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Extension Bulletin No. 424 June 1950

Diseases of Bulbous

Extension Service Institute of Agricultural Sciences The State College of Washington Pullman. Washington Key to Iris Diseases

Look first at this key to identify tentatively any particular iris disease, and then to the page indicated for a more complete description. More than one disease may occur on and at the same time, in which case the symptoms may overlap.

LEAF SYMPTOMS DISEASE PAGE Outer mottled, young inner ones not mottled .... Winter Injury 6 All leayes mottled, most evident on inner ones ...... Mosaic ...... 6 tips black ...... Black Tip ...... 9 Gray or grayish-brown spots with a dark border...... Lea£ Spot (Fire) ... .lO Black spots ...... Ink Spot ...... 12 Dark green or brown spots ...... Bacterial Blight ...... 14 Leaves yellowed ...... Usually one of the rots. See below.

FLOWER SYMPTOMS Discolored streaks in , may be ...... Mosaic ...... 6 Flowers lacking (in blooming-sized stock) ...... Blindness ...... 15 Flowers present but prematurely dead or wilted ...... Blasting ...... 17

BULB SYMPTOMS Tan sunken areas with brown sclerotia often present..Crown Rot ...... 18 Base shrunken, often covered by white or pinkish mold .... Basal Rot ...... 22 Basal plate gray, often surrounded by a dark crevice; dark streaks in fleshy scales sometimes present...... ...... 24 Tan sunken areas with blue mold often in center...... Blue Mold ...... 27 Black irregular patches on husks ...... Ink Spot ...... 12 Minor diseases ...... 30

Unless otherwise indicated, the photographs are of the ,-ariety W edgewood.

2 Diseases of Bulbous Iris By CHARLES J. GOULD* Associate Pathologist Western Washington Experiment Station

Because of the mild and moist climate in western Washing­ ton, this state has become the leading producer of bulbous iris. Production is confined largely to one variety, Wedgewood, which is popular for forcing in . Although our iris are recognized as the world's best, they do have their troubles at times. Most of these troubles are caused by one or more of the following maladies: FUngi These are small, simple plants which lack the power plant (chlorophyll ) necessary for using sunlight to produce their own food. They must, therefore, feed on dead or living plants or . Fungi are often spread by small, -like bodies called spores. And they may live from one season to the next either on the inside or outside of plants as hardened masses of tissue called sclerotia. Many, but not all, of our bulb parasites form these sclerotia. Viruses are protein-like particles, so mall we cannot see them with an ordinary microscope. They resemble fungi in that

* The auth01· wishes to express hi s sincer e appr eciation to the following fo t· their h elp: Dr. F olke J ohn son, Dr. L eo Campbell, Dr. E. P. Breakey, and Mr. vV. D . Courtney (U.S.D.A.) at the W estern Washington Experiment Station and Dr. G. A . Huber (formerly at the Western Washington Experiment Station); Dr. M. R Harris and Dr. G. \V. Fischer a t The State College of W ashing ton, Pullman; Dr. S. M. Dietz and Dr. F. P . McvVhot·ter a t Ot·egun State College, Col'Vallis; Dr. vVm . New­ ton, Mt-. R. J. H astings, and Mr. J. E . Bosher a t the D ominion Laboratory of Plant Pathology (Saanichton, B. C.); Dr. A. A. F oster, Dr. A . vV. Dimock, and Dr. L. F. R andolph at Cornell niversity ; Dr. eil W . Stuart, Dr. W. D. McClell an, and Dr. Philip Bt·ierley (U.S.D A. ) at the Plant Industrv Station, B eltsville, M a ryland; Dr. C. F. D oucette (U.S.D.A.) at the E ntomological L a bor ator y, Sumner , vVashin gton; Mr. J, S. \Vieman and associates ( Oregon State D epartment of Agriculture); Mr. G. \ V. Eade ( Washington State D epartment of Agt·iculture) and Mr. H. J_ R eynolds (form erl y w ith '\Ala hington State D epartment o f Agriculture); Iris gmwet·s-Francis Cher venka, R. G. Fryat·, C_ vV. Orton , H. D. Edmonson, E. C. Orton, Ben K a rsten, Jr., S. Van Lierop, and J ohn Onderwater. n,-_ G. A. Hubet· took the photograph of the bac terial disease illustrated on page 14. 3 they cannot make their own food but must rely upon living plants or animals for it. Infected plants usually contain the particles in all their parts. Thus, whenever a "daughter" bulb is taken from an infected plant, the virus or "disease" travels along. These are very small, thread-like worms. Many types com­ monly live in the soil without doing any harm, while others parasitize various plants. The nematode (or eelworm, as it is sometimes called) attacking iris is too small to see without a microscope. Physiological Disturbances A ll troubles which cannot be traced to some parasite are considered in this group. Bulbous iris are quite susceptible to bad weather. Frost may injure their leaves, the sun may burn the bulbs, and undesirable temperatures may prevent flowers from forming, or ruin them after they have formed. Because of this, they are correctly considered one of the most difficult of all bulb crops to grow commercially. Sanitation Burn or bury all diseased plants, bulbs, and infested debris well away from all bulb fields and sheds. If you use a pit, sprinkle discarded plants with lime and cover with dirt at the end of each day's operations.

4 AGeneral Control Program 1. Always plant well-graded stock of known disease-free ancestry. Establish a mosaic-free and eelworm-free fo un­ dation stock. 2. P lant on heavy, well-drained soil on which iris have not previously been grown for 3 or 4 . Ridge the rows. 3. Spray with homemade Bordeaux if leaf spot is trouble­ some. A dd Penetrol as a wetting and sticking agent. 4. Rogue all mosaic-infected plants. R ogue on the basis of symptoms as found on central leaves of new growth early in the season and on the basis of symptoms at the time of blooming. 5. Remove crown rot-infected plants and infested soil or sterilize the infested area. 6. Dig nematode-infected stocks 1 or 2 weeks earlier than normal. 7. · Avoid bruising in all operations. 8. Store bulbs under dry, airy conditions. 9. Discard all infected and moldy bulbs after digging and again before planting. 10. Treat nematode-infected stocks in a hot water-formalin bath for 3 hours. Cool rapidly after treating. Treat after the bulbs are cured, but before A ugust 15 in normal years in the Puyallup Valley. 11. Cure salable stocks with heat soon after digging. 12. Treat phnting sto: k with Tersan oon after cleaning. Dry or plant immediately . TERSAN TREATMENT Increa ed yields by dipping iris bulbs in Tersan have been obtained in several experimental tests at the Western Wash­ ington Experiment Station, and in some large-scale commercial trials by local growers. The experimental treatments showed that both healthy and diseased (crown rot and basal rot) stocks of Wedgewood and DeWitt varieties increased in yield. The "why and wherefore" of these increases are not yet known, but occasionally have been as high as 25 per cent over the untreated sets. The planting stock should be dipped for 5 to 15 minutes, as soon as cleaned, in a suspension of 1 pound Tersan in 9 gal­ lons of water. Either plant immediately or dry rapidly . to pre­ vent the sprouting. Tersan is safe on bulbs, but · ·it may irritate the skin of certain persons. Handle according to the manufacturer's recommendations. 5 t~osaic

c Fig. 1. MOSAIC. A-Healthy plant. B-Infected plant. C-Different types of leaf symptoms. SYMPTOMS Leaves and stems. Plants stunted, sometimes severely; stems often weak; or yellowish streaks against nor­ mal color or patches of normal green surrounded by yellow background. Symptoms strongest in sheaths and lower part of young leaves growing vigorously under cool condi­ tions, becoming less noticeable as temperature rises and the plants mature. Healthy plants of certain varieties, especially \ Vedgewood, normally show a slight mottling which be­ comes more evident with the maturing of older leaves. Winter injury and sometimes drought cause a regular pattern of flecks or squarish markings of white or pale green, usually confined to older leaves. The mottling from mosaic does not usually follow a regubr pattern and is most evident on the youngest leaves. Flowers. Dark teardrop markings on white, blue, and lav­ ender fl owers; clear feather-like markings on yellow fl owers. The ribbon-like markings, sometimes present on flowers, are apparently not virus-caused. On bud sheaths, bluish-green blotches on a pale green background, or, less often, yellowish 6 streaks. Not all infected plants show both leaf and flower markings. Mosaic symptoms develop more strongly in the green­ house than outdoors. from -grown, mosaic-infected plants are poor in quality and do not last long. Bulbs. Often fewer in number and smaller in size than normal. IMPORTANCE World-wide; major, especially on many Dutch, Spanish, and Tingi tana types, including the variety W edgewood; spread by in field and perhaps in storage; not spread by picking flowers. CONTROL Mosaic control in iris involves a special planting program for two reasons : first, diseased plants may not show symp­ tom's the season they are infected; and, second, mildly in­ fected plants are difficult to identify and eliminate. Emphasis should be placed upon establishing and maintaining a di­ sease-free foundation stock from which all planting stock can be selected. How to Establish a Foundation Planting 1. Begin with stock containing less than 10 per cent mosaic­ infected plants and preferably not over 5 per cent. 2. Dig stock selected for above use by hand, keeping clumps intact; select only the largest clumps, and plant them in units with the mother and its daughter bulbs together. These should then be rogued as a unit because if one bulb in a clump is infected, the other bulbs are usually infected also. An alternative procedure has been used successfully by one of our large growers. The largest mother bulbs were selected but planted without their progeny. This mother block was then rogued intensively for 2 or 3 years, by which time the virus was practically elimin­ ated and the progeny could be used for rapidly increas­ ing the foundation planting. With this method, the in­ crease was not as fast as with the clump method but much hand labor was eliminated. se only the largest bulbs for foundation plantings, whether they are mother bulbs or planting stock, since small bulbs are most likely to be infected. 7 How to Maintain a Foundation Planting 3. Never plant foundation and mother stocks alongside com­ mercial stocks. Keep them at least 200 yards from com­ mercial V\fedgewood stocks, German iris, and English iris to prevent spread of the virus by aphids. 4. Control aphids, especially in foundation stocks, by regu­ lar spraying with an insecticide, such as tetraethyl pyrophosphate, according to the manufacturer's direc­ tions. Then wait at least 24 hours before spraying with Bordeaux. Do not mix the two. Begin spraying at first sign of aphids in the spring and continue until han-est. Thorough weeding also keeps numbers at a mini­ mun1. 5. Rogue the foundation stocks as follows, remO\-ing the complete unit (mother and daughter plants) if Yirus symptoms are found in any plants of the unit. R emember that the largest plants and youngest leaYes show the best symptoms and that roguing is easiest when the sky is slightly overcast. Place rogued plants in a tight con­ tainer and remove from the field to pre,-ent cattering of aphids. Burn or bury the plants. a. In January or February, remove all obYiously mo­ saic-infected plants. b. In , thoroughly rogue the planting, remov­ ing all questionable plants. c. At time of flowering, rogue plants exhibiting flower symptoms together with any other questionable mottled and stunted plants. 6. Dig foundation stock 1 or 2 weeks earlier than normal to shorten the period during which aphids can spread mosaic. 7. Be careful to keep fo undation stock distinct from com­ mercial stock in the warehouse. Mixing can occur all too easily. 8. F umigate with 2 pounds methyl bromide for 20 hours at 70 ° F. when aphids first appear on bulbs in torage.

Causal Agent: his Vims I (Br. and M c\V.) Smith; thermal, dilution, and filter qualitie not determined ; ti·ansmitted b y wedge insertions into tems, hypoden11ic injections, and b y variou s aphids ( peach and potato). Seve1·al other viruses may possibly b e factors in the mosaic complex. R eferences : BI"ierley, Philip, and Frank P. M cWhorter. A M osaic D isease of his. Journal of Agric. R es. 53 :621-635, 1936. McWhorter, Frank P. Principle of Disease Control Applicable to Bulbous his. 01·egon Ag. Exp. Sta. Circ. of Information No. 221, July, 1940.

8 Black Tip

Fig. 2. BLACK TIP. Field view at right-Black tip wbic!-1 developed on tips of leaves killed by freezing in the winter of 1950.

SYMPTOMS Leaves. A black powdery layer developing on the tips of lea,·es. IMPORTANCE Widespread; minor. The fungus usually attacks only foli­ age that has been frosted or otherwise injured. CONTROL ] . Maintain proper cultural cond i ~ i o n s . 2. Spraying, as fo r leaf spot, may be of some benefit, but is usually unnecesary.

Causal Agent: Didymel/ina poeci/ospora 1\ic\ V. Perithecia si mila r to D . iridis except fo r size; ascospor es 6 x 25 u; conidia u su ally two-celled, 6-9 u x I 2-38 u. R eferences: M c\ Vhorter, F. P . Didymellina poecilospora, n. sp., a emiparasitic H eterosporium on Bulbous his. Phytopath. 27: 135-136, 1937. M c vV horter, F. P. P1·inciples of Disease Control Applicable to Bulbou s Tri s. O re. Exp. Sta. Circ. of Information No. 221, July, 1940.

q Leaf Spot (Fire) SYMPTOMS Leaves. Small brown spots that may enlarge, becoming ,0 inch or more in length and most numerous at first on the upper halves of leaves; mature spots are usually elongated, with white or light gravish centers, sometimes surrounded by a reddish-brown border. U nder certain conditions a t~1in greenish-black powdery mass appears in the gray area. Some of the tissue adjacent to the spot may turn yellow and, if the spots are large enough, the leaves collapse and die prema­ turely. Similar spots may develop on the stem and flower bud. Bulbs. Reduction in size of 1, 2, or more centimeters under conditions of severe leaf infection. The fungus apparently is not carried on the bulbs. IMPORTANCE World-wide; general; sometimes serious on bulbous iris, often serious on rhizomatous t ypes. Worse in: wet seasons; low spots in fields; under conditions of poor air movement; and where iris have been grown for m ore than I . This fungus, or strains of it, are also reported to attack , hemerocallis, freesia, and certain other plants. CONTROL I. Rotate, since the fungus overwinters in the dead foliage. 2. Plant in well-drained soil, avoiding low spots and loca­ tions of poor air movement. Adequate drainage during the winter is especially important. Ridging is very bene­ ficial. 3. Liming. at a rate of 1 to 2 tons per acre, has been recom­ n:ended in Canada and England. 4. D o not plant bulbous iris near rhizomatous iris o;· 111 fields in which volunteer plants are present. ~ - P lant as thinly as practicable and keep field weeded to increase air circulation. 6. Begin spraying in western Washington when leaves emerge, and keep both the new and old surfaces covered by repeated applications. This often means spraying every 2 weeks. Use homemade Bordeaux (8-10-100) to which is added 1 )13 quarts of Penetrol (Kay-Fries type) per 100 gallons. The Penetrol is used as a wetting and sticking agent. Shake it with three times its quantity of clean water before adding it to the Bordeaux mixture. Avoid spraying when the sun is exceptionally bright 10 I

Fig. 3. LEAF SPOT (FIRE). A-Diseased plant. B-Enlarged spot. and the weather warm, to lessen the danger from spray burn. In eastern Washington, if infection is not usually severe, it may be desirable to delay spraying until the leaf spot makes its appearance. Nate-Some of the untested new copper compounds and wetting agents may also be effective in controlling this disease and are worth limited trials, especially in home gardens. However, the Bordeaux-Penetrol combination has proven successful in both experimental and com­ mercial tests in western Washington, and is therefore recommended. 7. Rake up and destroy old leaves in home plantings.

Causal O q~anism : Didymellina macrospom Kleb. ( H eterosPMium iridis (F. & R .) J. Peri thec1a smooth, globose, dark brown to bl ack, averaging r6o x 200 u; ascospores hyali ne or lightly colored, oval-elliptical or spindle-shaped, two-cell ed , measuring 30- 54 u x 10-1 6 u; conidia cylindrical, rounded at the ends, echinulate, hyaline at first and later oli ve brown, usually 2-, but sometimes 4- or 5-septate and measuring 30-80 U X 14-20 U . References : Tisdale, W . B. Iris Lea f Spot Caused by Didymellina in"dis. Phy topath. 10:148-163, 1920. Huber, Glenn A. Study Control of F oliage Diseases of Iarcissi a nd Bulbous Iris. Florists' Review, F ebruary 4, 1937. Moore, W. C. Diseases of Bulbs. Bul. No. 11 7, Ministry of Ag 1·i culture a nd Fisheries (London) , 1939. 11 Ink Spot

Fig. 4. INK SPOT. (On bulbs of Iris ?'eticulata. ) SYMPTOMS Leaves and stems. Irregular black patches or blotches which appear soon after the leaves push through the ground; 12 such spots sometimes being surrounded by a reddish area. nder moist conditions the attack may be so e\·ere that the foliage w ithers and dies prematurely. Ink spot and leaf spot are easily distinguished. T he for­ mer is definitely black or sooty in appearance, while leaf spot is usually gray with a very thin greenish-black powdery mass in the center. Bulbs. Bulb infection is usually confined to Iris reticulata, on which it is often severe. Irregular inky black stain s, sometimes in the shape of rings and varying in ize and number on the husks; the fleshy scale underneath the husk may exhibit small yellow dots or irregular, elongated, sunken black craters with distinct margins; infected bulb some­ times rot leaving only the husk and a mass of black powder. The fungus may spread through the soil, attacking adjacent healthy bulbs.

IMPORTANCE Probably world-wide ; major for Iris reticulata, especially on the bulbs; usually minor for most bulbous iris on which it is generally found only on leaves, but seri ous attacks have occurred a few times on W edgewood and other varieties in the orthwest; worse in wet seasons and in plantings left undug fo r 2 or more years.

CONTROL 1. Dig bulbs every year. 2. Discard diseased bulbs, burning or burying them. 3. British Columbia worker recommend use of the hot water-formalin treatment. (See directions under nema­ tode.) The mercuric-chloride and 2 per cent Ceresan treatment has been recommended in O regon (see direc­ tions under blue mold) . 4. Rotate. 5. Avoid planting other bulbous 1n near Iris reticulata and English iris. 6. Spray with Bordeaux according to directions giY en under leaf spot (page 10) . Causal A gent: Mystrospo1-iwn ad1tstwn Massee. Conidia oblong, elliptical, or broadly fusiform with obtuse ends, mooth, dat·k smoky-bt·own when mature, 5-7 traversely septate with occasional longitudinal septa, measuring 46-60 u x 20-22 u . References: Green, D . E. The Ink Disease (or Bulb Scab) of l1·is R etintlata Caused by l\1Iystrospo1·ium ad1tst1Hn Massee. Jour. Royal. Hot·t. Soc. 61 :167-175, 1936. Moore, vV. C. Diseases of B ulbs. Bul. No. 11 7, Minis tt·y of Agriculture and Fisheries ( L ondon), 1939.

13 Bacterial Blight

Fig. 5. A bacterial leaf blight observed and studied by Dr. G. A. Huber in 1935. Diseased plants in a peat field. SYMPTOMS Leaves. Watersoaked areas near base of leaves and stems. These enlarge rapidly under moist conditions, becoming brown, and often causing leaves and stems to collapse and die. Bulbs. Smaller than normal when leayes are severely in­ fected. IMPORTANCE \ liJ orse in warm, wet weather. Serious in western \ liJ ash­ ington during 1935 on Wedgewood iris grown on peat soil. It has appeared sporadically since then, but never seriously. Studied and photographed by Dr. G. A . Huber. A bacterial blight has also been reported elsewhere on Iris reticdata.

CONTROL 1. Remove and destroy old leaves. 2. Dig bulbs and replant in a new location. If disease is common in stock, aYoid planting in peat or muck soils. 3. Practice suitable cultural methods, such as weeding, to provide ample air mo\ ement around plants. 4. Spray with Bordeaux according to directions given under leaf spot (page J 0). C:lUsal Agent: Bacterium s p. 14 Blindness

Fig. 6. A-Normal flower. B-Blasted, bud present but almost dead. C-Blind, bud lacking.

SYMPTOMS Flowers. Failure of flowers to develop from normally flowering-sized bulbs. This condition is sometimes confused with blasting, in which case form but sooner or later die. (See page 17.) Blindness is primarily a greenhouse prob­ lem. IMPORTANCE Blindness is a world-wide condition, occurring every year to a certain extent. It has been most prevalent in forced precooled stocks from bulbs grown the season before under cool, cloudy conditions.

CAUSE Blindness has been attributed to several factors. Some of the possible causes and their prevention are being investi­ gated under a cooperative agreement between the Western Washington Experiment Station and the Plant Industry Sta­ tion ( .S.D.A.), Beltsville, Maryland. Among the known or suspected causes of blindness ~re : 1. Use of too small bulbs for rapid forcing. 15 2. Use of too much heat in early forcing. 3. Failure of bulbs to completely mature in the field by the normal harvesting date. Blindness was especially prevalent during the winter of 1948-49 in certain greenhouses forcing Northwest-grown iris bulbs. This may have been correlated with the growing season in the Pacific orthwest in 1948, which was unusually cool and cloudy. Although growers in the area delayed dig­ ging as long as possible, the bulbs may have failed to mature properly, even though they were somewhat larger than normal. In the cooperative experiments mentioned above, warm curing treatments applied at Puyallup to such bulbs imme­ diately after harvesting in 1948 hastened the blooming, in­ creased the uniformity of blooming, and decreased the per­ centage of blindness when the bulbs were forced at the Plant Industry Station. The growing season of 1949 was almost the reverse of that in 1948, being unusually warm and dry. N eYertheless, the curing treatments applied after harvesting again hastened blooming. Hence it appears that Northwest-grown bulbs will probably benefit in most years by such a treatment. This assumption is supported by the previous work of Grif­ fiths, siwilar experiments in H olland and Canada, and some commercial trials in this area. The exact temperatures, their duration, best times of application, and many other facts re­ main to be definitely settled for this area. Our experiments have been confined to the variety Wedgewood. Because of this and the fact that the experiments have not been com­ pleted, the following measures are only suggestions for trial and not recommendations. They include suggestions to help control blasting as well as blindness.

CONTROL l Grower 1. Dig bulbs as late as practicable, to obtain proper ma­ J turity and size. 2. Give them a curing treatment as soon as possible after digging. Use 90 degrees for 10 days if the plants mature early and 90 degrees for 15 days if they mature late. Apparently the sooner the treatment can be given the better the results, although when applied to mixed (sal­ able and planting) stock as it comes from the field, the treatment will increase the percentage of blooming bulbs 16 •

in the field the fo llowing year, which 1s undesirable from the grower's viewpoint. Forcer 3. If bulbs are to be precooled, use 6 weeks at 50 degrees. For best results with precooling, use 10 em. and larger sizes only . Plant immediately after removing from the precooling chamber, using deep flats ( 5 to 6 inches) and good soil. Keep flats cool ( 48 to 52 degrees if possible) and moist until are 2,0 inches high and then fo rce at the following night temperatures: 11 and up- not over 60° F . 10 to 11 - not over 57° F. 9 to 10 -not over 55 ° F. 8 to 8_0-not over 52° F. _8,0 to 9-not over 48° F . 4. Lower both day and night temperatures during cloudy weather. Do not attempt to force bulbs harder to obtain · earlier blooms than the size of the bulbs will stand. 5. Provide good ventilation; keep soil moist at all times; avoid placing flats close to heating pipes ; avoid dead air pockets. Blasting SYMPTOMS F lowers. Buds or flowers may be w ithered and dead when they appear, or they may wilt and turn brown later. Blast­ ing is primarily a greenhouse problem, but may occur in the fi eld. POSSIBLE CAUSES Excessively high forcing temperatures, especially during cloudy weather; disease or attack of bulbs; uneven temperatures ; poor ventilation; plants too close to heating pipes; allowing soil to dry; too lean or too rich soil ; too thick planting. CONTROL Correction of the above conditions will help to eliminate blasting. Follow fo rcing procedure listed under blindness. R eferences: Gt·iffiths, David. Speeding Up F lowering in the Daffodil and the B ulbous Iris. U.S.D.A. Circ. No. 367. 1936. Stuart, . vV. , C. J. Gould, and S. L. Emsweller. A P r eliminary Report on the Effect of A fter-Harvest and Precooling Tempet·atures on the Forcing Performance of vVedgewood Iris Bulbs. Florists' R eview. pp. 24-26, July 28, 1949. Post, K enneth. F lori st Ct·op Production and Marketing . Orange Judd Pub. Co. 1949. ' 17 Crown Rot

A B c Fig. 7. CROWN ROT. A-Blasting of flowers and death of plants resulting from attack at the ground surface. B (bulb at left)­ Healthy plant. C (three bulbs at right)-Diseased plants. SYMPTOMS Leaves and stems. Infected plants are yellowed, stunted, and die prematurely, either from rot of the bulb or the stem and leaves just above the bulb; the latter appear soft and crumbly or fibrous. The outer lea' es usually turn yellow before the inner ones, and from the top downward. Under warm, moist conditions the surrounding ground may become covered with sclerotia, white at first and later tan or reddish­ brown, up to ~ inch in size. They may also develop on the stem and in the bulb. U nder warm. moist conditions the fungus grows through the soil, attacking other plants and producing a yellow patch. At digging time the fungus some­ times appears as a white mat around the hulbs and stems. Bulbs. A mass of dirt often clings to infected bulbs when dug; sclerotia are also sometimes present in the dirt and on the bulb ; the husk adheres tightly to the bulb at the point of infection and may be partly shredded : after infected bulbs have dried, the color of the husk is a dead. light tan; early 18 infection of the fleshy scales usually appears as a soft, white cheesy rot, w ith a sharp margin, but with no change in color from the normal bulb. As the bulbs dry, the infected tissues become dry, sunken, and tan colored; scattered dark raised lines are sometimes present ''· i ·~hin the sunken area; sclerotia are often found on or between scales; bulbs may be rotted completely with nothing but the husk and sclerotia left. In­ fection usually occurs at the tip, but may be elsewhere. Under suitable storage conditions, the infected area dries up; but under warm moist conditions, the fungus can spread to ad­ jacent bulbs in the tray. Other fungi often in,-ade crown rot­ infected bulbs and may alter the symptoms. Flowers. Flowers may be blasted as a result of attack on the stem base.

IMPORTANCE Probably world-wide; usually minor here, but major in war·m, moist areas such as the southeastern ; attacking all types of iris as well as many other ornamentals, vegetables, weeds, and other plants. It has occasionally been serious on and . Can attack and rot the outer scales of bulbs, but ordinarily not the inner scales. Narcissus bulbs, howeyer, may carry the disease from one field to another since the disease is easily overlooked ; worse in western Washington in warm, moist seasons on light soils and when iris are replanted on infested land.

CONTROL 1. Dig crown rot diseased stock 1 to 2 weeks early, since the disease may spread rapidly: in early summer. Imme­ diately after digging, discard all infected bulbs by burn­ ing or burying. (Healthy bulbs may develop from partly diseased ones if grown under optimum conditions. No salvage attempt, however, should be made except with expensive varieties, since the disease will be perpetuated in the stock.) 2. Dry bulbs rapidly by placing in thin layers in open trays. providing enough Yentilation and supplementing with extra heat if needed. 3. Do not dump dirt and debris from the cleaning opera­ tions w here bulbs are to be grown again. 4. None of the many tested at the Western Washington Experiment Station have been effective in reducing this rot. However, in view of the results of some 19 A 8 Fig. 8. CROWN ROT. A-Diseased bulb with adhering soil and sclerotia. B-similar bulb with dirt removed.

F ig. 9. CROWN ROT. Surface appearance of crown-rotted bulbs after being dried. preliminary experiments and growers' observations, the hot water-formalin treatment seems to be beneficial. Ap­ parently a 2,0- to 3-hour treatment is necessary for com­ plete control. See directions under nematode (page 25). 5. Plant on heavy, but well-drained soil. Poorly-drained areas and light soils usually show the worst infections. 6. Infected patches in the field usually appear late in the spring. If they are few in number, try one of the follow­ ing practices: 20 a. Carefully remoYe infected plants and soil to a depth of 10 inches and about 10 inches beyond the infested area. D o not permit any of this dirt or debris to be cattered when removing from the field. b. Chloropicrin (tear gas) has been used successfully by one large grower for sterilizing infested areas without the necessity of removing plants and soil. This ma­ terial should be injected not only in the infested area,

Fig. 10. CROWN ROT. Appearance of diseased bulbs after drying. Note sclerotia on and between the scales. but also around its margin. Use according to the manufacturer's recommendations. 7. Do not replant on infested soil for at least 3 or 4 years. 8. Grow a cover crop after iris in rotation practice. Accord­ ing to reports elsewhere, it would seem best to avoid the use of vetch when planting a cover crop on infested soil. 9. Formaldehyde can be used fo r small infested areas in home gardens. Drench loosened soil with 0 pint com­ mercial fo rmaldehyde in 3 gallons of water and apply at a rate of 0 gallon per square foot.

Causal O r ganism: ( Sclerot£wn delphi,lii Welch) o r ( S. rolfsii Sacc.). Sclerotia irreg. ular in shape but u sually roughly spherical, somewhat flattened at base, 0.1 to 1. 5 e m. o r large 1· and o ften coalescing in masses, white at first, chan ging through buff and tan to dark reddi sh-brown. S urfaces of the scle rotia a r e often pitted. R eference: M oore, \V. C. Diseases of Bulbs. Bull No. 117, Ministi·y of A g riculture a nd Fish erie (London), I 939. 21 Basal Rot

Fig. 11. FUSARIUM BASAL ROT. (On bulbs of variety DeWitt.) SYMPTOMS Leaves. May be lacking, or stunted and yellowed. Roots. Few or none; the fungus first invades the roots, rotting them as it progresses, later attacking the bulbs. Bulbs. Infected area at base shrunken, with husk adher­ ing firmly and sometimes matted with white or reddish-tinged mass of the fungus; basal plate and fleshy scales brown or reddish-brown and shrunken, with a fairly definite margin between decayed and healthy tissue; the rot is rather firm. IMPORTANCE nited States, Canada, and possibly England; minor in ~ Jo rthwest; most severe in warm climates such as the eastern United States; first described on Spanish and Dutch Iris on Long Island, New York; the only severe attack in western Washington was in 1948 and 1949 in one stock of De \ i\T itt; 22 occasionally fo und in W edgewood and other varieties; re­ ported elsewhere destructive to Imperator, Cajanus, Hart N ebrig, and Poggenbeek.

CONTROL 1. Avoid bruising when digging, cleaning, etc. 2. Sort and discard all diseased bulbs immediately after dig­ ging and again before planting. Burn or bury such bulbs. 3. Treat F usarium-infected st ocks in one of the following solutions (these recommendations are based upon tests in 1947-48 and 1948-49 at the Western Washington Ex­ periment Station on the variety DeWitt.) a. Ceresan M. T reat bulbs, p~efe r ab l y as soon as cleaned, but at least before September 1 (in P uyallup Valley) fo r 5 minutes in 1 pound Ceresan M per 75 gallons of ~a t e r. Dry rapidly. For treatments after September 1, use 1 pound Ce'resan M in 80 gallons of water and either plant the same day or dry immediately. This is :1 mercury compound which may injure roots if they are protruding. b. Tersan also giYes some control of this disease. Use it at a rate of 1 pound in 9 gallons of w ater fo r 5 minutes. A lthough this material is very safe on bulbs, it has usually given best results w hen used before the basal plate begins to swell. (Mechanical injury may have been a factor.) If Fusarium-infected stock is hot water-formalin treated fo r nematode control, give the bulbs one of the above disinfecting treatments soon after the bulbs have cooled. 4. Do not plant in infested soil for 3 or 4 years. 5. Plant on heavy, but well-drained, land.

Causal A gent : One or mo1·e strains of Fttsm·ittm oxyspontm Schlecht. References: C1·eager, Don B. F u sariu m Basal Rot of B ulbou s I ri s. Phytopath. 23 :7, 1933. M cClell an, W . D . Pathogenicitv of the Vascular Fusariu m of G lad iolus to Some Addit iona l h idaceou s P lants. P hytopath. 35:921-930, 1945.

2.) Nematode SYMPTOMS Leaves. Sometimes lacking or stunted if bulb infection is severe. There are no pimples (spikkles) such as in nematode­ infected daffodil leaves. Stems. L ight gray or yellow areas on stem where attached to bulb. Bulbs. Husk sometimes shredded at base; basal plate and outer fleshy scale separated by a dark, sunken crevice; yel-

A B c Fig. 12. NEMATODE-INFECTED BULBS. A-Typical streaks. B-Crevice separating outer scale and basal plate. C-Cross sect ion showing streaks within the bulb.

low, gray, or black streak in fleshy scales, usually beginning at the base and most numerous in outer scales; such streaks sometimes fusing and rotting the entire scale and bulb; basal plate honeycombed and grayish in color (remove basal cap to check this point, which is a very good one for diagnosis); sunken spots with dark margins sometimes present near tip of bulbs. Not all the above symptoms are necessarily present in all \·arieties. The gray discoloration of the basal plate is the most consistent general symptom of nematode infection. This basal-plate discoloration is often the only symptom present in English Iris; in W edgewood, the dark, sunken crevice is more common than the streaks; but in Imperator, the streaks are quite common. 24 Infection varies with the size of the bulbs, being most frequent as well as most apparent in the larger sizes. The large central bulb of a clump is often the only one that is infected. Since the infection progresses during the storage season, stock that did not exhibit infection at digging time may show it by planting time.

IMPORTANCE Holland, , England, Canada, nited States-prob­ ably world-wide; serious in areas such as Holland and the Pacific Northwe.::;t, but also destructive in many other re­ gions; attacking many types, including Dutch, English, Mor­ occan, and Spanish species; varieties Supreme and White Excelsior are quite susceptible; Wedgewood, Imperator, and Yellow Queen are somewhat less susceptible. This has been one of O}lr worst iris diseases in the past few years, but with the development of a successful hot water-formalin treat­ ment, is now being brotight under control.

CONTROL 1. Harvest infected stocks 7 to 10 days earlier than normal. 2. Bury or burn all diseased bulbs and the trash from all cleaning operations. 3. Treat planting stock, when dormant, in hot water (110° to 111 o F.) to which has been added formaldehyde ( .S.P.) in the proportion of 1 pint to 25 gallons of water. Treat for 3 hours after bath is stabilized at 110° F. Plant immediately or dry and cool promptly by spreading in thin layers in a cool place with good air circulation. Determining the optimum date for treatment is still difficult. In the Puyallup Valley it usually occurs from 3 to 4 weeks a"Her digging to ugust 15 in normal years (and about a week earlier near Portland and a week later near Mount Vernon). Many factors influence maturity, including climate and soil type. One possible guide for the best time to treat is a week after the basal cap most easily slips off. Treatment after the basal plates have begun to swell has always resulted in injury. 4. Some Holland reports indicate that injury is lessened by storing the bulbs at warm temperatures both before and after treatments. 5. Follow the hot water treatment, as soon as bulbs have cooled, with the Tersan disinfection (page 5) . 25 6. Treat planting stock regularly every 2 or 3 years as an insurance against reinfection. 7. Clean and grade infected stocks after handling healthy stock. 8. Disinfect used trays, cases, tools, etc., by treating with steam; dipping in hot water at 185 ° F.; or dipping in a solution of 1 quart fo rmaldehyde to 9 quarts of water. 9. Do not plant iris back on the same ground for 2 years after all volunteer plants have been removed, unless in­ fested ground is sterilized with EDB (ethylene dibro­ mide), DD mixture ( dichloropropylene and dichloropro­ pane), chloropicrin or some other suitable nematicide. Also, avoid planting healthy iris on land that gets sur­ face drainage from infested soil. 10. Until more is known of the exact host range of the iris nematodes, avoid, whenever possible, planting other types of bulbs on infested ground. 11. Keep healthy and infected, treated and untreated, stocks definitely marked and separate in warehouse.

Causal Agent: One or more species of nematode to be described and named b y Dr. G. Steiner in the near future. References: Steiner, G., and Edna M. Buhrer. The Bulbou Iris a Host of Tylenclms dipsaci, the Bulb or Stem Nema. Phytopath. 2J:IOJ·Io_c;, 1933. Courtney, \V. D . Iris Nematodes and Their Control. Proc. Bulb Growers Short Course, Puyallup, vVashington: 2S ·.l I' I 949· Hastings, R. J. Sanitation vs. Nematodes in Field and Shed. P roc. Bulb Growers Short Course, Puyallup, Washington: 32·45, I949·

HOT WATER TANKS Plans for the construction and use of hot water tanks are contained in Washington State College Experiment Station Popular Bulletin No. 184, Hot Water Tanks for Treating Bulbs and Other M aterials, written by W . D. Courtney, E. P. Breakey, and Loyd L. Stitt. Copies may be obtained from your local County Extension Agent.

26 Blue Mold

Fig. 13. BLUE MOLD.

SYMPTOMS Leaves. May be lacking, or stunted and yellowed, as a re­ sult of bulb rot. Roots. Few or none if attack is at the base. Bulbs. Symptoms vary, depending upon time of attack, varieties, species of fungus, etc. The husk may be normal in color but sunken and sometimes split at the center; the in­ fected fleshy scales at first may be soft and watery, white to greenish-gray in color, later becoming rather firm and yellow or brown. Mature spots on the sides are often more or less oval, sunken, dry, sometimes with a cavity under the husk, and often partially covered in the center with a blue-green powdery mold. Infected bulbs may decay completely, leaving nothing but the husk and a little debris. The infection often enters at a bruised area or a wireworm puncture, and may be only one scale deep. Many bulbs infected on the sides or tip 27 will grow, but when the rot begins at the base the bulbs u u­ ally decay completely.

IMPORTANCE Probably world-wide; usually general and minor in V\ ash­ ington, but occasionally serious; the varieties Imperator and Yellow Queen are particularly susceptible but most other types of bulbous iris can contract the disease. It is w orse on bulbs that have been attacked by nematodes, punctured by wireworms, bruised when dug or cleaned, stored in deep masses, and kept under cool, moist, closed condition .

CONTROL 1. Avoid bruising bulbs at any time, but particularly when digging. 2. D o not break up clumps until they are well ripened. 3. Cure rapidly by spreading thinly in trays (many growers use screen-bottom trays, but these must be handled care­ fully to avoid injury); and stacking coYered trays in field if the weather is suitable, or placing in a well-ve!!­ tilated room that can be heated if necessary. U se only enough heat with planting stock to keep the bulbs dry. 4. \ ,-oid "bleeding" by breaking up clumps as soon as the bulbs separate easily. Do not remove basal cap until it slips off easily. Store bulbs in layers not OYer 2 inches thick and slabs (bulb lets) in thinner layers. 5. Discard all infected bulbs by burning or burying. 6. Various fungicidal treatments have been used or pro­ posed. Part of the benefit from the Tersan treatment mentioned on page 5 is thought to be from control of blue mold. H owever, if bulbs are properly handled to avoid bruising and are properly cured, fungicidal treat­ ments for blue mold are usually unnecessary. a. A lime plus sulfur (SO :50 mixture) dust has been used by some growers here, and a mixture of sulfur and peat by growers in Canada. b. Arasan and Spergon dusts have been recommended by Canadian workers. (Arasan is the dry form of Tersan.) c. On severely-infected stocks the mercuric chloride and 2 per cent Ceresan treatment has been recommended in Oregon. se it only on such infected stocks since it has consistently reduced yields when tried on bulbs not infected with blue mold in our tests. Treat before 28 growth has begun and plant immediately. Soak bulbs 1 to 2 hours in water; transfer immediately to mercuric chloride solution ( 1 ounce in 70 gallons water) for 1 hour; then dip for 1 minute in 2 per cent Ceresan suspension (1 pound in 8 gallons water). 7. P lant early or, if planting must be delayed until the cool moist weather begins in the fall, store under well-ven­ tilated dry conditions. Some heat may be necessary, but too much heat is detrimental to large planting stock since it w ill increase the number of bulbs blooming in the field. ExcessiY e air movement is also undesirable since it dries out the bulbs. 8. A void wet soils. 9. The hot water- formalin treatment for nematodes may also be of some help in controlling this disease. 10. Disinfect trays and other equipment in the hot water­ fo rmalin bath, or spray or dip with formaldehyde, 1 quart ir'l 5 gallons of water. 11. Control of wireworms w ould undoubtedly reduce the prevalence of this disease. Soil fumigation with ethylene dibromide is effective; other possibilities are DDT and benzene hexachloride. Apparently no experiments on iris land have been made with these materials, so if you de­ sire to try them, do so first only on a small scale after consulting your nearest entomologist. Benzene hexachloride may give an off-flavor to root crops which might be grown later. The numbers of wireworms may also be reduced by planting land to alfalfa, fall-seeded cover crops, or alternat­ ing narcissus and cover crops for a 3- or 4-year period. 12. Ship in small containers rather than in large ones; a' oid m·erheating; prevent excessive dampness in warehouse; prm ide good ventilation during cold storage.

Causal Agent: Various species of P enicillium, including- P. corymbiferwn \iVes tling, P . hirs1~twn Dierckx, P. gladioli McCul. & Thorn., a nd P. digitatum Sacc. References: W eiss, Freeman, and Frank P. McvVhor ter. Rot ( Blue M old) of Bulbous Iris. Unnumbered .S.D.A. B ur. of Pl. Ind. Mimeo. Ci rc., 1933. M oore. W. C. Diseases of Bulbs. Bul. No. 117, Minis t1·y of Agricultme and FishPrie' ( L ondon), 1939. Bosher, J. E . and 'vV. Newton. The Control of Penicillium spp on and Iris Bulbs in Storage by Fung ic idal Dusts. Scientific Agriculture 28 :47-48, 1948

29 Minor or Uncommon Diseases GRAY BULB ROT Most of the symptoms described in the literature for this rot are confined to its effect on tulips. Comments concerning iris are few. Apparently major in Holland and probably world-wide. Reported in New Jersey and Jew Y ork in the United States and in Canada. Not known definitely to occur in Washington. Attacks tulips, hyacinths, scilla, narcissus, etc. It is a very virulent parasite, but fortunately grows slowly through the soil. Plants fail to emerge or are stunted and often die before flowering. Attacks show up early in season as contrasted with crown rot which appears later. Infected bulbs are gray, reddish-gray, or sometimes brown, usually at the tip, with dark brown or black sclerotia up to 73 inch in diameter on or in the bulb. A gray or somewhat darker mass of mycelium of the fungus (Sclerotium tuliparum IGeb.) is often present. Sort and discard by burning or burying all diseased bulbs after digging and again before cleaning. Avoid planting iris, tulips, or hyacinths for 4 years on land where this disease has appeared. In Holland, all diseased plants and adjacent soil are removed. Since this is apparently a rare, if not unknown, di­ sease here, we should either do likewise or disinfect the soil with chloropicrin according to directions under crown rot ( page 19 ) . The hot water-formalin treatment for 3 hours has been reported to control this disease in tulips, hyacinths, and narcissus.

RHIZOCTONIA NECK AND BULB ROT Yellowing and death of aboveground parts due to a soft, light-brown rot of the neck; bulbs may exhibit dark-brown le­ sions or be completely rotted. This disease has been reported recently from western Washington but is apparently of minor importance. Careful culling and rotation should control it.

RHIZOPUS STORAGE ROT Appears occasionally in stocks overheated in shipment or in excessively full trays kept under warm and moist conditions; bulbs are matted together and more or less covered with a ·white to gray mold, containing scattered, very small black bodies of the fungus. Proper aeration and cool, dry storage will ade­ quately control this disease. 30 BOTRYTIS BLIGHT AND BULB ROT Occasional attacks have been reported of various Botrytis (B. cinerea, etc.) species blighting flowers, spotting leaves, and rotting bulbs. MacLean ( unpublished data) has determined ex­ perimentally that various species found on some other bulbous hosts may also attack iris. This group of fungi is a potential menace, particularly to flowers, although bad attacks have not yet been reported. Spraying with Bordeaux, together with proper cultural operations in field and warehouse, should keep them under adequate control.

RUST This disease, caused by Puccinia iridis (DC.) Wallr., has been reported on wild species of iris in Washington but not on the cultivated types. It is quite important in certain areas, par­ ticularly in the southeastern United States. It is doubtful that it will ever become a factor here, but may be introduced occa­ sionally on imported stock. The spots are typical of most rusts, consisting of small, oblong, or oval, red or dark-brown powdery pustules, . often surrounded by a yellow area in the leaf. When such spots are numerous, the infected leaves die prematurely. Varieties and species vary considerably in resistance, many of the bearded types being quite resistant and many English types being quite susceptible. W edgewood and Imperator are resistant to at least two races of the fungus. All infected plants should be destroyed by burning.

SUNBURN The husk acquires a reddish or purplish tint when exposed to strong sunlight, especially soon after digging. The outer one or two scales may be damaged. Sunburned bulbs also become excessively dried, thereby losing weight as well as size, and are quite susceptible to attack by blue mold.

LATEST RECOMMENDATIONS Recommendations to control disease and insect pests of bul­ bous crops are revised annually on the basis of the latest results of research here and elsewhere. These are published by the Western Washington Experiment Station as Mimeographed Cir­ culars (No. 138 for spring treatments and No. 133 for fall treat­ ments) . They can be obtained from your local County Extension Agent.

31 How to Make Bordeaux-Penetrol Mixture (For 100 Gallons) An 8-10-100 formula refers to 8 pounds of copper sulfate, 10 pounds hydrated lime, and 100 gallons of water. Prepare as follows: 1. Prepare separate stock solutions of lime and copper sulfate, so that each gallon of the solution will contain 1 pound of these materials. Let the lime soak for 30 minutes before using. Dissolve the copper sulfate in warm water by sus­ pending in a cheesecloth bag near the top of the water in a nonmetal container. (An "instant" grade of copper sul­ fate which goes into solution rapidly is now available in rpany stores.) 2. Fill the spray tank about two-thirds full of water. Start the agitator. Put a '· piece of window screen or copper Wire strainer (20 mesh ) over the water inlet. 3. Add 10 gallons of the lime stock solution which has been stirred thoroughly. 4. ext pour in slowly 8 gallons of the copper sulfate solu- tion, meanwhile adding enough water through the hose to almost fill the tank. 5. Stir 1,73 quarts of Penetrol (Kay-Fries type) into 1 gallon of water and add slowly to the tank. 6. Use immediately or, if a delay is unavoidable for a few hours, add one heaping tablespoonful of ordinary table sugar.

(for 3 Gallons) Follow procedure as outlined above, but using only 5 ounces ( 19 level tablespoonsful) of hydrated lime in 6 quarts of water, and 4 ounces ( 7 level tablespoonsful) of copper sulfate dis­ solved in 6 quarts of water. Add the copper sulfate solution slowly to the lime solution, stirring continuously. Since Penetrol is sold only in large quantities, some other wetting agent that is compatible with Bordeaux and available in small amounts may be substituted.

Published and distributed in furtherance of the Acts of May 8 and June 30, 1914, by The State College of ·w ashington Exten sion Service, E. V. Ellington, Director, and U . S. D epartment of Agriculture cooperating. 7 Vz m-650 32