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Flea Beetles and Hornworms Love Chemical Fertilizers!


You Bet Your Garden
Question of the Week © 2018 Mike McGrath

Note: Hundreds of Mike's informative articles are available (in alphabetical order!) right here at the Gardens Alive website. To find Mike's answers to your specific garden problem, Click here and find your topic (like Weeds, Worms, Rhododendrons...) in our complete alphabetical archive of Questions of the Week.

Special Note: After 19 years and 51 weeks, organic gardening guru Mike McGrath has moved his Public Radio show You Bet Your Garden from Philadelphia to WLVT in Bethlehem, PA, where 'locals' (the Lehigh Valley, greater Philadelphia area, South Jersey and Delaware can watch the show on TV every Saturday morning at 10 am—including the famed Gardens Alive Question of the Week! The podcast and online stream can be accessed at www.wlvt.org; and the local affiliates around the country can pick up each week's show as usual. (If your affiliate is having trouble accessing the show, please email Mike's staff at YBYG@ptd.net.) Onward!

Flea Beetles and Hornworms Love Chemical Fertilizers!

Q. Amy in Augusta, Georgia writes: "I'm a beginning gardener. We planted three tomato plants in May and they flourished. However, come August we noticed hornworms on the plants. I made a homemade pesticide of soap, Cayenne pepper, garlic and water and sprayed it on my plants in the evening..."

A. There's a lot going on in this missive so I'm going to interrupt Amy to warm everyone: Never spray your plants with water—or heck, anything else—in the evening. You never want plants—especially disease-prone plants like tomatoes—to sit wet overnight; it's an invitation to illness. The only good time to spray is in the early morning, when the sun's rays will quickly dry off the leaves.

And the answer to ANY kind of caterpillar problem (despite their name, horn'worms' are caterpillars) is to spray the plants with the old original form of Bt; it'll kill any caterpillar that chews on the sprayed leaves but will harm nothing else. (Search the Gardens Alive archives for lots more about Bt and caterpillar control.)

Now back to our exciting story.

Amy continues that the spraying "seemed to help a bit with the hornworms, but we continued to see more on the plants. We then started seeing flea beetles and that's when we started wondering if the tomatoes were OK to eat—and how to get rid of the pests." She concludes her first email with "Please help, I have a love (no an obsession) with tomatoes! Please tell me if it's ok to eat a tomato that was infested with insects. And we would like to have an even bigger garden next year but not if all these bugs are invited to dinner!"

Flea beetles are common pests of eggplant and can make it a difficult crop for home gardeners to grow—including me. (Search the GA archives for tips on their control.) But I've never seen then on tomatoes. Hornworms—the larval form of the gigantic and impressive Sphinx moth—are the largest (and hungriest) caterpillars in North America, and well-known foes of tomatoes.

The basic tactic to fight hornworms is to keep an eye out for missing parts of your plants (in my garden it looks like deer damage) and then look for large deposits of their 'frass' (bug poop) at the bottom of your plants. If these you find, run your hands up and down the plants until you find something soft that isn't a tomato and squish it. Or just spray Bt at the first sign of damage and frass to miss sure you don't miss any of these excellent hiders.

Back to our question: Yes, it is safe to eat the good parts of fruits that have been insect attacked. Heck even if you accidentally eat a flea beetle that's just some extra protein in your diet. Oh—Amy also asked (in a fairly long email) if flea beetles were a danger to her pets; and the answer is no. They hop like fleas, but they are true beetles. (If you got real fleas outdoors, treat the soil with beneficial nematodes.)

Next step was to ask Amy our standard questions: 'are you growing in raised beds or flat earth? How do you water, what do you feed, etc., etc.'

She replied: "We would like to start a bigger garden next year in raised beds. Right now, they are growing in planters. As for feeding, we 'sprinkle' Miracle Gro on them once a week. I water them once a day in the evening."

OK—there are three potential stresses here. Why stress stress? Because stressed plants are more attractive to garden pests than happy healthy plants. A plant that's watered correctly and fed appropriately has the power to resist insect attack either through the development of naturally occurring chemicals that repel pests, or in the incredible case of sweet corn, the ability to generate pheromones that actually call beneficial insects to their aid when they're attacked—perhaps the coolest superpower in the plant world.

Plants that are weakened by incorrect watering and fed with cheap explosive chemical fertilizers, not so much. They're like somebody who over-imbibed and is now staggering down the wrong street in the wrong neighborhood with twenty-dollar bills spilling out of their pocket as they vainly search for a handkerchief. They are likely to attract unwanted attention that will give them a much worse outcome than a couple of flea beetles.

Containers: Need to be large for tomatoes: 17-inch pots with good drainage and only one tomato plant per pot. The pots should contain what's professionally called a 'soil-free mix'; aka potting soil or seed-starting mix. You'll have to go to a real garden center or order by mail to find the right kind, which means making sure that the mix does not include chemical fertilizers—which may be the only kind of bagged mix you'll find in big box stores. (Mixes with natural fertilizers like worm castings are fine; indeed better than fine!)

Watering: Watering every day guarantees problems. Plants want an inch of water or rain—preferably rain—once a week. Yes, once a week. If you water plants every day, their roots will stay at the very top of the soil. If you soak them deeply—it takes several hours to deliver an inch of water to a garden—and then let them 'go dry', they'll develop deep roots to follow the receding water. And deep roots make for healthy plants.

Food: I know as much about Miracle-Gro as a Kosher Rabbi knows about cuts of pork, but even I know that you don't 'sprinkle' the nasty stuff—you dissolve it in water and then use it to slowly weaken and kill your plants. Chemical fertilizers are combinations of elements that are highly explosive and present in their salt form—and neither explosives or salt are good for your plants. The only Miracle here is that people continue to fall for this nonsense.

Feed your soil; not your plants. Make sure their growing medium is rich with compost and your insect invasions will be few.

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