Plan now, save later: Proactive plant disease management

With warm temperatures this week, Iowans are doubtless getting antsy for spring, as spring means time for gardening! In addition to planning your annual garden around flavorful vegetables, sweet fruits, and pretty flowers, you may also want to consider how these choices will affect the long-term health of your plants.

To ensure that you enjoy healthy plants for the duration of the growing season, consider the following:

• History of plant disease problems in your garden beds
• Disease resistance traits of your selected cultivars
• Source of seed/cuttings- certified disease-free or not
• Other preventative disease management strategies

Let’s discuss why each of these items is important to your garden’s health. Even while you don’t necessarily want to think about your plants getting sick, in thinking about them getting sick, you can devise a plan to prevent disease incidence to your best ability.

History of plant disease problems in garden beds

If this is not your first season of gardening, you might remember how plants in your garden beds fared in years past. Perhaps you had some tomatoes that suffered from spots or peppers that succumbed to blight. My question for you is this- Do you know what diseases/pathogens were affecting your plants?

If so, great! You can plan on rotating plant species in that garden bed to known non-host for the pathogen that plagued you last year. Crop rotation is a fundamental integrated pest management (IPM) tool for limiting plant disease incidence in areas with history of known pathogen pressure.

In the event you don’t know or didn’t figure out what pathogens were afflicting your plants last year, there is not much that can be done in the way of proactive disease management. If diseases severely affect your garden this year, be sure to get a positive disease identification. (Submit a sample to the Plant & Insect Diagnostic Clinic [fees apply]).

Disease resistance traits of your selected cultivars

Knowing what pathogen was causing disease on your garden plants in years past can equip you with another IPM tool- host disease resistance. In addition to rotating plant beds to avoid subsequent years of infection from the same disease on the same host year after year, also try to find plant cultivars that have resistance to the pathogen that causes the problematic disease. There is, however, a caveat to host resistance- some resistance is complete (i.e., the pathogen cannot infect the plant) while some resistance is incomplete, called disease tolerance (i.e. the pathogen can infect the plant, but the plant has defense mechanisms that slow the pace of disease progression).

Note: host disease resistance confers resistance on for the pathogen/disease that it is stated for, so do not expect a tomato with bacterial leaf spot resistance to give protection against a fungal pathogen such as Septoria leaf spot, for example.

Source of seeds/cuttings

One of the principals of plant disease management is “exclusion”. This means simply preventing the introduction of inoculum into the growing environment. You can do this with some detrimental plant diseases by purchasing certified disease-free seed. Pathogens that are typically transmitted by seeds and cuttings are viral in nature and once introduced to an environment can persist on plant residue or with insect feeding (there are some bacterial, fungal, oomycete, and nematode pathogens that can be transmitted by seed as well, but in my opinion, seed-transmitted viruses are of most concern in the home garden).

Seeds/cuttings that are marked as certified disease-free also come with a caveat- when seeds and plant cuttings are sent for testing, the tests are destructive (i.e., the seeds and plant tissue are macerated when used for testing). A subsample of seeds from a seed lot or plant cuttings are sent for testing, and results are based on that subsample. So, while a seed lot can be certified disease-free, it is important to understand that the seeds and plant material you receive were not used for the testing and the chance of having diseased plant material/seeds is never an absolute zero.

Other preventative disease management strategies

Transplant seedlings- some diseases are most likely to infect young radicles germinating from seeds and are less likely to infect once a root system becomes more established. By transplanting seedlings into your garden bed, you might protect your plants from some diseases.

Seed treatments- There are different kinds of seed treatments that have different uses. Fungicide seed treatments can help protect young roots after seeds are planted. This can be useful in garden beds with history of seedling diseases. If you like to save your seed to plant for subsequent years, you might consider a hot water treatment to clean the seed/try killing any pathogens that might be on the seeds you harvested. For more on hot water seed treatments, see this publication from Louisiana State University: Vegetable Seed Sanitation: Best Practices to Ensure On-farm Food Safety 

Note: Not all seedborne pathogens can be killed or controlled via fungicide or hot water seed treatments. If you have questions about treating your seed, reach out to your local Iowa State Extension Educator or Specialist!