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Pest and Disease Alert!

By Paul James

What do you get when you combine a week’s worth of torrential rain followed by temperatures in the 90s? Miserable heat indexes? Count on it. Out of control mosquito populations? For sure. Weeds gone wild? Oh yeah. And unfortunately, you also get the greatly increased likelihood of a surge in fungal diseases and an explosion of insect pests. So get ready.

First Up — Pesky Pests

Let’s say you walk out into the garden and notice that your tomato is covered with aphids. What do you do? Well for many gardeners, the natural (albeit knee-jerk) reaction is to reach for a broad-spectrum insecticide — whether organic or synthetic — and spray everything in sight. But unfortunately, that’s the worst thing you can do. Here’s why.

When you use broad-spectrum insecticides — products that indiscriminately kill pretty much any and every insect in the garden — and you spray not only the plant under attack but the entire garden, you solve one problem but create a number of others. Yes, those products do indeed kill the pests that prey on your plants, but they also kill the beneficial insects that might have otherwise kept the pest population in check. And when you upset the balance between so-called bad bugs and good bugs, you’re asking for trouble down the line.

That’s because the reproductive rate of bad bugs is typically far greater than that of good bugs (remember, those aphids can be born pregnant!), which means the former return in droves before the latter have had a chance to recover. Thanks, Nature!

So the secret to managing pests is to target the individual pest, either by using a product that kills only the pest you want to control, or by limiting your spraying to only the plant that’s under attack. That way you simultaneously solve the problem and save the beneficials.

Here’s another secret: the effect is essentially the same whether you use an organic or synthetic broad-spectrum insecticide. For example, Spinosad is an awesome organic insecticide, but it kills indiscriminately, and it’s highly toxic to bees. And Bt (Bacillus thuringiensis), an all-natural bacterial insecticide that kills caterpillars and only caterpillars, is just as effective at annihilating monarch and swallowtail butterfly larvae as it is the dreaded cabbage loopers and corn earworms.

One advantage to using organic insecticides is that once they dry, they pose little or no threat to beneficial insects, including bees (the exception is diatomaceous earth, a powder). Spinosad, for example, is harmless to bees three hours after being applied. Most synthetic insecticides, on the other hand, can pose a threat to beneficials and bees for days after application. And the killing power of systemic insecticides can last for weeks.

I’ll readily admit that some pests are just plain tough to control, especially once they reach their adult stage. Squash bugs and vine borers top the list in my experience, at least in my current garden, which is why I’ve pretty much given up trying to grow squash. Asparagus beetles, and to a lesser extent striped and spotted bean and cucumber beetles are a pain as well, but I haven’t given up entirely on those crops. 

I have one final secret to share with respect to controlling insect pests, and it is hands down the most effective of all — keep your plants healthy! Like humans, plants are more susceptible to attack by invaders (pests and diseases) if they’re stressed by poor soil conditions, a lack of nutrients, not enough or too much water or sunlight, and so on. So keep all your plants healthy and happy, and you’ll have far fewer pests problems. 

And Now, Fungal Diseases

Anthracnose. Black spot. Rust. Downy and powdery mildew. Those are just a few of the fungal diseases that can ravage plants. But there are thousands more. Dealing with them can be a drag. Not dealing with them can be disastrous. Here’s what you need to know.

Fortunately, not all plants are prone to fungal invasion. But many popular plants – Coreopsis, crabapples, lilacs, Photinia, roses, and tomatoes, just to name a few — are highly susceptible, especially when spring weather is cool and wet, or humidity is high in summer (sound familiar?). However, there are things you can do to minimize the likelihood of attack regardless of weather conditions.

Choose plants with proven disease resistance — Plant breeders are constantly working to develop new varieties that are resistant to common fungal diseases. The information is typically found on the plant tag. Most new varieties of crabapples, for example, are far more resistant to mildew.

Water wisely — Overhead watering encourages fungal diseases, especially if leaf surfaces remain moist overnight. So try to water early in the morning, and water the base of plants rather than the leaves.

Improve air circulation — Avoid overcrowding plants so that air can flow around and through them. Stagnant air creates a breeding ground for fungi. Consider pruning the interior of plants to increase air flow within them.

Prune infected areas — At the first sign of disease, prune infected areas and dispose of the debris. Cut back to healthy tissue, sterilizing your pruners between each cut with a common household disinfectant. I use wipes containing bleach, or a solution of 10% bleach with water.

But even if you do all those things, your plants may still succumb to fungal diseases. Enter fungicides, which can be either organic or synthetic. Organic products such as Revitalize contain a bacterium that won’t harm honey bees or beneficial insects. Two other organic options are Horticultural oil and Neem oil. And in addition to being very effective fungicides, both also control various insects that prey on plants and are often responsible for the spread of fungal diseases. Spray early in the morning or late in the day when bees are less active.

Copper, sulfur, and zinc are also key ingredients in a number of fungicides, and they’ve been used for decades to control some of the worst pathogens. Keep in mind, however, that copper and zinc can be toxic to plants, so follow the label instructions to the letter. There are also systemic fungicides, which are absorbed by the plant and provide long-lasting treatment.

And lastly, folks, please understand that chemicals are chemicals, whether organic or synthetic, and both can be harmful. Both can be carcinogenic. And both can be deadly if used improperly. So read and follow to the letter the label instructions on any product you buy. 

Happy gardening, ya’ll.

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2 responses to “Pest and Disease Alert!”

  1. I am starting on a blank slate yard, just grass. We purchased home last fall. I’m so excited ! All this info will for sure, get me off to a great start. Thanks

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