Disease management begins in the greenhouse

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Damping-off (caused by Pythium spp., Phytophthora spp. and Rhizoctonia sp.) affects all vegetable seedlings and is also common among flowering bedding plants. Damping-off results in collapse of the plant at the soil surface. To prevent damping-off, avoid over watering because some fungi that cause damping-off prefer wet conditions.

Good sanitation is the key and ensures that root rot problems from one crop are not carried over to another crop. Root rot pathogens survive in the greenhouse in soil particles or plant parts clinging to containers, benches, walkways and equipment. If root rot occurs, remove and destroy the diseased plants. Also, remove healthy-appearing plants that are immediately adjacent to the dead plants, because the disease may have already spread to them although they are not yet showing symptoms. Plug sheets containing diseased transplants should not be reused.

Table 1. Products used in trials

Product

Active ingredient

Labeled

Aliette 80WDG

fosetyl-al

no

Banol EC

propamocarb

no

Endorse 11.3DF

polyoxin D zinc salt

no

Heritage 50WG

azoxystrobin

yes

Kocide 2000 54DF

copper hydroxide

yes

Moncut 70DF

flutolanil

no

Scholar 50WP

fludioxonil

no

Subdue MAXX EC

mefenoxam

no

Terraclor 75WP

PCNB

no

ZeroTol

hydrogen dioxide

 no

*Labeled for celery nurseries, applications in greenhouse not prohibited.
**Labeled for field and greenhouse use.

Greenhouse fungicide trial – Rhizoctonia

A greenhouse trial was conducted using registered and nonregistered products (Table 1). Inoculum was prepared by growing R. solani on potato dextrose agar for four weeks. Flasks filled with two parts millet and one part water were sterilized. Four 1.5 inch plugs of the infested agar were then placed into the flasks. The infested millet was allowed to grow for three weeks before being mixed (8 oz/1 ft3) into a soilless media (Baccto Professional Planting Mix, Michigan Peat Company, Houston TX). Three weeks after seeding into a 288-cell tray, healthy celery ‘Dutchess’ seedlings were planted into 3 inch pots containing the infested soilless media. Plants were watered as needed and fertilized twice weekly with 200 ppm of Peter’s 20-20-20 water soluble fertilizer (The Scotts Company, Marysville, OH). Eight plants per treatment were placed into a completely randomized design. Immediately after transplanting the seedling into the infested soil, fungicides were applied as a drench in sufficient volume to displace 10 percent of the water in the pots on the February 1 and 15. A plant health rating (1 to 5; 1=healthy, 2=chlorosis/minor wilting, 3=moderate wilting, 4=severe wilting, 5=plant death) and death percentage were assessed on February 7, 14 and 23.

Disease pressure was severe in this trial with 100 percent of the untreated inoculated plants dead just 7 days after inoculation (Table 2). All treatments had significantly better plant health ratings and lower plant death percentage than the untreated control throughout the trial. Terraclor 75WP, Moncut 70DF, and Scholar 50WP were the only treatments that completely prevented plant death in this trial. Kocide 2000 54DF, although statistically better than the untreated, did not offer acceptable disease control. No phytotoxicity was noted on any of the treated plants in this trial.    

Table 2. Control of Rhizoctonia root rot of celery seedlings with fungicide drenches

Treatment and rate/100 gal

Plant health* 23 Feb

Plant death (%) 23 Feb

Untreated inoculated

5.0

d**

100

c

Terraclor 75WP 8 oz.

1.4

ab

0.0

a

Moncut 70DF 1.1 lb

1.0

a

0.0

a

Endorse 11.3DF 8 oz

2.0

bc

12.5

ab

Scholar 50WP 4 oz

1.3

ab

0.0

a

Heritage 50WG 8 oz

2.0

bc

12.5

ab

Kocide 2000 54DF 1 lb

2.7

c

25.0

b

*Plant health rated on a 1 to 5 scale; 1=healthy, 2=chlorosis/minor wilting, 3=moderate wilting, 4=severe wilting, 5=plant death.
**Column means with a letter in common are not significantly different (Fisher’s LSD; P=0.05).

Greenhouse fungicide trial – Pythium

A fungicide trial was conducted to test various products against Pythiumdamping-off in the greenhouse (Table 1). Inoculum was prepared by growing several Pythium spp. on dilute V8 agar for 2 weeks. Flasks filled with two parts millet and one part water were sterilized. Six 4 centimeter plugs of the infested agar were then placed into the flasks. The infested millet was allowed to grow for four weeks before being mixed (8 oz/1 ft3) into a sterilized soilless media. Several 288-cell flats were cut into sections of 48 cells and filled with the infested soil. Celery ‘Dutchess’ seeds were planted into each cell on 29 Sep. Six 48-cell flat sections were used per treatment and placed into a completely randomized design. Fungicides were applied as a drench. The percentage of emerging celery seedlings was noted on September 20 and October 5.

Disease pressure was severe in this trial with the untreated inoculated flats averaging just 18.8 emerged seedlings compared to the untreated healthy control with 64.8 on October 5 (Table 3). On the final rating date, Aliette WDG and Banrot WP were the only treatments that had statistically more emerged seedlings than the untreated inoculated control according to our statistical tests. Due to the resistance of thePythium spp., Subdue MAXX was statistically similar to the untreated inoculated control and did not limit disease. No phytotoxicity was observed on any of the treated plant in this trial.

Table 3. Control of Pythium root rot of celery seedlings with fungicide drenches.

 

Treatment and rate/100 gal, applied at 14-day intervals

Germinated seedlings (ave.)

20 Sep

5 Oct

Untreated healthy control

40.8

a

64.8

a

Untreated inoculated

20.8

b

18.8

d

Kocide 2000 54DF 1.5 lb

21.5

b

21.0

d

ZeroTol 10 fl oz

20.3

b

16.3

d

Banrot 40WP 12 oz

38.3

a

32.0

c

Aliette 80WDG 4 lb

37.5

a

45.5

b

Subdue MAXX EC 1 fl oz

21.5

b

18.3

d

Banol EC 3 fl oz

14.8

b

13.5

d

*Column means with a letter in common are not significantly different (Fisher’s LSD; P=0.05).

Dr. Hausbeck’s work is funded in part by MSU‘s AgBioResearch.

Related Events

Related Articles

Related Resources