulb is most often attacked but other References parts are susceptible. The bulb often continues to BOEREMA, G. H. 1961. Notes on some un­ rot, becoming covered with a cobwebby gray usual fungus-attacks on flower bulbs II. Overdruk mass of mycelium. A grayish-black decay of scales uit Versl. en Meded. Plantenz k. Dienst no. 136. progresses until only a dry crumbly mass of bulb p. 210-217. fragments and black sclerotia remains. The scler­ GOULD, CHARLES J., and D. M. McLEAN. otia are numerous, white internally, black on the 1952. Black rot of iris,, tulip, and bulbs. outside, irregularly shaped, rounded if they are Phytopath. 42 ( 9) p. 514. on the surface, but flattened when between scales. Their size varies from 1/ 16 to Y2 inch or more.

Factors Affecting The black slime fungus grows best at cool temperatures when ample moisture is present. It apparently will not survive in the soil more than two years in the absence of bulb hosts in western Washington.

Importance and Host Range Black slime is more common in cool climates but is probably found throughout the world. It was serious in many stocks in the Pacific North­ west during the 195 Os but the repeated use of PCNB coupled with sanitary measures and the absence of weed hosts has reduced the disease status to a rarity. The fungus apparently only causes diseases on bulb crops including iris, cro~ cus, scilla, hyacinthus, and to a minor extent nar­ cissus. Leaf symptoms resemble those of crown rot, but the latter is most common during warm temperatures and appears late in the growing season. The incidence of black slime diminishes about the time that crown rot appears. 4. Rotate with non-bulbous crops. Do not plant bulb crops in infested soil for three years. Causal Agent During the rotation, remove all volunteer plants. Plantings may be made in infested Sclerotinia bulborum (Wakk.) Rehm. Scler­ sods if the soil has been fumigated or the otia are white at first, later black, smooth and bulbs are dusted in the furrow with a fun­ rounded ( Ys" to ~") or if between scales flat­ gicide. tened, and often fused into irregular masses 1;2" or more wide. Apothecia are light brown with asci 140 x 9!-L and ascospores 16 x 8fL.

6 These fungi hav:e a wide host range and are prob­ aby present in most sheds, greenhouses, and soils.

Causal Agent Blue Mold Various Penicillium species including P. cy­ clopium Westling and P. corymbiferum West­ ling. See Raper for descriptions.

References Symptoms RAPER, K. B., and CHARLES THOM. 1949. A Manual of the Penicillia. LEAVES. The tip (outer leaf) of the young SAALTINK, G. ]. 1971. The infection of sprout may be rotted and covered with a blue­ bulbs by Penicillium Sp. Acta Horticulturae 23: green mold. A water-soaked area separates the 235-241. diseased and healthy tissues. Severely infected bulbs may produce pale-green and somewhat stunted plants which die prematurely. FLOWERS. Poor quality flowers are produced from diseased bulbs. Rough and irregularly Control shaped brown spots may develop on the under­ 1. Prevent in jury at all times-while digging, ground stems. cleaning, grading, storing, precooling, and BuLBS. Bulb symptoms vary considerably de­ planting. Do not bounce bulbs while dig­ pending upon the species of Penicillium, variety ging, etc. Use sponge rubber wherever pos­ of tulip, time of attack, and environmental condi­ sible to reduce bruising. tions. They range from small yellow or light 2. Clean, dry, and store with good ventilation, brown spots to large light to dark discolored areas moderate relative humidity, and adequate with or without a definite margin. However, soon­ air circulation at all times. er or later the affected tissues become covered with a green or blue-green mold. Husks may or may 3. Discard diseased bulbs. not be split and discolored. The bulb may be con­ 4. Fungicide treatments have sometimes helped. verted to a dark powdery mass. Some types of Benzimidazoles formerly gave good control blue mold may only grow on the surface of the but in many areas the fungi developed re­ outer husk without causing further damage. sistance to them. See EM 4315 for other pos­ sibilities. Factors Affecting The disease is usually, but not necessarily, as­ sociated with injury from insects, sunburning, bruising, mechanical damage, mishandling, or Botrytis Blight (Fire) from some other type of injury. The increased trend to mechanization has probably increased Symptoms losses from blue mold. Cracking or loss of skins LEAVES. Young shoots may be diseased as they due to digging too early or too late or from rough emerge from the bulb. Infection occurs either handling facilitates infection. The disease is us­ from diseased bulbs or adjacent contaminated soil. ually more of a problem in storage at cool temper­ As these "fireheads" ("primaries" or "steckers") atures, although it can occur over a wide tempera­ emerge they appear more or less rottef.l , brown, ture range. High relative humidity and poor air stunted, distorted, and often rolled into a tight circulation favor the disease. Once infection has bundle. Sometimes the infection is only partial occurred, warm growing conditions stimulate and a curled one-sided diseased shoot develops. disease development. Under moist conditions, gray, fuzzy masses of spores and small ( 1-2 mm) flat black sclerotia Importance and Host Range develop on them. Blue mold is prevalent worldwide and is The spores, which are blown or splashed by sometimes serious, especially on bruised bulbs. rain, can infect leaves within 24 hours. The leaf

7 Botrytis blight spots start as very small, circular to oval, dark­ become covered with masses of spores. The dis­ green watersoaked areas which turn yellow to seased flowers later turn brown and dry up. gray-brown and are slightly sunken. Most spots Severely infected flower buds are unlikely to open. stop at this point and remain non-aggressive. BuLBS. The outer husk may be discolored, However, if there are enough spores present and/ split, and covered with small ( 1 mm) , circular, or humidity remains high for 48 hours, the spots flattened black sclerotia. Spots of 1-10 mm occur become aggressive and rapidly enlarge. on the outer fleshy scale. They are round to oval, Affected areas have a depressed center that sunken, have a yellowish-gray center with a nar­ is whitish gray to brown with a watersoaked row raised dark edge, and sometimes have one margin. Often gray masses of spores cover the or more sclerotia present. Such spots may enlarge surface of affected tissues. Infected stems and/or after planting, turn brown, and partially or com­ bulbs may cause leaves to turn red or purple with­ pletely rot the bulb. The fungus usually infects out any spotting. Hailstones also spot the leaves the new shoot by growing from these spots over but such spots are whitish, without a watersoaked the surface of the scale or husk to the emerging margin and are more irregularly shaped than are tip. Not all diseased bulbs produce diseased shoots. Botrytis lesions. The fungus persists longer on bulbs in storage FLOWERS. Infections on bulbs or on below­ under cool and moist than warm and dry condi­ ground stems may result in a light streaking of tions. red flowers. The stems above ground often be­ come infected, particularly in the leaf axils. Such Factors Affecting infections are gray to brown, often zonate, some­ High humidity (heavy fog or dew, light driz­ times covered with spores and/or sclerotia, and zly rain) is essential for sporulation and spread. may collapse. Spots on flowers may appear within Anything that retards air movement will favor 10 hours after infection. They are white or light infection, whether from crowded plantings, ex­ yellow to brown and usually enlarge rapidly and cessive weeds, or poor locations. The fungus is

8 active over a fairly wide temperature range with Importance and Host Range sporulation occurring between 5 and 27 °C ( 41- Botrytis blight is found wherever tulips are 81 °F). The optimum temperature for growth in grown and is by far the most serious disease of vitro is 20°C ( 68°F). Spores may survive for 6 tulips. The disease was first reported in Wash­ months when dry and sclerotia for 18 months ington some 60 years ago at Anacortes. There when dry, but usually survival is shorter when are no immune varieties but some are more sus­ moisture is present as in soil. More infection oc­ ceptible than others. The fungus usually only at­ curs when shoot growth is retarded by low tem­ tacks tulips but has infected other bulb hosts peratures and in heavy, wet soils. Plant injury under artificial conditions. from any cause, particularly from hail, will fa­ cilitate infection. The continued culture of tulips increases losses because of a build-up of the fungus Causal Agent in debris. Fireheads act as the primary source of Botrytis tulipae (Lib.) Lind. Conidia are gray­ spores for early spread of the disease. Splashing ish in mass, individually hyaline or clear gray, obo­ raindrops are mainly responsible for this initial vate, and variable in size ( 12 :. 24 x 8-20ft). Scler­ spread. Later, wind-blown as well as water­ tia at first white, later black, flattened, circular or splashed spores are involved. elliptical, and 1-2 mm in diameter.

9 References Factors Affecting GOULD, C. J. 1953. Blights of lilies and The nematodes are usually spread by sale of tulips. USDA Year book on Plant Diseases. p. diseased bulbs, blowing fragments of dry debris 611-617. (bulbs, leaves, or flowers) , movement of drain­ PRICE, D. 1970. Tulip fire caused by Botry­ age water, mechanical equipment, and flower tis tulipae (Lib.) Lind, the leaf spotting phase. J. pickers. However, they can also migrate through Hort. Sci. 45:233-238. soil for several inches. Heavy soils seem to favor PRICE, D., and ]. B. BRIGGS. 1974. The the nematodes and their survival. When dry, the control of Botrytis tulipae (Lib.) Lind. The cause nematodes may survive for at least 17 years, so of tulip fire, by fungicidal dipping. Exp. Hort. 26: disinfect contaminated equipment, boxes, and 36-39. Tulip fire. 1972. Leaflet 536. Ministry of Agriculture, Fisheries and Food. London. Control 1. Check all plants carefully before cutting flowers since the bent and discolored flower Bulb and Stem Nen1atode and stem are the best symptom. Have all (Eel worm) suspected cases verified by a nematologist. 2. Rogue all diseased plants plus those for 1-2 Symptoms feet around them as soon as detected. Also LEAVES. Affected leaves have small light yel­ remove soil, being careful tx> not scatter in­ low to white spots or swellings. Small ragged fested soil while removing from field. cracks are associated with these spots. Often they 3. When cultivating, etc., always cultivate clean coalesce and result in elongated cracks surround­ fields first, finishing with the diseased area ed by indefinite chlorotic or brown areas. Curl­ and then wash off and spray equipment with ing and distortion may also occur in severe at­ formaldehyde ( 1 : 10 dilution) . tacks. The best time to see symptoms is at or just before flowering. 4. Discard all suspicious-looking bulbs. FLOWERS. With slight attacks the first sign 5. 2 ~-hour treatment at 43 °C ( 110°F) has is usually a pale white to purple streak on one been recommended, but it· has two serious side of the stem just below the flower bud. This drawbacks: a) Since a single 2~-hour treat­ lesion enlarges as the flower develops, turns pale, ment usually does not give complete control, and often becomes blistered and split. The lower it must be repeated for one or two additional parts of stems may also have similar lesions and, years, and b) many tulip varieties are injured under severe conditions, may be twisted. One of even by this short treatment. Unfortunately, the best symptoms is the flower being typically the tulip race is slightly more heat resistant bent toward the side of the stem lesion. One or than the daffodil race. more of the flower petals often remain green 6. A soak in a nematocide solution has given above this infected spot. In severe cases, the plants partial control in Holland and England. are stunted and the petals may be severely de­ There are no nematocides registered for this formed and lack color. use in the United States. BULBS. Attacks usually start on one side just above the basal plate. Slightly infected bulbs may 7. The populations are much reduced by fallow­ not show symptoms at first but later, in storage, ing for a year as well as by soil fumigation. the outer scale develops silvery gray to brown A soil-applied nematocide has given effec­ patches. These patches merge indistinctly into the tive nematode control for iris and narcissus healthy tissues and are generally soft and spongy (EM 4313 and 4314) but has not been or mealy. In cross-section they appear as indefinite tested nor is it registered for use on tulips. gray or brown spots, sometimes becoming ring­ 8. Keep fields free of weeds since they may be like. Severely infected bulbs finally rot and be­ alternate hosts. come mummified. Nematode "wool" is occasion­ ally formed at the base.

10 srorage rooms. The reproduction rate is fantastic strands of the fungus. Sclerotia develop on the -a single diseased bulb may harbor 5 0,000 ne­ surface and between the scales. They are first matodes, so extreme care is needed when an in­ white, later becoming reddish-brown, rounded, fection is found. sometimes pock-marked and range in size from a pinhead to ~ inch. Diseased bulbs often have Importance and Host Range soil adhering. The white strands may ramify These nematodes are widely distributed through cracks in the surrounding soil and scler­ world-wide. However, they are not known to otia may also develop there. The fungus has a occur in the Pacific Northwest. The tulip race is mushrqom-like odor. It also spreads rapidly over particularly virulent and can attack narcissus, hy­ bulbs in storage if uncured bulbs are packed to­ acinths, and many other bulb and ornamental gether under warm, moist conditions. plants. Additional hosts include onions, peas, cu­ cumbers, and other vegetables and weeds. Ap­ Factors Affecting parently all tulip varieties are susceptible. The The crown rot fungus is active at warm tem­ tulip and daffodil races (and perhaps others) can peratures so the disease is more common on light interbreed so the potential exists for development soils if adequate moisture is present. The fungus of new types adapted to new conditions. Unfor­ is able to grow in culture from 8-40°C (47- tunately, tulips are susceptible to hot water in­ 1040F) with an optimum at 25-35 °C ( 77-95 °F). jury so such an eradication treatment is not safe The pH optimum is 3.0-6.5 but it will grow be­ to use. Because of this and the wide host range tween 1.4-8.6. In northern climates, the disease and virulence of the tulip race, it is particularly develops near the end of the growing season when important to detect and eradicate infections as the soil is warmest, particularly if late rains occur soon as observed. or irrigation is used. The fungus can be spread on cultivating and other equipment but is most Causal Agent likely introduced into new fields on infested bulb Ditytenchus dipsaci (Kuhn) Filip. The tulip srocks. race is more virulent than most other races. It can attack narcissus but the narcissus race does Importance and Host Range not attack tulips. However, the two races can hy­ Crown rot is found throughout the world but bridize. See the references for more details. is usually of minor importance. It can be serious, however, particularly in warm, moist climates or References in warm greenhouses. It is less serious on tulips HESLING, ]. ]. 1972. Host plants of tulip than on iris in the Pacific Northwest. The fungus stem eel worm ( Ditytenchus dipsaci) Pl. Path. 21: has an extremely wide host range, attacking many 107-111. other bulbs, ornamentals, and other plants includ­ Stem eelworm on tulip. 1972. Advisory Leaf­ ing common weeds. Therefore, it is likely that let 461. Min. Ag. & Fish. & Food, England. once a field is infested, it will always remain in­ THORNE, GERALD. 1961. Principles of fested unless fumigated. Nematology. p. 118-126. Causal Agent C'Jrticium rolfsii Curzi (Syn. Sclerotium rolf­ Crown Rot (Southern Wilt) sii and the apparent biotype S. delphinii). Scler­ otia irregular in shape but usually roughly spheri­ Symptoms cal, somewhat flattened at base, 0.1 to 1.5 em LEAVES. Leaves of diseased plants turn red, or often larger and often coalescing in masses; wilt, and die. white at first, changing through buff to dark red­ FLOWERS. The flowers may be blasted because dish-brown. Surfaces of the sclerotia are often of stem rot, which occurs just below the soil sur­ pitted. face. The stem is shriveled, discolored, and more or less covered with white thread-like strands of References the fungus. CMI Descriptions of pathogenic fungi and BuLBS. Infected bulbs have a whitish, more bacteria. No. 410. Corticium rolfsii. Eastern Press or less chalky rot and are covered with white Ltd., London.

11 in the soil. The problem is usually more severe where bulbs are forced in contaminated soil and held at mild temperatures under waterlogged con­ ditions. Optimum temperature for growth of the fungus is about 25 °C ( 77°F) but attacks can occur even at 10°C ( 50°F). Importance and Host Range Foot rot occurs wherever tulips are grown but the disease is sporadic in occurrence and ap­ parently rare in the Pacific Northwest. The fungus has a wide host range including bulbs, other or­ namentals, and vegetables. Tulips vary in suscepti­ bility. Causal Agent Species of Phytophthora including P. crypto­ gea1 and P. erythroseptica. See references. References BUDDIN, W. 1938. Root rot, shoot rot, and shanking of tulip caused by Phytophthora cryptogea Pethybr. & Laff. and P. erythroseptica Pethybr. Ann appl. Bioi. 25(4) p. 705-729. (RAM 18:183-184, 1939). MULLER, P. ]., 1967. A footrot of tulips. Dtsche Gartnerborse 67 p. 231-232 (bilb. 1, illus.) Hort Ab p. 637 37(3).

Foot Rot (Root Rot, Shootrot, or Shanking)

Symptoms LEAVES. Infected plants fail to emerge or are stunted in varying degrees with leaves premature­ ly turning yellow and later red. The base of the sprout is watery or even slimy, decayed, and gray­ brown to violet. FLOWERS. Flowers from infected bulbs may Gray Bulb Rot (Bad Soil) blast or only partially open. The base of the stem Symptoms may collapse from the decay. LEAVES. The first, evidence of the disease is RooTs. The initial infection will turn the a spot in the field where a group of plants either roots brown from where the disease progresses fail to emerge or emerge with partially decayed into the bulbs. shoots. Later infection causes leaves to turn red, BULBS. Decay starts at the basal plate, and wither, and die before flowering. Sprouts may the infection spreads more rapidly up the stem be rotted before emergence. These sprouts and then into the fleshy scales. the bulbs may be covered with soil that is held together by mycelia. Factors Affecting FLOWERS. The underground portion of the Waterlogging and poor drainage increase flower stem is often rotted and covered with a losses. The fungus may surviv:e for several years gray mold, sclerotia, and attached soil.

12 BuLBS. Large grayish-brown spots develop on the scales (particularly near the tip), which are often covered with a gray mold. A cross-section shows ring-like decayed scales. The rather dry decay first appears gray or pinkish-gray and later turns brown. The roots and base of the bulb may remain healthy for a while but eventually the entire bulb is usually decayed. Sclerotia form in or on the bulb stem and adjacent soil. They are Pythium Root Rot and Soft Rot l white or pinkish-white inside and whitish-gray to J brownish-black on the surface. They vary in size Symptoms ( 1-10 mm) and shape and are dull in color and LEAVES. In severe attacks the sprout may die slight! y rough. before or soon after emerging from the soil. Larger Factors Affecting plants may be stunted and the leaves may turn purplish red after flowering because of root or The fungus is able to grow in culture from bulb rot. The disease sometimes appears in 1-35 °C ( 32-95 °F) with an optimum about 20oC patches but may be randomly scattered, particu­ ( 68 o) , but most field infection occurs at lower larly in greenhouses. temperatures. Infection apparently occurs in late FLOWERS. When flowers are formed, they autumn or early spring and usually starts at the may be stunted and/or withered or blasted be­ tip of the bulb. Sclerotia may survive several years cause of root or bulb rot. Delayed flowering and in the soil. It is usually spread by cultivating and short flower stalks can also result. planting diseased bulbs. RooTs. Soft translucent watery spots appear which enlarge up to an inch long and eventually Importance and Host Range turn brown. The entire root system can be de­ The fungus is widely distributed throughout stroyed. Microscopic examination will reveal the the world but the disease appears only sporadical­ presence of oospores in the diseased tissues. ly. It has been collected in the Pacific Northwest BuLBS. Soft gray spots, often with a brown but no serious cases have been reported. Both border, usually start near the base of the bulb. field and greenhouse plantings can be affected. These spots enlarge rapidly, but remain soft and It is mostly confined to bulb crops, particularly pink to gray. Often a gray to yellow compact tulips, but other hosts are reported. layer of mold forms on the surface of the bulb. The odor from infected bulbs is disagreeable. Causal Agent Rhizoctonia tuliparurn Whet. and Arthur Factors Affecting (Sclerotium tuliparum). Sclerotia are white to The disease is most severe in wet soils. Once pinkish-white internally and whitish-gray to established ·the fungus can persist almost indefi­ brownish-black on surface, dull, slightly rough, nitely whether it is in the field, rooting cellar, globose to loaf-shaped, and variable in size ( 1- or greenhouse. Sandy soils and warm temperatures 10 mm). favor the fungus in the field. The fungus is References spread by infected bulbs, drainage water, culti­ CMI Descriptions of Pathogenic Fungi and vating equipment, and any other means (e.g., Bacteria. No. 407 Rhizoctonia T uliparum. Eastern bulb flats) in which contaminated soil is moved Press Ltd., London. around. In the greenhouse the disease is increased MOORE, W. C. 1950. Grey bulb rot of tulip. by planting precooled 5°C (41 °F) tulips in The Journal of the Royal Horticultural Society. sandy clay or peat soil and forcing temperatures Vol. LXXV, Part 3. March 1950. p. 113-117. above 13 °C (55°F). WHETZEL, H. H., and JOHN M. ARTHUR. 1925. The Gray Bulb-Rot of Tulips Caused by Importance and Host Range Rhizoctonia Tuliparum (Klebh.) N. Comb. Cor­ This disease probably has worldwide distri­ nell University Agricultural Experiment Station. bution and in certain areas is a serious problem. Memoir 89. It usually is more severe in greenhouses than in

13 fields. The causal agents have a wide host range, attacking other types of bulbs as well as many other crops. The fine-rooted varieties of tulips (e.g., Rose Coplan and Olaf) are more suscepti­ ble than others. Causal Agent Pythium ultimu1n Trow (and other Pythium Topple species) . Conidia usually terminal and spherical, 12-28JL in diameter. Oospores spherical, 14.7- 18.3JL diameter when mature having a thick wall (Sugarstem and central reserve globule surrounded by a gran­ or Wet Stem) ular layer of protoplasm with an imbedded small refractive body. Germination direct. Oospores Symptoms can survive in the soil. LEAVES. In greenhouses occasionally dark­ green water-soaked spots develop and exude small References drops. Cross-wise splits may also appear in the HUMPHREYS-JONES, D. R., and M. D. lower . de ROOY. 197 4. Control of pythium root rot STEMS. The upper internodes of the stem in five-degree tulips in the Netherlands and the exhibit the most common symptom, which begins United Kingdom. Second International Sympo­ as a water-soaked transparent spot often accom­ sium on Flower Bulbs. England. 1974. Acta Hor­ panied by exudation of small drops. A shriveling ticulturae 47. p. 83-90. of the stem occurs at this point resulting in an ROOY, M. de. 1972. Control of Pythium in eventual collapse of the stem and toppling of forced tulips. Bestrijding va Pythium bij tulpen­ the flower head. broeierig. Bloembollencultuur 8 3 ( 10) p. 219- 220, 222. (From Hort. Abstract 43, 2259.) Factors Affecting Topple is primarily a greenhouse problem. Control It occurs in the fastest growing part of the stem. The higher the temperature the faster the growth 1. Greenhouse-if the disease has been a prob­ and the greater the risk. It is also increased by lem, use steam-sterilized or fumigated soil high humidity. The cause is a temporary short­ or treat soil with a fungicide before planting age of calcium in the region of rapid elongation. (see EM 4315). Some research in England indicates . that a de­ 2. Use well-drained soil and flats with holes ficiency of nitrogen plus an excess of potassium fqr drainage. increases losses from topple. 3. P~t only healthy bulbs with the tip even with the soil surface. Importance and Host Range 4. Dipping bulbs in a fungicide before plant· Worldwide, mostly in greenhouses. Variable ing has given good control in Holland. in occurrence. The double early tulips and other varieties such as White Sail and Emmy Peeck are Do not let the soil temperature go above 5. more susceptible than many others. 10-11 °C (50-52°F) for the first week or two of forcing. Later, if the disease develops, Causal Agent lower the temperature to reduce stress on Calcium deficiency under certain conditions. the toot system. 6. Avoid overwatering. Reference 7. Field-remove diseased plants and soil if CHEAL, W. F., and E. ]. HEWITT. 1964. areas are small. The effects of rates of supply of nitrogen, phos­ 8. H areas are large, do not replant bulbs for phorous, potassium and magnesium on leaf and several years. Use a nonsusceptible crop for stem growth, flowering and 'topple' of Golden rotation (consult your local specialist). Harvest and Elmus tulip. Ann. Appl. Bioi. 53. p. 477-484.

14 ence of more than one virus in the plant; the re­ Control sult may be a combination of symptoms. In addi­ tion, some physiological disorders may also cause 1. Be certain that the bulbs have had the proper virus-like symptoms. temperature treatments for forcing. Healthy tulips can become infected with 2. Avoid excessively rapid growth by keeping by several different means. Occasionally the temperature low. If topple appears, lower tulip break virus can be spread from diseased to the temperature a few degrees. healthy plants on the knife used for cutting 3. Maintain good air circulation and avoid a flowers. However, this and cucumber mosaic high humidity. virus are usually carried by aphids. Others are transmitted by soil-inhabiting nematodes and in 4. Water plants regularly with water contain­ one case by a root-attacking fungus ( Olpidium). ing 0.06% calcium nitrate (2 oz. in 22 gal­ Most viruses are also transmitted in the daughter lons water) . bulbs. Thus it must be assumed that all parts of 5. Put flowers in a 1% calcium nitrate solution a diseased plant are infected and, therefore, should for 12 hours prior to shipping. be destroyed. General control measures include roguing suspected plants after flowers have opened; con­ trolling weeds which may serve as virus reser­ voirs; controlling aphids in field and in storage; Virus Diseases digging as early as possible to avoid attack; discarding small and discolored bulbs; treating in­ The virus disease called tulip break or mosaic fected soil for control of nematodes and the Ol­ is probably the oldest known virus disease of pidium fungus; planting late and planting tulips plants. It was described in 15 7 6 by Carolus separate from lilies. A promising means of estab­ Clusius and illustrated by him in 1583. However, lishing virus-free stocks is to use meristem-cultures; the fact that it was a disease caused by a virus however, research in this area is still in a prelim­ was not proven until about 50 years ago. It is our inary stage. most common and serious virus disease of tulips. The major virus diseases are briefly described Recent research has shown that there are 10 in the table. A more detailed discussion of tulip other known virus diseases (see the table) , four break virus is given on page 16. A summary of of which are serious; less is known about the other the less important virus-like problems that have six. Most of these are described from Holland, been reported on tulips follows. England, and Scotland where active research is ARABIS MOSAIC VIRUS. Transmitted by Xiphinema under way. The only recognized virus disease in nematode. Stunts plants. Leaves pale green with the Pacific Northwest is tulip break. However, severe yellow streaks, later turning brown. there is little doubt others would be found if a LILY SYMPTOMLESS VIRUS. Transmitted by aphids. thorough search were made by a virologist. Not a serious problem in tulips. Lily and tulip Viruses can cause many different symptoms. plantings should be separated. These vary with the virus (including different TOMATO BLACK RING VIRUS. Transmitted by ne­ strains), with the tulip variety, the period of plant matodes. Severe necrotic disease but occurs rare­ growth when infection occurs, and the climatic ly. conditions. Tulip varieties also vary in their sus­ TOMATO BUSHY STUNT VIRUS. Symptoms similar ceptibility to different viruses. In general the late­ to those of Tobacco necrosis virus. blooming varieties seem to be more susceptible TULIP HALO NECROSIS VIRUS. Leaves with to aphid-transmitted viruses, while the early elongated necrotic lesions surrounded by trans­ blooming varieties are more susceptible to viruses lucent border. Leaves may be curled and dis­ transmitted by nematodes and fungi. There are torted. too many vanettes to list them individually in PSEUDO-CORKY FLECK. This condition is not this bulletin. See the references for additional caused by a virus but symptoms are similar to details. regular corky spot (see table). It develops Attempts to identify virus diseases only by when early-dug bulbs are stored at tempera­ symptoms are complicated by the frequent pres- tures below 25 °C (77°F) after harvest.

15 Tulip Breaking (Mosaic) are regular and similar in all plants, not irregular and scattered as with tulip break. Other viruses Symptoms can also cause striping in the flowers (see table) . LEAVES. Diseased leaves have a light green BuLBS. The bulbs from infected plants are to yellow mottling or striping. The intensity of smaller than normal if infection is severe. the symptoms range from mild to severe depend­ ing on variety, degree of infection, etc. Plants Factors Affecting may be more or less stunted if infection is severe. Tulip breaking is most common in warm cli­ Stem symptoms resemble those on leaves. mates which favor large aphid populations. It is FLOWERS. The type of symptoms appearing also most common in late flowering varieties, on flowers depends upon time of infection, variety, which are usually exposed to increased aphid at­ etc. The most intense symptoms occur on pink, tack. This virus is occasionally transmitted when red, and purple , where the symptoms may cutting flowers, especially if the stems are cut low. be either jagged stripes or sectors. These color Transmission by aphids from bulb to bulb in breaks may be lighter (full break), darker (self storage has been proven. break), or both (average break). The white and yellow cultivars do not show this breaking, and Importance and Host Range the self break on dark colors is often overlooked. The disease is found worldwide and is more There are genetically variegated tulips that serious in warm climates. This virus also attacks may appear diseased. In these, the stripes or streaks lilies, which may then act as a source of infection

16 for other tulips. Many persons prefer having the diseased flowers because of their interesting color breaks. The virus eventually reduces bulb size.

Causal Agent Tulip Mosaic Virus or Tulip Flower Color Breaking Virus. There are two strains: a severe and a mild breaking type. The former is the most serious in reducing yields. Both are transmitted by aphids. (See Van Slogteren and Asjes.)

References AS JES, C. ]. 197 4. Control of the spread of tulip breaking virus in tulips with mineral-oil sprays. Second International Symposium on Flower Bulbs. p. 65. VAN SLOGTEREN, D. H. M., and C. ]. Tulip breaking-flower ASJES. 1970. Virus diseases in tulips. Daffodil and Tulip Year book. Vol. 3 5. Royal Horticultural Society, London. p. 85-97.

17 Yellow Pox Control Symptoms 1. Remove diseased plants as soon as flowers LEAVES. Plants may fail to emerge or are show enough color to exhibit symptoms. Do stunted with leaves showing torn silvery stripes this before picking flowers for sale. Rogue along veins in the greenhouse or ragged silver­ white and yellow-flowered varieties on basis gray spots in the field. of leaf symptoms. FLOWERS. Stunted or lacking. Stems have yel­ 2. Remove old flowers, which can serve as site low vascular tissue. for increasing aphid populations. BuLBS. Spots on the outer fleshy scale are 3. Spraying for aphids has not usually been very first white, later yellow, swollen, and sometimes productive. However, it may be a good in­ cracked. The vascular tissue also appears in cross surance policy, particularly on late-flowering section as small yellow dots. Severe! y infected varieties and/or in warm climates where bulbs usually decay completely. aphids are abundant (see EM 4315). Recent research in Holland indicates that spraying Factors Affecting with summer oil gives some control. This disease has not been thoroughly investi­ 4. Dig bulbs as soon as possible to escape aphid gated. Apparently a suitable combination of fluc­ attack. tuating temperatures, frost, and high moisture en­ courage the disease. 5. Discard the smallest planting stock, which is the most likely to be infected. Importance and Host Range 6. Control aphids in storage as additional in­ Yellow pox is a relatively new disease re­ surance (see EM 4315). ported from the Netherlands, France, and Japan. 7. Do not plant near lilies. Probably widespread, but only of local importance. 8. Growers who want to keep 'broken' tulips should separate them from healthy stocks by Causal Agent at least 100 feet. Corynebacterium oortii Saal. and H. P. Mass 9. Planting in windy locations helps reduce G. A rod-shaped motile bacterium with minimum, aphid infestation and therefore infection. optimum, and maximum temperatures for multi­ plication of 5 oC ( 40.6°F), 25-30°C ( 77-86°F) and 37oC (99°F), respectively.

References CMI Description of pathogenic fungi and bacteria. No. 375. Corynebacterium oortii. Eastern Press ttd., London. SAALTINK, G. ]., and H. P. MAAS GEE­ STERANUS. 1968. A new disease in tulip caused by Corynebacterium oortii nov. spec. Neth. J. Pl. Path. 75. p. 123-128.

Control Remove and destroy infected bulbs and plants.

Tulip breaking-leaves

18 Miscellaneous Diseases Fusarium Leaf Blight Fusarium avenaceum (Corda ex Fr.) Sacc (F. roseum) may occasionally infect tulips in the Anthracnose field and greenhouse, producing brown ragged Leaves and stems are affected with elongated or scorched irregular spots, particularly on the spots. These are watersoaked at first, and later young shoot, stem, and lower leaves. The spots become dry with dark margins. Black masses of may be later covered with a white or light pink spores often develop in the centers of such spots. mycelium containing orange masses of spores. Reported in California. Caused by Gloeosporium The fungus may be present in straw used for thumenii Sacc. F. tulipae Tomp. & Hans. mulching. High temperatures and high relative humidity favor the disease, so these conditions should be avoided. Also avoid injury and practice Blackleg good sanitation. (See Fusarium leaf blight of tulips. 1950. C. Gould, Phytopath 40: p. 965.) This disease, only recently reported from Hol­ J. land, has not yet been found in the Pacific North­ west. The primary symptom appears after bloom­ Miscellaneous Nematodes ing as a dark decay at the base of the stem. A Both Ditylenchus destructor Thorne and reddening and premature death of leaves follows. Aphelenchoides subtenuis Cobb. occasionally rot The stems shrivel, turn gray, and later a dull tulip bulbs without infecting stems or leaves (in black. Large irregularly shaped, torn, grayish­ contrast to D. dipsaci, page 10) . The early symp­ black spots appear on the husk of new bulbs, toms appear as orange-brown, odd-shaped patterns and sunken black irregular spots on the outer starting at the base of the bulb. These areas event­ fleshy scale. Sclerotia may develop between scales. ually become dark brown and corky. A cross-sec­ These are brownish-black, round or flattened, ir­ tion of an infected bulb shows brown rings. These regular, 2-5 mm in diameter and 0.5-1.5 mm nematodes have a wide host range. They are thick. The pathogen (Sclerotium wakkerii Boer. spread with infected plant material and soil. and Post.) can grow at near freezing temperatures Roots attacked bv the nematode Pratylenchus but has an optimum about 20°C. It prefers moist penetrans Cobb, sho~ small yellow to light brown soils and can also attack iris and lilies. spots which later enlarge and cause death of the roots. Weak pathogens usually enter the wounds Botrytis Measles resulting from the feeding of the nematode and are responsible for the continued rotting of the Botrytis cinerea Pers., the fungus responsible roots. Affected plants are usually found in patches for gray mold on many other crops, has infected in the field and damage is most common in light flowers in British Columbia. It causes small ( 1-2 soils. mm) watersoaked spots which become slightly sunken. Leaves were also infected. In Holland, the fungus was found mostly on bulbs, where it Rhizoctonia Blight ptoduced large, glassy, brownish-gray spots on the This is primarily a disease of tulips in the scales. A soft and light brown root rot occurred greenhouse. Symptoms are irregular orange to accompanied by development of large ( 2-10 dark brown flecks or stripes on the young shoots mm) blackish sclerotia. followed by more or less splitting of the leaves, particularly on the tip of the bottom leaf. Prob­ ably the best symptom is the roughened brown rot Fluorine of the top of the young shoots and of the lower Fluorine gas can produce grayish spots or leaf. Stems may have oval sunken spots covered stripes on leaves. Later these spots become trans­ with a gray to light brown mold and become parent white and necrotic, particularly near the brittle and break near the ground surface. Occa­ tip and along margins of leaves. Mature leaves sionally bulbs may be cracked, with a brown decay show more injury than immature ones. Varieties of the scales covered with a gray to light brown vary in susceptibility. Injury may occur near steel mold. The fungus ( Rhizoctonia solani Kuhn) has mills, aluminum plants, pottery works, etc. an extremely wide host range, survives in the soil

19 for many years, and can attack over a wide range through wounded tissue on bulbs kept at a high of temperatures but seems to do most damage on temperature. The fungi Rhizopus and Aspergillus bulbs under cool conditions. species are responsible for this disease. The follow­ ing should be helpful in controlling this disorder: Rust an.d Smuts prevent injury, provide good air circulation, and avoid overheating. Puccinia, Ustilago, and Urocystic species have been reported occasionally in different parts of Europe and Asia, but they seem to be of more scientific than commercial interest.

Sclerotinia Sativa Blind, Blasted, or Deformed The fungus Sclerotinia sativa Dray. and Groves has been reported only occasionally (in Canada) Flowers as causing a disease on tulip bulbs. It is a low­ Many of these problems can be traced to temperature parasite that usually attacks dormant overheating of bulbs after the flower embryo has plants. The symptoms on tulips (illustrated by formed. Blind, blasted, or deformed flowers can Drayton and Groves, M ycologia 3 5 : 5 17-5 28. be induced by forcing small bulbs too early or 1943) appear to resemble those on plants infect­ at too high a temperature. Over-heating while ed by Scler.otium bulborum. The fungus attacks bulbs are in transit is a common cause. One or tulip and narcissus bulbs and also causes a root two weeks at temperatures above 22 °C (73°F) rot of alfalfa and sweet clover. in September and October can easily damage the flower embryos. Two days at 38°C ( 100°F) and Skin Disease (La Reine) even one hour at 49° ( 120°F) can also harm them. Ethylene gas can cause similar damage (see Skin disease (La Reine) is caused by an un­ Ethylene). Consequently, a few bulbs from each identified fungus and is rather common on many shipment should be cut lengthwise to determine varieties in Holland. Attacks begin on the bulb their condition upon arrival. The young flower about flowering time and may cause a brown should be bright. A dull or discolored embryo lesion on the underground stem. At harvest the indicates poor quality. diseased bulbs can be recognized by an orange­ brown discoloration of the skin and light to dark­ brown irregular spots of variable size on the fleshy Blueing of Bulbs (Blawgroeien) scale plus a grayish-black crust of mycelia. Colorless, glassy spots, up to 1 em, first appear in the outer bulb scales and on the rounded side Smoulder of the bulb about blooming time. The tissue in the spot dies and turns brown; however, spots ap­ Smoulder appears about blooming time as a pear bluish when seen through the white skin. sudden wilting of the plant with the leaves turn­ The disease is usually found in the largest bulbs ing red. The lower stem has a soft gray rot, and seems to be related to rapid growth caused eventually becoming black with small (.1-.2 mm), by such factors as high light intensities during flat, round to oval, shiny black sclerotia. The flowering, heavy fertilization, etc. Varieties vary roots rot and bulb scales show a light grayish­ in their susceptibility to blueing. violet decay. The fungus (Sclerotium pernicio­ sum Van Slog. and Thorn.) is active at 9°C ( 48°F) and has an optimum of 17-20°C ( 63- Bud Necrosis (Core Rot 680F). It is uncommon. or Kernrot) Bud necrosis begins in the stamens as a decay Sooty Bulbs and spreads to other organs of the flower embryo Seriously diseased bulbs are calcified, shrunk­ or sprout. The affected bulbs will have either a en, and covered with a layer of black sooty spores. dead black center or develop incomplete or de­ Infection occurs at a high relative humidity formed plants. These plants can have dead black

20 remnants or parts that do not completely develop. Improper temperature treatments, ethylene gas, and mites may be implicated. Varieties vary in susceptibility.

Ethylene Damage It has been known for many years that ethy­ lene gas given off by apples and other fruits can adversely affect tulip bulbs. More recently it has been shown ·to be the cause of many disorders, including gummosis of bulbs, lack of roots, twist­ ed roots, distortion of shoots, production of many slender leaves without any flowers, decay of flower embryos and shoots, retarded flower development, Ethylene damage blasting of flowers, production of green petals, and production of colored petals with white tips. The type of symptom depends on the stage of development when the bulbs were exposed, con­ centration of ethylene, variety, etc. There are many sources of ethylene includ­ ing fruits, certain flowers, incomplete combus­ tion of gases from motors or heaters, and par­ ticularly Fusarium-infected tulip bulbs. Ethylene can even diffuse through the soil from diseased bulbs and affect adjacent healthy ones. Precau­ tions should be taken to control Fusarium and to be certain that the bulbs are not stored or shipped with fruits, etc. Only a small amount of ethylene can cause trouble. Heat damage Frost Injury may be a result of mechanical injury or ethylene Small spots develop on or between leaf veins. gas produced by Fusarium-infected bulbs. Later air pockets appear and become cracked. The tips of leaves may also be twisted. Nutrient Deficiencies Heat Damage It is not often that nutrient deficiency symp­ Temperatures above 40°C ( 104°F) cause the toms appear on tulips. Apparently bulb crops are outer bulb scales to become flabby and gray, us­ excellent at utilizing soil nutrients. Sand culture ually at the base. The flower bud is often blasted tests in England on tulips indicate that nitrogen and the affected scales are usually invaded by deficiency is the most important resulting in de­ Rhizopus bread mold, Aspergillus black mold, or creased bulb yield, leaf area, stem length, flower other fungi. size, and a retardation in flowering. When the small nitrogen-deficient bulbs were planted, they produced only single leaves. The leaves were more Gummosis upright, yellow-green, and, near maturity, both Blisters develop on the outer bulb layer and stem and leaves developed reddish tints. Mag­ are filled with a clear liquid that later becomes nesium-deficient plants had necrotic areas which light yellow or brown and hardens into a solid appeared after flowering on the two lowest leaves. gum. Bulbs become more resistant to this con­ (See page 14 for discussion on calcium deficiency dition as they mature. Some varieties, such as and Rees, A. R., 1972, The Growth of Bulbs, Madame Lefeber, are very susceptible. The cause Academic Press, N.Y.)

21 ~echanicall)anoage Hard Base Mechanical injury may cause the outer fleshy Hard base is the term used when the roots scale to develop white spots with a yellow mar­ grow upwards between the husk and scale and gin if it occurs early in the storage period. If the emerge at the tip of the bulb. The condition us­ injury occurs later, the spots become brown and ually results in a stunted plant. The cause is may become covered with blue mold if stored at suspected to be exposure to especially high or low a high relative humidity. Mechanical damage may temperatures, particularly when the relative hu­ occur any time, but the bulbs increase in suscepti­ midity is very low, resulting in a retardation of bility during storage. root development and hardening of the base.

22 Key

Plants missing or stunted and/ or with reddish leaves: bulbs more or less rotted.

Sclerotia on surface or between scales. Sclerotia circular and reddish-brown Crown Rot

Sclerotia irregular, flat if between scales and black ______Black Slime

Sclerotia globose, dull, slightly rough and black ______Gray Bulb Rot

No sclerotia; roots may or may not be present. Blue-green mold on surface or between scales Blue Mold

Brown rot often at base and ringlike __ __ . ______------Basal Rot

No sclerotia, roots more or less rotted. Root rot ring-like. Bulb with soft gray spots ______------Pythium Root Rot

Root decay general, bulb rot at base, base of stem decayed and slimy ______Foot Rot

Plants present. Flowers affected. Stem collapsed ____ ------Topple

Bloom slightly bent toward a light spot on stem ------Bulb and Stem Nematode

Flowers with irregular, jagged, light or dark streaks ------Tulip Break

Flowers and leaves spotted ______Botrytis Blight

23