Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop Progress Report — June 1998
Integrating Control of Botrytis, Powdery Mildew, and Downy Mildew in Flower Crops - PROGRESS REPORT
Title of Project:
Integrating Control of Botrytis and Powdery Mildew in a Greenhouse Crop
Date: 5/28/98
Institution where work is being conducted: Michigan State University, Cornell University, Texas A&M
Amount of Endowment Grant:
$50,000
Covering Period:
7/97 to 7/98
Anticipated Date of Project Completion/Final Report:
6/99
Individual(s) Conducting Project:
(List Project Leader First)
M.K. Hausbeck- Title Assistant Professor
Telephone Number: 517-355-4534
M. Daughtrey
L. Barnes
What temperature and relative humidity (RH) levels are necessary for Powdery Mildew (PM) to infect and sporulate on poinsettia foliage?
Effects of temperature and RH on the infection process were quantified using leaf disks cut from mature poinsettia leaves (cv. Freedom Red). One-cm-diameter (diam.) leaf disks, placed on 1.4-cm-diam. agar disks, were incubated for 48 hours over glycerol/water solutions that provided 35, 50, 65, 80, and 92% RH at 15, 20, and 25C in sealed containers. All germinated conidia produced appressoria. Maximum germination and appressoria production over the RH range was 8.4, 20.8, and 25.9% of conidia at 15, 20 and 25C, respectively. Maximum percentage of germinated conidia producing haustoria over the RH range was 44.9, 61.7, and 51.8% of conidia at 15, 20, and 25C, respectively. Secondary germ tube and appressoria were not formed at 15C, optimum conditions were at 25C between 50 - 80% RH. Under high RH, sporulation was initiated 9 days after inoculation at 20 and 25C. Conidial chains of 3 - 6 conidia in length were present I I days after inoculation. Can fungicides applied to stock plants protect cuttings from PM? Twelve days after inoculation, the untreated control had 40.1% leaves infected, and reached a maximum of 92.8% infection 90 days after inoculation. The Terraguard and Systhane drench treatments did not provide acceptable disease protection. Leaves infected in the Terraguard spray treatment remained below 4% until 29 days after fungicide application. Cuttings removed from stock plants sprayed with Systhane remained free of disease until 62 days after fungicide application.
Can healthy cuttings be produced from PM-infected stock plants?
Poinsettia stock plants infected with PM were treated with the fungicides Terraguard, Systhane, and Strike. Five applications were made at 10-day intervals. Cuttings were removed from fungicide-treated infected stock plants 3 days after the final fungicide application. Each cutting included a leaf which had developed prior to the initiation of fungicide applications. At the initiation of fungicide applications, stock plants had an average of 24.2% of foliage infected. After 5 fungicide applications, percentage of infected foliage on stock plants was 3 1.3, 12.3, 12.2 and 12.6% for the control, Terraguard, Systhane and Strike treatments, respectively. Sixteen days after the last fungicide treatment 3 PM colonies were present on the cuttings; however, these colonies were not viable at the following rating. At the final disease rating, 49 days after the last fungicide application, cuttings removed from Terraguard and Systhane treated stock plants had no visible PM colonies; one colony was present on the cuttings removed from Strike treated stock plants. Cuttings removed from untreated stock plants had 19.3 and 92.6% leaves infected at the initial and final ratings, respectively. A replicate of this experiment conducted at the same time with the stock plants grown in the same greenhouse but with younger plants had different results. At the initiation of fungicide applications, plants had an average of only 4.3% infected foliage. After 5 fungicide applications, percentage of infected foliage was <0.3% for the fungicide treatments. Cuttings removed from treated stock plants remained completely free of PM for the entire experiment. Cuttings removed from untreated stock plants had 8.8% and 56. 1% foliar infection at the initial and final ratings, respectively.
What fungicides/chemicals will control PM on gerbera daisy?
Studies were conducted to compare new fungicides with standard products in controlling PM on gerbera daisy (cv. Festival yellow). Strike provided good PM control throughout much of the trial but infection became obvious 14 days after the first Strike 1 oz treatment and approximately 21 days after the first application in the Strike 2 oz treatment. Of tile 3 systemic fungicides that are labeled for PM control, Strike performed the poorest under the conditions of this trial. The fungicide Medallion provided no PM control at either application rate in this trial. The contact, surface-active fungicides/chemicals Triact and Zero Tolerance both provided generally good PM control, as long as they were applied at 7-day intervals. A silicate-based chemical (soluble silicate=potassium meta silicate) provided fair to good control at the 2000 ppm rate when applied at 7-day intervals.
What fungicides/chemicals will control downy mildew on snapdragon?
Disease pressure was high in this study with 93.5% of the untreated control plants diseased. Subdue MAXX 2MC completely suppressed spore production and prevented plant stunting. Acrobat appears promising as an additional tool for chemical control of down mildew.
