Biological pest control: parasitoids

¿Hablas español? Aquí esta una traducción: Control biológico de plagas: los parasitoides

Parasitoids are natural enemies of pests that, like predators (ladybugs and flower flies) can help us keep pest populations at bay or eliminate them from our gardens.

Parasitoid or parasite? Let’s learn the difference between these terms

Before saying more about this group of natural enemies, let me tell you that it is very common to confuse the term “parasitoid” with the term “parasite.” Parasites and parasitoids have in common the need for a host for their development. The difference between the two types of organisms is that parasitoids kill their host to complete their life cycle. That is, the parasite can live at the expense of the host without having to kill it, while the parasitoid ends up killing its host upon completion of its life cycle. Parasites are generally known to be annoying and even transmit diseases to animals, plants, and humans, while parasitoids are beneficial insects, as they help us control pests.

What is a parasitoid?

Parasitoids are insects that insert their eggs into the body or egg of another insect (host) in order to complete their life cycle. Parasitoids go through complete metamorphosis, four different stages of development: egg, larva, pupa, and adult. To finish their development, the parasitoids must feed on their host, and the females first deposit their eggs in their host. As soon as the parasitoid egg hatches, the larvae begin to devour the tissues of their host. Once the larvae reach a certain size, they become pupae, after which the adult emerges, killing the host.

Parasitoids can be classified according to their oviposition (egg-laying) behavior. Endoparasitoids are the parasitoids that lay their eggs inside the body or egg of their host. In contrast, ectoparasitoids oviposit on top of the body of their host, that is, on the surface of their body. To see these fascinating creatures in action you can, watch a video of endoparasitoids and one of ectoparasitoid activity.

Life cycle of an ectoparasitoid (adapted from Presa-Barra et al 2020)

life cycle steps of an ectoparasitoid

Life cycle of an endoparasitoid (adapted from Presa-Barra et al 2020)

life cycle steps of an endoparasitoid

Some ways to identify signs of parasitism in our gardens

Observing parasitoid pupae on top of pests

parasitoid wasp pupae on a caterpillar
As ectoparasitoids pupate outside their host, pests can sometimes be seen carrying “sachets” (the pupae in their cocoons) over their body, as seen in this photo. In this case, the parasitoid deposited many eggs on the caterpillar, which eventually pupated. After several days, those pupae will emerge as adult parasitoids. Photo: Mike T.

Observing colonies of aphids

aphid mummy
Sometimes we can observe aphids that look empty and have an opening in their body, as in this photo. This indicates that an endoparasitoid first parasitized and then emerged from that aphid. In this case, the parasitoid deposited an egg inside the aphid and completed its cycle inside it. Finally, it emerged creating a hole in the dead aphid. Photo: NY State IPM program.

Diversity of parasitoids

Most parasitoids belong to flies (Diptera) and wasps (Hymenoptera). Thousands of species of parasitoids are known from both groups, with Hymenoptera containing the most identified parasitoid species.

Parasitoid flies: Tachinidae

Within the group of parasitoid flies, the Tachinidae are one of the most important groups for biological pest control. Most of these flies are larger than a housefly, 2mm-20mm. This group is very diverse and some Tachinidae are very hairy and dark in color, while others may appear pale to the naked eye, or have bright colors such as yellow or orange. Most Tachinidae are endoparasitoids. Tachinidae attack leaf caterpillars, fly larvae, adult beetles, and other pests much larger than themselves. In this video, you can see how a Tachinidae fly parasitizes a caterpillar.

Parasitoid wasps: Mymaridae, Braconidae, and Ichneumonidae

Parasitoid wasps are one of the most studied parasitoid groups for biological pest control.

The Mymaridae are a group of very small parasitoid wasps that specialize in parasitizing eggs. All members of this group of parasitoids parasitize eggs of bedbugs, beetles, and pest flies in our garden.

very tiny wasp
These parasitoids are minuscule. To give you an idea, this photo shows a Myrmaridae on a person’s finger. Photo: gbhone

Ichneumonidae and Braconidae

These groups of parasitoid wasps are much larger than the Mymaridae. Most are around 1cm long, with 5cm being the record for the largest parasitoid wasps in North America, which belong to the genus Megarhyssa sp.

The Ichneuomonidae and Braconidae attack several pests including caterpillars, fly larvae, and aphids as shown in the image below.

an attach by Ichneuomonidae and Braconidae wasps
Parasitoid of the group Bracononidae attacking aphids. Photo: UGA CAES/Extension

Some of these parasitoids have a very long ovipositor, such as that of the species Megarhyssa macrurus, which is used to deposit its eggs in pests that are hidden between leaves or inside the trunk of trees. In this video, you can see Megarhyssa macrurus ovipositing on a tree trunk to attack a larva.

a wasp with a long ovipositor
Parasitoid wasp with a long ovipositor. Photo: gailhampshire

How to help parasitoids

There are several very effective practices for the conservation of parasitoids in our green spaces.

  1. As much as possible, avoid using broad-spectrum pesticides to control pests, as most of these also affect parasitoids. If you decide to use pesticides, opt for specific options and always use them as directed on the label.
  2. Diversify your planting (increase the types of plants grown) so that parasitoids have more spaces available to survive, a variety of prey to feed on, and/or nectar to supplement their diet. Crop diversification offers the presence of a wide variety of prey, which parasitoids can attack and use to survive when there are no pests in their green spaces. By increasing plant diversity, one provides parasitoids with resources that keep their populations in high numbers, which helps them better control our crop pests as soon as they appear.
garden plot of Swiss chard and flowers
One way to help parasitoids is by diversifying crops, as seen in this garden, where you have combined vegetables and flowers. Photo: W. Murphy

In the case of a pest invasion, you also can acquire parasitoids in local insect hatcheries or on the internet and release them into your garden. This will lead to pest control and in some cases the establishment of those parasitoids in your garden, which can help fight future pests. It is important to note that for this to work, it is important to carry out the two other practices already mentioned above.

Find out more

Presa-Parra, E., Hernández-Rosas, F., Bernal, J. S., Valenzuela-González, J. E., Martínez-Tlapa, J., & Birke, A. (2021). Impact of Metarhizium robertsii on Adults of the Parasitoid Diachasmimorpha longicaudata and Parasitized Anastrepha ludens Larvae.  Insects, 12(2), 125.

Patt, J. M., Hamilton, G. C., & Lashomb, J. H. (1997). Foraging success of parasitoid wasps on flowers: interplay of insect morphology, floral architecture and searching behavior.  Entomologia experimentalis et applicata, 83(1), 21-30.

Wäckers, F. L. (2004). Assessing the suitability of flowering herbs as parasitoid food sources: flower attractiveness and nectar accessibility.  Biological control, 29(3), 307-314.

By Darsy Smith, a Ph.D. student in the Department of Entomology at the University of Maryland, College Park. This article was published originally on the department’s Spanish-language blog, Extensión en Español.

Let’s find skipper butterflies in Maryland using iNaturalist!

A Silver-spotted Skippper on wild bergamont flowers in Maryland, observed recently by iNaturalist user Andy Wilson

I have been writing blog posts for Maryland Grows on a regular basis for a while. To do this, I usually meet with Christa, the blog manager, every 6 months and plan on the topics I will cover over the next few months. When we do this, we seek to cover the needs we see from readers, but sometimes the topics come to us as a result of our discussions. This is exactly what happened for today’s topic. Today, let me tell you the story of how this came to be, and at the same time show you a great free tool available at our (literal) fingertips!

The story

Picture myself and Christa on Zoom, planning dates and topics for the next few months. It is February and it is cold outside. We have been making our way through the upcoming months, thinking of what each one will look and feel like, and what will be growing and buzzing around in each of them. August comes. How is August in Maryland? What do we usually see around? What issues are common in green spaces in August?

I think of August and in my very pollination-biologist-biased way start thinking of the pollinators we see in August… And what comes to me is “butterflies!” I remember writing about butterflies in the past, so maybe butterflies are a bit redundant as a blog topic. However, I don’t remember writing about a specific group of butterflies called “skippers,” which are common in Maryland. So, sure, let’s write about skippers, but what skippers are around in August? As we discuss and try to narrow down the topic, I open this incredible tool I use very regularly to learn about local species, report observations I make, and do research in my lab. This magical incredible tool is called iNaturalist.

So, there I am, opening iNaturalist’s website, and doing a quick search to find out the most common and most abundant skippers we find in Maryland in August. I am doing this, and Christa is intrigued; what am I doing? How am I figuring this out? I decide to share my screen to show her what I’m doing. Christa is amazed. You can do all that with iNaturalist?! The world needs to know! So, there we have it. Our blog topic showed itself to us. Today’s blog will be about what iNaturalist is, how to use it, and what type of information we can share with and learn from it. I hope that this blog will motivate you to start using it as well, and, like me, every time learn something new about species here and elsewhere in the world.

iNaturalist; ever heard of it?

We live in the times of social networks, like Twitter, Instagram, and Facebook… And as it turns out, social networks are really useful to science too! iNaturalist is one of those networks!

iNaturalist is a global social network that allows people to submit, find, and explore biodiversity observations from around the world. What does this mean? This means that through this network, every time a person observes an organism anywhere in the world, they can take a picture of it, upload it to iNaturalist, and then have the network help them identify what it is through its picture (using image recognition software), its location, its date, and the input of other members. This information is then stored in a public database, which can then be explored easily by anybody, including scientists, you, me, kids, conservation agencies, and more! At the end of the day and using all these data, the network can output maps and other information of any species ever added, allowing for the reported localities to be found, and, if the user wants to, visited to try to see the organism in question. Today, iNaturalist has over 5 million users worldwide, with over 109 billion observations of over 380,000 species!

OK. But how does iNaturalist work?

To explain this, let’s come back to my skippers story. I am talking to Christa and want to know what the most abundant skipper in Maryland may be, and whether it is present in August. To do this, I first go to the iNaturalist website (if on a computer; otherwise, I would open the app on my phone). This is what the page looks like.

Screen shot of the iNaturalist home page

Once I get to that page, I click on “Explore” on the top left, which will open a search box, where I can type “Skippers” under species, and “Maryland” under location.

screenshot of how to search on iNaturalist website

And here is where the fun starts. When I do this, I start accessing all the data that all people who ever submitted data have provided, allowing me as a citizen and as a potential blog writer to benefit from the power of what we call “citizen science”. But let’s come back to the story. At this point, I have my first list of results, which looks something like this:

Screen shot of iNaturalist page showing skippers in Maryland

Here, I can see that there are several thousand observations of skippers in Maryland and that 48 species are recorded. If I select “SPECIES” I can see each species, their names, and the number of observations submitted for each. And bingo! This is one of the things I was after! I now can know what are the likely most common species, since those that have been seen many times are likely also the most abundant and common. Here, three species are kind of at the top with over 2000 observations each: Sachems, Zabulon, and Silver-spotted skippers.

Cool. I have a species selection now, but are they abundant in August? Let’s see that for Sachems and you can check the other ones yourself 😊. If I click on Sachems, the following opens up:

Screen shot from iNaturalist showing Sachem butterfly

This is the page that gives ALL information on Sachems. Here, I can see that skippers have been observed a lot and recently by specific people, but most importantly, I can see a little figure that shows when most observations happened, an indication of when the species is the most and least abundant throughout the year. If I filter this page by location (using the tool on the top right) and for MD, it seems that in August we are likely to see these skippers, but that we may see them more at the end of August than at the beginning of the month. So, maybe skippers are a good species to talk about.

But instead of telling that myself, let’s have iNaturalist tell you about it. How? Click on the “About” tab right below the picture! This is (the beginning of) what will appear:

screen shot of iNaturalist species info page

Want to know if the species is protected or rare here or elsewhere? Click on “Status” and you will have the most updated information!

Great, so now we can learn so much about the species. However, how do I find where to find it in Maryland? Simple! If you click on “Map”, a map of all observations will appear, with regions that have the most observations shown with boxes of darker color shades.

Screen shot from iNaturalist - map of Sachem species

This map can be zoomed into your town, neighborhood, or whatever region you would like to focus on, and, once you’re ready, you can even hover over the red boxes to select specific observations you may want to look at. Doing so will tell you where, when, and by whom the observation was made, and you will be able to see a picture of the observed organism. If one clicks on “View” on this observation, all its details will come up in a new window.

Screen shot from iNaturalist - observations of Sachem species
Screen shot from iNaturalist - observation of Sachem species butterfly in Maryland

Wow. I can have so much information here… including access to open access and lovely pictures of the species I am looking for (the small CC mark on the picture means that this picture is in the public domain).

And one more thing. Did you notice the green flag “Research Grade” that appears by the name? This flag indicates that the observation identification has been confirmed by many users, and for that reason can be trusted so much that it has a quality level that makes it appropriate for research purposes (these are the types of data we use in my lab). Isn’t that cool?

Anyways, a blog is supposed to be short and this one is getting long, so I will not go into how to submit observations to iNaturalist. However, know the following: you can do it from your phone or computer, and this is very easily explained in a couple of super neat and short how-to tutorials here.

Oh, and last but not least! iNaturalist is global! This means that you can submit and consult observations anywhere in the world. Are you on vacation and want to know what species are there? No problem, check the app and it will help you with that! Did you just move to a new place and wished you were more knowledgeable of the species in that new place? Great, iNaturalist can give you a hand with it!

I can speak about the wonders of this network for hours, but really the best way to realize it is by using it! So, go ahead and take a look at it and I hope you will find it as useful and easy-to-use as I do. And who knows, maybe after doing it, it will also inspire you to write about something you learned as it did for me and Christa! 😊

By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.

Anahí also writes an Extension Blog in Spanish! Check it out here, extensionesp.umd.edu, and please share and spread the word to your Spanish-speaking friends and colleagues in Maryland. ¡Bienvenidos a Extensión en Español!

How can you improve your soil?

a sloping landscape partially planted with cover crops
A cover crop of spring seeded oats is included on this slope with grass and trees. Photo: A. Bodkins

Healthy soil can sustain plant growth, prevent environmental damage, mitigate stormwater runoff, and help recharge and clean groundwater. 

Soil type is probably not something that people consider when they move to a new property, so it reminds me of the statement “you get what you get and you don’t throw a fit”. However, it is no secret that soils are not all created equally in their ability to grow plants. To make matters worse, the soil is constantly being manipulated to accommodate our needs. When infrastructure like roads and buildings are constructed soil is moved and in many instances, there may not be any native soil profiles still intact on the property. Often a small layer of topsoil is put back onto the landscape after construction and regrading of the land, but there is no guarantee that it was the topsoil found there before construction began. Once the excavation is completed there is no going back. This article from Penn State Extension, Can Disturbed Soils Grow Healthy Landscape? is a great read. If you suspect that the soil you are planting vegetables into has been hauled in from another location, it is wise to get the soil tested for lead content. Some labs also test for heavy metals like arsenic (As), cadmium (Cd), and chromium (Cr), which can be found in soils on old industrial sites.

Soil is the gift that can keep giving, but there are some management practices that can help improve all soils. The physical, chemical and biological processes of soil are all interconnected. If you want to learn more about your own soil, I recommend the Kansas State publication that walks you through the steps to Estimate Soil Texture by Feel. Knowing the soil texture in your garden is one piece of the soil puzzle.

Soil organic matter increases water holding capacity, improves water infiltration, serves as a source of micro and macronutrients, and provides large particles for micro and macroorganisms to break down.  Soils that are high in clay or sand can benefit from the addition of organic matter, which comes from anything that was once alive. Macro and microorganisms help to break down organic matter and release nutrients into the soil. There are many forms of organic matter that include compost, plant material,  livestock waste, humus or leaf litter.  

dark soil is rich in organic matter
A cross-section of healthy soil. Photo: USDA

Cover crops are another way to improve your soil because they capture excess nutrients that are left over from the growing season and prevent the nutrients from becoming environmental pollutants. Cover crops also prevent soil erosion from wind and rain during the late fall, winter, and early spring seasons when weather is not appropriate for most vegetable or agricultural crops. Once cover crops are terminated they can be plowed into the soil and add organic matter. This is called green manure. I’ve found that in my own garden, cover crops can also help prevent weeds from growing. Some cover crops like forage radishes die and create natural pathways through the soil for water to flow.

buckwheat cover crop planted over a vegetable garden soil
Buckwheat that I planted as an early season spring crop to help reduce weed germination in my vegetable garden. I had planned to terminate it and plant a late crop of cucurbits, but changed my mind after it was growing so beautifully and I saw all the insects that were visiting it daily.

Other management practices to help your soil include regular soil testing to monitor any changes and keep the soil pH in the correct range for your desired plants. Limit soil compaction by keeping vehicles, equipment, and even people from walking through gardens, especially when the soil is wet. At the very least, I think the best practice for improving and keeping your soil healthy is to leave it alone as much as possible, keep it covered with plants that are not invasive, and let the natural processes of the Earth work together to benefit the soil.

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, MarylandRead more posts by Ashley.


This year, the University of Maryland Extension Master Gardener Grow It Eat It Program celebrates the resource that supports all life on earth – soil! Look for soil education programs offered by your local Master Gardener program, and visit the Home & Garden Information Center website for more information about soil health.

did you know soil is a natural resource and a living ecosystem

Celebrate National Moth Week

A moth feeding on nectar of a purple  verbena flower
Hummingbird Clearwing. Photo: M. Talabac

The last full week of July is National Moth Week, and I encourage everyone to take a closer look at the vast diversity of moths that fill our natural world. Butterflies and moths belong to the same insect group, but moths far outnumber butterflies in species diversity. Since many moths have muted colors or fly at night, we’re largely unaware of this bounty. Let’s take a whirlwind appreciation tour of the group to illustrate the amazing, bizarre, and quirky features of this major insect order.

Moth adults come in all shapes and sizes, and like butterflies, wings are their most prominent feature. There are “micro-moths” whose wingspans are less than an inch, and giant “silk moths” up to 6 inches, making them the largest moths in North America. (Our native silk moths are not closely related to true silk moths, but they got the name because people thought they could be farmed for silk.) The wings of some moths look like mere slivers, seemingly insufficient for flight, while others are tucked around their body so they look fairly cylindrical. Some lay so flat at rest with their wings spread that you’d swear they were two-dimensional.

Some species unabashedly bear flashy colors and patterns in broad daylight because they’re chemically defended, often using substances the caterpillars ingested from their host plant, similar to how Monarch butterflies use milkweed toxins. Giant Leopard Moths, white with bold black leopard spots and a metallic blue abdomen, can exude golden droplets of a distasteful substance from their shoulders when disturbed. Wasp-mimicking species use warning colors to gain protection – few predators want to risk a sting – while other species use a different tactic and pretend to be inedible objects, like lichen, twigs, dead leaves, or even bird droppings.

Other moths hide vivid wing colors until prodded, their forewings camouflaged and covering their body at rest. When disturbed, they flash their colorful hind wings or expose eyespots that stare back at the predator. These bright patterns or eye-like designs startle a predator into rethinking an attack, making the moth appear too big to prey upon or giving it time to flee.

For seemingly defenseless creatures (no stinger, no jaws, no horns or sharp projections, and a soft body), adult moths use some clever strategies for survival. Great camouflage is the baseline strategy, but some moths can hear ultrasound produced by hunting bats. When the flying moth hears a bat homing in on it, the moth drops out of the sky and disappears from the bat’s radar. Milkweed Tussock Moth adults actually click back ultrasonically at a pursuing bat as a warning about their distaste, in case the bat ate others like it and regretted it.

It can be surprisingly hard for our dexterous fingers to pick up moths and densely-bristled caterpillars, so you can imagine other animals without hands have an even harder time if their strike isn’t spot-on. As with butterflies, wing scales can be slippery and may shed as the wings are grabbed, allowing the moth to slip away and escape.

Blooms that attract moths tend to be white or pale in color, or pink, dull red, or purple, and often have a strong, sweet scent, especially at night. As with butterflies, they prefer bloom shapes or clusters of flowers that provide a “landing platform” where they can sit and sip nectar, though some moths will hover while feeding instead. The sphinx moth group, which includes clearwings and the adults of hornworms, are the classic examples of “did I just see a small hummingbird?” At rest, they have a silhouette more like a fighter jet.

Moth caterpillars have a dazzling array of colors, patterns, and shapes. A few are spiny and have skin-irritating properties, like the cute Saddleback caterpillar that looks like a brown terrier wearing a neon-green blankie. I have been stung multiple times over the years by accidentally brushing up against them when handling plants because they’re inconspicuous when sheltering underneath leaves. It sure smarts for a few minutes, but I still think they’re beautiful and adorable.

Some caterpillars resemble a walking toupee or dust bunny, like the flannel moth caterpillars (another no-touch group), or a fringed carpet that blurs their body outline. Slug caterpillars include species whose body fringe looks made of spun glass (as one species is so-named) while the Monkey Slug looks like some sort of faceless alien Muppet with a fun hairdo and a herky-jerky gait. (Don’t touch that one either.)

Slug family caterpillars also include featureless speed bumps, with no discernable head or legs unless flipped over. (No slime on these slugs though, thankfully.) Maybe they’re trying to mimic leaf galls, though it’s an odd choice to me if so, since galls can be attacked by parasitoid wasps or foraging birds. Some giant silk moth caterpillars have colorful knobs on their body or spiny horns that look like they belong in a punk-rock band. (With a name like Hickory Horned Devil, you can’t go wrong.) The caterpillars of other moth families have multi-hued patterns, detailed stripes, marbling, zigzagging squiggles, or big eyespots above their heads that mimic a snake staring you in the face.

Inchworms are aptly named because their slender, long bodies inch along in a loping gait. Many disguise themselves like leaf stems or twigs when not feeding by standing on their hind legs ramrod-straight and freezing like a living statue performer. (This family’s name is Geometridae, which means “earth-measurer.” And they do, once inch at a time.) One family member, the Camouflaged Looper caterpillar, decorates itself with bits of leaf or petal that it’s eating, becoming a walking parade float of flair. As it matures and eats new things, its costume changes.

brown and black moth with orange marks on its body
Tobacco Hornworm

While a minor handful of moth caterpillars are home or garden pests or ravenously gregarious feeders, the great majority do not cause us humans any trouble. Plenty of caterpillars and adult moths alike feed hungry birds, bats, beneficial wasps, predatory bugs, and other organisms that help keep our ecosystem in balance. With over 2,500 moth species documented in Maryland to date, you could make a long-term hobby out of cataloging all the species found in the smallest of yards. (A good gateway to developing an interest in all of the other wondrous insects you’ll encounter in the process!)

Want to explore more about moths? Check out the National Moth Week website for tips on finding moths, activities for kids, and more.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. All photos in this post are hers. Read more by Miri.

Learn what not to do in your garden this summer

Do you do to-do lists?  I do. They help keep me focused and organized.  And boy is it satisfying to check things off.  But this time of year, I have another list, a summer What Not To-Do List for my garden.  This keeps me from serious missteps which can harm plants or waste time and money.   

Don’t: Plant

First on my What Not To-Do List is planting.  It’s just too hot and dry for plants to establish well.  Spring and fall are your best planting times.  Be wise and wait.  I know there are plant bargains to be had now.  As a career tightwad I’m tempted, too.  Don’t succumb.  

Don’t: Dig or Divide

No digging and dividing either.  Most plants prefer to have this done in spring or fall so they can settle in and develop robust roots before extreme weather.  So step away from that shovel. If you do plant or divide plants in summer you will need to water, water and water again, a significant time drain.  And still, your plants will be stressed. Very stressed.  

Don’t: Prune

Third on my What Not To-Do List is pruning.  Trees hate to be pruned in summer.  They weep copious sap and those wounds attract the abundant insects and diseases afoot now.  Summer pruning courts disaster.  Instead, prune trees in the dormant season – January to mid-March – when they are less vulnerable.  

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Tomato Talk: Wilts and Tips for a Big Harvest

Nothing causes that sinking feeling like walking into the garden and seeing one or more tomato plants wilting. Not just some lower leaves that are yellowing, curling, or drying up from leaf spot diseases. No, I’m talking about healthy green leaves and stems that start to go limp. Oftentimes, this spells the beginning of the end for the affected plant(s) so it’s important to figure out what’s causing the wilting symptom. Even if you lose one or more plants this year you’ll want to prevent a recurrence next year. UME’s Home & Garden Information Center seems to be getting more tomato wilt questions this year than usual.

Wilting may indicate that roots or stems are injured, soil moisture has been too high or too low, or that the vascular tissue directly below the epidermis (skin) of tomato stems is blocked up with fungal or bacterial pathogens. Plants with disease-caused wilt should be removed. Here are some possible causes for wilted tomato plants in Maryland.

Fusarium wilt– this disease is caused by a soil-dwelling fungus. Lower leaves turn yellow and leaves and stems begin to wilt, often on one side of the plant. Leaves may revive overnight. Cutting affected stems lengthwise with a razor blade (directly below the surface) will reveal brown discoloration or streaking. The disease rarely infects all of the tomato plants in a row or a bed.

This fungus can survive in the soil for years even if the tomato is not grown in that location. One solution is to grow resistant varieties- look for those that are resistant to at least two of the three known races of fusarium wilt. Example:

Nature’s Bites F1: Fusarium Wilt 1, Fusarium Wilt 2, Fusarium Crown & Root Rot, Leaf Mold, Root Knot Nematode, Tobacco Mosaic Virus

Another option is to grow tomato plants in containers filled with compost and soilless growing media. Don’t set the containers on the garden soil that had the fusarium wilt problem last year. 

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