Researching yesterday’s post on bacterial blight, I was astounded at the number of diseases caused by Pseudomonas. Pseudomonas [soo-doh-MO-nas] is a genus of bacteria that most of us gardeners end up fighting.
These bacteria are commonly found 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
To date, more than 500 strains of Pseudomonas have been sequenced. Here is a list of the most common bacterial diseases caused by Pseudomonas:
In nearly all of these diseases, small dark spots appear and expand into odd-shaped dead areas. It’s all downhill from there.
These are some tough SOBs. These bacteria 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. Most importantly, be sure to space plants far enough apart so they dry off rapidly. And avoid overhead watering.
Pseudomonas isn’t all bad
As handy as it would be to say that all Pseudomonas are bad, it ends up that some of these soil bacteria help plants stay healthy. In fact, they practically make life possible on Earth. Life sure is messy, isn’t it?
Some Pseudomonas protect plant roots against disease-causing Fusarium fungi and Pythium oomycetes. They also protect against plant-eating nematodes. And other strains help activate disease resistance within wheat and other cereal crops. Some Pseudomonas can metabolize pollutants and are used in bioremediation.
Finally, Pseudomonas is also responsible for the formation of most of the 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 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 is a hitchhiker, but not a parasite. There are some pretty bizarre examples of phoresy in my post on the subject. You may want to check it out.
Anyway, 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 along 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. If it is X disease, you will see pits and grooves near the graft union. If you cut into the wood, you will see brown areas in the phloem. These other symptoms are also common:
The fruit from infected trees tends to be pale, pointed, small, and nasty tasting.
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 they provide a source of infection to many important fruit and nut trees in our landscapes. Almonds, 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 they are non-reservoir hosts. This means that they can catch the disease but not spread it. Scientists don’t yet understand why that is, but they’re working on it.
X disease management
Since scientists have been unable to reproduce the phytoplasmas responsible for X 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 responsible for spreading 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, it’s a good idea to get help. Contact your local Master Gardeners or Department of Agriculture for verification. They can also help you figure out the safe removal and disposal of any 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 a diverse collection of garden crops.
Celery, potatoes, sweet potatoes, and tomatoes are all susceptible to blackheart. Wherever it occurs, the causes of blackheart are the same. Unless it is seen in almonds. Then it’s a fungal disease called Verticillium wilt.
Causes of blackheart
Blackheart is caused by a lack of 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 miniature flood pushes oxygen out of the soil’s macropores and micropores. Blackheart takes hold.
Blackheart is also caused by extended periods of cold temperatures, like those in your refrigerator. You may be surprised to learn, as I was, that blossom end rot and blackheart result from similar conditions and may appear in tandem. Before adding calcium to your soil, be sure to have it tested first. Too much of a good thing can be a bad thing.
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 directly related to calcium uptake problems. That doesn’t mean your soil needs calcium. It means they can’t access enough of it. The only way to know how much calcium is in your soil is with a lab-based soil test. In many cases, the problem is irregular watering, soil salinity, and excessive fertilizer, specifically magnesium, nitrogen, or potassium.
Blackheart of tomatoes and potatoes (sweet and otherwise)
Commonly affecting potatoes and tomatoes, blackheart causes them to turn black in the middle. [Unfortunately, I was unable to find licensable photos.] Fruit suffering from blackheart looks perfectly normal on the outside. Like hollow heart, which creates cavities within tubers, blackheart is seen as dark areas with distinct edges inside the fruit. These darkened areas start out 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. This can happen to people. And it happens in beets, potatoes, seeds, and watermelons.
If you cut a beet, potato, seed, or watermelon in half and find the empty space in the center, it has hollow heart. Also known as hallowheart, this condition indicates that the plant faced more stress than it could handle. [The same might be said for people, but I digress.]
Sadly, this was the only licensable photo of hollow heart I could find.
Hollow heart of beets
If you cut into a beet and find an empty center, it’s time to get your soil tested. Hollow heart in beets is most commonly caused by a boron deficiency. If you look closely at the petioles, you will see that they are cracked, deformed, or smaller than normal. If the cavity is rotting, it may be black heart.
Hollow heart of potatoes
Hollow heart in potatoes is related to the water supply. And hollow heart is only one potato problem caused by irregular watering. Splitting and spraing (brown lines) are also water-related. Cold injury can also cause hollow heart in potatoes.
Hollow heart in seeds
Garden peas and other seeds can also develop hollow heart. This occurs when unusually high temperatures occur right after germination begins. Because this disorder happens so early in the plants’ development, it leaves plants 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.
Hallowheart of watermelons
Hollow heart in watermelons is mostly caused by insufficient pollen transfer. Poor pollination occurs when temperatures are low or when there are not enough pollinators in the area. Somehow, poor pollination causes the interior of a watermelon to develop triangular, often symmetrical gaps in the fruit. Seedless watermelons are more likely to develop hollow heart than seeded varieties, and orange and yellow-fleshed watermelons are the most likely to develop this condition. I have no idea why. What I do know is that you can attract more pollinators to your watermelon patch by adding flowers that appeal to both honey bees and bumblebees. You can offset low temperatures with row covers.
Hollow heart in watermelons can also occur when they are hit with too much fertilizer combined with not enough water, making the cells responsible for producing fruit unable to keep up with the cells producing rind.
Bottom line: a steady supply of water, planting at the appropriate time, and the right amount of nutrients can help prevent hollow heart from occurring in your garden.
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. This meant infected plants were removed right away, and the spread of disease was limited. Like another virus that shall remain unnamed, the PVY virus has been mutating a lot lately, making it more difficult to manage. Recent mutations have fewer symptoms, making infected plants harder to identify. They stay in place longer, increasing the spread of 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). Botanists sure do like their acronyms, don’t they?
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 at the time of infection, environmental conditions, potato cultivar, soil health, virus strain, and the presence of other viral diseases, 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. If you look on the underside of infected leaves, you will see 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 many of 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. It’s all about toxins.
Like other members of the nightshade family, potatoes produce toxins. The toxins produced by potatoes are called solanine and chaconine. These toxins are part of a potato plant’s defense mechanisms. They are produced in abundance when tubers are exposed to light. The green color under a potato’s 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. They get moved to a shipping truck and roll down the freeway with 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 of those potatoes will have shifted from storage mode to growth mode. That’s when trouble starts.
Is peeling enough?
Many people say that peeling the green skin away makes the spud safe to eat. That’s not entirely accurate. While most of those toxins are stored in the skin, they are still present in the rest of the potato. Just as a moldy cheese will also have mold growing throughout its interior, even if you can't see it. Peeling a green-skinned potato may not be enough. And cooking them does not affect the toxins.
All that being said, if you are generally healthy with a good digestive system, you may be fine with an occasional green-skinned potato. 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). What you can do is store your potatoes in a dry, cool 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 it was homegrown, you can.add it to the compost pile or plant it instead of putting your tummy at risk.
Powdery scab may sound like an adolescent skin problem, but it is a disease of potatoes that leaves them 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 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 members of the nightshade family can also become infected with powdery scab. Once infected, plants are more susceptible to other diseases, such as potato mop-top and potato 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 a potato’s skin. Those lesions grow bigger and bigger and then 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
The easiest way to prevent powdery scab in your potato patch is by planting only certified disease-free eye potatoes. I know it’s tempting to use spuds and other vegetable starts from the grocery store. They’re certainly convenient, and you already have them, 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 many years. If you are growing in containers, this is less of a problem. If a disease appears in that case, you can toss the soil in the trash and start over. Hopefully, you catch it before spores have been released. Other practices that will help prevent powdery scab include:
Infected potatoes aren’t the only way powdery scab can enter your garden. To prevent this disease, you need to monitor these other potential pathways:
I’m 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.
Strawberry vein banding is a viral disease spread by strawberry aphids, but you will never know it has infected your plants until another virus comes along.
As soon as another virus infects your plants, usually strawberry crinkle, suddenly the leaf veins of your strawberry plants start to turn yellow. And if the strawberry mottle virus comes along, well, those yellowing veins won’t be visible. This mess is called strawberry decline, a topic for another day.
Symptoms of strawberry vein banding
Leaves of infected plants tend to be significantly smaller than the leaves of healthy plants. The yellowing of veins, when visible, first appear in new growth. This yellowing appears erratically; sometimes only part of a vein has turned yellow. The two halves of each leaf may be held 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 somewhat more obvious.
Symptoms appear more strongly in the second and third leaves, but are not likely in later growth. [Weird, right?] Unfortunately, the other symptoms include stunting and reduced fruit and runner production. Your strawberry crop can be reduced by nearly 20% because of vein banding. As soon as another virus takes hold, you can lose your crop entirely.
Strawberry vein banding vectors
Strawberry vein banding is generally carried by strawberry aphids. It can also be transmitted by taking grafts from infected plants. Strangely enough, coming into contact with dodder can also spread the disease, but 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 be prevented by only installing certified disease-free plants, placing those plants in quarantine when they first arrive, and removing any plants that you suspect are infected.
Since aphids can fly at certain 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 they should be avoided 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 strawberry plants.
Strawberry pallidosis is one of several viruses that make up a condition called 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
Similar to other strawberry viral diseases, symptoms of strawberry pallidosis include stunting, significantly reduced fruit and runner production, and older leaves turning red or purple. An additional symptom of strawberry pallidosis is that roots are brittle and show fewer rootlets.
Managing strawberry pallidosis
Unlike many other strawberry viral diseases, pallidosis is spread by whiteflies. This makes controlling the disease more difficult. 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 you can.
Strawberry mottle is an unassuming viral disease that can cut your strawberry crop by 30%.
Strawberry mottle is one of several viruses that can affect strawberries. Appearing on its own, the damage tends to be relatively isolated. All too often, however, more than one virus appears at the same time. Collectively, this condition is called virus decline and it can eliminate any chance at 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 carried by insects, most commonly by strawberry, melon, and cotton aphids. This virus is also spread by vegetative propagation of infected plants. Unlike the strawberry mild yellow edge virus, which is retained 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. This makes outbreaks remain relatively localized. [Ten feet away probably looks impossible to a 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 a plant’s cells to produce more viruses, which then clog the works.
Strawberry mottle first appears on young leaves as smaller than normal leaves that may also show yellow distorted areas. Plants may be stunted and they certainly 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 are left in place over the winter, but that doesn’t mean you have to rip out your plants every year. [Note: don’t actually rip plants out of the ground. Instead, cut them off at soil level to leave valuable soil microbes in place.]
As always, 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.
For some reason, strawberry plants tend to get infected with more than one virus at the same time. 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 at the same time as the mottle virus, both of which are transmitted by some aphid species. 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 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 a lot like water-stress, fertilizer burn, overly acidic pH, boron toxicity, or bad weather, it is important to rule those things 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, plants infected with strawberry mild yellow edge virus should be removed to reduce the chance of spread. Aphids carrying the strawberry mild yellow edge virus are disease vectors for life. The only thing to do if the disease is present is to use insecticidal soap on each and 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 is a very productive method that 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 for a longer period of time. This makes infection more likely.
As always, place new plants into quarantine until you are sure that they are disease-free.
Strawberry crinkle might sound like a delicious new candy bar, but 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 is now found worldwide. Spread by aphids, this disease is commonly seen 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 and/or streaked flower petals, and crinkled leaves are all symptoms of strawberry crinkle virus. Vein spotting may also be seen, as well as lesions on petioles (leaf stems) and stolons. Infected plants may appear top-heavy, exhibiting a form of epinasty. These symptoms can vary in intensity.
Strawberry crinkle virus management
Since bees are so important 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 get rid of aphids, well, be on the lookout.
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. [Email me if you'd like the recipe.]
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.
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.
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.
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 little cherubs in today's post, but that's not the case. The bacteria responsible for halo blight are no angels. Halo blight is a major bean disease, worldwide, affecting kidney beans, lima beans, snap beans, scarlet runners, and many 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 leaves.
In common blight, those lesions have wide, lemon-colored borders, and they continue to grow. Bacterial brown spot lesions have narrow light green borders and the centers tend to dry out and look tattered. Halo blight lesions tend to stay small and they 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, while symptoms of the other two diseases are difficult to distinguish from each other, both being the same water-soaked lesions seen on 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 get water to the roots without creating a potential disease site. This is especially important when temperatures are between 68 and 74°F (20 to 23 °C). Unlike many other blights, halo blight bacteria prefer these slightly cooler temperatures.
Also, be sure to start with certified disease-free seed, and place new plants into quarantine before exposing the rest of your garden to whatever they may be carrying. Speaking of carrying disease, the bacteria responsible for halo blight can also travel on rain splashes, wind, pet fur, shoes and clothing. If you have been exposed to halo blight, you might want to change your clothing and swap shoes to avoid spreading the disease throughout your garden. Finally, when your bean plants have completed their life cycle, cut them off at ground level, leaving soil microorganisms in place, and add plant debris to the compost pile. Leaving plants to break down in the garden can provide potential overwintering sites.
Fixed copper or Bordeaux mixture may be used to prevent halo blight. Plants infected with halo blight should be removed and destroyed, followed by a 2 to 4-year crop rotation program.
You can grow a surprising amount of food in your own yard. Ask me how!
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