Garden Word of the Day
Take $5 off planting calendars from Forging Time with the code DAILYGARDEN841. This is an excellent resource with some amazing photos.
Pseudomonas [soo-doh-MO-nas] is a genus of bacteria that most of us gardeners end up fighting.
These bacteria reside in plant debris, soil, and water. They also hide out in many dicot seeds. But don’t worry, Pseudomonas only infects plants with leaves and stems. The rest of your garden is safe. *wink*
Pseudomonas plant pathogens
Scientists have sequenced the DNA of more than 500 strains of Pseudomonas. Here is a list of the most common bacterial diseases caused by Pseudomonas:
Nearly all these diseases feature small dark spots that expand into odd-shaped dead areas. It’s all downhill from there.
These are some tough SOBs. They have evolved to survive rugged conditions. Their cell walls are equipped with pumps that eject antibiotics and other unwanted materials before they can do anything, so chemicals are often ineffective. Because of this, prevention is your best management tool. Spacing plants far enough apart so they dry off rapidly is the best prevention. And avoid overhead watering.
Pseudomonas isn’t all bad
As handy as it would be to say that all Pseudomonas are trouble, it ends up that some of these soil bacteria help plants stay healthy. They practically make life possible on Earth. Life sure is messy.
Some Pseudomonas protect plant roots against disease-causing Fusarium fungi and Pythium oomycetes. They also protect against plant-eating nematodes. Another strain helps activate disease resistance within wheat and other cereal crops. Some Pseudomonas can metabolize pollutants and are part of bioremediation efforts.
Finally, Pseudomonas are responsible for most snowflakes and raindrops that fall on Earth.
Now you know.
If you grow apples, cherries, kiwifruit, mulberries, nectarines, peaches, pears, plums, or walnuts, you need to know about bacterial blight.
Bacterial blight is not the same thing as common bacterial blight, which attacks legumes. To make matters worse, many people call another bean variety of blight ‘bacterial blight’. I know, it gets confusing. Let’s see if we can clarify some of this.
The cause of bacterial blight
Bacterial blight, also known as blossom blight or shoot blight, is caused by a bacterium called Pseudomonas syringae. There are over 50 different strains of this bacteria that cause plant disease. Common examples include bacterial canker, bacterial speck, citrus blast, and halo blight. Pseudomonas syringae is commonly found on the exterior surfaces of healthy plants. It is only when bacteria get inside, through wounds or natural openings, that the trouble starts.
Bacterial blight symptoms
Like the other diseases caused by this pathogen, the first symptom is water-soaked areas on leaves. These areas turn brown and mushy and often have yellow halos. If these spots occur early in a leaf’s development, leaf curling and twisting may also occur. Leaves may also start dying from the outer edge, with the infection moving inward toward the center. Twigs may exhibit black streaks, and it is common for infected blossoms, branch tips, and leaves to die. If infected twigs develop a shepherd’s crook shape, it’s probably fireblight.
Managing bacterial blight
Pseudomonas syringae is most commonly spread by wind and rain. Insects and your garden tools can also be part of the problem. You have to assume that the disease is present. These bacteria can survive in diseased plants, infected plant debris, and soil.
Once a plant is infected, you can try to save it by trimming 10 to 12 inches below infected areas, making sure to disinfect your pruners between each cut. You can dip them in a 10% bleach solution for 30 seconds, though bleach is hard on tools. You can also use bathroom cleaner or other spray disinfectants that contain at least 70% alcohol. Just be sure to give it a few minutes to work before making another cut. Infected plant material should be bagged and thrown in the trash right away.
Prevention is easier. To prevent bacterial blight from taking hold in your landscape, use these tips:
Fixed copper sprays may also help.
Also known as cherry X disease, peach X disease, and cherry buckskin disease, X disease makes fruit small, pale, and bitter. It can affect stone fruits, such as apricots and cherries. Once a tree is infected with X disease, it must be removed to prevent the infection from spreading to other trees.
What causes X disease?
X disease is caused by phytoplasma. Phytoplasmas are microscopic, one-celled bacteria that have no cell walls or nuclei. To me, that’s just weird. Animal and plant cells and most bacteria have clearly defined cell walls that hold their insides in, where they belong, and a central nucleus that runs the show. I have a hard time wrapping my brain around these phytoplasmas. Maybe they are like parasitic amoebas, even though amoebas are animals. But I digress.
So how does a cell with no wings, legs, feet, or brain find its way to our fruit trees?
The answer is phoresy. Phoresy describes the relationship between two organisms in which one player is a hitchhiker but not a parasite. There are some pretty bizarre examples of phoresy. You may want to check it out.
Phytoplasmas catch rides inside sap-sucking leafhoppers, planthoppers, and psyllids without harming their hosts. When a cherry leafhopper feeds on an infected plant, the phytoplasma responsible for X disease is sucked into the insect’s gut with the sugary sap. When that vector moves to an uninfected plant and begins feeding, the pathogen is transferred to the new plant, causing infection.
What does X disease look like?
This disease can take up to 9 months to appear after infection occurs. Eventually, trees infected with X disease produce pale fruit that is small and leathery. Symptoms are commonly seen on only one branch at first. The leaves on infected branches may appear bronzed and small. Older leaves tend to fall off. Beyond that, symptoms can vary, depending on the tree species.
X disease is often mistaken for root rot. To figure out which it is, look closely at the graft union. That’s where the rootstock was grafted onto the fruiting stock. Pits and grooves are visible near the graft union if it is X disease. Cut into the wood and see brown areas in the phloem. These other symptoms of X disease are also common:
The fruit from infected trees tends to be pale, pointed, small, and nasty.
X disease hosts
There are two types of X disease hosts: those that don’t mind the infection (reservoir hosts) and those who succumb to the disease (non-reservoir hosts). Reservoir hosts are a problem because they look perfectly healthy but provide a source of infection to many important fruit and nut trees in our landscapes. Almond trees, chokecherries, sweet and sour cherries, Japanese plums, clovers, and dandelions are all reservoir hosts. [Dandelions?!!? Yes, dandelions.]
Nectarines and peaches can also become infected with X disease but are non-reservoir hosts. This means that they can catch the disease but not spread it. Scientists don’t yet understand how that happens, but they’re working on it.
X disease management
Since scientists have been unable to reproduce the phytoplasmas responsible for this disease in the lab, there are currently no treatments for this fatal disease. To reduce the likelihood of X disease occurring in your landscape, do your best to manage the insect pests responsible for carrying the pathogen.
The insects that spread X disease are often found on beets, burclover, ceanothus, curly dock, hawthorn, and pyracantha. Because of this, it is a good idea to maintain some distance between these plants and vulnerable trees.
If you suspect X disease has infected one of your trees, get help. Contact your local Master Gardeners or the Department of Agriculture for verification. They can also help you figure out the safe removal and disposal of infected trees.
No, we’re not discussing those yummy chocolate cherry cookies, though I may have to try baking a batch after researching this post!
The cherry crinkle we are exploring today is a condition that occurs in cherry trees. Cherry crinkle looks like a viral disease, but it’s not. Also known as cherry vein clearing, this condition is believed to be a genetic mutation that may or may not be related to a boron deficiency.
Cherry crinkle symptoms
Vein clearing, especially in the margins, is the most common symptom of cherry crinkle. Vein clearing refers to the way veins look lighter or more yellow than normal. I wasn’t able to find a photo that I could use, but these other symptoms may also occur:
Cherry crinkle management
If you suspect cherry crinkle, send a sample of soil to a lab for testing. This will tell you if your boron levels are low. It’s not a good idea to add nutrients without a soil test because too much of a nutrient can cause just as many if not more, problems as a nutrient deficiency.
If boron isn’t the problem, the tree is probably a mutant and should be replaced.
Cherry crinkle can be spread to unaffected trees by grafting mutated scions onto healthy wood. When shopping for a cherry tree, try to find one listed as unlikely to crinkle.
Blackheart is a disorder caused by environmental conditions. It occurs in celery, potatoes, sweet potatoes, tomatoes, and other garden crops. The causes of blackheart are the same. If seen in almonds, it’s a fungal disease called Verticillium wilt.
Causes of blackheart
Blackheart is the result of insufficient oxygen or too much CO2. How can you control those levels, you might ask. It’s easy. Picture this: it’s a hot day. Your plants are wilting. You add water, a lot of water. Your intentions are good, but now the ground is saturated. This localized flood pushes oxygen out of the macropores and micropores of the soil, and blackheart takes hold. Blackheart is also caused by too many cold days, like in your refrigerator.
Blackheart of celery
If young tissues in the middle of your celery plants turn black, it may be blackheart. Much like blossom end rot of tomatoes and tip burn of lettuce, this condition is a calcium uptake problem. It means plants cannot access enough of it. It may be a calcium soil deficiency or insufficient water. An inexpensive lab-based soil test is the only way to know what is in your soil. Irregular watering, soil salinity, and excessive fertilizer, specifically magnesium, nitrogen, or potassium, can interfere with calcium uptake.
Blackheart of tomatoes and potatoes (sweet and otherwise)
Commonly affecting potatoes and tomatoes, blackheart causes them to turn black in the middle. Fruit suffering from blackheart looks perfectly normal on the outside. Like hollow heart, which creates cavities within tubers, blackheart creates dark areas with distinct edges inside the fruit.
These darkened areas start as random spots that can expand. There may be small cavities, but they are mostly absent. These symptoms are similar to soft rot and Phytophthora root and stem rot, except that the interior stays firm. Eventually, these darkened areas will rot. If your seed potatoes have blackheart, they will grow into weak plants, if they grow at all.
To prevent blackheart from occurring, use these tips:
I hope the only blackhearts you have to deal with are the ones found in comic books.
Sometimes things look fine on the outside when the inside is damaged.
If you cut a beet, potato, seed, or watermelon in half and find a hole in the center, it has hollow heart. Also known as hallowheart, this condition indicates that the plant faced more stress than it could handle.
Hallowheart of watermelons
Hollow heart in watermelons is a pollination problem. Poor pollination occurs when temperatures are low or when there are not enough pollinators in the area. Somehow, poor pollination causes the interior of watermelon to develop triangular, often symmetrical gaps in the fruit. Seedless watermelons are more susceptible to hollow heart than seeded varieties, and orange and yellow-fleshed watermelons are the most likely to develop this condition. Improve pollination rates in your garden by attracting pollinators with flowers that appeal to honey bees and bumblebees. You can offset low temperatures with row covers.
Hollow heart in watermelons can also occur when they get too much fertilizer and insufficient water. The cells responsible for producing fruit cannot keep up with the cells producing rind under those conditions.
Hollow heart of beets
If you cut into a beet and find an empty center, it’s time to send a soil sample to a lab for testing. Hollow heart in beets is commonly a symptom of a boron deficiency. Look closely at the petioles (leaf stems) for signs of cracking, abnormalities, or stunting. If the cavity is rotting, it may be black heart.
Hollow heart of potatoes
Hollow heart in potatoes can be a weather problem or a water problem. Potatoes are greedy plants. They need a lot of water and nutrients to produce those fat tubers. Hollow heart occurs when a developing potato is hit with cold weather, followed by hot weather. Or when a sudden dry spell ends with an extended wet period. Like that one time you forgot to water them and then gave them extra water to make up the difference.
Where the cavity occurs will tell you its cause. Water or nutrient stresses that occur later in the growing season create holes at the bud end of the tuber. These cavities do not have a brown center. When hollow heart appears at the stem end of a tuber, cold weather followed by hot weather is the culprit. Brown centers are a common symptom of stem end hollow heart.
Hollow heart in seeds
Garden peas and other seeds can also develop hollow heart when unusually high temperatures occur right after germination begins. Because this disorder happens so early in the plants’ development, it leaves them vulnerable to several fungal diseases. The best way to avoid hollow heart in peas and other seeds is to plant at the optimal time of year for each species.
Bottom line: regular irrigation, planting at the appropriate time, and the right amount of nutrients can help prevent hollow heart in your garden.
Potato Virus Y
Potato virus Y (PVY) is the Big Daddy of potato problems, right up there with early blight. And potatoes aren’t the only plants at risk. Peppers, tomatoes, and groundcherries can all catch PVY. Losses can be as high as 80%. Infected potatoes that make it to harvest don’t last in storage. And who wants to eat an infected potato?
Potato virus Y is spread by aphids but not in their saliva. Instead, these microscopic potyviruses stick to aphids’ mouthparts (stylets). As the vector aphids feed, they spread the disease. Your shoes, clothes, and garden tools can also transfer this virus.
The many flavors of PVY
PVY used to be easy to identify, leading to the early removal of infected plants and reducing the spread of disease. Recent PVY virus mutations have made identification more challenging. There are fewer symptoms, so infected plants stay in place longer, spreading disease to nearby plants.
The most common variations of PVY include PVYO (ordinary), PVYC (uncommon), PVYN (necrotic), PVYNTN (tuber necrosis), and PVYN-Wi (a recombinant strain). The tuber necrosis strain can cause potato tuber necrotic ringspot disease (PTNRD).
Potato virus Y symptoms
Brown spots on leaves and tubers are the first sign of potato virus Y infection. Other symptoms vary depending on the plant age and health, environmental conditions, potato cultivar, soil health, virus strain, and other coinfections, such as PVA, PVS, and PVX.
Chlorosis, curved midribs, leaf crinkling, mosaic, mottling, and vein distortions are early signs of PVY. Infected leaves feel rough (rugose) compared to healthy leaves. The underside of infected leaves exhibits dark lesions and black streaks on the midrib. As the disease progresses, leaf loss and stunting are common. This disease is easily mistaken for calico (alfalfa mosaic virus).
Potato virus Y management
Chemical treatments are not effective against potato virus Y, so these good cultural practices are your best line of defense:
Potatoes come in many colors: blue, purple, red, yellow, and white. But why does potato skin turn green sometimes, and can it hurt you?
The simple answer is yes. Green-skinned potatoes can make you sick. According to WebMD, you can peel green-skinned potatoes, but those potatoes are still not entirely safe to eat because of toxins.
Like other members of the nightshade family, potatoes produce toxins. The toxins produced by potatoes are called solanine and chaconine. These toxins are defense mechanisms produced in abundance when the tubers are dug up and exposed to light. The green color under potato skin is chlorophyll. You can use it as a signal that lets you know a spud’s chemistry has changed.
Why do potato skins turn green?
Tubers belong underground. Uninjured potatoes are relatively stable in cool, dark locations. Expose them to light once, and nothing happens. Expose them to light several times, and things start happening. Imagine, if you will: First, they get dug up at the farm and see daylight for the first time. Then they are moved to a shipping truck and rolled down the freeway for more sunlight. Drop them off at the processing plant, and they get more light. You get the idea. By the time they leave the grocery store (where they got even more light) and arrive at your kitchen, some potatoes will have shifted from storage to growth mode. That is when trouble starts.
Is peeling enough?
Many say that peeling the green skin away makes the spud safe to eat, which is not entirely accurate. While most potato toxins are in the skin, they are also present in the rest of the potato. [Just as moldy cheese has mold growing throughout its interior, even if it is invisible.] Peeling green-skinned potatoes may not be enough, and cooking them does not affect the toxins.
Healthy individuals with good digestive systems are generally not harmed by occasional green-skinned potatoes. If you notice any of these symptoms, however, see a doctor:
Preventing green-skinned potatoes
You can’t control what happens to your potatoes before they arrive at your home (assuming you haven’t started growing your own yet). You can store your potatoes in a dry, chilly location with as much darkness as possible. Your refrigerator or pantry are ideal.
If an occasional green-skinned potato appears, throw it in the trash if it was from the store. If homegrown, add it to the compost pile or plant it.
Powdery scab may sound like an adolescent skin problem, but it is not. It is a potato disease that leaves spuds looking, well, scabby. You can cut away the affected bits and eat the rest of your potato, but the skin is where most of a spud’s nutrients are stored, so that’s a shame.
Also known as corky scab, let’s see what we can learn about this disease and how to prevent it.
The powdery scab disease
Powdery scab is a disease caused by one-celled creatures known as Cercozoa. They are not bacteria, fungi, or viruses. Instead, they are parasitic amoebas. Specifically, it is Spongospora subterranea that causes powdery scab. These microscopic critters exist around the world. Tomatoes, nasturtiums,, and other nightshade family members can also become infected with powdery scab. Once infected, plants are more susceptible to other diseases, such as potato mop-top and scab. Powdery scab spores can remain viable in the soil for up to 10 years.
Powdery scab symptoms
Small, purple lesions that look like pimples first form on the skin of an infected tuber. Those lesions grow bigger until they rupture, sending spores in all directions. Those spores are white. To the naked eye, these spore clusters look like scabs. You may also see galls on infected roots, leaf wilting, or discolored stems.
How to prevent powdery scab
Infected potatoes are not the only way powdery scab can enter your garden. Other potential pathways include infected bulbs, corms, rhizomes, firewood, planting containers, shoes and clothing, and soil from introduced plants.
I am a big proponent of buying used garden gear from yard sales and thrift stores. But you have to wash everything thoroughly before using it. And always put new plants into quarantine.
Chemical controls are not effective against powdery scab. But these practices can help prevent powdery scab:
Whatever you do, do not give in to the temptation to install spuds and other vegetables from the grocery store. These plant sources may be convenient and inexpensive, but they can bring a world of hurt to your garden. Produce bought at grocery stores is certified safe to eat, but it can still carry soil-borne diseases that may linger in your soil for decades. If you are growing in containers, this is less of a problem. If any disease appears in that case, toss it in the trash and start over. Hopefully, you catch it before any problems spread to the rest of your garden.
Strawberry Vein Banding
Strawberry vein banding is an invisible viral disease spread by strawberry aphids. You will never know it has infected your plants until another virus infects your strawberries.
As soon as another virus infects your plants, usually strawberry crinkle, the leaf veins of your strawberry plants suddenly start to turn yellow. And if the strawberry mottle virus comes along, those yellowing veins won’t be visible. This triple threat is called strawberry decline.
Symptoms of strawberry vein banding
The leaves of infected plants tend to be significantly smaller. Vein yellowing, when visible, appears erratically in new growth first. Sometimes only part of a vein has turned yellow. The two halves of each unopened leaf may look closer together than is normal, and the margins, or leaf edges, are wavier than normal. Some crinkling of the leaf surface may also occur. As the leaf opens, the bands of yellow become a little more obvious.
Symptoms appear more strongly in the second and third leaves but are not likely in later growth. Unfortunately, the other symptoms include stunting and reduced fruit and runner production. Vein banding can reduce strawberry crops by nearly 20%. If another virus takes hold, you can lose your crop entirely.
Strawberry vein banding vectors
Strawberry aphids and other aphid species carry strawberry vein banding to your plants. Grafts from infected plants also spread the disease. Strangely enough, dodder can also spread the disease, but the sap from an infected plant cannot. Stranger still, a clone of the vein banding virus can infect turnips, a completely unrelated species.
Strawberry vein banding control
In a word, you can’t. Strawberry vein banding can only be prevented by installing certified disease-free plants, placing plants in quarantine when they first arrive, and removing any infected plants.
Since aphids can fly at points in their development, the threat of this and other viruses is constant. All you can do, besides the preventive measures listed above, is monitor your plants for signs of aphids and control them as well as you can. Insecticides and insecticidal soaps work against aphids, but your strawberry plants need honey bees and other pollinators to produce fruit. Those insecticidal controls will impact your helpers, too, so avoid them while plants are flowering.
Closely monitoring your strawberry plants and keeping other plants that might host aphids at a distance can go a long way toward preventing vein banding in your garden.
Strawberry pallidosis is one of several viruses that make up strawberry virus decline.
Infected with only one of these diseases, strawberry plants often remain symptomless. It isn’t until a second virus enters the game that symptoms begin to appear. These other viral diseases include strawberry vein banding, crinkle, mottle, mild yellow edge, and beet pseudo yellows.
Symptoms of strawberry pallidosis
Stunting, reduced fruit and runner production, and older leaves turning red or purple are all symptoms of strawberry pallidosis. Also, roots are brittle and show fewer rootlets.
Managing strawberry pallidosis
Unlike many other strawberry viral diseases, whiteflies bring pallidosis to the garden. Management strategies are the same for all strawberry viral diseases: only install certified disease-free plants, quarantine new plants, remove infected plants, and control whiteflies as much as possible.
Strawberry mottle is an unassuming viral disease that can cut your strawberry crop by 30%.
When strawberry mottle occurs alone, the damage tends to be relatively isolated. All too often, however, more than one virus appears simultaneously in a condition called virus decline. Virus decline can eliminate any chance of enjoying a sweet, juicy strawberry from your garden, no matter how well you care for your plants.
Vectors of strawberry mottle disease
Strawberry mottle is transmitted by insects, most commonly by strawberry, melon, and cotton aphids. Infected plants can also spread the disease. Unlike the strawberry mild yellow edge virus, which stays in an aphid’s gut for its lifetime, the strawberry mottle virus can only be transmitted for 2 or 3 hours after an aphid or other insect has fed on an infected plant, keeping outbreaks relatively localized. [Ten feet away probably looks impossible to a mostly flightless bug that is only 1/8” long.]
Symptoms of strawberry mottle
As insects pierce plant cells to suck out the sugary sap, viruses move from the insect’s saliva to the plant. As viruses tend to do, these pseudo-lifeforms start reprogramming plant cells to produce more viruses. All this reproduction clogs plant veins.
Strawberry mottle first appears on young leaves as smaller-than-normal leaves. They may also show yellow distorted areas. Stunting may occur, and they produce less fruit and runners than they might otherwise. As the disease progresses, symptoms become more severe, with older leaves turning red.
Strawberry mottle management
Strawberry mottle is more likely when plants stay in place over the winter, but that doesn’t mean you must rip out your plants each year. [Note: don’t rip plants out of the ground. Instead, cut them off at soil level to leave valuable soil microbes in place.]
To reduce the likelihood of strawberry mottle appearing in your garden, only buy certified disease-free plants and always place new plants in quarantine. As much as possible, try to control aphids around strawberry plants. If a plant becomes infected, remove it.
Strawberry Mild Yellow Edge Virus
For some reason, strawberry plants often get infected with more than one virus simultaneously. Strawberry mild yellow edge virus is one of those diseases.
Strawberry mild yellow edge virus is a long name for a disease that can reduce your strawberry crop by as much as 30%. Strawberry mild yellow edge virus often appears when the mottle virus does. They are both transmitted by aphids. Nematodes may also add raspberry ringspot virus to the mix.
Strawberry mild yellow edge virus symptoms
As with most viral diseases, stunting is a common symptom of strawberry mild yellow edge virus. Older leaves may turn bright red, but the leaves around the crown nearly always exhibit yellow margins or edges, hence the name. These yellowed areas eventually die and turn brown. Leaf cupping may also occur.
Since these symptoms look much like water stress, fertilizer burn, overly acidic pH, boron toxicity, or bad weather, it is important to rule those out before deciding on a plan. Once strawberry mild yellow edge virus has made an appearance in your garden, there are steps you can take to minimize the damage.
How to manage strawberry mild yellow edge virus
Even though the fruits of infected plants are still edible, remove plants infected with strawberry mild yellow edge virus to prevent the disease from spreading.
Aphids carrying the strawberry mild yellow edge virus are disease vectors for life. You can try to use insecticidal soap on every aphid that might be a carrier. Just be sure to do this at a time when honey bees and other pollinators will not be attending the flowers. Common lambsquarters and other Chenopods can also carry this disease, so keep these plants away from your strawberry plants.
This disease is most common when plants are grown using a matted-row method. The matted-row system allows parent plants to send out runners, or daughter plants, which will produce fruit the following spring. This highly productive method has been around for a long time. It gets its name because the runners end up intertwined, creating a mat. The only problem with the matted-row system is that it means plants are in place longer, making infection more likely.
As always, put new plants into quarantine until you know they are disease-free.
Strawberry crinkle might sound like a delicious new candy bar. Instead, it is one of the most destructive viral diseases a strawberry plant can face.
Strawberry crinkle virus was first seen in Oregon and California in 1932 and now occurs worldwide. Spread by aphids, it appears in tandem with other aphid-transmitted diseases, such as mottle, mild yellow edge, pallidosis, and strawberry vein banding. As aphids feed, their saliva transfers the virus to every plant they visit.
Strawberry crinkle virus symptoms
Wilting, reduced runner production, smaller fruit, deformed or streaked flower petals, and crinkled leaves are all symptoms of strawberry crinkle virus. Vein spotting and lesions on petioles (leaf stems) and stolons may also occur. Infected plants may appear top-heavy, exhibiting a form of epinasty. These symptoms can vary in intensity.
Strawberry crinkle virus management
Since bees are critical to strawberry formation, insecticides are generally not an option against the aphids that carry this disease. Use these tips to prevent strawberry crinkle virus from impacting your strawberry crop:
Hopefully, your strawberry plants will never become infected with the crinkle virus. Until we figure out a sustainable way to eliminate aphids, we must be vigilant against these pests.
Zucchini Yellow Mosaic
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, bread, and the ever-popular chocolate zucchini cake, zucchini can be a very productive plant, but only 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. These two viral diseases often occur in tandem with zucchini yellow mosaic. Watermelon mosaic infections exhibit blistered leaves, while zucchini yellow mosaic has long, narrow leaf lobes, creating a shoestring or ferny appearance.
Zucchini yellow mosaic host plants
In addition to infecting zucchini, zucchini yellow mosaic also infects other cucurbits, including cantaloupe, cucumbers, melons, pumpkins, squash, watermelon, and some gourds. Aphids bring this disease to your garden.
Zucchini yellow mosaic management
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 effective at managing zucchini yellow mosaic because the disease has often been transmitted before you even know the aphids are there. Reflective mulches can discourage aphids. Remove or cover the reflective material before it gets too hot, or your plants will cook where they stand. Row covers can reduce access to susceptible plants.
This disease can also travel on infected garden tools and seeds, so sanitize your garden tools regularly and get your seeds from a reputable source (and not that zucchini from the grocery store).
Remove infected plants and replace them 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.
Growing corn makes a dramatic statement in the garden. Reaching ten feet or more, modern corn plants can be grown alongside other garden giants, such as sunflowers and hollyhocks. Unless they become infected with corn stunt, that is.
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 practically eliminating kernel production.
Corn stunt disease complex
Some people see corn stunt as a single disease. Other people see it as part of a complex along with maize bushy stunt mycoplasma and maize rayado fino virus (MRFV). Other people include maize chlorotic dwarf virus in the corn stunt complex. Any combination of these diseases can be devastating to your corn crop. [And you don't need to remember all the names to be able to see there is a problem.]
Corn stunt symptoms
Healthy corn plants produce one or two ears of corn, depending on whether they are early or late-maturing varieties. Plants infected with corn stunt are significantly shorter, 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 in completely. You end up with a lot of empty spaces. The kernels that 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 carried by leafhoppers. Corn leafhoppers (Dalbulus maidis), in particular, host the bacteria (Spiroplasma kunkelii), 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. The first generations of emerging bacteria are less effective at spreading the disease than those that occur later in the season. Insecticides are generally not effective.
Juicy, sweet kernels of corn transform, overnight, into hideous, purple-gray, 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).
Do you see spirals on your watermelons?
Watermelon mosaic (WMV) is a viral disease that can infect cantaloupes, squash, and other cucurbits, along with some legumes, such as peas and alfalfa, and many chenopods. Infected watermelons look like they have ringworm.
There are two different watermelon mosaic viruses: WMV1 and WMV2. While these are two distinctly different viruses, they are similar enough.
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 occurs along leaf edges (margins) and veins. Leaves may also be small, 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, and fruit production is minimal.
How to prevent watermelon mosaic
Spread predominantly by aphids and occasionally leaf miners, watermelon mosaic virus can also travel on garden tools and clothing, so sanitize your tools regularly. The virus survives inside aphids for only a few hours, so physical barriers between potential carriers 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 , 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 ineffective against watermelon mosaic because the disease is transmitted before the chemicals kill the carrier. You can use reflective mulches under susceptible plants to repel aphids. If you use reflective mulch, remove it before the summer sun uses it to cook your plants.
We’ve all heard that beans cause gas, but did you know beans rust? Well, not rust like the undercarriage of a New England truck, but rust just the same.
Bean rust, like other plant rusts, is a fungal disease. Rust is found worldwide and it can wipe out your bean crop if it takes hold early enough in the growing season.
California’s cool, wet springs are just the conditions needed for rust to thrive. Add overhead watering or a decent breeze and the stage is set for an epidemic. Fungi are so efficient that, under ideal conditions, the disease cycle can be repeated every 10 to 14 days!
There are several strains of bean rust. Two of the most common are Uromyces appendiculatus and Uromyces phaseoli typica, but you don't need to know the Latin to recognize bean rust in the garden.
Bean rust symptoms
Similar to other rusts, bean rust prefers moist places and moderate temperatures (65 to 85°F). While it can occur on any aboveground portion of a plant, bean rust is most commonly found on the underside of leaves. Pods can also be affected. At first, it just looks like tiny white or yellow bumps. Then those bumps break open and turn into bright orange, reddish, or yellowish flecks. Those flecks are pustules that are made up of more fungal spores than any of us cares to count. [Okay, some scientists love counting things like that.] A yellow outer ring is sometimes visible. Leaves may begin to curl downward and plants may develop a scorched appearance. These symptoms are easy to see and make identifying the condition simple. Getting rid of it is something else all together.
Bean rust control
The fungi that cause bean rust can be spread by ants, aphids, and gardeners. It can stick to tools, fingers, and clothing. As with many other plant diseases, prevention is far easier than eradication. Use these tips to prevent and control bean rust in your garden:
Keep in mind that rust pustules are easily dislodged and can land somewhere else, or on the soil, where they can be bounced back up into your plants by rain, wind, and overly exuberant irrigation. And be sure to disinfect your tools after removing rust-infected leaves, to avoid spreading the fungus to healthy plants.
With a name like halo blight, you might expect to read about little cherubs, but that’s not the case. The bacteria responsible for halo blight are no angels.
Halo blight is a global disease of legumes, affecting kidney beans, lima beans, snap beans, scarlet runners, and other bean varieties.
The halo blight bacteria (Pseudomonas syringae pv. phaseolicola) enters plants through tiny wounds, often caused by insect or herbivore feeding or injury, and through natural openings, such as the stoma.
Symptoms of halo blight
Halo blight is frequently confused with bacterial brown spot and common blight. In all three cases, small, water-soaked lesions appear on the leaves. In common blight, those lesions have wide, lemon-colored borders and keep growing. Bacterial brown spot lesions have narrow light green borders, and the centers tend to dry out and look tattered. Halo blight lesions stay small and have prominent light green halos, hence the name.
Leaves are not the only place damage occurs. Pods can also become infected, making them inedible. Pods infected with common blight have lesions with red or rust-colored borders. Symptoms of the other two diseases are difficult to tell apart, as both have the same water-soaked lesions on the leaves.
Managing halo blight
As with other diseases, prevention is the easier way to go. Since moisture is needed for halo blight to develop and spread, avoid overhead watering and save the sprinklers for your lawn. Furrow irrigation will direct water to the roots without creating a potential disease site. Halo blight is most likely when temperatures are between 68 and 74°F (20 to 23 °C). Unlike many other blight diseases, halo blight bacteria prefer these slightly cooler temperatures.
Use these tips to prevent halo blight in your garden:
Fixed copper or Bordeaux mixture treatments may prevent halo blight.
You can grow a surprising amount of food in your own yard. Ask me how!
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