Lauterbach: Wet springs nurture diseases

Special to the Idaho StatesmanMay 9, 2014 

It is spring, after all, so our weather is unsettled. We've had a lot of free water (hurrah!), but that means we may be in for some fungus diseases (boo!) that are uncommon in this arid region.

Fungus diseases that occur during wet springs include black spot on roses, powdery or downy mildew on a broad variety of plants, fireblight on apples, pears, and pyracantha (rarer on other shrubs), peach leaf curl on peach and nectarine leaves, and early blight on Solanaceous plants such as tomato, potato, pepper and eggplants. Some of these diseases may quickly kill your plants.

Check your rose foliage for black spot, a disease named for what it does: leaves black spots on leaves. This fungus disease attacks new or young leaves first, and as the black spots age, they develop yellow areas around the spots, ultimately turning the whole leaf yellow, then dropping off.

Prevent infection and/or control with fungicidal soap and wettable sulfur sprayed on the rose foliage when needed. This fungus will produce spores every three weeks, so keep checking. You may also prune off damaged parts of your plant, putting the diseased parts in landfill-bound trash (NEVER in compost). This sanitation must extend to infected leaves that have dropped on the ground to prevent recurrence of the disease.

Some folks spray a mixture of skim milk and water (1/3 milk) and claim it works to clear up such disease. They also use that spray on infestations of powdery and downy mildew, both of which may appear during this damp spring. Both mildews appear as white or grey-white matte cover on leaves.

Fireblight turns leaves black, terminal twigs droop in a shepherd's crook fashion, and sap oozes from branches or twigs. If you catch it early, you may be able to control it with Bordeaux spray or prune the branch eight to ten inches lower (that is, toward the roots). Prunings should be sent to landfill, and clippers or loppers sterilized between bushes, trees or plants.

Peach leaf curl first appears as reddening areas on emerging leaves, then these areas thicken and blister, and leaves then curl. These areas bleach to white, hosting velvety spores of the fungus. Leaves may fall off, and new, more normal leaves emerge unless wet cool weather persists. Pick up spore-bearing leaves and send to landfill.

To avoid losing plants to early or late blight, immediately mulch susceptible plants with a splash-preventing medium after transplanting. Tomato, potato, and pepper (chile) plants are especially vulnerable to blights. "Late" blight may occur early.


I don't think it's completely safe to set out tomatoes, peppers and eggplants until June 1, even though our average last date of frost is May 10.

Remember the weather bureau takes and forecasts temperatures for a height about 5 feet off the ground, and since cold falls, it's colder at ground level. Few studies of this difference have been made, but one found ground level temperature 6 degrees colder than the weather bureau reported.

Calculating temperatures at that height, though, serves fruit tree growers, leaving those planting at ground level to refigure temperatures for in-ground crops.


The air we breathe contains moisture (H2O), the concentration depending on the level of humidity, and that moisture can be extracted even in our low humidity area. As earth cools in evening, reaching the dew point, atmospheric water vapor forms as dew, a collectable water source. We're not suffering from drought, but that may face us in the future as the population (and need for fresh water) grows and warm dry weather moves northward. Our grocery prices are reflecting the California drought.

Arturo Vittori, an Italian designer, has come up with a brilliant solution to drought: towers that extract moisture from air. He calls his innovation "WarkaWater Towers, and a four-person team can build one in less than a week, using local materials. They're named for the Warka tree, around which Ethiopian villagers gather to chat.

WarkaWater towers stand about 30 feet tall, are vase-shaped, and made of bamboo or local stalks woven together. Inside each tower a plastic mesh of nylon and polypropylene gathers moisture and funnels it to the basin at the bottom of the tower.

Vittori estimates each tower can collect at least 25 gallons of clear clean water each day in Ethiopia, the first country he tried this in. About four-fifths of that country is dry and arid.

Margaret Lauterbach: or write to Gardening, The Idaho Statesman, P.O. Box 40, Boise, ID 83707

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