Diagnosing Plant Problems Is Key to Success

Blossom end rot on tomatoes resembles a disease, but is actually caused by calcium deficiency.

Every gardener encounters problems at some point. Nature is our host, greeting gardeners’ hubris with humble pie served by drought, disease, and pest invasions. In the old days one could blame ignorance for missteps in managing pests and diseases; fortunately, our increased understanding of nature’s rules has allowed us to move beyond “spray and pray” and into the role of conscientious gardeners.

Becoming conscientious is not always easy. When we see sad plants, our automatic reaction may be to apply one or both of the supposedly universal panaceas: water and chemicals. Taking the time to diagnose plant ailments can require patience and perseverance, but understanding why problems happen increases your chances of success and prevents future mistakes.

Reducing the misuse and overuse of pesticides and herbicides is another advantage to accurate diagnoses of plant problems. If you think your tomato has a fungal disease and it’s actually suffering from a calcium deficiency (blossom end rot), spraying fungicide is ineffective, a waste of money, and introduces potentially harmful chemicals into your garden and food.

Solving plant problems means accepting the garden as an ecology with numerous interconnected elements to consider. A classic example is black sooty mold, a leaf-dwelling fungus resembling its name. Sooty mold grows on the sugary secretions left behind by aphids, which are placed and protected by ants, which harvest the sugar for food. Fungicide won’t help much if the cause (ants and aphids) sticks around. In this example, an ecological approach would call for eliminating the ants and spraying the aphids off the plant with water, thereby reducing the sooty mold’s “habitat.”

Knowing why plants droop or get eaten can seem overwhelming at first, and the list of potential causes is sizable. It might ease your mind to know that 90% of plant problems are water-related, either directly or indirectly. The vast majority of gardeners overwater, saturating the soil and creating an anaerobic environment that starves roots of oxygen. Another common mistake is watering a little bit everyday, resulting in drought-prone shallow roots.

A good place to start is identifying the plant species. Plants typically have associated problems, and knowing the species can help you narrow down the causes and management strategy. If you need help identifying your plant, you can go to an independent nursery or contact your local Master Gardener program (a free service). The UC Integrated Pest Management program is an excellent resource, offering visuals of different plant problems and least toxic management strategies. Their website can be found at www.ipm.ucdavis.edu.

Where you go from there is dependent upon the situation, but factors to consider are the time of year, the weather, diseases and pests the plant is susceptible to, and where on the plant the problem is occurring (all over or confined to one part of the plant). You might also think about non-biological causes, such as accidental pesticide exposure, “blade-itis” (damage by mowers, weed whackers), or burns from a heat-reflecting wall. A final tip is to always check the soil if in doubt about whether to irrigate. A drooping plant can be a sign of too much water or not enough, and the top 1”-2” of soil may be dry even if there is plenty of moisture below.

If the UC Integrated Pest Management website seems overwhelming, try their diagnostic tool at www2.ipm.ucanr.edu/diagnostics. Providing information such as the plant species, which parts of the plant are affected, and the type of damage, allows the diagnostic tool to identify one or more causes. This makes a good starting point, especially for those who are new to identifying plant problems.

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website at sjmastergardeners.ucanr.edu.

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  • Blog Author

    Nadia Zane

    Nadia Zane is a UC Master Gardener, a landscape designer and Stockton native. She has a fondness for California native plants and sustainable landscaping, which she utilizes in her work for Native Beauty Garden Design. She is a member of the CA ... Read Full
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