What’s Eating My Zinnias? 7 Pests and How to Manage Them
Nobody dislikes zinnias, but many dislike the host of pests they bring to the garden. Follow along with master naturalist and experienced gardener Sarah Jay as she covers 7 common pests of zinnias and how to manage them.
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If I want a flower that won’t fail me, even in the hottest summers, I go for zinnias. They bring so many beautiful butterflies and bees to the garden, and boost pollination for my summer veggies. Unfortunately, zinnias also attract several common garden pests.
These warm-weather flowers pop up in my garden every year as they continually seed out and naturalize. They aren’t invasive, and they aren’t hard to remove if they pop up somewhere undesirable. But they sometimes attract pests in gardens that don’t have a host of natural predators around.
While it can be intimidating to go out to the garden to see your zinnias covered in aphids, they and other pests are actually pretty easy to deal with. The following strategies ensure you have a lovely zinnia patch without the risk of perpetually multiplying pests.
Aphids
These pear-shaped insects congregate in large numbers and are very common in gardens; it’s almost not worth mentioning them since they’re so ubiquitous. The pesky pests cover the stems of zinnias, feeding on the plant’s sap, eventually moving to leaves and flowers if they aren’t controlled.
How To Identify
The type of aphid that loves to munch on zinnias is the black bean aphid (Aphis fabae). This species has the characteristic round shape all aphids have, with a dark black body that is easy to see against the light green of your zinnia’s stems. Some but not all may have wings.
Another indication that aphids are present is the presence of ants. Ants like to harvest the honeydew that aphids secrete as they feed on plant matter. If you’re unable to determine whether or not you’re dealing with aphids, check for a trail of ants and follow it to the source.
In later stages of aphid infestation, plants take on a sooty mold that develops from the honeydew secretion. It’s at this point that leaf and shoot distortion takes hold. But most likely you’ll notice them before this happens.
How To Prevent
For all of the zinnia pests we cover in this piece, the best line of defense is a large number of beneficial predators. It’s possible to bring in a ton of these guys with plantings in just a week or two.
Include a diverse array of nectar plants nearby that beneficial predators enjoy. The number one aphid predator is the lady beetle. Lady beetles (ladybugs) eat the heck out of aphids every chance they get. Alyssum is a great host plant for them. It’s also a wonderful companion to many garden veggies.
Lacewings, parasitic wasps, soldier beetles, and syrphid flies also dine on these little grubby guys. Aster family flowers bring in lacewings, flies, and wasps, so plant those along your garden. Goldenrod is a great host for soldier beetles if you have the space. These bring in small songbirds that eat aphids as well.
How To Remove
If your arsenal of predatory insects hasn’t arrived yet, or you need a quicker solution, start with a strong stream of water from a hose. This knocks them off the plant and prevents them from feeding further.
Follow up with insecticidal soaps or horticultural oils (like neem) if regular spraying doesn’t do the trick. Always apply these when the plants aren’t flowering, or just outside the pollinator activity window. This occurs in late evening or early morning. A light mist is enough. No need to oversaturate.
Mites
Both broad mites and spider mites love zinnias (probably just as much as you do). Dealing with them is different depending on the mite in question. Both are very tiny, so you likely won’t see them on the plant. But you will see signs that they’ve been there.
How To Identify
Broad mites from the species Polyphagotarsonemus latus are a common pest across ornamental plants. They inject plants with a toxin that causes leaf curl, cupping, and thickening. They may also cause dwarfed leaves as they feed on the zinnia plant sap. Damaged leaves and buds can drop, or they become discolored and stiff.
Spider mites are easier to notice when they’re in large numbers. At this point, they develop tightly-woven webs that cover zinnia leaves. As they feed, they cause yellow stippling on leaves and an overall dusty appearance. If their numbers are large, you’ll see tiny dots moving on your plant among the webs.
How To Prevent
Predatory mites are a prevention for both broad and spider mites. These bugs appreciate mint plants and love to eat a ton of mites as they chill out on your favorite spearmint. Lady beetles also eat mites.
Both of these pests like dusty conditions. Keeping your plants free of dusts, and in consistently moist – but not waterlogged – conditions limits their ability to take hold. If you need to clean a lot of plants quickly, a strong stream of water from a hose helps. This knocks mites off your plants as well.
How To Remove
For both pests, pruning away damaged areas is a good start. This removes the mites that are feeding in that area, and limits the need for pesticides, which can damage other beneficial insects. Remove entire plants that have been strongly affected.
Finally, insecticidal soaps, horticultural oils, and neem are all solutions if none of the above worked for you. Always avoid spraying in peak pollinator activity and when flowers are open (if possible).
Earwigs
When you’re growing zinnias from seed planted directly in the garden, earwigs are a legitimate pest concern. Otherwise, they can actually help you with aphid control, as they feed on aphids regularly. In large numbers, though, they like to chomp on zinnia flowers. This is no good for gardeners who love to see their zinnias thriving.
How To Identify
Earwigs are easy to see, as they’re larger than most of the pests on this list. Adults are about ¾ of an inch long, with a small set of forceps at the end of their bodies. They are usually brown or reddish brown, and some have a small set of wings. Young earwigs are just slightly smaller than adults, and they lack wings.
You won’t see these guys out during the day, as they prefer the dark. Go out at night with a UV light to see if the bite marks on your zinnias are from earwigs. They also live under rocks and logs. Roll over any of those next to your zinnia bed to see if they are under there.
How To Prevent
Because earwigs love to consume decaying material, the first thing to do is maintain the culture of your garden. Remove decaying materials from the area where your zinnias grow. This includes dead leaves, rotting logs, and the like. They also enjoy areas thick with weeds and ivy.
Earwig predators include toads, birds, and ducks. Planting trees and native berry plants in your yard attracts songbirds who eat earwigs. Toads are most common in areas where logs and leaves are present, but since you need to clear those to prevent earwigs, make a toad home to invite one to your garden. Simply bury a terracotta pot halfway in the soil, and you might find one living there a few days later.
How To Remove
Aside from cultural controls, it’s hard to remove earwigs without putting pollinators at risk. If you must use chemicals, organic slug baits with spinosad are an option. Sprinkle a ring of these around your zinnias in the evening and wet the bait. They’ll munch on it and die.
Leafminers
These little guys you probably won’t see are the larval stage of a fly. This flying pest lands on zinnia leaves and deposits its egg in the leaf tissue. Then the little guy hatches and burrows in between the leaf surface and underside, while consuming the inner tissue as it progresses to pupation. Then it drops to the soil surface and, after some time, emerges as an adult fly. Then the cycle continues.
How To Identify
Leafminer damage is very specific and easy to notice once you’ve seen it. If you see little tan trails through the leaves of your zinnias, that’s them. Before the larvae get going, the adults cause light colored stippling from their ovipositing activity on the leaf surface.
Thankfully, there’s not a ton of damage that leafminers cause to zinnias. However, their trails are unsightly. Zinnia seedlings suffer the most damage, though, as they don’t have a lot of leaf tissue to give.
How To Prevent
Because they are so common and don’t do a ton of damage, there’s not much that needs to be done to prevent this zinnia pest. Cover your seedlings with a row cover to prevent flies from reaching the leaves.
When leafminer numbers are high, it’s likely their primary predator, wasps in the Diglyphus genus, will come to gobble them up. You don’t need to do anything to attract them to your garden.
How To Remove
The best course of action for removing leafminers is simply to snip off the leaves where they’re feeding. Look for those trails and then remove them. There are no effective pesticides for leafminers.
Thrips
Another common zinnia pest of little concern is thrips. These guys don’t threaten the lives of your zinnias, but they, like leafminers, cause cosmetic damage that is unsightly. The most common species that causes damage to zinnias is the western flower thrip (Frankliniella occidentalis). It can spread tomato spotted wilt virus as it feeds on zinnias.
How To Identify
Western flower thrips are elongated, slender, and usually orange or yellow in color. Adults have bristle-like hairs on their abdomen, and they may have wings. Because they’re only one-twentieth of an inch long, you’ll likely see their damage before you see them. And they’ll probably be gone by the time you notice.
When determining if thrips are the culprit, look for thin, papery leaves, stunted growth, and leaf drop. Petals may take on dark discoloration where thrips fed while zinnias were budding.
How To Prevent
Predatory thrips, pirate bugs, and green lacewings are the best predators for this zinnia pest. Parasitic wasps also love to eat them. Plant their hosts to bring them in. Eliminate dust, which thrips love, by spraying plants with water in the morning.
Thrips tend to feed on stressed plants, so keeping your zinnias happy with proper watering, soil, and siting is a good start for keeping them away. Row covers are another viable option where thrips have been an issue in the past.
How To Remove
There aren’t good insecticides for controlling thrips, at least not any that are particularly effective. Avoid spraying them as they probably aren’t on your plants when you notice damage. In a greenhouse, however, insecticidal soaps and horticultural oils are a viable option.
Lygus Bugs
Do you notice stippling on your plants along with small dark spots of excrement? It might be lygus bugs taking a nibble of your zinnia’s juices. These are true bugs, which don’t go through a complete metamorphosis like other insects do. They aren’t a huge problem for zinnias, but here’s some info in case they go to town on your flowers.
How To Identify
Most often, you’ll see the damage before you see these bugs. Also called tarnished plant bugs, these guys insert their proboscis into the plant tissue and inject a toxin while simultaneously feeding on the juices. This leaves “sting marks” on new shoots and buds.
The bugs themselves are about ¼ of an inch long with a brownish body that has white and black markings. They lay eggs in soft areas of the flower, including the buds.
How To Prevent
Keep your garden free of weeds to keep lygus bugs away. Several common annual and perennial weeds host them. Row covers are a viable option for keeping them away and preventing their feeding on buds and shoots on developing plants.
Tachinid flies and parasitic wasps feed on lygus bugs, as well as green lacewings, spiders, and minute pirate bugs. Very often, native plants, especially native asters and yarrow, bring these pest-eaters into your zinnia patch and give them a place to stay.
How To Remove
If all of the above hasn’t proven useful to you, you can follow up with horticultural oils or insecticidal soaps. As mentioned previously, avoid spraying too much at once, and avoid spraying when pollinators are active to prevent damage to them.
Whiteflies
Another highly common pest in and outdoors is the whitefly. These guys show up as the weather warms and dissipate when it cools off. Like all the other pests listed here, they pierce the surfaces of leaves, stems, and sometimes buds to consume plant juices. Like aphids, they secrete honeydew as they feed.
How To Identify
If you brush your zinnias and dozens of small moth-like creatures start flying around, you’ve likely got a pest infestation of whiteflies. They are most common in greenhouses, but do crop up in in-ground plantings outside too. Adults are tiny with whitish to yellowish coloring and four wings.
They congregate on leaf undersides until they’re disturbed. It’s here they lay their eggs. In extreme cases, they cause leaf yellowing and leaf drop. Their honeydew builds up and develops sooty mold as well.
How To Prevent
Green lacewings and pirate bugs keep large populations of whiteflies under control. Parasitic wasps feed on eggs before they hatch. If you have a population of whiteflies hanging around your zinnias, look at the leaf undersides. Empty eggs with an exit hole have been parasitized. This is one indication the good guys are on the case.
In greenhouses, use yellow sticky traps to attract and kill them. Outdoors, these are more of a dicey option as they attract other insects that are drawn to the color yellow. This could mean sacrificing beneficial insects as well as whiteflies, which is the opposite of what you want.
How To Remove
Remove egg-covered leaves by hand to keep their numbers down. If there are super heavily infested zinnias that couldn’t handle the removal of leaves, take the whole plants out and toss them in the trash.
Use a strong stream of water from a hose to knock adults off the plant. Most of the time whiteflies aren’t a huge issue outdoors, and a regular water bath keeps them from doing too much damage.
Final Thoughts
Zinnias are fairly carefree plants that provide so much to gardens, even in the hottest weather. Keeping them pest-free isn’t always possible, but when you plant an array of nectar plants, it’s easy to have a garden full of helpful insects that keep zinnia pest populations down.
Use cultural and mechanical methods of control first before jumping to pesticides. It may take a week or two, but consistent care and monitoring will pay off. And your zinnias will bloom over and over through spring and fall.
