Disease Discussions: Correct Culture Can Stop Diseases By A.R. Chase and Margery L. Daughtrey

ARC: How important are cultural controls when you help a grower minimize a disease? I know I like to spend 90 percent of the discussion on water management, using pathogen-free seeds or liners, and giving the plant the best nutrition. Then I tell them what they can do if they cannot make any changes in how they produce the crop. I rarely am able to get the point across that prevention can be far more effective and even less costly than treating with fungicides
or bactericides.

MLD:Cultural controls are right up there with inoculum when it comes to determining if a disease outbreak is going to happen. If there is really good drainage, and roots haven’t been injured by a dry-down or overfertilization, it’s very hard for Pythium to attack roots. If there are only a few hours per day in which leaves and petals are wet, Botrytis hasn’t a chance.

ARC: I think if growers knew how hard it is to make some diseases happen when we (plant pathologists) want them to, they might take cultural control more seriously. I know I felt better the year I heard everyone doing IR-4 trials on Pythium had trouble getting any disease. It all goes back to the disease triangle, doesn’t it? Without a susceptible plant and pathogen and just the right environment, nothing will happen.

When I started at the University of Florida, I did some trials using overhead and hand irrigation to demonstrate that no disease occurred for Alternaria and Helminthosporium leaf spots when the leaves were kept dry — even when I loaded them up with inoculum. That was 34 years ago and I don’t see anyone stopping overhead irrigation unless the law gets on them about regulating water quality or run-off. I think water is the most critical element. If you had to pick one factor, what would you pick?

MLD:Water wins for sure! Watering is every bit as important today as it was when growers dealt with potted plants grown in pasteurized field soil. Overhead boom watering often provides conditions that we researchers would give our eye teeth for when setting up a bacterial disease control trial: Water splashing and swirling across the bench is ideal for bouncing bacteria from plant to plant and creating conditions for infection (think of Xanthomonas bacteria traveling across a poinsettia propagation area). To get conditions that let disease really rip for an experiment, we often have to resort to building a plastic tent over the bench.

ARC: That reminds me of my least favorite cultural control for diseases: nutrition. I spent many years doing research on this topic at the University of Florida only to decide that although nutrition does affect disease expression it more directly affects plant quality. You cannot sell a stunted, off-color plant even if it is disease-free. I know there are a couple notable exceptions including Fusarium wilt. Do you ever recommend changing plant nutrition to manage a disease?

MLD:Some of the “physiological diseases,” those that aren’t contagious, have nutritional answers, such as increasing calcium uptake to prevent scorch in hybrid lilies (as Bill Miller has taught me). And, conveniently, lowering the pH of calibrachoas and petunias to make conditions less conducive to Thielaviopsis also brings the benefit of reducing iron deficiency chlorosis in the leaves. But you’re right; most of the time pushing growth for a fast, on-time finish is more important to the grower than subtle effects of nutrients on disease. Sanitation (excluding pathogen inoculum) and good cultural conditions for the crop are always beneficial for disease management.

Important Cultural Control Methods

  • Water method – overhead, drip, ebb and flood
  • Water time of day
  • Well-drained potting media
  • Humidity management
  • Water amount
  • Pathogen-free seeds and plugs and cuttings
  • New or clean pots and flats
  • Remove diseased plants ASAP
  • Covered structure
  • Sufficient plant spacing
  • Raised benches
  • Soil pH
  • Nutrition level
  • Nutrition balance
  • Light level

A.R. Chase and Margery L. Daughtrey

A.R. Chase is plant pathologist at Chase Agricultural Consulting LLC and can be reached at archase@chaseresearch.net. Margery L. Daughtrey is senior extension associate at Cornell University’s Long Island Horticultural Research & Extension Center and can be reached at mld9@cornell.edu.