Splotchy Beet Leaves Mean Miners at Work

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Swiss chard leaf with telltale leaf blotches: leaf miners are at work! Source: thatbloomingarden.wordpress.com

The beet leaf miner (Pegomyia betae) is the larva of a small, rarely seen fly, as is its lookalike cousin, the spinach leaf miner (Pegomyia hyoscyami)*. But the damage caused by leaf miners is highly visible: translucent tunnels and patches on beet, Swiss chard and spinach leaves as well as those of other plants of the Amaranthaceae family (formerly the Chenopodiaceae family), like the common weeds lamb’s-quarters (Chenopodium album) and redroot pigweed (Amaranthus retroflexus).

*Since the beet leaf miner and the spinach leaf miner are practically indistinguishable and have the name life cycle, host plants and treatments, I’ll simply refer to beet leaf miner throughout this article. Who knows which one you really have?

Beet leaf miners are often fairly discreet, causing damage to a leaf or two here and there and not really affecting the harvest to any great degree. But then, of course, there are years when the population seems to explode and almost every plant over half a continent is affected. And not just a leaf or two per plant, but most leaves, often with several leaf miners working each leaf. In such bad years, beet leaf miners can completely obliterate the harvest.

Even in the worst years, though, you’ll notice that the insect has less impact on beets (beetroots) than on Swiss chard and spinach. That’s because they don’t attack the beet’s root (the part usually harvested), but only the leaves. Since the plant usually has enough green tissue to carry on photosynthesis in spite of their presence, you may still end up with nice, sweet beet roots. With plants whose leaves are harvested, though, like Swiss chard and spinach, there is often little left to harvest.

Symptoms

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Beet leave with a large splotch of leaf miner damage. Source: freespiritgardens.org.

Beet leaf miner is an easy pest to recognize. The leaves of the infested plant become marked first with translucent tunnels, then these grow to become blotches. The upper leaf surface takes on the texture of parchment while the lower one eventually turns brown. Further inspection will reveal one or more small whitish larvae (maggots) inside the leaf. The blotches are caused by the larvae as they eat the cells that make up the inside of the leaf, leaving only the upper and lower epidermis intact.

Life Cycle

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The female leaf miner fly looks like a small gray housefly. Source: Janet Graham, Wikimedia Commos

The female beet leaf miner hatches from a pupa that overwintered underground. Depending on your climate, she’ll likely be active in late April or May, earlier in mild climates. She lays eggs on the underside of the leaf of the chosen host plant. After about five days, the tiny larvae emerge from the eggs and either settle on the leaves of that plant or on neighboring plants. They pierce a small hole under the leaf and crawl inside. Then they start to feed.

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Leaf miner larvae (maggots). Here, the upper surface of the leaf has been removed so you can see them more clearly. Source: www.obsessedbynature.com

At first, they form tunnels, then enlarge those into larger and larger blotches, especially when the tunnels of several larvae merge as is often the case. The blotches can even come to nearly cover the leaf. After two or three weeks of feeding, the larvae exit the leaf, drop to the ground at the foot of the affected plant and form a small brown pupa underground. After 3 to 5 weeks, adults emerge from the pupae and the cycle begins again.

Each generation lasts about 30 to 40 days and there are usually three generations per year (more in climates with very long growing seasons), the first being generally by far the most damaging. The last generation remains in their pupa all winter … and the cycle starts again the following spring.

This insect has many natural predators, including parasitic wasps, most of which are too small to be readily visible, but they are behind the sudden population crash that inevitably follows a banner beet leaf miner year.

How to Prevent Damage

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Leafminer eggs are found underneath the leaf. Source: www.leafmines.co.uk

As soon as your beets, Swiss chard and spinach have 4 to 6 true leaves, start checking the underside of the leaves for eggs. They are tiny, oblong, about 0.7 mm in length, white and found in clusters of 3 to 12. Just knock them into a cup of soapy water to remove them. Or squash them.

Placing sticky yellow traps near plants can also be useful if you put them out at the 4 to 6 leaf stage. They are only effective on the flies, of course, not the larvae. Note that these traps attract pest insects, not beneficial ones.

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Keep leaf miners off your plants with floating row cover. Source: wimastergardener.org

Another possibility is to exclude them from your plantings. For this to work, you need to sow beets, Swiss chard and spinach in a location where there were none the previous year and cover the spot, after sowing, with floating row cover to prevent the female flies from even approaching them. If you don’t rotate your crop, this method won’t work, though, since the pupae overwinter where the host plants grew the year before and will be trapped under the row cover when they hatch, able to feed at will.

Or try simply delaying sowing beets and their relatives. If you sow at the end of May or in June rather than early in the season, the first generation of female flies—the generation that does the most damage!—will have gone elsewhere. Any damage due to subsequent generations is not likely to be of much concern.

Too Late, The Miners Are Already at Work

It’s too bad that no one warns gardeners when a bad year for leaf miners is expected. If so, we could do something to prevent them. Most of us, however, just react when we see the damage, so…

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If only a few leaves have been harmed, simply remove them. Source: www.sciencesource.com

If there just a few leaf tunnels here and there, simply cut off the affected leaves and you’ll nip the infestation in the bud. Or squish the larvae inside the leaf: there’s a special satisfaction in that!

If most of the leaves are affected, though, the easiest solution is to pull and destroy the plants. (If you do so, remember you can harvest and use any intact leaves.) Then resow. There is almost always plenty of time for this, as spinach, beets and Swiss chard are all fairly fast growing.

In general, there is little use spraying conventional insecticides once damaged leaves are visible, because the larvae will already be safe inside the leaf where most pesticides can’t reach them. However, if you notice small, grayish flies near your young plants, you might be able to kill a few with insecticidal soap or neem spray.

Theoretically, you could use systemic insecticides—ones that penetrate plant tissues and are carried throughout the plant by the plant’s sap—to make the leaf toxic to leaf miners … but remember you and your family will be eating these plants later. Do you really want to make vegetable plants poisonous? In any case, systemic insecticides are no longer available to home gardeners in most countries.


Beet leaf miners: the damage they cause can sometimes seem pretty discouraging, but most gardeners quickly learn to live with them.20180623A thatbloomingarden.wordpress.com

2018: The Year of the Beet

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Beet ‘Merlin’ : Source: Sakata Seed, National Garden Bureau

Every year, the National Garden Bureau, a non-profit organization promoting the pleasures of home gardening, selects one perennial, one annual, one edible plant and one bulb to celebrate. It’s a great way to discover a new plant or to learn a bit more about a plant you may already be growing.

Here’s the third of 2018’s four plants, the beet (Beta vulgaris). Go to 2018: The Year of the Coreopsis and 2018: The Year of the Calibrachoa to learn more about this year’s perennial and annual honorees.

A Trip Back in Time

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All the beets of every description grown anywhere in the world trace their origin back to the rather inconspicuous sea beet (Beta vulgaris maritima). Source: miluz, Flickr.

The wild beet (Beta vulgaris maritima) is a coastal plant usually called sea beet and grows naturally in Europe, North Africa and into the Middle East, mostly around the Mediterranean and Caspian seas and along the Atlantic coast.

It was originally cultivated as a medicinal plant as far back as the second millennium CE, possibly domesticated in Mesopotamia, and used both to treat fevers and constipation and also as an aphrodisiac, then later for its edible leaves. Curiously, the root itself was not consumed, since the wild species only has fairly woody brown roots not worth harvesting.

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Spinach beet (Beta vulgaris Group Cicla) is grown for its edible leaves, not its stringy roots, and is the most primitive form of the domesticated beets. Source: damsoncottagegarden.com

This early form corresponds to what we know today as spinach beet or perpetual spinach (B. vulgaris Cicla Group), once a popular vegetable, but largely forgotten today. Studies show it was known and used by most of the peoples the region: Mesopotamians, Egyptians, Greeks, Romans, etc.

The vegetable with the bulbous root we know in our era as the beet (beetroot in the United Kingdom), which taxonomists put into the B. vulgaris Conditiva Group, is of unknown origin, possibly derived from more tuberous-rooted plants found in North Africa. It only became popular in Germany and Russia near the end of the 1500s and didn’t catch on in the rest of Europe until the end of the 18th century.

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Swiss chard, sugar beet and mangelwurst are all beets, but were developed for different uses than the table beet. Source: farm2mountain.com, crystalgreen.com & http://www.rareseeds.com

Swiss chard (B. vulgaris Flavescens Group), whose thickened petioles are believed to have resulted from a mutation, sugar beet (B. vulgaris Altissima Group), a commercial crop that provides 20% of the world’s supply of sugar, and mangelwurst or mangel beet (B. vulgaris Crassa Group), whose leaves and bulbous roots are mostly used as animal fodder, are all beets as well.

Family Portrait

The beet was long placed in the Chenopodiaceae family, now eliminated, its members now nested within the Amaranthaceae. It’s a biennial, usually flowering the second year. However, unless you’re growing beets for their seeds, you would normally raise them as an annual crop, sowing them in the spring for a summer harvest or late summer for a fall one. In mild climates, beets are sown in the fall as a winter crop.

The flowers, quite unremarkable, are wind-pollinated. Any of the beets (beetroot, sugar beet, Swiss chard, etc.) can cross with any other.

Lots of Color

Beet (beetroots) are much more variable than most people think.

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Beet roots come in a wide range of colors. This Rainbow Beet Mix includes many of them. Source: RH Shymway Seed, National Garden Bureau

First, the reddish-purple color we know so well is only one of the beet’s colors. There are yellow and golden beets as well as white ones, plus candy cane beets with distinct red and white zoned roots. The petioles are the same color as the root, but even the leaves can be purple, as in the popular both ornamental and edible beet, ‘Bull’s Blood’.

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‘Bull’s Blood’ beet is often grown as an ornamental, yet both its leaves and root are edible. Source: www.osborneseed.com

This range of colors comes mostly from various betalains, which are antioxidant pigments. Some people are unable to break down betalains, either ever or occasionally, leading to “beeturia” (red urine), a harmless but I would suspect rather startling condition. Betalains have long been used as a coloring agent in tomato paste, jams, jellies and sauces and were once used as rouge and lip stain (hence the expression “red as a beet”).

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Cylindrical beet ‘Taunus’: more beet in less space! Source: Bejo Seeds, National Garden Bureau

The root shape is usually globular, but there are also cylindrical beets, much like carrots. I find them practical, as you can get more beet root in less space … and they’re easier to slice. Other shapes include top-shaped, flattened and blocky.

Chowing Down

Beets are a common vegetable, even a staple food in many regions. In Eastern Europe, for example, borscht (beet soup) is served with nearly every fall and winter meal. Beets are eaten boiled, roasted, steamed, raw and pickled, cold or warm, sliced, diced, mashed and grated, on their own or in mixed into salads and soups. The traditional Pennsylvania Dutch pickled beet egg is made by marinating hard-boiled eggs in beet juice and vinegar. And of course, if you’ve ever eaten a hamburger in Australia, you know that it will be coiffed with a slice of pickled beet rather than a slice of tomato.

Beets are high in fiber, vitamins A and C, antioxidants, calcium, potassium, phosphorus and folic acid and have more iron than most other vegetables, making them popular with the health conscious. Beet powder is sold encapsulated as a nutritional enhancement, slices are dried to make healthy chips and beet juice is being marketed as a natural energy drink. Wine (red wine, one would presume) has also been made from beet juice. Beets (mostly sugar beets) are even being used to produce bioethanol and may be helping drive your car!

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‘Early Wonder Tall Top’ is a dual purpose beet, grown for both its leaves and its root. Source: sagegarden.ca

The leaves, called tops, are edible as well and can be eaten raw or cooked as you would spinach. Some varieties, like ‘Early Wonder Tall Top’, are considered dual purpose beets, grown for both tops and roots. Also, beet sprouts (freshly germinated seeds) are easy to grow on a windowsill, even in winter, and baby beet leaves are catching on as a salad ingredient. And of course, many gardeners know that, as you thin your beets, you always harvest the thinnings, even though their roots are still unswollen, as the first beet crop of the season.

Beets have a reputation of having an “earthy” taste that some people don’t appreciate. This is caused by the presence of geosmin, the same organic compound that produces the “soil after rain” smell most people recognize well, as the human nose is extremely sensitive to geosmin and is able to detect it at concentrations as low as 5 parts per trillion. Geosmin is not present in all beets (if it bothers you, look for beets with a “mild flavor”), plus it is eliminated by pickling (geosmin breaks down in acid conditions, such as in vinegar).

Growing Beets

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Sowing beets. Source: www.diynetwork.com

Beets seeds are generally sown directly in the garden, although they also grow well in containers, usually in early spring or late summer in temperate areas, as they do best under cooler temperatures. Sow them about ¼ to ½ inches (1 to 1.25 cm) deep and 1–2 inches (2.5 to 5 cm) apart and keep the soil evenly moist to encourage germination.

There is no need to add mycorrhizal fungi to the soil of beets when you sow. Beets, along with their close relative, spinach, are among the rare plants that do not form associations with soil fungi.

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The beet seeds you buy aren’t actually individual seeds, but a small cluster of seeds in a dried fruit. Source: http://www.quickcrop.ie

Beet “seeds” are actually glomerules, little clusters of 2–4 seeds, and usually at least two will germinate. As a result, beets always need thinning. That said, there are now a few “monogerm” beet varieties on the market, with more sure to come in the future. This characteristic is still pretty rare and will be mentioned in the variety’s description.

To thin beets, pinch or cut back seedlings at their base when they are 1–2 inches (2.5 to 5 cm) tall, leaving plants about 3 to 5 inches (8 to 15 cm) apart. This will encourage larger and better-shaped roots for harvest. (To a certain degree, the larger the spacing, the larger the beet.)

Beets prefer slightly acidic soils with some boron content (to meet this need, consider watering them with seaweed fertilizer) and limited nitrogen. They are highly salt tolerant and will grow in soils few other plants will tolerate. Beets like about 1 inch (2 cm) of water per week.

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‘Boldor’, one of the golden beets. Source: BejoSeeds, National Garden Bureau

Most beets mature in 50–95 days. Roots are normally harvested by gently pulling the tops or digging the roots when they are about 2 1⁄2” to 3” (6.5 to 7.5 cm) in diameter, but can be harvested larger or smaller as desired.

Finally, beetroots store well, both in the ground, indoors in a cold room … and practically forever once pickled!


The National Garden Bureau recognizes the beet is a perfect food for the health conscious as well as an easy and fun-to-grow vegetable for all ages.  It could very well be the kale of the 21stcentury!

Take advantage of the Year of the Beet to grow this ancient yet constantly renewed vegetable in your own garden!20180204A Beet_Merlin_Sakata, National Garden Bureau.jpg

Swiss Chard: The Easy Salad Vegetable

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20150429BSwiss chard (Beta vulgaris cicla) is  a selection of the wild beet or sea beet (Beta vulgaris maritima), the same plant that gave us the garden beet or beetroot (Beta vulgaris crassa). But instead of producing a swollen edible root, Swiss chard provides markedly thickened petioles and much larger leaves. Both are edible and can be used much like spinach, raw in salads or cooked. Moreover, Swiss chard complements spinach well as it starts producing when the ever-so-early spinach starts to go to seed. Swiss chard is however much easier to grow than spinach. In fact, it is probably the easiest salad vegetable.

20150429AYou can sow Swiss chard early spring once the soil is slightly dry, even though there may still be a bit of frost in the air. Sow seeds 1/2 to 1 inch (1-2 cm) deep in a rich, well drained soil and a sunny location, either in the ground or in containers. As the foliage is beautiful (there are varieties with red, pink, orange, yellow, green or white petioles, a color that also extends into the foliage), Swiss chard looks as much at home in a flowerbed as in a vegetable patch. Don’t be afraid to sow it fairly densely, as the seedlings and young plants are edible: as you thin them, harvest the young greens for the kitchen, then leave about 8 to 10 inches (20 to 25 cm) between the final plants, the ones that will remain in the garden for rest of the summer.

The secret to Swiss chard in the home garden is to not do like supermarkets and cut the whole plant when you harvest. Instead, pick only the outer leaves. That way the plant will continue to grow new ones from the center throughout the summer… and your harvest can continue until severe frost. Depending on your local climate, you may still be eating fresh Swiss chard in November!

You can keep surplus chard seeds for about 4 years as long as you keep them cool and dry. And if you live in a mild climate (USDA zone 6/Agriculture Canada zone 7 or warmer), you will be able to produce your own Swiss chard seed, because the plant is a biennial and will bloom and produce seeds the second year. In colder climates… well, just buy more seed when you run out!

Swiss chard: so colorful, so easy to grow. No garden should be without it!