BLIGHT OF CHRYSANTHEMUM

Transcription

1 McFADDEN: BACTERIAL BLIGHT 4 sprinkling can, "hose-on" sprayer or other coarse nozzle. A half inch of water should be used in applying the material followed with an additional half inch as a seal. Mylone may be applied in the same manner or the dry material may be mixed with sand and broad cast over the soil surface. It should be mixed thoroughly and uniformly into the soil to a depth of five to six inches with a rotary cul tivator. After mixing the soil should be drenched with an inch of water. Since these materials are toxic to, three weeks should be allowed for dissipation of the ma terial before planting. LITERATURE CITED. Tisdale, W. B., and George D. Ruehle. Pythium root rot of aroids and Easter lilies. Phytopathology : Miller, H. N. Soil sterilization. Proc. Fla. State Hort. Soc. 6: -.. BACTERIAL BLIGHT OF CHRYSANTHEMUM Lorne A. McFadden Sub-Tropical Experiment Station Homestead Several important diseases of chrysanthe mums are known to occur in Florida. Bacterial blight caused by a soft rot organism, Erwinia chrysanthemi Burk. et al has steadily increased in economic importance in Florida over the past few years. Unless controlled, this disease could cause serious losses especially to chry santhemum propagators who either grow cut tings for their own use or offer cuttings for sale. First reported to occur in a greenhouse in New York state, this disease is now found in most of the major chrysanthemum growing areas of the United States. All varieties tested are susceptible to some degree when artifi cially inoculated and placed under optimum conditions for disease development. In Flo rida the disease has consistently occurred in such vareties as Indianapolis White, Iceberg and several others. Losses and Importance In general loss of due to bacterial blight range from to % although losses of % are not uncommon in certain varieties. The rapidity with which blighting occurs makes this disease of prime importance. Since it is not always possible to detect the disease, infected may be used for propagating thus introducing the dis ease into new areas. The propagator who can offer disease-free chrysanthemum cuttings has a decided advantage. Symptoms The symptoms expressed by bac terial blight, although variable, are not likely to be confused with other important chrysan themum diseases. The first external symptom in established under field conditions is a wilting of one or more branches which later become blighted at or near the succu lent growing tip (Fig. ). Affected areas turn dark brown to black, collapse, and become dry and brittle. In propagating benches the patho gen may invade the pith and vascular ele ments of cuttings yet produce no visible dis ease symptoms (Fig. ). When the stems are pressed firmly with the fingers they are easily flattened due to the hollow pith region. In very susceptible varieties, such as Indianapolis White, infected cuttings may be severely blighted. More commonly rooting will occur although dark necrotic areas are visible on both stems and leaves. In many instances a dark brown veinal necrosis of the leaves is the most characteristic external symptom. Cuttings that show marked necrosis usually die or the remain stunted and of poor quality. Bacterial blight is readily diagnosed when stems are split open. The pith area is reduced to a reddish-brown, jelly-like rot which later dries leaving a completely hollow pith. On occasion the pathogen causes external blight ing of the epidermal cells resulting in death of affected branches. Conditions favoring the disease - Climatic conditions in Florida during the spring, sum mer, and fall months are especially favorable for development of the blight disease. High temperature and high humidity are essential for optimum growth of the organism. Disease development is arrested under conditions of low temperature and low relative humidity. In addition, the pathogen is highly respon sive to the condition of the host plant. Suc culent, fast growing tissues are the most ra pidly and severely attacked while which are "hard" or less succulent tend to be less susceptible. The current trend in chrysanthe-

2 4 FLORIDA STATE HORTICULTURAL SOCIETY, 8 Table. A. Control of bacterial blight of chrysanthemums when the ends of inoculated cuttings (iceberg) vere dipped in rooting hormone powder containing various concentrations of formulations containing streptomycin. B. Same as above which were placed in soil and maintained for weeks for observation on the Iathhou8e bench. Ten () each treatment. Treatment of Active Ingredient (*) A No. showing external symptoms No. rooted Approx. length of roots (cm) No. of diseased B Approx. height of (in.) Condition of Unlnoculated Control. 7. Excellent Inoculated Control Agri-Strep * k..7 Fair Fair Fair-poor Poor Agri-mycin ** Fair-good Fair Poor Poor Agri-mycin ***.... U. U Fair-good * Streptomycin sulfate T& - Merck & Company ** Streptomycin.#; oxytetracycline.# - Chas. Pfizer & Company *** streptomycin.7#; oxytetracycline.l8#; tri-basic copper sulfate (metallic) 4.$ - Chas Pfizer & Co. Table. A. Control of bacterial blight of chrysanthemums when inoculated cuttings (iceberg) were momentarily dipped in various formulations containing streptomycin. B. Same cuttings as above which were placed in soil and placed on the lathhouse bench for observation. Ten () cuttings each treatment. Treatment of Active Ingredient (ppm) A No. showing external symptoms No. rooted Approx. length of roots (cm) No. of diseased B Approx* height of (in.) Condition of Unlnoculated Control Excellent Inoculated Control. k.o Fair-poor Agri-Strep all dead... Fair; lower leaves yellov Stunted; lower Same as above Agri-mycin all dead... Fair; lower Same as above Poor; lower Agri-mycin Q 4. 4.o Fair-good Fair-good; lower Poor-stunted; lower leaves yellow

3 McFADDEN: BACTERIAL BLIGHT 4 mum production is to root succulent fastgrowing tips and to force young into soft, rapid growth. It is under these condi tions that the bacterial blight pathogen causes extensive damage. Spread of the disease Stock may harbor the disease yet show no visible disease symptoms. Thus, apparently healthy cuttings may be diseased and serve to infect adjacent cuttings when placed in a moist medium to root. It is not uncommon to observe distinct patches of diseased cuttings in the propagat ing bench. Under field conditions the pathogen is in troduced in wounds made during the pinching and pruning operations (Fig. ). Hence, the pathogen may be spread from infected to healthy on fingernails or tools. Spread of the disease in soils has not been experiment ally demonstrated. Control Every effort should be made to control the disease in stock beds, in propa gating benches, and to prevent spread of the organism during pinching and pruning in the field. In previous tests (), (), it was shown that streptomycin suppressed growth of the organism both in vivo and in vitro. In the experiments reported here a comparison was made of some of the commercially available streptomycin formulations. Experimental Since the blight organism appears to be spread primarily during the propagating and pinching operations, it is during these periods that every effort should be made to control the disease. Four methods of treating chry santhemums were tried using three formula tions containing streptomycin. All treatments were repeated at least times with minor variations. (a) Antibiotics added to rooting hormone powder. Unrooted Iceberg chrysanthemum cuttings were first inoculated by placing the freshly cut basal ends in a dilute water sus pension of the bacterial blight pathogen. Af ter drying, the ends of the cuttings were light ly dusted with Rootone rooting hormone con taining various concentrations of streptomycincontaining formulations. All cuttings were placed in a Perlite-peat moss mixture to root under intermittent mist. The disease failed to produce external symp toms in many of the treatments including the inoculated, untreated controls (Table -A). This reaction appears characteristic of the va riety Iceberg. When treated in a similar man ner, the variety Indianapolis White, became severely blighted. Rooting was both delayed and reduced by some treatments. Cuttings receiving in excess of.% active Agri-Strep and Agri-mycin in rooting hormone pow der were delayed in rooting and/or the num ber of roots was reduced in comparison to the untreated controls. Although Agri-mycin did not appear phytotoxic at %, %, and % (active) concentrations, some injury re sulted at the % (active) concentration. Two percent active ingredient of either Agri-Strep or Agri-mycin caused severe injury to cuttings (Fig. 4). The above cuttings were placed in soil in individual clay pots and maintained on the lathhouse bench for observation. After weeks each plant was observed for both external and internal disease symptoms, if any. These data (Table -B) clearly indicate that Ice berg chrysanthemums may be internally in fected yet show no visible disease symptoms. Treated showed a marked reduction in disease incidence when compared to the untreated controls.although yellowing of fo liage and reduction in size and vigor of treated were observed to occur in most of the treatments, treated with Agri-mycin at the dosages employed showed only slight phytotoxicity. Agri-mycin also of fered fair disease control. (b) Antibiotics as liquid dip treatments. The variety Iceberg was inoculated in a man ner similar to that already described and later treated by immersing momentarily, entire cut tings into the treatment solutions. The cuttings, after drying, were placed in a Perlite-peat moss mixture for rooting under intermittent mist. Eleven days after treatment rooting was not markedly delayed by any of the treatments although some reduction in number and length of roots resulted from the higher dosages (Ta ble -A). In general Agri-mycin gave slightly less disease control and was less in jurious than some of the other treatments. Three weeks after potting the cuttings in soil, a high incidence of disease was noted when each plant was cut open to expose the pith and vascular tissues (Table -B). All treatments when compared to the uninoculated controls appeared to reduce the size

4 4 FLORIDA STATE HORTICULTURAL SOCIETY, 8 and vigor of the depending upon the concentration employed. Plants treated with Agri-mycin and Agri-Strep at ppm (active ingredient) in the cutting stage later died, whereas those treated with Agri-mycin did not die even at the highest concen tration employed; foliar yellowing occurred at all treatment dosages except Agri-mycin at and ppm of active ingredient. (c) Absorption of antibiotics through cut ends. In this test cuttings of the variety In dianapolis White were inoculated and the cut basal ends allowed to set in Agri-mycin at,,,, and ppm (active ingredient) for minutes. The cuttings were then placed in a Perlite-peat moss mixture to root under intermittent mist. Cuttings set in Agri-mycin at and ppm (ac- Table * The reaction of unrooted chrysanthemum cuttings (Indianapolis White) vhen inoculated vith Erwinia chrysanthemi and set in vater suspensions containing Agri-mycin. Ten (; cuttings each treatment placed under mist to root and data recorded days later. Treatment of active No. of cuttings ingredient rooted (HP) Approximate length of roots () Disease incidence Agri-mycin (veil rooted) *.O (many roots) 8 healthy; questionable (veil rooted)» (many roots) 8 healthy; questionable (rooting fair). (fev roots) healthy 6 (poorly rooted). (fev roots) healthy; questionable Uhinoculated Control (veil rooted) k.o (many roots) healthy Inoculated Control (poorly rooted). (fev roots) badly diseased Table h. Control of bacterial blight of chrysanthemum vith formulations containing streptomycin. Plants of the variety Iceberg vere inoculated by placing a small drop of inoculum on the open vounds made during the pinching operation. Sprays vere applied immediately after inoculation. Treatment no. treated no. diseased No. healthy Color of foliage Agri-Strep ppm (active) ppm (active) Yellov Pronounced yellov Agri-mycin ppm (active) ppm (active) Yellov Pronounced yellov Agri-mycin lbs./loo gal. lbs./loo gal. Nearly normal Slightly yellov Water sprayed (inoculated) Water sprayed (uninoculated) 7 Normal Normal

5 McFADDEN: BACTERIAL BLIGHT 4 tive), rooted normally after days whereas rooting was poor in cuttings receiving and ppm active ingredient. dis ease control was apparent at all concentrations employed and blighting of cuttings did not occur in the treated even at the lowest concentration whereas severe blighting oc curred in the inoculated controls (Table ). (d) Antibiotic Sprays. In certain chrysan themum varieties such as Iceberg, evidence is convincing that the blight organism is spread about in field plantings during the pinching or pruning operation. Plants of the variety Iceberg were first in oculated by placing a small drop of a water suspension of the bacterial pathogen on each of the open wounds made during the pinching operation. Immediately following pinching, the were sprayed with the various treatments. Disease development days after treatment showed that infections had occurred through the open pinching wounds. The uninoculated controls were not diseased. g Fig.. Erwinia chrysanthemi inoculated cuttings showing stem cut open to expose internal infection on right while infected cutting at left shows no visible disease symptoms. Fig.. Chrysanthemum plant showing typical symptoms of bacterial blight. Fig.. Bacterial blight of chrysanthemum (var. Iceberg) showing internal infection which occurred through pinching wound under field conditions.

6 44 FLORIDA STATE HORTICULTURAL SOCIETY, 8 All treatments reduced disease incidence compared to the water sprayed, inoculated controls (Table 4). Control was somewhat better in treatments receiving Agri-mycin and Agri-Strep both at ppm of active ingredient. However, yellowing of the sprayed foliage was most pronounced at this concen tration. Agri-mycin at pounds per gallons was the least phytotoxic and gave fair to good disease control; an increase in concentration to pounds per gallons failed to give a corresponding increase in dis ease control and caused slight yellowing of the sprayed foliage. Agri-mycin and Agri- Strep at ppm of active ingredient also gave fair to good disease control but caused yellowing. Discussion.--The results of these tests clear ly show that extreme care must be exercised when chrysanthemums are treated with formu lations containing streptomycin. The range of streptomycin concentrations in the various formulations used that gave adequate disease control, without injury, appear very narrow. Streptomycin injury to chrysanthemums is characterized by foliar yellowing, delayed rooting, reduction in number of roots, and stunting or hardening of treated. Strep tomycin does not appear to be translocated to a marked extent although absorption is known to occur (). Although the foliage of treated may be adversely affected, new growth appears normal and green. Formu lations containing streptomycin are not recom mended for routine use on chrysanthemums against bacterial blight although they may have limited use in propagating nurseries Fig. 4. The effect of formulations containing streptomycin when used as supplements to rooting hormone powder on the rooting of inoculated Iceberg chrysanthemum cuttings: Treatment (uninoc. control); (inoc. control);, 4,, 6 (Agri-Strep at.,.,.,.% active ingred.); 7, 8,, (Agri-mycin at.,.,.,.% active ingred.) and,,, 4 (Agri-mycin at.,.,.,.% active ingred.).

7 TAYLOR: EFFECT ON GROWTH 4 when used on specific varieties where disease losses are extensive. Such could then be used as stock from which cuttings may be taken for future propagation. In experi ments discussed here, all treated cuttings were first inoculated by placing freshly cut basal ends in a dilute water suspension containing the pathogen. The inoculum potential under these conditions is considered extremely high in comparison to that expected under normal nursery practices. It has been found that at any given concentration of streptomycin, con trol diminishes as the inoculum potential in creases (). When used as a supplement to rooting hormone powders a concentration not in ex cess of.% active ingredient of Agri-Strep or Agri-mycin, and Agri-mycin at. to % active ingredient is suggested. As a cutting dip treatment, Agri-Strep and Agrimycin both at ppm active ingredient and Agri-mycin Q at an active concentration of to ppm are suggested. The lat ter material appears somewhat safer to use and offers considerable disease control. When the basal ends of cuttings were set in water suspensions of Agri-mycin for minutes, it was shown that concentrations of and ppm (active ingredient) almost complete ly inhibited the disease without serious delay in rooting. Although all growers do not use rooting hormone powder as a regular practice, it is suggested that such a compound be used when chrysanthemum cuttings are treated with formulations containing streptomycin in order to hasten root formation. Chrysanthemum varieties differ in their tol erance to streptomycin. The variety Iceberg was severely yellowed when sprayed with formulations containing streptomycin whereas Indianapolis White appeared uninjured in the same test. * LITERATURE CITED. Burkholder, W. H., L. A. McFadden, and A. W. Dimock.. A bacterial blight of chrysanthemum. Phyto pathology 4:-6.. AAcFadden, L. A. 6. Studies on the chemotheropy of bacterial blight of chrysanthemum, caused by Erwinia chrysanthemi. Thesis, Cornell University.. Robinson, R. S., R. L. Starkey, and O. W. Davidson. 4. Control of bacterial wilt of chrysanthemums with streptomycin. Phytopathology 44: EFFECT OF FREQUENCY OF FERTILIZATION AND LIGHTING PERIOD DURATION ON GROWTH AND FLOWERING OF POT-GROWN MUMS James L. Taylor Florida Agricultural Experiment Station Gainesville Pot-grown chrysanthemums have become in creasingly popular as a specialty item in the floriculture industry of Florida. Optimum cul tural conditions are not known and many growers rely on information obtained from commercial catalogs and cultural handbooks. Information gained from such publications is frequently a summary of cultural practices employed by growers and suited only to limit ed growing regions. Valid cultural information is unavailable to commercial growers in the state; therefore, this experiment was estab lished to test, under Florida conditions, the effect of lighting period duration and frequency of fertilization on the growth and flowering of pot-grown chrysanthemums. Experimental Procedure This experiment was to test the effect of three lighting period durations and three fer tilizer application frequencies on the growth and flowering of chrysanthemums. The ex perimental design was a split-plot-with light ing period duration as main plot treatments and fertilizer application frequencies as sub plot treatments. Treatments were replicated three times and one pot, containing three, was the experimental unit. Rooted cuttings of Chrysanthemum morifolium var. Climax, a ten-weeks variety, were used as index. Three were placed equidistant in seven-inch plastic azalea pans containing a soil mixture of three parts fine sand and one part native peat. All re ceived supplemental illumination for one week after planting, when each plant was pinched and the breaks allowed to develop.