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Pest Patrol

Here are common pests in local gardens, trees and homes, and ways to prevent and eradicate them. Or, in a few cases, overlook them.

By Carol O’Meara

Between summer’s buzzing bees and burst-ing blooms is an army of bugs dedicated to turning your home and garden into an all-you-can-eat buffet. But you needn’t worry about the season’s onslaught of bugs and blight if you look out for pests before they inflict their worst damage.

Here’s a look at the county’s top offenders in gardens, trees and homes. If you take early action against them, you’ll be safe from all but the most persistent pests.


Vegetable Gardens

The bane of tomato lovers, early blight is a fungus spread by water, insects and gardeners. If your plants turn yellow from the bottom up, and the older leaves get brown spots, pick off the diseased leaves, use drip irrigation to prevent splashing water from spreading the spores, and keep the ground free of debris. To protect your plants before the disease arrives, dust healthy leaves with sulfur.

Flea beetles get a jump on the season by attacking early, and they can kill young plants by heavily feeding on them. Several species assail a variety of plants, but grapes and tomatoes, cabbages and other vegetables often fall victim through mid-July.

To repel the beetles, tent plants in floating row covers that admit sun and water, but not insects. Or dust plants with diatoms earth made from crushed fossilized diatoms. The dust irritates the bugs’ bodies and they hop off to find less grating haunts. But you must reapply the dust often. If the beetles do get the upper hand, try Spinoza, an organic product that stops them cold after they eat it (caution: Don’t use Spinoza on plants in bloom or it may harm honeybees).

With a taste for bean leaves, the Mexican bean beetle is a ladybug cousin gone bad. Adults resemble large ladybug beetles, with a rusty color and 16 black spots on their backs. They lay eggs on the underside of leaves that take one to three weeks to hatch. The larvae are odd, bright-yellow creatures covered in huge spines. The beetles feed on the undersides of bean and soybean leaves, rasping off the green tissue and leaving lacy remains.

July and August are the months when the most damage occurs, so scout bean plants for signs of this pest and control it by hand picking. If you’re squeamish, spritz the larvae with insecticidal soap.



Leaf curl aphids lie in wait on trees until the spring’s first shoots unfurl. Then they emerge from eggs at the base of leaf buds and attack. But most gardeners don’t notice the damage they inflict until summer. Though tiny, these creatures roll the leaves of peach, plum and ash trees into a sticky, sugary mess.

Once they settle on trees, controlling them can be a challenge because the curled foliage is perfect protection from many predators. Though rarely harmful to the trees, leaf curl aphids turn leaves into an unsightly mess. Clip off and dispose of the affected leaves to get rid of the colony.

If you have yellowing leaves on trees and shrubs, iron chlorosis could be the problem. In Colorado, alkaline soils (those with a high pH) make iron—an essential nutrient—unavailable to the plant. The loss of iron is one cause of chlorosis, which makes leaves turn yellow, become stunted or develop dead patches. In severe cases, it can kill the plant.

If you’re tempted to add sulfur to lower the soil pH, hold off; many soils in Colorado are calcareous, with particles of calcium carbonate (limestone) making them almost impossible to acidify. Instead, give your tree iron ch-elates, which hold iron in such a way that the plant can absorb it, either by mixing iron ch-elates into the soil at planting or spraying the foliage with it early in summer. Not all ch-elates work in high-pH soils, so look for FeEDDHA (iron ethylenediamine-dihydroxyphenyl acetate).

Alarmed by distorted little lumps on the leaves of your hackberry tree? Those lumps are hack-berry nipple galls, the cozy homes of developing psyllid insects that feed on tree sap as they nestle in the center of the lump. The galls occur when developing larvae stimulate the plant cells to abnormal growth, and expand as the psyllids feed. Although unsightly, the galls are just ugly nuisances that won’t threaten the tree’s health.



When yellow jackets and wasps terrorize your picnic table, it’s time to keep the striped marauders at bay. These scavengers have a sweet tooth, so use it against them with traps baited with sugar water or heptyl butyrate. Be sure to place the trap away from patios or play areas. Wasps flying around a tree mean honeydew-producing insects such as aphids or scale are attacking the tree and should be controlled.

Boxelder bugs, the freeloading flat black bugs with red stripes on their backs, invade homes in fall in search of overwintering places. After spending summer on female boxelder trees, the bugs move indoors, where they wander around exploring walls and ambling on furniture and floors.

The good news is they don’t eat or reproduce inside; the bad news is they paint the house with a pheromone that attracts other box-elder bugs, making your home party central. When abundant, they can stain walls and other surfaces with their excrement. If you have a box-elder tree, consider replacing it with a different plant. Indoors, soapy water or a spritz with a household cleanser stops them in their tracks.

To keep out the bugs, repair or replace damaged screens, seal areas where wires and pipes enter the house, and seal external cracks and spaces around doors, windows, roof lines and fascia boards.

When food scraps entice ants inside, they keep returning to the buffet and bring plenty of friends along. To eradicate them, follow the insects to their point of entry and mark the spot. Then go outside to see where they exit your house, follow them to their nest, and dust around its entrance with diatomaceous earth.

Inside your home, put one teaspoon of liquid soap in one quart of water, spray along the trail of ants to kill them, and then wipe up the area. Caulk the opening through which the ants enter, both inside and out. If this doesn’t work, make an ant bait by mixing a small amount of boric acid into food that foraging ants feed on. Be careful to keep it away from pets or children by placing it in out-of-the-way areas or enclosed in “bait stations,” like straws.

To prepare the bait, first determine what they like, typically something sweet like honey or jelly, or greasy like peanut butter. Add approximately 1 teaspoon of boric acid per cup of food bait. Place the bait in an area visited by ants (note: Boric acid is a soil sterilant and should never be placed on soils where plants are growing, or that may be used for growing plants in the future). The bait should kill the ants in 10 days to two weeks.


Leaf cutter bees aren’t your typical bad bugs, but they have a habit that drives some gardeners nuts. The size of a honeybee, but with dark coloring and white stripes, this pollinator cuts round pieces of leaves to use in nest building. They prefer roses and lilacs, and they leave the plants with oddly shaped foliage. Shy and often elusive, leaf cutters are not a social bee (they don’t live in colonies), and rarely sting, doing so only if you grab them.

They overlap the cut leaves to form a long, cigar-shaped nest, then pack sections of it with pollen and nectar, lay their eggs, and seal the sections with a leaf. Each nest can hold over a dozen larvae, and a single bee can produce up to 40 eggs in a season. It’s best to ignore these bees; they won’t permanently harm your plants.

Aphids are small, pear-shaped soft-bodied insects that attach themselves to tender new shoots and unopened blooms with straw-like mouths to suck up the sap. A shiny, sticky coating on plants is the hallmark of their greed; they drink sap in so quickly their bodies can’t process it, and expel it in a sugary solution.

If you see hundreds of small insects lined up along new buds and stems, blast them with a strong jet of water to hose them off the plant. On the ground, poor eyesight and tiny brains prevent them from finding their way back again. Control severe infestations with insecticidal soap.


Hungry deer can strip a shrub in less than 10 minutes. Discouraging them is a challenge, since they quickly get used to deterrents. Dogs can be helpful in keeping out deer, especially if they’re brave enough to challenge them at the edge of the property. But some cities have rules against dogs harassing wildlife, and deer might get physical with Fido.

Instead, install fencing that’s 8 feet tall or higher. If you can’t afford fencing, try motion-detector sprinklers that deliver a powerful water blast when a deer’s motion triggers it (it also works for rabbits), or electronic deer repellents. Both are sold at garden centers. The latter is a battery-activated post that lures deer with a sweet scent and delivers a harmless shock when the deer touches the post. Deer have good memories, and quickly learn to stay away from the vicinity of the posts.

Or try old-fashioned repellents that work in two ways—with either a bad taste (hot-pepper solutions) or smell (rotten eggs, coyote-urine formulas, blood meal). Reapply repellents after rain or high winds. Planting deer-resistant plants, like blanket flower, larkspur,
Austrian copper rose, ‘blue mist’ spirea, lilacs, Oregon grape holly, daffodils, black-eyed Susan, purple coneflower, marjoram, thyme and lavender, is also a good idea. For more suggestions, visit www.ext.colostate.edu/pubs/natres/06520.html (the “www” is required for this site)

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