Key takeaways
- Plant diseases are mostly bacterial or fungal — controlled with bactericides or fungicides, but only some of those products are safe to combine with biocontrol programs.
- Disease begets disease: a sick plant becomes more susceptible both to other pathogens and to insect pests — many of which are themselves disease vectors.
- Prevention beats treatment — the cheapest, safest, most reliable disease control program is the one you never have to deploy.
- Five preventive levers: plant spacing, insect control, scouting, sanitation, and crop rotation.
- Most disease pathogens favor darkness, heat and high humidity — engineer the environment against them.
As it is with humans, plants get sick too. Most plant diseases are bacterial or fungal, and most can be prevented — with proper spacing, sanitation and insect control — long before any spray is needed.
Overview
Illness breeds illness. Plant diseases can make plants more susceptible to disease and more prone to pest attack. Ironically, many diseases are transmitted by pests in the first place — thrips, aphids and whiteflies are well-known virus vectors, while soil-pest activity opens wounds that fungal pathogens then exploit.
Diseases in plants are typically bacterial or fungal. Controls are accordingly either bactericides or fungicides. Many pesticides target specific pathogens or pathogen lists, but not all are safe to combine with biological pest control programs. The safest options are often safe because of when they’re applied rather than what they contain.
As with biological pest control, prevention is the answer to ultimate disease control: stop it from happening and you won’t have to deal with the consequences. Most of the safer products work best as preventive medicine for plants, though some are effective curatively as well.
Prevention Practices
Before reaching for sprays, deploy the simple cultural practices that prevent disease pressure from building in the first place.
Plant spacing
Plant spacing is critical. The greater the distance between plants, the less likely that spores and other inoculum will move between them. Wider gaps improve air circulation and increase light penetration to inner foliage, both of which keep plants drier. Most disease pathogens thrive in darkness, heat, and moisture or high humidity — spacing engineers all three against them.
Insect control
Insect pests are probably the number-one cause of disease spread among plants. Effective insect control is therefore one of the highest-leverage disease prevention tools. Insect screens are a terrific idea from the disease standpoint — they provide maximum separation between vectors and your crop. Healthy pest programs against thrips, whiteflies and aphids reduce virus pressure for free.
The best disease control program is an aggressive insect-control program. Most plant viruses arrive on thrips, aphids and whiteflies — not by spores in the air.
Scouting
Scouting your plants provides early insight into disease manifestation. Finding disease symptoms on a single plant — and removing that plant — can genuinely save the day. Wash your hands and the surrounding area immediately after disposal. This is very important because of the human role in pathogen transmission.
Sanitation & Rotation
Sanitation is fundamental. Like some pests, growers themselves can transmit plant diseases via hands, tools, hoses, footwear and clothing. Establishing whole-greenhouse sanitation procedures can be of immense value — clean up now and avoid headaches later. This may also include the sanitation or sterilization of growing media: many plant pathogens get their start in tainted substrate. Today, you can often add living organisms to the soil (mycorrhizae, Trichoderma, Bacillus subtilis) that displace pathogens naturally — no costly steam sterilization required.
Outdoor crops should be rotated often. Many growers know not to plant cole crops in areas where another cole crop has been grown within the past three years. Same-family plantings can amplify the family-specific pathogens that build up in soil — rotation breaks those cycles.
Scouting & Resources
Get more information. Many books help with identifying, preventing, and correcting disease problems. A good place to start is your local cooperative extension office — staff are typically familiar with the common plant diseases problematic in your given area and can recommend region-specific resistant cultivars and timing strategies.
And scout. Scout. Scout. Yes, we’re back to that again. Just can’t stress its importance enough. Whole-house scouting on a fixed cadence — combined with the prevention practices above — reduces disease pressure to the point where chemical intervention becomes rare. The cheapest disease control program is the one you never have to deploy.
Scout. Sanitize. Space your plants. Control your insects. Rotate your crops. Do all five and chemical disease control becomes the exception, not the routine.
For over 30 years, Green Methods has been a leader in the production and application of beneficial organisms used in biological pest control and integrated pest management programs.