Curly dwarf may sound like the punchline from a bad joke, but this viral disease can ruin your artichoke plants.
Curly dwarf is spread by insects, and can be fatal, so knowing what it looks like can help you keep it from spreading to uninfected plants. While only found on artichokes, in the field, cardoons, sunflowers, and zinnias have been infected in laboratory tests.
[Unfortunately, I was unable to find a single image of an artichoke plant infected with curly dwarf, but I will keep looking. Please let us know if you have one!]
Curly dwarf, also known as artichoke curly dwarf, is caused by the artichoke curly dwarf virus (ACDV). While very little is currently known about this particular virus, we do know that it is almost found in tandem with another virus (Artichoke latent virus), which seems to have no disease symptoms.
Symptoms of curly dwarf
Severe stunting, leaf curling, and reduced bud production, with buds remaining small and often misshapen, is a clear indication that your plant has become infected with curly dwarf. Leaves may also have dark, dead areas.
Preventing curly dwarf
We do not yet know which insects spread curly dwarf, but we do know that it can be transmitted to uninfected plants. For this reason, it is important to remove any infected plants as soon as they are identified. The curly dwarf virus is commonly spread when infected plants are divided for propagation purposes, so only use certified disease-free plants.
Since the virus also lives on milk thistle (Silybum marianum), keeping those weeds away from your artichoke plant may reduce the chance of infection.
You’ve proba-bly never heard of proba bugs. They are another relatively new pest on the California scene. And they love artichokes.
Proba bugs (Proba californica) have been around for some time, but they used to prefer coyote brush. Coyote brush is a common native plant found along highways in agricultural areas of California. At some point (around 1997) a proba bug decided to give artichokes a try. From that moment on, proba bugs have become an increasing threat to artichoke plants. So, what do they look like?
Proba bug description
Adult proba bugs are plain brown and only 0.2 inches long. [That means you could line up 3-1/2 proba bugs across the top of a dime.] Nymphs start out looking like pale yellowish green aphids, except that they move a lot faster than aphids, due to their long legs. During the next to developmental stages (instars) they are reddish-brown, and then they develop light and dark bands on they abdominal area during the final two instars. [I couldn't find any usable photos of proba bug nymphs - sorry!]
Proba bug lifecycle
Proba bugs are active year round (just a lot slower in winter). As temperatures begin to rise, usually in March, they begin feeding and breeding in earnest. Eggs are laid on artichoke petioles (leaf stems) and hatch within 20 to 30 days. Nymphs go through five instars before reaching adulthood.
Damage caused by proba bugs
The damage caused by proba bugs is similar to that of lygus bugs, only proba bugs are more aggressive in their feeding habits. Adults and nymphs feed on young artichoke leaves and at the base of developing buds. They feed by piercing the tissue and injecting a toxin that kills plant cells. As the surrounding leaf tissue continues to grow, these punctured areas turn into brown dead spots that dry and fall off, leaving a shot hole appearance. Feeding on the base of flower buds causes the bud [the part we eat] to turn black. Not very appetizing. This phytotoxin also causes stunting and deformed flower buds. Severely affected leaves will be smaller than normal and chlorotic.
Controlling proba bugs
Until relatively recently, commercial artichoke fields were treated with organophosphates and chlorinated hydrocarbon insecticides. Use of these neurotoxins is being phased out, so proba bugs are becoming more of a problem. Infested fields can lose 20 to 30% of the harvest to proba bugs. Farmers are now removing the coyote brush near their fields and tilling the crop residue under, in a practice called stumping, to help combat this pest.
Natural predators, such as big-eyed bugs, damsel bugs, minute pirate bugs, and spiders all feed on the nymph stage of proba bugs, so avoid using broad spectrum pesticides.
You can help protect your artichoke plant by cutting the plant off at ground level, once flower production is done for the year, and monitoring for signs of infestation in March and April.
Cardoons (Cynara cardunculus) are edible thistles from the sunflower family.
Eaten the same way as celery, or cooked into stews and soups, cardoons are a maintenance-free perennial. The familiar, grocery store variety of artichoke is a type of cardoon, but there are differences.
Native to the dry climate of Morocco, cardoons are unfazed by drought, making them an easy choice in California and other Mediterranean climates. Also known as artichoke thistles, cardoons produce magnificent pinkish-purple spiked flowers from April through July, but it is the stems that are eaten.
Wild cardoons are sturdy herbaceous perennials that grow 3 to 5 feet tall, with deeply lobed, greenish-grey leaves that can be spiny, hairy, or downy (a condition called tomentose). The fleshy taproot is very good at finding water. And pollinators love the big, showy flowers!
Cardoons are grown for two different crops, using different cultivars. The familiar globe artichoke (Cynara cardunculus var. scolymus) is grown for its large edible flower buds. The plant referred to as ‘cardoon’ (C. cardunculus var. altilis) is grown, instead, for its edible leaf stems. Since the wild ancestor to cardoons featured painful spines on those stems, spineless cultivars have been developed. Our domesticated artichokes and cardoons are so closely related that they can cross-pollinate, so they should be grown a fair distance from one another.
How cardoons grow
Cardoons need a long, cool growing season, making them an excellent winter crop in the Bay Area. Seeds are started late fall to mid-winter and they transplant easily. These plants grow slowly, at first, but don’t let them fool you. Cardoons can get quite large, averaging 3 feet in all directions. Plants need full sunlight, moderate amounts of water, and good drainage. Watering regularly improves the flavor of cardoon stems. They are frost sensitive, so some protection may be needed in the form of mounded straw or dry leaves around the base of the plant during winter. The plants often die back to ground level after flowering, but they will come back, year after year, adding structure and color in winter, and a spectacular show in spring and early summer.
Only the tender, inner stalks are eaten. These are harvested before the plant goes to flower. Much like celery, these stalks are wrapped in fabric, paper, or straw during the 30 days of growth. This etiolation, or bleaching, keeps the stems white and tender. Traditionally, the stalks were buried under a mound of soil as the plant grew, but that just sounds like too much work. The stalks are then peeled and treated with a little lemon juice, to prevent browning. Simmer for 30 minutes or so and add to any number of Moroccan, African, Greek, Italian, or Persian dishes. In addition, cardoon seeds contain a high quality oil, similar to sunflower oil and safflower oil.
Cardoon pests and diseases
Like its close cousin, the artichoke, cardoons are vulnerable to feeding by slugs and snails, and the artichoke plume moth. They are also susceptible to the viral disease artichoke curly dwarf. Other than that, they are relatively indestructible.
An invasive weed
Cardoons are so hardy, and they self-seed so readily, that they are categorized as a Most Invasive Wildland Pest Plant by the Invasive Species Compendium. What this means to you, as a home gardener, is that it is very important that mature flowers are deadheaded before seeds can spread. This will protect the environment and prevent your yard from filling up with pokey thistle plants. Cardoons grow and spread so readily that some researchers are studying them as a source of biofuel and bioplastics materials.
Invasive weed or delicious vegetable, cardoons have been part of the human diet since ancient times, only falling out of public favor over the last 100 years.
As easy as it is to grow, perhaps it is time for a cardoon in your foodscape!
Artichokes are a ritualistic food that require patience, good conversation, and a nice glass of white wine to be truly appreciated.
Modern artichokes (Cynara cardunculus var. scolymus) have evolved from the cardoon, a plant still grown in Spain and Portugal as a vegetable for its stalks and immature buds, and as a source of plant-based rennet for cheese making. Artichokes found in grocery stores today tend to be larger and tougher than is ideal. Gardeners can enjoy a more tender and flavorful experience by growing these prehistoric-looking members of the sunflower family (Asteraceae) themselves. As a health benefit, artichokes contain more antioxidants than most other vegetables.
Artichoke buds & flowers
The artichokes we eat are actually spiny, immature flower buds. Each artichoke that we buy or harvest is made up of a cluster, or inflorescence, of hundreds of smaller flowers, protected by modified leaves called bracts. Once these flowers bloom, the meaty bracts and the base, or heart, are too tough to eat. The lovely purple flowers are nice to look at, however.
Do you have space for artichokes?
Artichokes can be grown practically anywhere, but they are large plants, averaging 4 to 6 feet across, so be sure to give them room to grow. They prefer cool, moist summers (or relatively shady spots) and mild winters. The majority of the commercial crop is grown in the central, coastal areas of California. While most artichokes are grown as annuals, the plants can actually be grown as perennials, producing edible buds for 4 or 5 years. Under the right conditions, you may be able to harvest as many as 30 artichokes per plant per year. To get the most out of your artichoke plants, it is important to provide light soil (add compost!), water in summer and improve drainage for winter.
Artichokes & temperature
Timing is critical when starting artichokes from seed and when selecting varieties. The heirloom varieties (‘Violetta Precoce’, ‘Green Globe’, or ‘Romanesco’) are very temperature sensitive and will not grow well in northern regions. ‘Opera’ and ‘Imperial Star’ are better choices for colder areas. ‘Green Globe’ and ‘Imperial Star’ perform well in the San Jose, CA area.
Artichoke varieties & propagation
Artichokes are either green or purple. Traditionally, artichokes are a warm weather crop that can be propagated vegetatively or by planting seeds. Varieties that perform better through vegetative propagation include Italy’s large purple Romanesco, Spain’s medium green ‘Blanca de Tudela’, and Peru’s spend ‘Spinoso e Inguano’. Vegetative propagation refers to division and root cuttings.
To divide an artichoke plant, simply wait for new growth to appear in spring. Sink a shovel between the new shoot and the parent plant, lifting the new growth with the shovel and transplanting it elsewhere. Root cuttings can be taken from established plants and placed in a favorable growth medium (moist soil) and allowed to create a new stem and become a complex, independent plant.
How to grow artichokes from seed
Many varieties of artichoke perform well when grown from seed, but it may take a period of vernalization before flowering begins. Green ‘Harmony’ or ‘Symphony’ and purple ‘Opal’, ‘Concerto’ or ‘Tempo’ can all be grown from seed. Since artichokes have deep taproots, they are not well suited to container gardening. Seedlings should be handled very carefully when transplanting. It is easiest to simply plant them in the ground where you want them to give the taproot the freedom to grow deeply, without interruption. Artichoke seeds should be sown 1/4 to 1/2 inch deep at a time when temperatures are expected to be in the 70 - 75º range for a few weeks.
Artichokes are heavy feeders. Using a side dressing (adding fertilizer or aged compost next to plants, where it is watered into the soil around the roots, rather than digging it in), each mature plant will need 1/10 of a pound of nitrogen at the beginning of the growing season. Plants will also benefit from 1 cup of ammonium sulfate and 2/3 cup of ammonium nitrate during the harvest season. If you are like me and prefer a more natural approach, simply keep mulching the area around each plant with aged compost. Blood meal can provide the nitrogen.
Artichoke pests & diseases
Aphids and slugs are an artichoke’s most common pests. At the end of each growing season, many pests can be thwarted by cutting the stems to ground level and covering with mulch. Artichoke plume moths can be a problem in perennial beds. Artichoke curly dwarf is a viral disease that causes stunting and dark, necrotic (dead) spots. To avoid this problem, use only disease-free stock. Botrytis, or grey mold, is a fungal disease that occurs after extended periods of warm, wet weather.
Harvest your artichokes when they are about the size of an apple for the best flavor and tenderness.
A funny side note about artichokes: the fleshy leaves contain a chemical, called cynarine, that inhibits certain taste receptors, making water and other things taste sweeter!
Spring is the time of year when it is common to see white powdery patches appear on leaves. This bane of gardeners is called powdery mildew, and it can occur in autumn, as well.
Cucumber, melon and other cucurbits are susceptible to powdery mildew. You may also see it on tomatoes, roses, snapdragons, chrysanthemums, peas, artichoke, beets, grapes and wheat.
What starts as a small white spot, powdery mildew expands to engulf an entire leaf as the nutrient-sucking fungi bleed the life from your garden. It can be found on either side of a leaf and sometimes on stems.
Powdery mildew identification
Powdery mildew is a fungal disease. It is caused by different types of fungi (e.g., Erysiphe spp., Sphaerotheca spp.), depending on which plant is affected. Contrary to common belief, moisture and humidity are not needed for these fungal beasties to appear.
The white powder seen on leaves is actually thin layers of fungal tissue (mycelium). Other symptoms of powdery mildew include:
How does powdery mildew grow?
Powdery mildew fungi simply need living plant tissue to survive and thrive. To make matters worse, their spores are carried on the wind, so the battle never ends. The reason powdery mildew seems to disappear in the heat of summer is that these microorganisms prefer shade and temperatures between 60° to 80°F. Our California summers are simply too hot for the spores to reproduce. Instead, they remain dormant until conditions improve.
Not only does powdery mildew cause leaf loss, it can also weaken a plant. This lowers production and increases susceptibility to other pests and diseases, such as citrus blast. Leaf drop can also lead to sunburn damage.
Powdery mildew management
Prevention and vigilance are the best ways to counteract powdery mildew. These tips can help, but nothing will eliminate powdery mildew in the garden:
Some people recommend spraying plants with a baking soda solution, but this can add too much salt to your soil.
More recent research shows that spraying the soil with milk before planting and then spraying the leaves of susceptible plants when the disease is most likely to start appearing can significantly reduce the incidence of powdery mildew in your garden.
You can grow a surprising amount of food in your own yard. Ask me how!