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A spectrum of solutions for garden problems

“Tasty homegrown tomatoes beat store-bought any day and are well worth the effort you make to keep them healthy. Fungal infections are the most serious challenges you may face.”

— David Deardorff and Kathryn Wadsworth, “What’s Wrong with My Vegetable Garden?” (2011)

We’re growing several different kinds of tomatoes in raised beds this year, and so far we haven’t had any problems with diseases or insect pests.

Perhaps the biggest challenge for successfully growing tomatoes so far has been the fluctuating temperatures in Medford. Recently, the temperature went from a high of 102 degrees to a high of 66 degrees within just a few days, and nighttime temperatures have dropped below 50 degrees a few times so far in June.

As Deardorff and Wadsworth note in the Plant Portrait section of their book, tomatoes (Solanum lycopersicum) thrive when daytime temperatures range between 75-85 degrees and nighttime temperatures stay above 55 degrees. As I discussed last week, temperature is one of the four essential elements of successful vegetable gardening, along with water, sunlight and soil health. Wide temperature fluctuations do not provide ideal growing conditions for tomatoes, which could lead to secondary problems with insects and/or diseases.

In Bandon, where we are growing tomatoes in raised beds inside a hoop house, daytime and nighttime temperatures have been more consistent. However, the emitters we’ve been using for irrigation may be the cause of yellowing leaves at the base of some of the plant stems. Wet foliage (a primary water issue) encourages secondary problems for tomatoes such as fungal and bacterial infections: leaf spot, powdery mildew, fusarium/verticillium wilt or phytophthora blight.

At both locations, my goal is to address primary issues with the growing conditions before secondary issues with insects and diseases crop up. In Medford, my best course of action is to modify the effects of fluctuating temperatures with shade cloth, which could double as a light blanket during nights when the temperature drops below 55 degrees. In Bandon, we need to change our irrigation system to driplines that will more efficiently water the soil, rather than the plant foliage.

Hopefully, these remediation strategies will ensure that my plants stay healthy enough to ward off insect and disease problems; however, if these issues do come up, Deardorff and Wadsworth offer plenty of organic solutions.

For plants in the Solanaceae family — tomatoes, tomatillos, eggplants, peppers and potatoes — the authors provide 10 pages filled with charts that picture and describe different plant symptoms, present a diagnosis of the problem based on the symptoms, and list solutions from an integrated pest management perspective.

IPM strategies range from least toxic to most toxic: a) cultural changes such as altering growing conditions, planting polycultures and rotating crops; b) physical-mechanical changes such as using row covers, hand-picking beetles off plants or spraying aphids with a hose; c) biological changes such as introducing beneficial insects/nematodes or adding indigenous microorganisms (IMOs) to the soil; and finally d) using products with naturally occurring chemicals such as insecticidal soap, neem or horticultural oil, copper, sulfur and pyrethrin.

Sulfur and pyrethrin are commonly suggested chemical remedies for insect pests; however, although “natural,” both also kill beneficial insects and are poisonous to fish, pets and people. They should be used with caution and only when other remedies have failed or if a severe infestation occurs.

Sulfur is a yellow mineral mined from the earth that kills insects by disrupting their metabolism. It’s also shown effectiveness as a fungicide by preventing fungal spores from germinating.

Pyrethrin is made from the dried flowers of a relative of the garden mum — Chrysanthemum cinerariifolium — and ground into a powder that is mixed with water and sprayed onto plants. It paralyzes insects on contact, but can remain potent for several days and may kill other, unintended insects.

For those of us who are trying to increase the diversity of insects in our garden, particularly caterpillars and bees, the side effects of using sulfur and pyrethrin usually outweigh the benefits.

Less toxic chemical remedies are recommended to solve disease problems in the vegetable garden. Baking soda, like sulfur, prevents fungal spores from germinating; unlike sulfur, however, it’s nontoxic to mammals, insects and fish. Be careful, though; sodium bicarbonate can burn the leaves of some plants.

Bacillus subtilis is a naturally occurring bacterium that kills fungal pathogens on plants by competing for nutrients and attaching itself to the fungi’s cell walls, eventually destroying them. The bacterium is nontoxic to humans, birds and fish, but some people may have an allergic reaction, and some strains of B. subtilis can produce toxins for insects, including beneficials.

I think it’s important to reiterate that sulfur, pyrethrin and B. subtilis are all approved for organic gardening, but that doesn’t mean their use doesn’t carry risks. It’s not difficult to understand why Deardorff and Wadsworth advise gardeners to use these remedies with caution and only after less toxic strategies have failed. They represent the far end of a spectrum of solutions to problems in the vegetable garden that begins with growing healthy plants by providing the growing conditions the plants need to protect themselves from insects and disease.

Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at Rnowak39@gmail.com. For more about gardening, check out her podcasts and videos at https://mailtribune.com/podcasts/the-literary-gardener and her blogs at www.bardsgardentours.com.

My garden to-do list this week

I’m settling into a weekly summer routine:

• Harvest leaves, shoots, roots, fruits and flowers

• Thin out seedlings as needed

• Pinch back herbs, prune tomato side shoots/suckers, prune bottom leaves to increase air circulation

• Deadhead spent flowers to next growth node

• Apply foliar sprays/soil drenches with fermented plant juices every 7-10 days

• Monitor plant growth, take pictures

• Collect plant debris and clippings, including weeds, for compost and fermented plant juices