Posts Tagged ‘Tomato Hornworm’

It’s getting really hot pretty much everywhere, so we’re going to focus on keeping your plants well-watered. Plants transpire (evaporate) water vapor through tiny holes on their leaves — mostly on the underside. This helps to cool the plant and draws nutrients from the soil and roots to the upper parts of the plant. On hot or dry, windy days plants can lose a lot of water, sometimes faster than they can take it up, and that can stress them making them more vulnerable to insects and disease.

  • When the temps get into the 90’s and above you may need to water your plants twice a day — early morning and late evening.
  • Container plants are especially vulnerable in this hot dry weather. Check for wilting.
  • Some wilting can be normal for certain plants, but if they look really droopy and the soil is dry don’t wait, water right away.
  • Check newly planted trees and shrubs. Keep them well watered — deep watering is best.
  • Water deeply in advance of hot Santa Ana winds. Don’t wait for it to start blowing.
  • A good layer of mulch, 2 -3 inches, will keep plant roots cool and will cut down on evaporation.
  • Make sure bird baths are clean and have plenty of fresh water
  • Make sure you drink plenty of water while you’re out in the garden — heat exhaustion and heat stroke are no fun.

Garden pests are hard at work this month so stay on top of it.

  • Keep aphids under control by knocking them off with a spray water from the hose.
  • You can try the same for whiteflies and be sure to wash off the sticky honeydew too.
  • Watch for tomato hornworms, they’ll be chomping on your tomatoes this month. They’re hard to see; look for their frass (poop). Click for a pic.
  • Keep an eye out for ladybug larvae which have a voracious appetite for aphids. Protect them and let them do the work for you.

Ladybug larva. It looks scary, but it's one of the beneficial insects you'll be happy to have in your garden.

It’s time to divide your Iris. Lift the clump up with garden fork, snap off leaf fans with about 3 inches of the rhizome attached. Trim leaf fans back to 5 inches tall and replant them in soil amended with compost. Water well.

Garlic scapes should be popped off when they are in a full curl, but don’t throw them away!

Chop scapes up and saute them in olive oil and serve over pasta. They’re really good in scrambled eggs too.

Keep an eye on your garlic for signs that the bulbs are ready to harvest. When the bottom 3 or 4 leaves start turning brown it will be time to lift the bulbs and cure them. Depending on the variety of garlic this should start near the end of July into August.

Treat yourself to a bouquet of flowers to enjoy indoors — that is why you grow them right? I love scattering a few small vases filled with flowers through the house.

And finally, start plans for your fall vegetable garden.


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We are deep into spring and on our way to summer though it sure doesn’t feel like it in Southern California. We’ve got cool temps, wind and rain which is unusual for this time of year. What’s not so unusual are the garden pests that have started to make their appearance in my garden and which will soon be plaguing Mary Beth and the rest of you in somewhat cooler zones. So we thought that for the next few weeks we’d look at organic ways to deal with the bugs and diseases that bother us in the garden.

We’d like to point out first of all that some nibbling of leaves, flowers and fruits is normal. Bugs are supposed to be in your garden. Live with it. Insects are part of the whole wonderful cycle that makes this all work. We are not striving for a bug-free zone, we are looking to create a balance in the garden. That said there are times when you need to get the upper hand especially when something is devouring your herbs or, perish the thought, your beautiful tomatoes.

This week we’ll be looking at Bt or Bacillus thuringiensis. The most commonly used form of Bt, the one you’ll likely see at your nursery, is Bacillus thuringiensis kurstaki. It is used for controlling leaf-eating caterpillars like cabbage worms and tomato hornworms (although they are called worms they are really caterpillars). Another form, Bacillus thuringiensis israelensis, is used to control certain fly larvae like mosquito larvae which can be a problem in ponds.

Here’s what Colorado State University Extension has to say about Bt:

“The most commonly used strain of Bt (kurstaki strain) will kill only leaf- and needle-feeding caterpillars. In the past decade, Bt strains have been developed that control certain types of fly larvae (israelensis strain, or Bti). These are widely used against larvae of mosquitoes, black flies and fungus gnats.

More recently, strains have been developed with activity against some leaf beetles, such as the Colorado potato beetle and elm leaf beetle (san diego strain, tenebrionis strain). Among the various Bt strains, insecticidal activity is specific. That is, Bt strains developed for mosquito larvae do not affect caterpillars. Development of Bt products is an active area and many manufacturers produce a variety of products. Effectiveness of the various formulations may differ.

Insects Controlled by Bt

Kurstaki strain (Bonide Thuricide, Safer Caterpillar Killer, Greenstep Caterpillar Control, etc):

  • Vegetable insects
    • Cabbage worm (cabbage looper, imported cabbageworm, diamondback moth, etc.)
    • Tomato and tobacco hornworm
  • Field and forage crop insects
    • European corn borer (granular formulations have given good control of first generation corn borers)
    • Alfalfa caterpillar, alfalfa webworm
  • Fruit crop insects
    • Leafroller
    • Achemon sphinx
  • Tree and shrub insects
    • Tent caterpillar
    • Fall webworm
    • Leafroller
    • Red-humped caterpillar
    • Spiny elm caterpillar
    • Western spruce budworm
    • Pine budworm
    • Pine butterfly

Israelensis strains (Vectobac, Mosquito Dunks, Gnatrol, Bactimos, etc.)

    • Mosquito
    • Black fly
    • Fungus gnat

San diego/tenebrionis strains (Trident, M-One, M-Trak, Foil, Novodor, etc.)

    • Colorado potato beetle
    • Elm leaf beetle
    • Cottonwood leaf beetle”
We (back to Bees and Chicks now) have used Bt for years and find it very effective and safe when used according to package directions. It is not harmful to humans, pets, or beneficial insects like bees. It can be used up to the day before harvest (I’d still want to wash sprayed fruit before eating).
Nonetheless, you shouldn’t go spraying everything willy-nilly. Be sure first of all that a caterpillar is what is eating your plant. Some insects that look like caterpillars are really worms, most notably rose slugs, and Bt will not kill worms. (Note that these are called slugs, but are really worms! For info on how to identify and control rose slugs click here.)  If it is a caterpillar eating your plants, spray just the affected plants/area. You must be very thourough because the caterpillar needs to eat the BT for it to be effective. You may need to repeat the application every 5 – 7 days while the insects are active. We have usually gotten good results with just a couple of sprays.
A note of caution here: Bt will kill good caterpillars as well as bad. If you have a butterfly garden or plants that attract butterflies, DO NOT spray when these caterpillars are feeding.
Bt is but one tool in the organic arsenal. Next week we will take a look at more.

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Mary Beth: Oh how wonderful it is to be standing in the garden looking at those beautiful tomatoes, feeling proud of my babies and thinking of all the delicious meals I’m going to make. Mmm.

Almost ready to harvest

Almost ready to harvest

Wait! Something catches my eye. WTF?! Something is chewing big chunks of my plants! My tomatoes!

A shiver runs down my spine as I spot the culprit. A big, fat green monster — the dreaded Tomato Hornworm! And once again the game is on as I become obsessed with finding the beasts.

So good at hiding in plain sight

Hiding in plain sight. Those little nubby feet are strong!

They are the masters of camouflage so it takes a bit of practice to spot them. The best way to find them is to look for their poop; little black droppings on the leaves below where they munch. I track up the plant from the poop. Looking for the damage, squinting, concentrating…yes! Gotcha!!

Warning, the first time you see one of these guys it’s a bit freaky, they’re huge and kind of scary looking. Touching one will be the last thing you’ll want to do, but be fearless and get rid of it. And know that where there is one, there are others. So check each and every one of your plants carefully. Tomato Hornworms are eating machines that will devastate your plants in a day or two.

Look at all those little "eyes"! Eww!

Look at all those little "eyes"! Eww!

I pull the pest off the plant (they have quite a grip) and throw it over the fence, or if I’m feeling ruthless I let the dogs have a go with it (hilarious, but not pretty). They’re way to big to squish, so I mostly take the coward’s way out and toss them as far as I can hoping that the birds will find them. Weird as it sounds it’s very satisfying to find those buggers.

So if you’ve been wondering what’s been eating your tomato plants, here is the likeliest suspect.

P.S. Technically these are Tobacco Hornworms, but most people identify them as Tomato Hornworms. They are the larvae of the Hummingbird Moth. The caterpillars can grow to 4 inches in length and are easiest to spot in the early morning or at dusk when the temperature is cooler. They’ll also eat potato plants, eggplants, and peppers. Here are a couple of links to more info — Colorado State Master Gardener and University of Minnesota.

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