Cucurbit Tobacco Soybean

Blue Mold Control Recommendations

2004 BLUE MOLD CONTROL PLAN

P. B. Shoemaker, W. C. Nesmith, C. S. Johnson, and T. A. Melton

The following factors were identified as the key forces driving blue mold epidemics:

  • Protracted periods of blue mold favorable weather.
  • Changes in the pathogen, especially resistance to fungicides, means that Ridomil Gold is ineffective against resistant strains.
  • Current production practices allow the pathogen to be strategically placed and propagated in the heart of the belt rather than on the edges of the belt.
  • Commercialization of transplant production has enhanced movement of infested/infected transplants from both distant and local sources.
  • Early arrival of the causal agent gives the pathogen more time to build up and spread at critical stages in the crop.
  • Greenhouses and float-systems serve as local incubators of blue mold during periods when natural conditions otherwise would not favor blue mold.
  • Poorly equipped sprayers are a major limitation to achieving control with current fungicide options.
  • Over-lapping planting dates and cropping stages increase the opportunities for the pathogen to reach high populations more often during the season than with past production approaches.
  • Close spacing of tobacco plants favors disease development and impedes spray efforts.
  • Cultural practices that prolong juvenile growth or delay maturity increase the risks of damage from blue mold.

Control Plan

Blue mold is controllable. Good control requires a change in production attitudes and activities. Limitations of current control options and the epidemiology of this disease dictate that success will be dependent upon the tobacco industry operating in a community and regional effort for the benefit of all, rather than growers operating independently. A committee involving growers, transplant producers, county extension agents, plant pathologists, and agronomists developed the following control plan. This plan should be used to guide community control efforts throughout tobacco-growing areas.

General strategies for blue mold control:

  • Manage your own crop as much as possible.
  • Make the environment less favorable for the pathogen to survive and infect your tobacco.
  • Use more than one control method.
  • Keep the pathogen out of tobacco and your community for as long as possible.
  • Protect tobacco plants with fungicides when they are most vulnerable.
  • Manage plant beds, greenhouses, and fields to favor tobacco, not blue mold.
  • Manage the crop to get to harvest quickly, but not prematurely.
  • Don't forget about other diseases.

Protect transplants from blue mold:

  • Grow your own plants, or buy them from a reputable, local source.
  • Follow recommended greenhouse hygiene and sanitation practices.
  • Don't seed any earlier than 7-9 weeks before transplanting.
  • Manage temperature and ventilation systems to minimize leaf-surface moisture by reducing relative humidity and condensation.
  • When blue mold advisories have been issued and weather permits, remove plant bed covers to aid drying of the foliage.
  • Irrigate beds early in the day to allow drying before nightfall.
  • Follow a recommended clipping schedule for greenhouse plants (remove clippings from trays and dispose of them far from transplants).
  • Use a regular, preventative-fungicide spray program in greenhouses and plant beds.
  • Promptly destroy ALL plants within the system, should blue mold occur in beds or greenhouses.
  • Do not set ANY plants from blue mold infested sources.

Preventative spray program for tobacco transplants:

  • Use one of the following fungicides: mancozeb (Dithane DF Rainshield NT) or ferbam (Carbamate, where labeled, not in NC).
  • Begin sprays as soon as plants can tolerate the chemical.
  • Continue sprays until plants go to the field.
  • Apply every 5-7 days until plants are set or destroyed (a 5-day spray schedule is highly recommended).
  • Start with 3 gal/1,000 sq. ft. of spray solution for small plants, increasing to 6-12 gal/1,000 sq. ft. as plants grow.
  • Destroy surplus plants as soon as you know they're no longer needed (or continue your fungicide program until plants are used).

Greenhouses:

  • Use 0.5 lb of Dithane DF Rainshield NT/100 gal of spray solution or 2-3 lbs of Carbamate (where labeled) (1 tsp/gal for Dithane DF Rainshield NT or 2-3 tablespoons/gal for Carbamate). A 5-day spray schedule is highly recommended.

Plant beds:

  • Use 2-3 lb of Carbamate or 1 lb of Dithane DF Rainshield NT/100 gal of spray solution (2-3 tablespoons/gal of Carbamate or 1 tablespoon/gal of Dithane DF Rainshield NT).

Blue mold control recommendations for the field:

Select a blue mold management plan BEFORE you transplant, utilizing both cultural practices and fungicides.

Cultural practices to improve blue mold control:

  • Field selection: avoid shady, wet-natured locations with poor drainage, for example: sites near streams.
  • Row and plant spacing: avoid close plant spacings that favor disease development, for example: 48 inch rows with 20 inch plant spacings will also save labor, reduce barn space requirements, and make it easier to spray than narrower spacings.
  • Fertilization: avoid excess nitrogen fertilization. Follow recommendations for your state.
  • Topping and sucker control: early topping and improved sucker control slow disease progress.
  • Harvesting: In burley, don't cut fields early to avoid blue mold losses. Remember, in healthy crops, you gain 200 lb/acre/week after topping. In some instances, it may be advisable to destroy or early-harvest to reduce the threat of blue mold to nearby tobacco. In flue cured, removing the bottom leaves may help with air flow in the field.

Fungicides for field blue mold control:

  • For Ridomil-resistant blue mold (predominant type): Use a labeled protectant fungicide: Dithane DF Rainshield NT at 2 lbs/100 gal or Acrobat MZ at 2.5 lbs/100 gal. Actigard systemic plant activator may be used as a preventive once plants reach 18 inches tall (see label for precautions).
  • Start spraying early when blue mold has been forecasted for your area.
  • Use the Blue Mold Forecast System and Local Extension Advisories to know when to begin sprays. DON'T WAIT UNTIL YOU SEE BLUE MOLD ON YOUR FARM BEFORE STARTING SPRAYS!
  • For Ridomil-sensitive blue mold (blue mold during the past 7 years has NOT been sensitive to Ridomil): Use Ridomil Gold applied broadcast at 1 pint preplant incorporated and at 1/2 pint to row-middles (ridges if flue-cured) at layby; apply PPI treatment within 3-7 days of transplanting and use flat-fan nozzles on drops to apply layby soil treatments. Ridomil will not control all types of blue mold but is of value for controlling Pythium diseases and black shank.

Spray volumes required:

You need MAXIMUM COVERAGE to get good control when using Dithane DF Rainshield NT or Acrobat MZ. Use plenty of water when spraying these foliar fungicides:

  • 20 gal of water/acre following transplanting
  • 40 gal of water/acre near layby
  • 60 gal of water/acre when plants are waist high
  • 80 gal of water/acre when plants are chest high
  • 100 gal of water/acre when plants are shoulder high or near topping

Spray application for Dithane DF Rainshield NT and Acrobat MZ:

  • Spray every 5-7 days, adjusting the schedule according to weather conditions.
  • Use high pressure (100-250 psi) hydraulic sprayers with a piston or diaphragm pump and hollow cone nozzles.
  • To obtain good coverage with a boom sprayer, you need to provide drive-through rows wide enough for your tractor.
  • Use multiple drop nozzles so that leaves at the bottom and middle of the plant receive spray. Both top and bottom leaf surfaces MUST be well covered.
  • For air blast sprayers: mix fungicide at 2X concentration. Apply 1/2 the gal/acre used with the hydraulic sprayer, being careful to spray all plant surfaces.

Spray application for Actigard:

  • Apply at a rate of 0.5oz / acre.
  • Begin applications after plants reach a height of 18 inches.
  • Apply prior to the appearance of disease in the field.
  • Make up to two applications on a 10-day schedule.
  • Apply in a minimum of 20 gallons of water per acre, but not more than 50 gallons of water per acre.
  • Another registered blue mold product should be used prior to 18" for early season control and after final Actigard aplication if conditions are conducive for disease.
  • See label for precautions.

NOTE: It is the user's responsibility to follow all usage directions on the pesticide label.

Want more information?

Follow these links to the fungicide providers:

Follow these links for more information and statewide publications:

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by North Carolina Cooperative Extension Service is implied.

The Burley Tobacco Blue Mold Seminar was sponsored by University of Kentucky and R. J. Reynolds Tobacco Company together with North Carolina State University, the University of Tennessee and Virginia Tech cooperating.

This service is provided by the North Carolina State University departments of Plant Pathology and Marine, Earth, and Atmospheric Sciences.

Back to the Blue Mold Forecast Homepage
Page last updated by Matthew Miller on May 25, 2005.

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