Friday, May 28, 2010

We get problems in May!

    An odd year?!?

    So many questions! Weird weather, the usual spring pest problems, and much more. So today we have a grab bag of odds and ends.

    What's up with this weather?

    2010: a strong El NiƱo year!
    NASA climate scientists inform us that January through April were warm worldwide. But there are regional anomalies, and we are in one of them (weather isn't climate).

    Below average temperatures every month of 2010. April and May had high temperatures below average by as much as 10 - 15 degrees. If we complete May without breaking 90 degrees, it will be the first time since 1971. Pleasant as that may be for gardeners, the weekly rain and cool temperatures have played havoc with plants and crops.

    My peppers aren't growing!

    Summer vegetables are off to a sluggish start. Soil temperature should be 60 degrees for tomatoes, and it barely reached that mid-May. Soil temperature of 70 degrees is best for peppers and eggplant, and it is still only in the low 60's! Transplants are sulking: growth is slow, nutrient deficiencies are showing up, and pests are eating the seedlings faster than the plants are growing.

    An overview of early-season vegetable problems:

    Virus or weather?
    Too soon to tell.
    o Holes in leaves = earwigs (small holes), snails and slugs (large holes). Organic baits are available.
    o Leaf edges burnt = windy weather drying the leaves of seedlings that were just out of the greenhouse. They'll grow out of it.
    o Leaves crinkled = cold soil, probably. Some virus diseases cause crinkled leaves on tomatoes and peppers. If it is on random plants, suspect virus; replace the plant. If it is on most plants, suspect weather; they'll grow out of it.
    o Leaves curling = overwatering. Cool weather reduces the need for irrigation.
    o Leaves purple = phosphorus deficiency. Cold soil inhibits uptake of this nutrient. They will outgrow it when soil warms up.
    o New leaves yellow = pH problem. Apply sulfur or fertilizer containing micronutrients. Overwatering can mimic this due to root damage.
    o Older leaves yellow = lack of nitrogen. Organic fertilizers release more slowly in cold soil.
    o Plants not growing = cold soil.

    The leaves of my roses are ugly!

    Weekly rain and high humidity have caused more disease problems than usual. The only thing keeping it from being even worse has been cool temperatures. Many diseases simply cause cosmetic damage, and we can wait for dry weather to stop the cycle of infection. The major rose diseases are: o Black spot: spots on the upper leaf. Prevalent during warm, damp weather.
    o Downy mildew: spots on the upper leaf, eventual leaf drop. Prevalent during cool, damp weather.
    o Powdery mildew: white poweder on leaves, new shoots, buds. Hasn't shown up much yet; prefers warmer, drier conditions.
    o Rust: orange spots on the underside of the leaf. Requires leaves be damp for 2 - 4 hours; heavy spores spread by splashing water via wind, rain, and sprinklers.

    Disease management is a matter of making the environment less fungus-friendly. Wider-spaced plants in full sun rarely get severe infections. Trim out infected portions and throw them away, prune to open up the bushes and keep them from contacting each other. You can prune hard if rust is severe. Water at ground level.

    I am dubious about the effectiveness of fungicides for home gardeners. You have to spray at least weekly, get thorough leaf coverage (top and bottom), and they aren't effective after the plant is infected. Some are very toxic: anything with Warning or Danger on the label is best avoided by home gardeners. Sulfur and copper sprays are safer, but work only as a protective barrier. The good news is roses outgrow most diseases here when we get lower humidity.
For more, plus pictures, click here

    Written for the Davis Enterprise, May 27, 2010

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