Our unusually wet spring in Klamath Falls could lead to more plant disease and fungal growth in our gardens than is typically seen. Even so, not all of the unusual plant issues we are seeing are disease although many resemble disease.
Plant pathologists refer to issues caused by disease pathogens “biotic”: they are caused by living things like bacteria and fungi. Abiotic issues often resemble disease, but are caused by non-living agents: wind, fertilizer burn, weather, herbicide injury, ozone injury. Following are five abiotic plant issues that have recently been encountered at the OSU Klamath Basin Research and Extension Center office.
Edema: Edema has shown up repeatedly this season — most notably in gardens with season extension (like high tunnels or plastic row covers). In plants, edema is often expressed as swelling in the midrib on the back of the leaf. Edema is seen in leafy greens: lettuce, kale, collards, spinach, beets and a few other plants. Odd swellings along the midrib are most common, though separation of the leaf layers, blistering, and peeling of the outermost leaf layer occur in extreme situations.
Factors contributing to edema include excess moisture and a large differential between the daily high and low temperature. Especially when watered late in the day, movement of the water through the plant is reduced when the temperature drops quickly at the end of the day. Not much can be done about edema — try to reduce the difference between high and low temperature, especially if using plastic cover. This might mean taking the cover on and off more frequently, or putting it on earlier in the day to trap more heat underneath. Watering earlier in the day is also recommended.
Nutrient deficiency: The symptoms of nutrient deficiency vary with the specific nutrient at issue. Take peaches and nectarines: the most common nutrient deficiencies for these fruits include magnesium, iron and zinc. Magnesium deficiency shows up as yellow margins on the leaves resulting in a “V” shape: lack of iron is associated with leaves that are mostly yellow, but the veins still green. Zinc deficiency often results in a loss of leaves along the stem with leaves at the stem tips very small. Any of these could be mistaken for plant disease.
pH: pH nutrient and pH issues can be intertwined. If the soil pH is incorrect for the plant, it can inhibit the plant’s ability to take up a certain nutrient, even when available in excess. An example we’ve been seeing is iron deficiency in blueberries and rhododendrons, both of which require an acidic soil (low pH). It takes a considerable amount of product and time to nudge the pH. If your soil pH is 8.0, for example, and you want to grow blueberries which need 4.5 to 5.5 pH, you’ll need to add 3.3 pounds of aluminum sulfate or .5 pound of sulfur for every 10 square feet of soil you are trying to amend. That’s a lot of product. For more detail, read the fact sheet “Changing the pH of your soil,” at https://bit.ly/2KovWNg.
Cold damage: Cold damage can be tricky because it shows up in different ways on different plants, does not always show up immediately after exposure to cold, and varies by how mature the plant growth is when the cold exposure happens. Brand new leaves are more likely to suffer damage than older leaves on the same plant. Cold damage might show up as discolored leaves — red, purple — on plants that don’t typically exhibit those colors. On more tender plants, the leaves may turn black and shrivel up altogether. Cold might also impede the unfurling of larger leaves, like on corn or canna — in which case the leaf surface might be rumpled or wrinkled looking when it finally finishes opening. Even plants that are considered cold hardy are damaged when there is an unseasonal cold snap after warm weather.
Blossom end rot: Common in tomatoes, and less so in squash and peppers, blossom end rot is a result of the poor movement of calcium through the plant while the fruit is developing. The time to make sure calcium is sufficient is at planting or before: sprays to the fruit itself are not useful. If there is a history of blossom end rot in your garden, amend your soil with calcium, and water early in the day. The large difference between day high and night low temperature also plays a role here, contributing to blossom end rot issues in Klamath.
Nicole Sanchez is horticulture faculty at OSU’s Klamath Basin Research and Extension Center. For more information on this or other gardening topics, contact Nicole at Nicole.firstname.lastname@example.org or 541-883-7131.