We get questions....garden 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 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.

For more, plus pictures, click here

Written for the Davis Enterprise, May 27, 2010

Bayer Advanced Fruit, Citrus, & Vegetable Insect Control -- a good idea?!?

“I’ve heard there is a new systemic insecticide for vegetables and fruit trees.”
Yes, indeed: Bayer CropScience has introduced Bayer Advanced™ Fruit, Citrus & Vegetable Insect Control, which you pour on the ground around edible crops. It goes up into the plant and kills insects that are feeding on the plant.
My god, what a terrible idea!
“Keeping your plants protected from listed damaging insects has never been easier.”
Just because you can do something, doesn’t mean you should!

The active ingredient imidacloprid (Merit) is a widely used neo-nicotinoid systemic insecticide. We recommend it for control of some pests on ornamentals, in situations where you and bees won’t be exposed to it, and it is useful on houseplants. It is the active ingredient in a popular flea control product on pets. It is heavily used on some agricultural crops in California, including head and leaf lettuces and citrus, as well as on turf and ornamentals.

I understand the basic principle of toxicology: the dose makes the poison. How toxic a material is depends on how much you ingest. There are doses that are considered safe for humans. Neonicotinoids are especially toxic to insects and much less so to humans. But the regulatory agencies base their safe dosage on assumptions about our current intake of the product by other sources. You are ingesting imidacloprid regularly when you eat conventional produce, walk across commercially-maintained turf, pet a cat that has been treated with Advantage®, etc.

Ok, so you put this insecticide on the ground, it is taken up by the roots, goes up into the plant and kills anything that sucks or chews on the plant. Then it breaks down steadily in the plant over time. Apparently Bayer and various regulatory agencies believe that it’s ok for you to eat whatever the plant produces because it has diminished to less harmful levels in the plant.

This all assumes you follow the label instructions for the rate per square foot, that you only apply it once a year, and that you wait the specified interval before harvest. Why, one wonders, is it a 21 day waiting period for lettuce, but a 45 day waiting period for Swiss chard?

You can download the 10-page label from bayeradvanced.com. Read about imidacloprid at the cooperative-extension maintained site http://extoxnet.orst.edu/

Here’s what anybody selling, buying, or using this product needs to know:
• You must carefully follow the rate of application per square foot of garden space.
• The product is in the plant, including the part you consume. If it provides “Season-Long Protection!” then it is in the plant all season. Including when you harvest.
• It is important to check the interval before harvest for a particular crop, which ranges from 14 to 45 days after application.
• You cannot use this product more than once a year. In California we have two full vegetable growing seasons.
• Imidacloprid is very toxic to bees of all kinds. Bees are exposed to it through pollen.
• You should not apply it when trees are blooming or bees are foraging nearby. It can be taken up by the roots of nearby flowering plants. Your garden needs to be entirely separated from plants that bees might visit. Sub-lethal doses to bees have unknown effects. It is one possible factor being reviewed in Colony Collapse Disorder, but has neither been ruled in or out as a cause.
• It is very toxic to earthworms.

I am concerned that the manufacturer and the regulatory agencies have not considered California’s unique gardening climate.

I don’t know if the baseline for acceptable “average” intake from other approved uses has been updated since the mid-1990’s (that is the only data I could find online). There have been many new approved uses of imidacloprid in the last decade, including urgency permits for new pests. Imidacloprid is the pesticide of choice for many of the new pests that arrive in California, so I would guess that we are consuming more and more of it.

I personally would not use it or sell it for edible crops, and urge nursery professionals, Master Gardeners, and landscape gardeners to discourage its use.

Fungus weather!

Rain every week is leading to many disease problems. Here is a chart that reviews some of the common diseases we've been seeing at the nursery recently. I have been removing specific fungicide recommendations from my articles, as availability of specific products has changed. In most cases fungicides aren't necessary, application is impractical, and oftentimes labeled products really don't work.

Good news: hot, dry weather stops the spread of most diseases. And one thing we can count on in the Sacramento Valley is that we will eventually get hot, dry weather!

Chart of spring diseases