Four practices can help prevent the spread of disease in vegetable and flower gardens. They include mulching, good clean-up, crop rotation, and making sure there is good air flow between plants.
Mulching prevents diseases that splash up from the soil during rain or overhead watering and is especially important for tomatoes. Place mulch around seedlings as soon as they are planted, not touching the stems, and spread it out much further than you expect the plant to grow. If you’ve grown tomatoes or any other plant before, you know that they always, always grow larger than you expect them to!
Fusarium wilt and verticillium wilt are two long-lived fungal diseases that can splash onto plants from the soil and are also spread by re-using old plant stakes or tomato cages that haven’t been properly sanitized. In the case of tomatoes, rotating them out of the area for 5-7 years should help.
Bacterial spot and bacterial speck are soil-borne diseases that are bacterial rather than fungal. They affect both tomatoes and peppers. Bacterial speck is also seed-borne, so do not save seeds from an infected plant.
Powdery mildew is a fungal disease that affects many ornamental plants including zinnias, roses, bee balm, crabapple, lilac, snapdragon, and spirea, as well as cucumber and squash. It appears as a white powder covering leaves and stems. It is usually not fatal, just unsightly. Another fungal disease, downy mildew, appears on the undersides of leaves and often appears bluish in color. The top of the leaf may show large brownish specks or appear pinched or crinkled. Roses, pansies, impatiens, grapes, squash and cucumbers are particularly susceptible.
Both fungal and bacterial diseases generally can overwinter in plant debris. This is why it’s a good idea to scrupulously clean up all diseased leaves and stems at the end of the season. Burn the debris if at all possible. Alternatively, bury it a couple feet deep, or bag it and put it out with the trash. Do not compost it as most home compost systems do not get hot enough to kill disease.
Another way to help control fungal diseases is to space plants so as to allow for good air flow between them. In addition, avoid overhead watering because it creates humid conditions in the plant canopy that are conducive to fungal growth.
Before storage, tools like clippers, loppers, stakes and tomato cages should be wiped clean of soil using a dry rag and then disinfected with either bleach or alcohol. To use bleach, make a 10% bleach solution – one part bleach and nine parts water – and soak the items for 30 minutes. Rinse the tools very well and dry them afterward as bleach is corrosive to metal. Alcohol is easier and safer to use as it can be wiped on and left to dry. The bottles of 70% isopropyl alcohol that you buy at the drug store will work just fine.
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