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We get questions.....
Written for the Davis Enterprise, May 27, 2010
An odd year?!? We get questions!
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 Niño 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.
Rose problems
Downy mildew
Botrytis
Raspberry horntail borer
false Katydid
Katydid or earwig damage
What is making holes in my roses?
Earwigs and katydids. Earwigs are the black insects with pincers on the rear. They hide under the petals during the day, feeding at night on tiny thrips and mites. Unfortunately, they also nibble on the rose petals. Try organic baits. They are also readily trapped with oil: pour a quarter-inch of fragrant cooking oil in a bowl and place it on the ground near plants that show damage. Drawn by the aroma, they crawl in and drown. Paper bowls make disposal easier.
Katydids have just hatched out. These grasshopper relatives disperse through the garden, chewing small holes in leaves and flower petals, and sometimes damaging young developing fruit of nectarines and oranges. Their damage is minor and transient, and they aren't readily controlled. We recommend mechanical control: stomp them when you find them.
Why are the tips of my rose bush withering?
Raspberry horntail borer is the larva of a wasp. She oviposits on the upper stem, where the stem is still soft. The larva hatches and bores into the plant's cambium. It bores around the stem in the water-conducting tissue (xylem), and when it has made a couple of loops around everything above that point suddenly wilts. Just prune it out. Look for the red spot on the stem, go down 6 to 12 inches further, and cut.
What is killing my pear tree?!
Fireblight is a bacterial disease that causes rapid dieback on members of the apple branch of the rose family: apples, crabapples, pears; pyracantha, photinia, loquat. It infects when temperatures are between 55 - 80 degrees and humidity is high. Normally we surpass 80 degrees quickly in May, so fireblight is usually a problem for just a few weeks. This year it is continuing much later in the season. Fireblight infects through the blossoms and tender new growth. Prune the dying portions well below the point of infection and put the prunings in the trash.
Why is there so little fruit on my apricot, plum, and cherry?
Brown rot fungus was very severe this spring, blighting the blossoms and killing them before fruit could set.
What is that purple-flowered tree?
People are inordinately attracted to purple flowers of all kinds. Using a broad definition to include mauve and lavender, we have several possibilities. Empress tree
(Paulownia tomentosa)
was blooming in April, with several nice specimens at a house on Pole Line Rd. near Covell. Locusts (
Robinia
) have purple, pink, or white flowers in April that resemble wisteria. Jacaranda trees will be blooming soon, if they weren't too severely damaged in the December freeze. Purple varieties of Crapemyrtle will begin blooming in July:
Lagerstroemia
'Zuni' and 'Catawba' are two good selections.
Melia azedarach
flowers
Melia azedarach
habit
The tree blooming now has a compound leaf (divided into leaflets) that is shiny and dark green. There are sprays of light purple, almost teal blue flowers. The species form has a round crown, while a selected variety makes a tight "umbrella" shape. The tree is
Melia azedarach,
the China berry, and the umbrella-shaped form is M. azedarach 'Umbraculifera', also called Texas umbrella tree. It is the street tree on a couple of side streets off Tulip Lane. Tough, drought-tolerant, it is not common in the trade, having some drawbacks. The yellow berries that follow the flowers are messy and poisonous. Some people are very allergic to the blossoms, including me. I used a zoom lens to take the pictures here!
Do we have leafcutter ants in Davis? I see ants going up my cherry tree, and there are holes in the leaves.
No, thank goodness! Usually when we see ants going up a tree, we suspect there may be aphids or scale present. The excretion of those insects is sugar, and the ants harvest it. They even go so far as to carry the insects from tree to tree, farming them. But cherries are unique. One of the identifying characteristics of any cherry is the presence of a set of glands at the base of each leaf. This shiny gland excretes a sugary solution, perhaps to attract pollinators for the nearby blossoms. Ants just happen to like this as well. In this particular case they are harmless. The holes in the leaves are probably from shothole fungus, or possibly from the afore-mentioned katydids.
What are those little red bugs I see running all over the place? And where did all the aphids go?
The red things are predaceous mites, eating harmful spider mites as they scurry crazily over leaves and flowers. They are entirely beneficial. Gardeners transplanted from the east coast often mistake them for chiggers. These good guys don't bite us.
These predaceous mites are among many beneficial insects helping control pests in your garden. Aphids have been less of a problem than usual this year, because cool weather slowed their population growth and allowed leatherwing beetles and ladybird beetles to keep them in check. So there are advantages to cooler weather! But your peppers and eggplant wouldn't agree.
Ladybug on rose bud
Leatherwing beetle
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© 2010 Don Shor, Redwood Barn Nursery, Inc., 1607 Fifth Street, Davis, Ca 95616
www.redwoodbarn.com
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