With the 4th of July right around the corner, watermelons are a common sight. But watermelon mosaic is something I hope you never see.
Watermelon mosaic (WMV) is a viral disease that can also infect cantaloupes, squash, and other cucurbits, along with some legumes, such as peas and alfalfa, and chenopods. Infected watermelons look like they have ring worm.
There are two different watermelon mosaic viruses: WMV1 and WMV 2. While these are two distinctly different viruses, we are going to throw them together for the sake of this discussion.
Symptoms of watermelon mosaic
Symptoms of watermelon mosaic virus vary by host, but the first sign of infection is light discolorations in the leaves. This irregular chlorosis is usually seen along leaf edges (margins) and along veins. Leaves may also be smaller than normal, deformed, blistered, or wrinkled. That wrinkling is called rugosity. Finally, infected fruit develops a mottled appearance. The mottling looks like light-colored rings just under the skin. Warty growths may also appear. Fruit production is significantly reduced.
How to prevent watermelon mosaic
Spread predominantly by aphids and occasionally leaf miners, watermelon mosaic virus can also be carried on garden tools and clothing, so sanitize your tools regularly. The virus is only able to survive inside aphids for a few hours, so creating physical distance between potential carriers of the virus can also reduce infection. Crop rotation and removing infected plants can break this disease triangle.
Weeds, such as lambsquarters, cheeseweed, goosefoot, and Russian thistle, can act as vectors for this disease, so keep them away from your watermelon and other susceptible plants.
Horticultural oil spray can also interrupt transmission of this virus, but may cause problems of its own.
Insecticides are not effective because the disease is transmitted before the chemicals can kill the carrier. You can use reflective mulches under susceptible plants to repel aphids. If you use reflective mulch, be sure to remove it before the summer sun uses it to cook your plants.
Cantaloupes are a unique type of muskmelon. And American cantaloupes aren’t actually cantaloupes at all.
Did you know that melons are actually berries?
It’s true! Because the fruit, or pericarp, of a cantaloupe is produced by a single ovary, cantaloupes are considered berries. Specifically melons are modified berries called pepos. Pepos are formed from an inferior (meaning internal, not less than) ovary and they feature many seeds. Pumpkins and cucumbers are also pepos.
Also known as rockmelons, cantaloupes are members of the squash family. Like other cucurbits (Cucurbitaceae), cantaloupes feature a hard outer rind that protects the lush fruit inside.
Types of cantaloupe
Here, in the U.S., our cantaloupes have a strongly textured, or ribbed, rind and bright orange flesh. This North American variety (Cucumis melo var. reticulatus) is not technically a true cantaloupe.
How cantaloupes grow
Cantaloupes are vining annuals that love heat. Temperatures between 85°F and 95°F are ideal, and these plants can tolerate temperatures as high as 104°F. Cantaloupe’s bisexual flowers are mostly pollinated by bees, so a healthy bee population is important for a good melon crop. Whereas a single bee visit is enough to pollinate other crops, cantaloupes are fickle and may need 10 to 15 bee visits before pollination is completed.
Cantaloupes can be grown successfully in all types of soil and they even seem to thrive in our heavy clay, as long as there is good drainage. Cantaloupes are sensitive to root rot diseases, so proper soil aeration goes a long way toward keeping cantaloupe plants healthy.
To grow your own cantaloupes, wait until temperatures are well above 60°F and plant single seeds 3” to 6” deep in loose mounds. Mounds should be 3 feet apart and in full sun. Keep the mound moist, but not soggy, until germination occurs.
Cantaloupes are moderate feeders, which means a top dressing of aged compost after germination is probably all that is needed. [Of course, you should still conduct a soil test to make sure your plants have access to all the nutrients they need.]
Cantaloupe pests and diseases
Aphids, green peach aphids, in particular, cucumber beetles, cutworms, leafhoppers, leaf miners, root knot nematodes, seed-corn maggots, silverleaf whiteflies, spider mites, squash bugs, and wireworms may all pester your melons, but many of these pests can be thwarted by row covers and regular monitoring. The real threat to your melon crop is disease.
Cantaloupes are prone to several fungal diseases, including belly rot, downy mildews, Fusarium wilt, Monosporascus root rot, powdery mildew, sudden wilt, and Verticillium wilt. Aphid-borne viral diseases, such as cucumber mosaic virus, cucurbit yellows stunt disorder, watermelon mosaic virus, and zucchini yellows mosaic virus may also occur, as can bacterial angular leafspot.
Proper plant spacing and the use of a trellis can interrupt many of these diseases cycles by improving air flow. Fruits grown up a trellis will need to be supported with hammocks. Melons growing on the ground should be protected with a layer of straw or sawdust, a board, or some other material that gets them up off the soil.
Choosing resistant varieties, removing weeds, maintaining good air flow, and avoiding overhead watering will all help keep your melon vines healthy.
That being said, weeds can be a serious problem in cantaloupe beds as hideouts for pests and diseases. Stay on top of those water and nutrient thieves from the start to ensure a healthy crop of melons later in the summer. And watch your watering. Heavy rain (or over-watering) can cause fruit split.
Cantaloupes are ready for harvest when a thin crack can be seen encircling the stem end and the fruit comes away from the vine easily. This is called the “full slip” stage. Cantaloupes should be eaten as soon as possible after being harvested, as they tend to lose moisture more quickly than many other members of this family. If you end up with a bumper crop of melons, your best method of preservation is to try your hand at canning some preserves. Cantaloupe pairs nicely with peaches and nectarines. And be sure to save seeds for next year's crop!
The majority of the world’s cantaloupe crop is grown in China and shipped around the world. Believe me when I tell you that harvesting a fresh melon from your yard is a very satisfying and delicious experience.
And halved cantaloupes make lovely ice cream bowls...
What summer picnic would be complete without watermelon?
Sweet, refreshing, and adaptable, watermelon is another easy-to-grow addition to your foodscape.
Botanically, watermelon is a type of berry called a pepo. It is also a gourd. As a member of the cucurbit family, watermelons are cousin to cucumbers, squash, pumpkins, and other melons.
History of watermelon
Watermelons were cultivated 5,000 years ago, in Ancient Egypt. Watermelon seeds were even found in King Tut’s tomb! Watermelon ancestors were not the bright red, sweet fruits we know. In fact, the original watermelons tasted pretty awful. They were bitter and hard. People grew them anyway, because these melons could hold water for weeks and even months, if stored properly. [That’s how they got their name - get it?] Five thousand years ago, that was a really Big Deal. As plumbing became a thing, watermelons had to up their game. Over time, and with selective breeding, they became the sweet summer picnic favorites that we love.
How to grow watermelon
Watermelon plants (Citrullus lanatus var. lanatus) can take up some space. The 5-sided vines may reach 10 feet in length and the leaves are large. Plant watermelon seeds one inch deep in groups of 6 to 10 seeds. These seeds should be planted in ‘hills’ that are 3 to 4 feet apart. These hills are mounds of loose, rich soil two feet in diameter. Once seedlings emerge, save the best 3 and snip the others off at ground level. Mulch around the plants to reduce weeds and retain moisture. Individual watermelons can be grown in a container, but it should be large - at least 5 gallons. They can also be grown up trellising or on stock panels, but each melon will need a hammock.
In San Jose, California, it is best to plant watermelon in May and June, though seeds can be started two weeks after the last frost date. Seeds will not germinate at temperatures below 70°F. Row covers can be used over seedlings to protect them from pests and to retain some heat. Watermelons prefer a soil pH of 6.0 to 6.8. Watermelons do require a significant amount of water to produce fruit, but avoid getting the leaves wet to prevent fungal disease. If the leaves wilt in the afternoon, don’t worry about it. If they stay wilted into the evening, check moisture levels. Once fruit starts to appear, you will want to get it up off the ground with some straw. This reduces the chance of belly rot. Reduce watering just before your watermelons ripen to increase sugar levels and intensify the flavor.
Watermelon pests and diseases
Like most plants in the Bay Area, watermelon are likely to be attacked by aphids, cutworms, crickets and grasshoppers, armyworms, cabbage loopers, leaf-footed bugs, earwigs, flea beetles, leafhoppers, leafminers, nematodes, slugs and snails, thrips, whiteflies, and spider mites. As a cucurbit, watermelon is also subject to stinkbugs, cucumber beetles, and squash bugs. Many of these pests can be thwarted by dusting your melons with kaolin clay, a non-toxic fine powder that clogs up their breathing holes.
Diseases that can affect watermelon include damping off, powdery mildew, downy mildews, verticillium wilt, root rot, fusarium wilt, angular leafspot, curly top, and white mold. Nearly all of these diseases are related to overhead watering, so don’t do it. Most watermelon varieties are resistant to anthracnose, but seedless watermelons are not. Unlike other cucurbits, watermelon is not susceptible to cucumber mosaic and I have no idea why. Unsuitable environmental conditions can lead to blossom end rot, bitter fruit, blossom drop, and poor pollination.
One nice thing about growing watermelon is that you can plant the seeds in a raised bed, straw bale, or container, and then let the vine cover unplanted areas, or areas that are looking poorly. The large leaves shade the ground, stabilizing temperatures and making the soil more habitable for worms and beneficial soil microorganisms. Add a little mulch and you can be preparing that area for planting next season. Add a watermelon plant to your foodscape every summer and save the seeds for next year's crop!
What’s up with seedless watermelons?
Seedless watermelon production began in the 1990s. Seedless watermelons happen because plant breeders do two things:
The resulting offspring have 33 chromosome and are highly unlikely to have viable seeds.
Now you know.
Sweet, juicy melons are a gardening favorite. Easy to grow, productive and delicious, what’s not to love?
It just wouldn’t be summer without slicing through the hard outer rind of a melon and devouring the sweet, refreshing wetness within.
Melons are members of the Cucurbit family, along with pumpkins, squashes, and even luffas! Within the melon family, there are several different groupings (by genus) of some familiar, and some not so familiar, melons:
How melons grow
Like their cousins in the squash family, melons grow on vines. Unlike other vegetables crops, however, each vine has both male and female flowers. The male flowers generally appear first and usually only last for one day. Melon pollen is very sticky, so wind pollination does not occur. Honey bees are needed to carry the pollen from one flower to the next. If there are not enough honey bees in your area, you can use a fine paintbrush to transfer the sticky pollen to the female flowers, or you can break off a male flower, remove the petals, and apply the pollen that way. [I collect the pollen-carrying stamen for hand-pollinating, just in case.] Female flowers can be identified by the miniature fruit (ovary) at the base of each blossom.
How to grow melons
Melon seeds are big and easy to work with. In the Bay Area, melons can be planted in May and June. They really love hot weather. Prepare the planting area by digging compost into the soil and creating hills. Each hill should be approximately 4 feet square. Plant 3 to 5 seeds, one inch deep and two inches apart, into the middle of each hill. Water the area well. Once your seeds have sprouted and grown into seedlings with a few sets of leaves, snip the smallest plants off at ground level, rather than thinning by pulling them out. This lets the remaining plant’s roots and helpful soil microorganisms stay undisturbed. Melons need to be watered every 2 or 3 days during the peak of summer. Sometimes even more. Regular watering can help prevent the fruit from splitting open. Side dressing melon plants with aged compost during the growing season also improves both crop quantity and quality. Side dressing simply means putting compost next to the plants and watering all those yummy nutrients into the surrounding soil. Easy and effective.
You may want to add a layer of straw or sawdust under your melons, to get them up off the ground. This helps prevent rotten areas, and insect and fungal infestation. Melons can also be grown in containers, towers, or straw bales, and trellised. The fruit itself will need personal hammocks if you use a trellis. You can tell a melon is ready to harvest when you see a slight crack around the stem where it is attached to the fruit. This is called the “full slip” stage. Crenshaw, casaba, and some honeydew varieties do not develop a slip. Casaba and honeydew melons can be stored for several weeks, while other varieties are best eaten right away.
Troubleshooting melon problems
Melons are susceptible to the same problems as cucumber, pumpkin, and squash. Use the symptoms listed below to find (and solve) your melon problems!
Cutworms, wireworms, crickets and grasshoppers, various beetles, earwigs, stinkbugs, and thrips may also try getting into your delicious melons, so be vigilant! (A light dusting of diatomaceous earth might help, too.)
All too often, gardeners hear the myth that members of the Cucurbit family can cross-pollinate. This is simply not true. Pollination between different species does not occur. What can happen is two different types of melon can cross-pollinate. In fact, that’s how Crenshaw melons came about - Persian melons were crossed with casabas.
As you prepare to start growing your own melons, be sure to Plant It Forward with any leftover seeds!
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 pluck an orange from a tree and a tiny white insect flies out from under a leaf. On the underside of that leaf is a strange white spiral. You have discovered whiteflies.
Whiteflies are not related to flies at all. Instead, they are close cousins to aphids, mealybugs, soft scale and armored scale. These pests cause billions of dollars in plant damage each year, sucking the sap from 500 different plant species, including your cabbage, cucumbers, eggplant, melon, squash, and tomatoes.
Whiteflies got their name because most of them look like tiny white flies. Adult bodies are actually yellow or black, but they are hard to see. Whiteflies have 4 white wings and are often no bigger than 1 mm, which means you could stand 14 of them, end to end, across an American dime.
There are more than 1500 whitefly species, worldwide. In California, we have 10 whitefly species that cause problems in the garden:
Whiteflies are quick and difficult to see. It is easier to tell if a garden is infested with whiteflies if you see white spirals on the underside of leaves. These spirals are whitefly eggs.
Adult females walk a spiral path, laying eggs in a waxy trail that holds the eggs to the leaf. In warmer parts of California, whiteflies can breed year-round. Whiteflies can reproduce at mind-boggling rates. They go through four developmental stages, or instars. Eggs hatch out as nymphs, called crawlers. The next three stages are nearly immobile, much like scale insects. The final instar is a pupal stage.
At each stage, these pests use piercing mouthparts to suck sap from the phloem of a wide variety of garden edibles and ornamentals, causing leaf drop and a general failure to thrive. The honeydew (sugary poop) left behind is host to sooty mold. Honeydew also attracts ants, which then protect whiteflies from their natural enemies. Some whitefly larva may transmit viral diseases, such as cucurbit yellow stunting disorder and tomato yellow leaf curl. Also, adults can carry other pathogens. Low whitefly populations are not a significant problem, but they can make trees look shabby.
Heavy whitefly populations are very difficult to control. Any leaves with whitefly eggs should be removed and discarded. If the leaf looks particularly healthy, you can simply rub your thumb over the eggs to destroy them. Reflective mulches repel adult whiteflies, aphids, and leafhoppers. Also, yellow sticky traps can be used to trap and monitor whitefly populations.
Natural predators, such as minute pirate bugs, green lacewings, big-eyed bugs, and hummingbirds are the best defense against whitefly infestations. You can attract these garden helpers by planting zinnias, bee balm, hummingbird bush and pineapple sage.
Whitefly population explosions are often created when gardeners apply broad-spectrum pesticides that kill off beneficial predators, or when ants are allowed free access to host trees. Ants can be prevented from protecting whiteflies by applying a sticky barrier around the trunk. Dusty conditions can also put the odds in favor of whiteflies. Washing off dusty plants with a garden hose can help reduce whitefly populations.
According to companion planting lore, whiteflies can be discouraged from an area by planting basil, mint, thyme, and nasturtium. I don’t know if that works, but those plants are nice to have, in any case.
You may be surprised to learn, as I was, that plants release chemical compounds when bitten by insects or herbivores. These chemicals communicate with nearby plants, telling them to start protecting themselves against specific threats. These chemical messages also alert parasitic wasps and other beneficial insects, calling in the troops to protect the plant.
Researchers have recently learned that silverleaf whiteflies have developed the ability to flip this self-defense mechanism to their advantage. It works like this. Whiteflies are known to carry viruses. When a whitefly bites a plant, the plants used to defend themselves against the whiteflies. Now, they work harder to defend themselves against potential viral infection and create a more suitable whitefly habitat. This misinformation spreads to nearby plants, creating a cascade effect that can be very difficult to manage.
It’s a war zone out there!
Mites are tiny spiders that suck the living juices from nearly a thousand different garden plants. Being closely related to ticks, some varieties of mites also suck blood from mammals, like us! The study of mites and ticks is called acarology.
Mites prefer soil that is high in organic content with plenty of moisture. Unfortunately, that describes nearly all of our container plants and many of the microclimates found in Bay Area gardens. A highly adaptable critter, there are over 42,000 species of mites worldwide. Aside from nest mites, dust mites, varroa mites, and many others that attack birds, animals, and bees, respectively, common garden mites include gall mites, spider mites, and thread-footed mites.
Spider mites get their name because they build protective webs around eggs and feeding areas. The most common spider mites in the Bay Area are the two-spotted spider mite, the strawberry spider mite and the Pacific spider mite. They are often found on the underside of leaves, where they pierce plant cells to feed. These mites are very small, usually less than 1 mm (0.04”) long, so they are all too easy to overlook until the damage becomes significant. It doesn’t take long for a population to develop, either. A single female can lay 20 eggs a day and live for up to 4 weeks. Since each offspring hatches within 3 days and becomes sexually active in only 5 days, a single, fertilized female and her offspring can produce millions of spider mites in a single season!
An interesting note: female spider mites have two sets of chromosomes, like we do, but males only have one. If an egg is fertilized, it will hatch female. If it is not fertilized, it will hatch as a male. Also, female spider mites are able to “decide” whether to lay male or female eggs, depending upon environmental conditions. To control spider mites, insecticidal soap is your best bet. Neem oil can also help. If chemical pesticides are used, repeated applications will be necessary (and progressively ineffective, as mites can develop resistance).
Most thread-footed mites, also known as white mites, feed on fungi and algae, a few varieties have evolved to attack leaves. Specifically, the cyclamen mite and the broad mite are able to inject toxins that thin the cell walls of mature leaves. Damaged leaves display puckering, twisting and stunting.
The only known effective chemical pesticides against mite infestations are endosulfan, dicol, and ethyl bromide fumigation. Endosulfan was globally banned due to its toxicity to humans and its ability to accumulate in an environment, Dicol is considered a “moderately hazardous” pesticide, closely related to DDT, and the state of California classified ethyl bromide as carcinogenic and a reproductive toxin - not anything you want to be spraying on food plants.
Broad spectrum pesticides do more harm than good because they also kill beneficial insects that feed on mites. You can buy predatory mites that help control mite infestations. If an infestation is discovered, sprays of water can be used to displace mites and make life harder for them. Garlic extract and oil of clove, rosemary, cinnamon, mint and others can also be effective. These natural treatments can be dangerous to plants, however, so use them carefully. The same goes for sulfur, especially on cucurbits. Observation and prevention are far easier than eradication.
One of the easiest ways to avoid mite infestations is to create a quarantine area for new plants. This protects established plants from new infestations and gives you the time needed to see if a new plant is carrying any pests or diseases. Also, proper irrigation reduces water stress in established plants, making them better able to protect themselves. Mites prefer dusty conditions, so keeping garden paths, trees, shrubs and other areas clean can significantly discourage mites. Encouraging beneficial insects, such as lady beetles, lacewing, and pirate bugs, by providing water and habitat, can significantly reduce mite populations without the use of pesticides or sprays.
Cucurbits are members of the squash family.
This family is a thick-skinned group that grows on vines and keeps its seeds in a line down the center of their fruit. The squash, or cucurbit, family is made up of cucumbers, gourds, luffas, melons, pumpkins, squash, watermelons, and the inevitable zucchini. These plants love hot weather and many of them have protective bristles.
Most of the 975 cucurbit species are susceptible to frost and many are trailing annual vines with tendrils. They tend to have large bristle-haired leaves and both male and female flowers (monoecious).
Cucurbits have relatively large seeds and they do not transplant well after the first 3 weeks. It is best to directly sow seeds in the ground. As a group, cucurbits grow fast. They need very little nitrogen, but they use a lot of potassium and phosphorus. Side dressing plants with aged compost goes a long way toward creating a big harvest.
Cucurbits prefer full sun and deep, infrequent watering. During the hottest days of summer, it is a good idea to keep an eye out for wilting leaves, a sure sign that you waited too long to water!
These semi-climbing plants benefit from the use of trellises, stock panels, or ladders. Heavier fruits can be supported using hammocks or net bags. This keeps the fruit off the ground, preventing fungal disease, rot, and pest damage.
Cucurbit pests and diseases
Regularly watering in the early morning allows cucurbit leaves to dry out before evening, preventing powdery mildew and other fungal diseases. Because of the wide leaf coverage of most cucurbits, weeds are seldom a problem. Cucurbits are frequently attacked by cucumber beetles, flea beetles, squash vine borers, and squash bugs, so squash those bugs whenever you see them!
Be sure to harvest fruits regularly, to ensure continuous production. Once plants believe they have completed their reproductive cycle, you generally won't get any more fruit.
Yesterday, I curb-scored 8 very nice tomato cages. While they come in a variety of sizes and shapes, the most common type are concentric circles held at different heights, usually with three legs.
You can grow a surprising amount of food in your own yard. Ask me how!