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Need to get rid of garden pests without industrial pesticides? Here are an expert’s tips on dealing with six of the biggest threats to your plants.

You’ve spent all spring and summer lovingly tending to your garden, and it’s quite a beautiful sight. Unfortunately, you’re not the only admirer.

There are myriad pests out there who want nothing more than to feast on the literal fruits (and veggies) of your labor. Not only do many go straight for your precious crops, others will attack the leaves and stems, which has a direct impact on your plants’ overall health and the quantity and quality of their edible output.

We spoke to Frank McDonough, an avid home gardener and Botanical Information Consultant for The Los Angeles County Arboretum & Botanic Garden, the 127-acre historical site in Arcadia, CA that hosts a multitude of diverse plant life.

Here are his tips on how to keep your plants healthy and pest-free.

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Larvae

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Cabbage moth caterpillar (Mamestra brassicae) despite its name it feeds on many different plants, it is however partial to cabbages and other members of the brassica family. The larva can grow up to 5 cm long and fully grown Cabbage Moth caterpillars are extremely variable in colour. Within a single brood there can be caterpillars of several shades of green and brown, with some being almost black. Eggs are pale green when first laid in batches of sixty or more on the underside of the larval food plant but within three or four days have dark centres as the caterpillar develops inside. The caterpillars hatch within about 7 days and are fully grown in about 30 days when they pupate in the soil. Newly hatched Cabbage Moth caterpillars are less than 2mm long and pale green with black speckling, head and prothorasic plate. Within a week and into their second instar slightly darker and lighter shades of green begin to show amongst the brood. At two weeks old and at about 10mm in length distinctive variations in intensity of colour are evident ranging from dark brown to pale green The adults emerge in about 14-21 days unless over wintering. The Cabbage Moth has a wing span of approximately 40mm and is generally dark with variable shades of brown and feeds on planta such as Red Valerian. #mothcaterpillar #moth #cabbage #cabbagemoth #ukwildlife #britishwildlife #uklarvae #larvae #springwatch #thebritishwildlife

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Remember “The Very Hungry Caterpillar”? Yeah. That book spoke the truth. McDonough advises to keep your guard up for larvae if you’re growing tomatoes, cabbage, Brussels sprouts, or any of the kale crops.

Beyond simply plucking the budding butterflies off your plants, McDonough uses Bacillus Thuringiensis (Bt). “This is a natural bacteria that is ingested by the worms as they eat up my plants and it kills them,” he says.

He also recommends preventative measures, suggesting that if you see butterflies hovering around your plants, assume they’re laying eggs. Spray Bt to nip the problem in the bud.

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True Bugs

From the Hemiptera order of the insect family (with up to 80,000 members), true bugs can be a particularly nasty nuisance.

“They are piercers and suckers, which means they take their snout, pierce it into the leaves of the plant, and inject a toxin into it,” McDonough warns. This toxin dissolves the leaf, creating a soupy mess that the bugs then suck up for nutrition.

While there are powerful pesticides that can take them out, for a safe alternative, McDonough recommends using diatomaceous earth, a silicon-based fossil ground into a microscopic powder. The particles are just big enough to puncture the joints, the only soft spots on the well-armored bugs.

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McDonough also uses a very thin mesh covering (which he calls a “plant sock”) to keep his plants protected from not only true bugs, but almost any other pest interested in his plants. If you have row crops, consider constructing a semi-hoop covering similar to a mini-quonset hut.

For potted plants, McDonough recommends procuring 3’ bamboo stakes. “I put around three or four up them around the pot, straight up and down,” he says. “Then I drape the shade cloth over that and I’ll cinch it at the bottom with a bungee.”

For a simple solution, turn the table on these suckers and hoover them up with a vacuum, especially if you encounter a cluster. Just be sure to empty the contents into the outside trash before returning the vacuum to the house.

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Mammals

As annoying as possums, raccoons, squirrels, rabbits, skunks, rats, and other mammalian garden pests can be, you may have some moral quandaries around their permanent removal. You also might have a hard time hunting them considering so many are reclusive and nocturnal.

How will you know they’re roaming around? “The complete and total disappearance of nearly ripe fruit,” McDonough says. “And if they’re really hungry, they’ll just eat the greens.”

McDonough’s humane method to frightening off these furry foes is a motion-activated scarecrow. “It squirts water and makes a racket all of the sudden all at once,” McDonough says. It’s an effective deterrent for anything larger than a rat, including hungry deer.

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As for dealing with a rat problem, the key, according to McDonough, is making sure your surroundings are inhospitable to the rodents. If a tree branch touches or is very close to a structure, trim it back. Also, try to keep your yard clean of debris such as leaf piles and wood stacks, which make excellent rat living quarters.

Aphids

Slow-moving aphids are like something out of a sci-fi horror movie. They are a silent vector for an astonishing number of serious plant diseases and can devastate your entire garden.

“When they’re not pushing clones of themselves out their rear ends, they’re pushing sugary exudate,” McDonough says. This sugary expulsion leads to a problem called sooty mold, which stunts your plants’ growth.

To combat aphids, arm yourself with insecticidal soap spray. The mixture of soap and oil mixed in water provides a killer combo of potassium salts and fatty acids. (Purchase a bottle or make your own with cooking oil.)

You want the spray to leave a lasting impression on your plants so avoid using it in the rain and spray early or late in the day, especially during the summer, to prevent immediate evaporation.

Continue to examine your plants vigilantly for aphids given that one or two can turn into a swarm almost overnight thanks to the magic of asexual reproduction.

Be on the lookout for aphids when, or just after, skies are overcast. Lack of sunlight will weaken the epidermis of the plants and make them more succulent, enabling aphids to more easily access precious sap. Also, if you fertilize often, it’s likely that your plants are well-fed with nitrogen, which attracts the insects.

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Spider Mites

“This is number one for me and for a lot of people,” McDonough laments. If you spot webs and stippling on your plants, it’s a good sign spider mites are making their mark. Their presence will ultimately lead to yellowed, distorted leaves which is no bueno. 

One of the major reasons spider mites are so difficult to treat is that there aren’t chemicals that will harm them that won’t also harm humans. Sulfur will eradicate them, but unfortunately, it also burns plants.

Thankfully, McDonough has a two-pronged approach to dealing with these aggravating arachnids: increase humidity and increase air circulation.

Start with a good mulch to retain moisture. Step two: “Give your plants a shower once a day,” McDonough advises. “You’re not irrigating them. You’re just misting them. This increases the humidity of the area and that increased humidity is more attractive to predaceous mites and other mite predators.”

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Snails / Slugs

McDonough admits he does not have a snail or slug problem at the Aboretum, courtesy of the grounds’ noted population of peacocks which feast on the little buggers.

But if you don’t have loud, colorful birds to take care of the issue, he recommends using Sluggo (containing iron phosphate) though cautions that it’s mostly safe around pets so long as they don’t ingest a lot of it. A squirt bottle filled with ammonia will also do the trick.

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If you prefer a non-lethal alternative, you can also physically remove snails and slugs from your plants. But despite their notoriously slow mobility, McDonough admits this task is tougher than you’d think. They generally come out after midnight, feed, then return to their hiding place before sunrise. In other words, prepare to stay up late and bring a flashlight.

For those of you who enjoy the company of snails and slugs, consider planting a sacrificial bed. The mini-buffet will keep them distracted from feasting on the rest of your garden. 

More All-Natural Options

How Eggshells and Coffee Grounds Can Make Your Garden Grow

Header image courtesy of sanjeri / Getty Images

David is a food and culture writer based in Los Angeles by way of New York City. His work has appeared in the Los Angeles Times, CBS Local, Mashable, and Gawker.
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