Cavitation is the sound of water breaking.
While we don’t normally think of water being able to “break”, the columns of water that move upward through a tree’s veins can be broken, allowing air bubbles to form or simply severing a pathway for life-giving water.
Trees use a lot of water
The general rule of thumb for how much water a tree needs each week of summer is 10 gallons of water for every inch of trunk diameter, as measured at knee height. This means a large, mature tree, with a trunk diameter of 18”, will need 180 gallons of water every week at the peak of summer, on average. The flow of that water is critical to a tree’s health.
In healthy trees, water is absorbed through the roots and pulled upward through tubes called xylem. There are thousands of xylem in a mature tree. Picture the xylem as straws that run the vertical length of a tree. Water moves through xylem in a process called transpiration.
Transpiration refers to the way negative pressure is created within xylem as water evaporates from the surface of the leaves. This occurs because of surface tension, or the tendency of water molecules to stick together. When one water molecule leaves the plant through evaporation, lower water molecules are pulled upward.
Bubbles can be bad
Bubbles might be fun to play with, but bubbles in veins are bad. Just as air bubbles in an IV tube can kill you, so, too, can bubbles block the flow of life-giving water for a tree. Rapid transpiration can cause air bubbles to form in xylem. If too many air bubbles remain in place, it can kill a tree. Cavitation is much like an embolism for trees. Small, infrequent bubbles are not a serious problem. Large, fixed bubbles are deadly.
During periods of drought, the rate of evaporation on the surface of the leaves is so great that xylem can collapse and break, like a rope pulled too tautly. These breaks halt the flow of water completely, also killing a tree. Cavitation also occurs in response to thawing after water within a tree has frozen.
The sound of silence
If you could hear higher frequencies, it would sound similar to popcorn popping. In most cases, the frequency of this sound is too high for us to hear, but it can, occasionally, be heard. [It might be fun to try using a stethoscope on a tree…] I can only imagine that our peaceful summer walks in the woods sound more like a riot of trees screaming for water to our dogs…
Bottom line: make sure you irrigate your trees properly to keep them healthy, especially during summer.
Has a largish beetle with stripes ever hissed at you? It was probably a ten-lined June beetle. Ten-lined June beetles (Polyphylla decemlineata), also known as watermelon beetles, can kill mature trees outright.
Ten-lined June beetle description
The stripes are a giveaway for this relatively large beetle. Averaging 1.5 inches or longer, male ten-lined June beetles have distinctive antennae made up of overlapping scales, called lamellate plates. When these pests feel threatened, those plates are closed up and air is forced between the back and wings to create a hissing sound. Adult females do not fly. Eggs are 1/16" long, oval and cream-colored. Larvae have a white body and a brown head. They can grow to 2” in length with 3 pairs of legs.
Damage caused by ten-lined June beetles
Almond, apple, cherry, and plum trees are susceptible to damage caused by larval feeding of ten-lined June beetles. Trees may simply not thrive, at first. By the time the damage is significant, it is usually too late to save the tree. Adult ten-lined beetles feed on leaves, but that damage is insignificant.
Ten-lined June beetle lifecycle
Ten-lined June beetles are relatively long-lived insects. It takes 2 years to complete one generation of ten-lined June beetles. They can exist in the larval stage for up to 4 years. Larvae are found in the top 14” of soil where they feed on roots. Each summer and early autumn, adult females emerge from the soil and release pheromones to attracts males. Males fly from dusk until midnight or so. After mating, the females return to the soil where they lay eggs.
Ten-lined June beetle controls
Heavily infested trees must be removed and the surrounding soil fumigated to prevent infestation of nearby trees. Luckily, that is rarely necessary in a home garden. Because female ten-lined beetles do not fly, populations spread slowly. Commercial growers use soil insecticides to kill beetles in the larval stage. Aboveground insecticides are not effective.
Tachinid flies parasitize these pests, but not significantly. Because male ten-lined June beetles are attracted to light, you can capture them on your porch with a butterfly net and feed them to your chickens, or simply squish them whenever you see them.
Bulb mites, also known as spinach crown mites, refer to a small collection of very tiny pests that can damage your onions, garlic, saffron crocus, and spinach plants.
Bulb mite description
Bulb mites are a collection of pests from the Rhizoglyphus and Tyrophagus genus and they look like miniature ticks with spiky hairs. These pests may be tiny, but they can cause significant damage. Ranging in size from 1/2 to 1 mm long, you could 15 to 30 or more of them nose-to-tail across a dime. If you were to look at one with a magnifying glass, you would see that they are a shiny, creamy white, with four pairs of brown legs.
Bulb mite host plants
As the name implies, bulb mites infest bulbs, such as tulips, daffodils, and saffron crocus. They can also be found under the root plate of garlic and onion, or in the crown of spinach plants.
Damage caused by bud mites
Bud mite feeding is not particularly destructive by itself. The problem lies in the wounds created by that feeding. These damaged areas allow organisms responsible for decomposition to get inside your plants, causing them to rot. Overall stunting, leaf distortion, and softened stems are common responses to bud mite feeding.
How to manage bulb mites
Protect your bulbs against bulb mites by inspecting them before planting. Infested bulbs should be destroyed. Crop rotation and the removal of post-harvest plant debris can interrupt this pest’s lifecycle.
If you grow red raspberries, you need to monitor leaves early in the season for yellow rust.
Like its cousin, the bright orange rust seen on the underside of rose leaves, yellow rust is a fungal disease. Unlike many other fungal diseases, this rust only occurs on the outside of plants. This is not the same yellow rust seen on wheat, rye, and barley, which is called stripe rust. Stripe rust is caused by Puccinia striiformis.
Symptoms of yellow rust
Plants infected with yellow rust (Phragmidium rubi-idaei) will initially have yellow pustules, called aecia, on the tops of the lower leaves. These symptoms are usually only seen in spring and early summer. In early to mid-summer, yellow to orange pustules, called uredinia, are found on the underside of leaves. As summer progresses, these growths darken and a black spot can be seen in the middle, if you look closely. You may also see orange spots on the fruit. Similar infections that occur later in the season may be late leaf rust (Pucciniastrum americanum), or the more severe orange rust (Arthuriomyces peckianus). In any case, infected leaves wither and die, reducing the plant's ability to perform photosynthesis. This can reduce crop size significantly.
Yellow rust control
Pruning for good air flow helps leaves and stems dry out, making life more difficult for this fungi. Since yellow rust spores (teliospores) overwinter in fruiting canes, or floricanes, pruning those canes out at the end of the growing season can break this disease triangle. The canes of summer-bearing raspberries won’t produce any more fruit anyway, so you might as well. Just be sure to dispose of the trimmed canes in the trash, and not the compost pile.
Left in place, these spores then spread the infection to the next season’s primocanes, or vegetative growth. Also, keep the area around the plants clear of dead leaves and other plant debris. If your raspberries are especially prone to yellow rust, you may want to cut the first spring growth of new canes back to ground level. Don’t worry, the root system will put out new canes pretty quickly. That first growth is the most likely to have become infected.
Fixed copper sprays and lime sulfur are recommended for severe outbreaks. Otherwise, you can simply remove infected leaves by hand and improve the air flow between plants to keep this disease in check and protect your delicious raspberries.
Resistant varieties are available, so check with your local Department of Agriculture or Master Gardeners for recommendations for your area.
If you grow peas or lentils, you should know about pea seed-borne mosaic. The same is true for fava beans and chickpeas.
[Sadly, I was unable to find any freely available photos of pea seed-borne mosaic, so you will have to go by the description or search for your own images. The purple-podded peas pictured above are perfectly healthy.]
Symptoms of pea seed-borne mosaic
Stunting, deformation, and rosette-type growths at the ends of stems are all signs of pea seed-borne mosaic. Chlorosis, downward cupping, vein clearing and swelling, and the classic mosaic or mottling of mosaic diseases may all be present in infected plants. Vein clearing is a common symptom of viral infections and it refers to the way leaf veins appear translucent. Seeds tend to be shriveled and discolored. Infected plants are slow to reach maturity, but don’t leave them in the ground long enough to notice. Pea seed-borne mosaic infection is easily mistaken for chemical overspray, nutrient toxicities, and water-stress. Laboratory tests are needed to be sure of infection. You can often take zip-lock bagged samples to your local Department of Agriculture for analysis.
How to control pea seed-borne mosaic
The pea seed-borne mosaic virus (PSbMV) is carried to your garden on aphids. I would tell you to control the aphids, but that is an ongoing battle in the garden. Do the best that you can. Plants infected with pea seed-borne mosaic should be removed immediately. Unfortunately, some infected plants will never show symptoms. As aphids feed on these asymptomatic plants, they then carry the disease to nearby plants, spreading infection. For the most part, as the name implies, this viral disease is carried by infected seeds. Plant infected seeds and the aphids do the rest. To prevent pea seed-borne mosaic from occurring in your garden, only buy clean, disease-free seeds.
This disease can overwinter in nearby weeds, such as shepherd’s purse, vetches, and black medic. It can also be carried on alfalfa and sugar beets without causing the host plants any problems. If you notice outbreaks of pea seed-borne mosaic, and you know your seeds were clean, look at what is growing nearby.
You can prevent pea seed-borne mosaic by planting resistant varieties.
Fig trees can be stately and highly productive, but fig mosaic can take a toll on your fig tree. Fig mosaic is a complex of several, as yet unidentified, viral diseases that all infect Ficus subspecies.
Fig mosaic symptoms
Yellow leaf mosaic patterns are a common symptom of fig mosaic. These patterns are brighter yellow toward the center of each spot, fading to light yellow before reaching the healthy green leaf tissue. As the condition progresses, a rust-colored band appears around the edge of each mosaic spot. Leaves may also be deformed. Infected fruit shows mild mosaic patterning but may be smaller and less abundant than on healthy trees. Most often, fig mosaic causes early fruit drop, all but eliminating your crop.
How fig mosaic is spread
Fig mosaic is spread by eriophyid mites. As the mites feed, the virus is transmitted through their saliva. Fig mosaic can also be spread by grafting and cuttings.
Fig mosaic management
Trees take time to grow, so having to remove an infected tree is best avoided. Begin by only installing disease-free tree and planting them at the proper depth, giving them the irrigation and food they need to stay healthy. Monitor your fig trees for sign of mite feeding. You will need a 20x hand lens to see these tiny sap-suckers. Fig mite feeding is usually seen around bud scales and young leaves and it often causes a faint russetting. Twig stunting and leaf drop may also occur.
Sulfur treatments and horticultural oils have been shown to control fig mites.
Go take a look at your fig tree to see if mites might be present. If they are, get rid of them so that you can enjoy many years of sweet, delicious figs.
Beetles among your squashes and melons is never a good thing, especially when they carry the squash mosaic virus.
Squash mosaic is second only to cucumber mosaic in damage to cucurbits caused by disease. There are two strains of squash mosaic, strain 1 affects melons most often, while strain 2 prefers squash. In either case, your crop will be lumpy, discolored, and significantly reduced, but still edible.
Crops vulnerable to squash mosaic
All cucurbits are susceptible to squash mosaic. This includes your zucchini and other summer squashes, melons, gourds, cucumbers, and pumpkins. Watermelons, however, are not susceptible to squash mosaic. Some legumes and umbellifers can also become infected with squash mosaic.
Squash mosaic symptoms
Squash mosaic causes a dark green mottling or mosaic pattern on leaves, as well as blistering, yellowing (chlorosis), leaf hardening and distortion, and vein clearing. Vein clearing is a common symptom of viral disease and it refers to the way leaf veins become almost translucent while the rest of the leaf remains green.
Squash mosaic carriers
Unlike other mosaic diseases, squash mosaic is not spread by aphids. Instead, striped and spotted cucumber beetles, leaf beetles, and 28-spotted ladybird beetles are the most common vectors of squash mosaic. Many other beetles are also capable of hosting the virus. As these insects feed, their saliva transfers the virus to the plant. This is why it is so important to remove infected plants right away.
Squash mosaic controls
In addition to removing infected plants, beetle control is important in the prevention of squash mosaic. And beetles can be tough to control. The virus can stay viable inside a beetle for up to 20 days, so it is worth the effort. A single beetle can infect dozens of plants in that time frame. To control beetles, handpicking is always an option, if you are quick enough. You can also use neem oil to kill beetle eggs. Encouraging beneficial predators, such as ladybugs, mantids, and solider bugs, in the garden with fresh water, insectary plants, and little or no chemical use is probably the easiest method of keeping beetle populations within reasonable limits.
Squash mosaic can also be carried on melon seeds, so be sure to get clean, disease-resistant seeds from a reputable supplier (and not that melon from the grocery store).
Certain chenopod weeds, including lambsquarters, goosefoot, Russian thistle, and kochia, provide overwintering sites, so keep these weeds away from your cucurbits.
As with many other viruses, tools, clothing, and other surfaces can also become carriers. To prevent the spread of this disease, sanitize tools regularly and avoid working around plants while they are wet.
Warty zucchinis with skinny leaves may mean the zucchini yellow mosaic virus has infected your plants.
No garden would be complete without the versatile, fast-growing zucchini. A favorite in stir-fry, breads, and the ever popular chocolate zucchini cake, zucchini can be very productive plant, as long as it stays healthy.
Zucchini yellow mosaic symptoms
Whitened leaf veins, mottled, abnormally small leaves with alternating light and dark areas, and deformed, warty fruit are all signs of zucchini yellow mosaic. These are also symptoms of watermelon mosaic and papaya ringspot virus, two viral diseases that often occur at the same time as zucchini yellow mosaic. Watermelon mosaic infections tend to include blistered leaves, while zucchini yellow mosaic has the added symptom of leaf lobes becoming long and narrow, creating a ‘shoestring’ or ferny appearance.
Zucchini yellow mosaic host plants
In addition to infecting zucchini, zucchini yellow mosaic also infects other members of the cucurbit family, including melons, squash, pumpkins, some gourds, cucumbers, cantaloupe, and watermelon. The disease is transmitted by aphids.
Zucchini yellow mosaic management
As anyone who gardens knows, controlling aphids is difficult. These pests seem to appear overnight, in huge numbers. And all it takes is one aphid to get the whole process started. Unfortunately, insecticides are rarely useful in managing zucchini yellow mosaic, because the disease has often been transmitted before you even know the aphids are there. Reflective mulches can be used to discourage aphids, just be sure to remove the reflective material before it gets too hot. Row covers can also be used to reduce access to susceptible plants.
This disease can also be spread on infected garden tools and seeds, so be sure to sanitize your tools regularly and get your seeds from a reputable source (and not that zucchini from the grocery store).
Infected plants should be destroyed and replaced with resistant cultivars.
Since this virus is only viable for a few hours within their aphid carriers, creating a physical barrier of tall, non-host plants around your cucurbits can be enough to prevent the aphids from getting to the plants while the virus is still active.
Speckled, mottled, or otherwise deformed leaves and fruit usually indicate a mosaic disease.
Mosaic diseases are caused by a variety of viruses that can infect the majority of your garden plants. Since these diseases are difficult or impossible to treat, recognizing and removing infected plants right away can help prevent the disease from spreading.
Symptoms of mosaic diseases
The classic mottled appearance of infected leaves is only one symptom of mosaic disease. Leaf cupping, blistering, stunting, crinkling, and other distortions are also common symptoms of mosaic disease. Stems may be shortened, creating a bushy appearance to vines.
Plants infected early in the growing season rarely produce fruit. Interestingly, plants infected later in the season retain their healthy, earlier growth and fruit production, while future growth is distorted. Fruit may also show the same mottling and other distortions seen on leaves. Warty bumps are common.
Plants that host mosaic diseases
It would be easier to list plants that are not affected by mosaic disease. Plants commonly infected with mosaic diseases include:
Common mosaic diseases
While there are dozens (hundreds?) of mosaic diseases, some of the more common varieties include:
Mosaic disease management
Generally speaking, mosaic diseases are not curable. Infected plants should be removed. This means that prevention is a far better course of action.
Depending on the specific virus, it may be carried in to your garden on seeds or tools, or by aphids, dryberry mites, and any number of other sap-sucking pests. Removing weeds that could provide overwintering sites, creating physical barriers with row covers and walls of non-host plants, and regularly sanitizing your tools goes a long way toward preventing mosaic disease from taking hold in your garden, as does buying clean, disease-resistant seeds and plants from reputable suppliers.
While mosaic diseases make plants look funny, the fruit of infected plants is still safe to eat. The viruses responsible for mosaic diseases are not harmful to people.
Growing your own corn makes a dramatic statement in the garden. Reaching 10 to 12 feet in height, modern corn plants grow in tandem with other giants, such as sunflowers and hollyhocks. Unless they become infected with corn stunt.
Corn stunt does not mean ears of corn will suddenly start doing gymnastics over the fence into your neighbor’s yard. Instead, this bacterial disease will infect the phloem of corn plants, reducing them in size and all but eliminating kernel production.
Corn stunt disease complex
Some people see corn stunt as a single disease, while others see it as one part of a complex of three disease, the other two being maize bushy stunt mycoplasma and maize rayado fino virus (MRFV). Yet others include maize chlorotic dwarf virus in the corn stunt complex. Any combination of these diseases can be devastating to your corn crop.
Corn stunt symptoms
Healthy corn plants produce one or two ears of corn, depending on whether they are early or late maturing varieties, respectively. Plants infected with corn stunt are significantly shorter than normal, often only 5 feet tall, and may produce 6 or 7 ears. That may sound great, but it’s not. These ears are small and they do not fill properly, meaning there ends up being a lot of empty spaces. The kernels that do develop are not well attached, in a condition known as “loose tooth ears”. Infected plants will also exhibit pale yellow new leaves at the top. As these leaves mature, they tend to turn reddish.
How corn stunt spreads
Corn stunt is caused by Spiroplasma kunkeliiI, which is carried by leafhoppers. Corn leafhoppers (Dalbulus maidis), in particular, carry this disease with them, spreading it as they feed.
Corn stunt management
You can prevent corn stunt by using reflective mulches that deter leafhoppers. Planting your corn as early as possible in the growing season has been shown to reduce the impact of corn stunt infections. Apparently, the first generation of emerging bacterium are not as effective at spreading the disease as those that occur later in the season. Insecticides are generally not effective.
You don't have to grow corn to have a reason to worry about seed corn maggots.
Seed corn maggots mostly feed on decaying organic material, but sometimes they feed on the roots and seeds of over 50 different garden plants. Also known as the bean seed fly, seed corn maggots may be tiny, but they can ruin several of your crops.
Seed corn maggot description
Seed corn maggots (Delia platura) are small, dark grey flies with grey wings, black legs, three stripes on the back, and scattered bristles. Less than 1/4” long, seed corn maggot adults looks nearly identical to onion maggot flies. White or off-white larvae are legless and have rounded tails and pointed heads. Pupal cases are brown and hard and look like skinny footballs.
Seed corn maggot damage
Seed corn maggots often feed on the seeds of corn, peas, beans, and soybeans but they do not always kill the embryos within the seeds. When those seeds germinate, they are spindly and rarely make it to maturity, wasting valuable resources. Other crops commonly attacked by seed corn maggots include cucumbers, melons, onions, peppers, and potatoes.
Seed corn maggots may tunnel into the stems and roots of many different garden plants and feed on spinach leaves, often providing points of entry for other pests and diseases.
Seed corn maggot lifecycle
Adult flies emerge in spring and begin feeding on nectar and honeydew. After mating, females lay an average of 270 eggs in the soil, near the surface. One week later, larvae emerge and begin feeding. One to three weeks later, larvae move back into the soil where they pupate for one to three weeks, or over the winter.
How to control corn seed maggots
The key to controlling corn seed maggots is in the soil. While I am a proponent of no-dig gardening, repeated appearances of corn seed maggots warrants disturbing the top 2 or 3 inches of soil on a regular basis during the spring and summer months. Research is being conducted on the possibility of beneficial fungi being used to control these pests, but it is not currently an option.
As is nearly always the case, prevention is far easier. You can reduce the odds of seed corn maggots attacking your crops by waiting for the weather to warm up before planting, and spacing plants properly. Anything that slows germination or initial seedling growth makes it easier for seed corn maggots.
Juicy, sweet kernels of corn transform, overnight, into hideous, purple-grey, tumors. And these tumorous galls are delicious!
Introducing, corn smut.
Now, corn has many pests and diseases: corn earworms, European corn borers, seed-corn maggots, soft rot, seed rot, fusarium root and ear rot, maize dwarf mosaic, pythium stalk rot, and damping-off disease, just to name a few. If you are an American corn farmer, corn smut is not what you want to see in your field. A lot of money and effort have gone into eradicating corn smut in North America.
Corn smut in your garden is something else entirely.
While this distant cousin of mushrooms reduces crop size and makes ears of corn unmarketable for July picnics and canning purposes, it is edible and delicious. Unlike other corn problems, corn smut is said to taste like truffles, with a sweet, earthy, inky flavor. If it appears in your garden and you don’t want it, your local chef would love to hear from you!
To my way of thinking, if life gives you lemons, make lemonade. Or, if you are given corn smut, make quesadillas! Corn smut can be eaten raw, or added to many dishes, such as omelets, soups, sauces, meat dishes, or even desserts! As an extra bonus, corn smut is high in lysine. This means eating it with corn, or any other seed, provides a complete dietary protein.
Corn smut description
Also known as devil’s corn, common smut, boil smut, Mexican truffles, or huitlacoche [pronounced weet-la-COH-cheh], corn smut is a parasitic fungus that can occur on any aboveground portion of a corn plant as purplish blobs covered with papery greenish-white tissue. These fungi prefer meristem tissue and the galls are mostly seen on the ears of corn. Ear galls are significantly larger than those which form elsewhere on the corn plant.
Corn smut gets its purple color from pigments called anthocyanins. These are the same pigments found in blueberries, raspberries, and purple cauliflower. When you cook with corn smut, don’t be surprised to see the purple color change to black, because it will. Purple pigments generally don’t hold up well to heat.
Corn smut lifecycle
The corn smut fungus (Ustilago maydis) infects plant ovaries, causing kernels to swell up into large purple galls that are filled with fungal threads, called hyphae, and spores. Corn smut spores are already in the soil and can be carried on the slightest breeze or splashed water from rain or irrigation. Dry conditions and temperatures between 78°F and 93°F are all that corn smut needs to get started. Adding nitrogen or applying manure increases the chance of corn smut developing on your corn plants. Plant injuries also increase infection rates.
Corn plants try to defend themselves against corn smut by blasting the invaders with reactive oxygen (hydrogen peroxide). Sadly, from the corn plant’s perspective, this bubbling action simply spreads the smut spores.
If smut appears on your corn, fear not! Instead, harvest the galls while they are young and have the texture of a foamy popcorn, kind of firm and spongy. These moist galls are ready for harvesting 2 or 3 weeks after infection appears. As the galls mature, they turn dry and are mostly filled with unappetizing dry, black fungal spores.
Love it or hate it, corn smut is here to stay, so you may as well learn to cook with it (or sell it).
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.
You can grow a surprising amount of food in your own yard. Ask me how!