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. Cytospora canker is a collection of symptoms caused by several species of Cytospora fungi. This disease also occurs on ash, birch, cottonwood, elm, maple, willow, spruce, and other conifers. Some Cytospora fungi are host-specific, while others can infect multiple tree species. Sadly, Cytospora canker can be fatal.
Cytospora canker lifecycle Cytospora canker fungi infect trees and shrubs that are stressed or weakened by injury, frost damage, drought, or pests. Spores enter your garden on wind and rain. Infection can occur at any time of year, but trees are most vulnerable during dormancy. Fungal spores enter through tiny wounds in the roots or bark and begin growing in the xylem and phloem. This fungal growth blocks the flow of water and nutrients. If infection occurs in the trunk, the tree will die. Cytospora canker symptoms The first sign of Cytospora canker is often the random dieback or flagging of tree or shrub branches. You can see long, narrow cankers on infected stems and branches. These fungi grow so rapidly that cankers may or may not be sunken or discolored. You might observe the bark split along the edge of these cankers as the tree tries to defend itself. These cracks allow for the formation of a callus that blocks the fungi from entering the rest of the plant. Sometimes this works, and sometimes it doesn’t. Sometimes, this girdling occurs without any visible cankers. Gumming is another defense trees use. Gumming is when stems and fruit ooze out a sticky sap. If you cut into a diseased stem, you may notice discoloration and a funky smell. If you see tiny black spots, you are looking at the fruiting bodies of the fungi. Cytospora canker prevention and control The easiest way to prevent Cytospora canker is to keep your trees and shrubs healthy in the first place. Healthy plants are less likely to become stressed enough to be vulnerable to infection by fungal spores in the first place. Since drought and flooding are the most common conditions that make trees susceptible to Cytospora canker, regular irrigation during summer and proper drainage in wetter months can prevent infection. These other tips can help you prevent Cytospora canker in your landscape:
Once infection occurs, remove any affected stems and branches by cutting close to, but not damaging, the branch collar. Be sure to disinfect your cutting tools with a household cleaner or ethyl alcohol between each cut. Then apply a fungicide to each cut. Do not use sealants, as these treatments can trap spores and moisture where you least want them. There are no known chemical controls for Cytospora canker, so keeping those trees and shrubs healthy is your best bet. The fungi responsible for take all disease, Gaeumannomyces graminis, is found in the soil. It enters young plant roots and can often be seen as dying patches in a lawn or field. Take all disease symptoms The fungus enters the xylem and blocks the flow of water, causing stunting, yellowing, and reduced tillering. Tillering refers to the way lateral shoots emerge from the base of the stem, a common growth style of cereals. Infected plants mature faster than normal and have bleached seed heads and blackened roots and crowns. Preventing take all disease There are no effective chemical treatments against take all disease available to gardeners. There is a seed treatment that shows promise, so be sure to get certified disease-free seeds from reputable suppliers. Excessive liming and nutrient imbalances exacerbate this disease. If take all disease appears in your lawn, there isn’t much you can do besides improving drainage. If it appears in your barley, corn, millet, rice, sorghum, triticale, or wheat, the best thing you can do is rotate crops. Oats and rye, while cereal grains, are not susceptible to take all disease. Take all disease can build up in the soil, particularly in monoculture crops that are grown in the same place year after year. There is one soil amoeba that feeds on the take all disease fungi. This unique protozoa is a type of vampyrellid. Vampyrellids are affectionately known as soil vampires because of the way they leave puncture marks in their victims.
Streaked avocado skins may indicate a disease known as sunblotch.
Sunblotch identification Unlike sunburn damage, which bleaches leaves, sunblotch appears as yellowish, reddish, or white streaks on the stems and skin of avocado fruits. Common symptoms of sunblotch include stunting, distorted leaves and petioles, and reduced fruit production. Rectangular cracking in the bark of older branches may also occur. Unfortunately, this disease can go unnoticed for years before symptoms become visible. By then, several nearby trees have probably become infected. Cause of sunblotch Until recently, botanists thought sunblotch was a genetic disease. Now we know it is a viroid infection. Viroids are the smallest known infectious pathogens, and they only attack plants. Unlike viruses, which contain DNA and RNA, viroids only contain RNA. This particular viroid attacks many tropical and subtropical plants, including avocados. Sunblotch control Trees infected with sunblotch must be removed and destroyed. Tree removal is expensive and potentially dangerous, so prevention is the only option. Sunblotch spreads through infected pollen, seeds and budwood. You can’t do anything about infected pollen if the source is on someone else’s property (besides educating your neighbor). But you can invest in disease-free bare-root trees. You can also ensure that any grafting projects you take on involve only healthy trees. And be sure to sanitize your garden tools after working on potentially infected trees with a household cleaner. Mottled, stunted cilantro plants may have apium virus Y disease.
Apium virus Y disease is carried by aphids. This viral disease is also found on celery, carrot, dill, and poison hemlock. It can infect parsley, as well, but no visible symptoms occur. Apium virus Y disease symptoms Leaf mottling or mosaic patterns, stunting, cleared veins, and leaf distortions are all symptoms of apium virus Y disease. Older leaves may have yellow blotches, brown lesions, and yellow or brown line patterns. Younger leaves show only faint mottling. Lesions may form on petioles (leaf stems). How to prevent apium virus Y disease Since this disease is predominantly carried by aphids, you can help prevent this disease by controlling aphid populations (as much as is possible, of course). The virus can also be carried on clothing and tools, so be sure to sanitize your tools regularly and avoid walking through areas known to be infected. The virus does not remain vital for very long once it is inside an aphid. Creating physical barriers and increasing the distance between potential carriers can reduce the likelihood of this disease. Crop rotation and the CAREFUL removal of poison hemlock can also help control this disease. There are no effective chemical treatments for apium virus Y disease. Plum pox is one of the most destructive diseases of stone fruits, and I hope you never see it. Also known as sharka disease, plum pox was first observed in Bulgaria in 1915 and now occurs in many parts of Canada, Chile, Europe, India, the Middle East, and North Africa. In Europe, 100 million stone fruit trees are infected with the plum pox virus (PPV), resulting in 80–100% crop losses.
The disease appeared in a Pennsylvania orchard in 1999, which led the U.S. Department of Agriculture to declare an extraordinary emergency that gave them access to the funds necessary to remove and destroy infected and exposed trees. Plum pox appeared again in 2006 in Michigan and New York. The Department of Agriculture responded quickly and thoroughly. These eradication efforts have cost over $65 million. And the Pennsylvania stone fruit industry may never recover. Plum pox was declared eradicated in the United States (for the time being). Plum pox symptoms There are multiple strains of the plum pox virus, but the results are always unfortunate for stone fruit trees. Symptoms can be very subtle. They can vary by virus strain and host cultivar. Generally, leaf veins turn yellow and light green, or yellow rings may appear on leaves, fruits, and pits. These symptoms may disappear during the heat of summer, only to return in autumn. Leaves may also exhibit crinkling, curling, and puckering. Cultivars with large, showy flowers may become variegated. Fruit may be deformed, turn brown, or develop concentric colored rings. Premature fruit drop may also occur. Unfortunately, these symptoms do not usually appear until the infection has been present for 2 or 3 years. During this time, several other nearby trees can become infected. Plum pox transmission The plum pox virus (PPV) can travel long distances on infected plant material and insects. Grafting infected scions can transfer the infection to healthy trees. Several aphid species can carry this virus. How to avoid plum pox Removing infected trees is expensive, and halting the spread of plum pox is the responsibility of everyone growing stone fruits. These tips can help prevent plum pox in your garden (assuming you don’t live where plum pox is already a problem):
Plum pox may not kill fruit trees, but it can reduce production so much that you will probably end up replacing the trees anyway. Infected trees often produce misshapen, acidic fruit. Efforts are underway to develop resistant cultivars, but those trees are not yet available. You’ve probably read dozens of articles and posts about the wonders of dish soap as a pesticide, fungicide, and surfactant in the garden. All of those posts are wrong.
How dish soap works
Dish soap is a detergent. Dish soap cleans dishes by cutting grease, oil, and wax. Dish soap generally contains colorants, fragrances, bleach, enzymes, phosphates, and rinsing agents. None of those are good for your plants. Dish soap damages protective, waxy coatings used by plants and insects. If you wash this protective coating away, infection, infestation, and dehydration become more likely. Dish soap v. insecticidal soap Insecticidal soap is not a detergent. It is a soap specifically formulated for use on plants. It must be used properly to be safe and effective. While liquid hand soap is a soap and not a detergent, it contains fatty acids that are phytotoxic (poisonous to plants). Despite popular opinion, dish soap does not belong in the garden. Save it for your dishes, and your plants will thank you. Raspberries and white spruce share a disease called late leaf rust and raspberry rust. Mid to late summer, spores of this fungal disease infect red and purple raspberries. Yellow rust is similar but produces yellow to orange pustules in early to mid-summer.
Late leaf rust symptoms The first symptom of late leaf rust (Pucciniastrum americanum) is small yellow (chlorotic) spots on the top of older leaves. These spots generally begin appearing in lower portions of the plant, slowly spreading upwards into younger leaves. As the disease progresses, reproductive uredinia form on the underside of leaves, containing masses of spores. Extreme infestations can defoliate the entire plant. Fruit and flowers can also be infected, which causes them to rot. Of course, if all the leaves have fallen off due to disease, there probably won’t be any fruit or flowers. If the fruit has already formed, late leaf rust will appear as tiny orange spots on individual drupelets. Affected fruits will also ripen unevenly. Late leaf rust lifecycle Spores of this disease overwinter in white spruce and infected raspberry canes. Wind can spread these spores, so your upwind neighbor’s raspberries can directly impact yours. Late leaf rust control Like other rusts, late leaf rust is best avoided by pruning plants for good airflow and avoiding overhead watering. Also, be sure to remove spent canes each year. Throw infected plant material in the trash, not the compost pile. Fixed copper sprays may help prevent and treat late leaf rust. Just before your cantaloupes, cucumbers, squashes, watermelons, and pumpkins are ready to harvest, they suddenly wilt and die, taking your crop with them.
Unlike slow wilts, caused by lack of water (or too much water), or vascular diseases, such as Verticillium wilt and Fusarium wilt, sometimes leaves of cucurbits droop suddenly, and the entire plant collapses. It is sudden wilt, also known as parawilt. Sudden wilt is a soil-borne fungal disease that appears after heavy irrigation on hot, sunny days. Contrary to what you might expect, lots of water combined with hot sun is not what melons and squashes need. Sudden wilt occurs when there is an imbalance between water uptake and water loss, combined with certain fungi. Sudden wilt symptoms Sudden wilt starts as yellowing of the crown leaves, followed by total collapse of the entire plant. Death soon follows. If you dig up an affected plant, you will see that the roots are straw-colored or dark. There are three different fungi responsible for sudden wilt, and each one has unique symptoms: • Pythium spp. - appears as brown root rot • Acremonium cucurbitacearum - corky bands on discolored roots • Rhizopycnis vagum - upper portions of the taproot turn reddish and corky Sudden wilt treatments There are no chemical controls against sudden wilt. Careful water management, proper plant spacing, and removal of crop residue after harvest can help reduce the chance of sudden wilt in your garden. Monitor your cucurbits for signs of sudden wilt near the end of the growing season. Good drainage and 2- to 3-year crop rotations can help prevent this disease from wiping out your cucurbit crops. And let the soil dry out completely between waterings. Cucumber green mottle mosaic is a viral disease that can take a big bite out of your cucumber, watermelon, and other melon family crops. This cucurbit disease comes in on infected seeds. And there is no known cure. Before 2013, it was only in Russia, China, Japan, Korea, India, Spain, and Israel. Scientists believe it came to the U.S. on infected seed. Cucumber green mottle mosaic enters plants through wounds and root-to-root contact.
Cucumber green mottle mosaic control
Since there is no cure for this contagious disease, remove infected plants and a few of their neighbors to prevent it from spreading. Using certified disease-free seeds and placing new plants in quarantine can help prevent this disease from infecting your soil. Since this virus can travel on tools, shoes, and clothing, good sanitation practices can help protect your plants. If you grow red raspberries, 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 infections, this rust only occurs on plant exteriors. When yellow rust occurs on wheat, rye, and barley, it is called stripe rust, a Puccinia striiformis infection.
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. Black spots 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 more severe orange rust (Arthuriomyces peckianus). Either way, infected leaves wither and die, reducing the plant’s ability to perform photosynthesis, which cuts crop size significantly. Yellow rust control Pruning for good airflow helps leaves and stems dry out, making life more difficult for these 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. Canes of summer-bearing raspberries won’t produce any more fruit, so you might as well. Just dispose of these canes in the trash and not the compost pile. If unproductive canes stay in place, any spores they contain will spread the infection to the next season’s primocanes or vegetative growth. Keep the ground around cane fruit 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. Their root systems will quickly put out new stems. That first growth is the most likely to have become infected. Fixed copper sprays and lime sulfur can treat severe outbreaks. Otherwise, remove infected leaves by hand and improve the airflow 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, watch for 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 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. Vein clearing describes how leaf veins appear translucent. Seeds shrivel and become discolored. Pea seed-borne mosaic infection is easily mistaken for chemical overspray, nutrient toxicities, and water stress. Laboratory tests are needed to verify this infection. You can often take ziplock 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 by aphids. Do the best that you can control them. Remove any plants infected with pea seed-borne mosaic and dispose of them in the trash. 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. The only way to prevent pea seed-borne mosaic from occurring in your garden is to buy certified pest- and disease-free seeds. This disease can overwinter in nearby weeds, such as shepherd’s purse, vetches, and black medic. 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 of this publication, unidentified viral diseases that all infect the Ficus subspecies. How fig mosaic spreads All eriophyid mites,, especially fig mites, can bring fig mosaic to your trees. As they feed, their saliva transfers the virus to plant tissues. Grafting and cuttings can also spread the fig mosaic virus. 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. 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. Look for signs of mite feeding if you suspect fig mosaic. Look around bud scales and young leaves for signs of mite feeding. You may also see faint russeting. Twig stunting and leaf drop may also occur. Fig mosaic management
Trees infected with fig mosaic must be removed and destroyed by a professional. Tree removal is expensive. You can help prevent fig mosaic with these tips:
Sulfur treatments and horticultural oils can control fig mites. And those delicious figs are worth the effort. Beetles among your squashes and melons are never good, 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 both cases, your crop will be lumpy, discolored, and significantly reduced, though still edible. Crops vulnerable to squash mosaic All cucurbits are susceptible to squash mosaic, including cucumbers, melons, pumpkins, and zucchini. Except for watermelons, they do not get 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, blistering, yellowing (chlorosis), leaf hardening and distortion, and vein clearing. Vein clearing is a common symptom of viral disease. It refers to how leaf veins become almost translucent while the leaf blades remain green. Squash mosaic carriers
Unlike other mosaic diseases, aphids are not responsible for squash mosaic. Instead, striped cucumber beetles, leaf beetles, spotted cucumber 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, so remove any infected plants. Squash mosaic controls In addition to removing infected plants, beetle control helps prevent 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. Handpicking is one way to control beetles, but only if you are quick enough. You can also use neem oil to kill beetle eggs. Encourage beneficial predators, such as ladybugs, mantids, and soldier bugs, in the garden with fresh water, insectary plants, and little or no chemical use. Supporting beneficial insects is the easiest method of keeping beetle populations within reasonable limits. Squash mosaic can infect seeds, so get clean, disease-resistant seeds and seedlings from a reputable supplier (not that melon from the grocery store). Certain chenopod weeds, including lambsquarters, goosefoot, and Russian thistle, 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 leaves 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, 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. Speckled, mottled, or otherwise deformed leaves and fruit usually indicate a mosaic disease. Mosaic diseases are a collection of viral infections that can infect most of your garden plants. Since these diseases are difficult or impossible to treat, recognizing and removing infected plants as soon as possible can help prevent the disease from spreading. Symptoms of mosaic diseases The classic mottled appearance of infected leaves is only one symptom of a mosaic disease. Leaf cupping, blistering, stunting, crinkling, and other distortions are other common symptoms of mosaic diseases. Stems may also be shorter, creating a bushy appearance to vines. Fruit may also show the same mottling and other distortions seen on leaves. Warty bumps are also commonly seen. 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. Distortions only occur in post-infection leaves and fruit. Plants that host mosaic diseases It would be easier to list plants that are not affected by mosaics. But the plants most commonly infected with mosaic diseases include the following: Common mosaic diseases While there are dozens (hundreds?) of mosaic diseases, some of the more common varieties include this list: Mosaic disease management
Generally speaking, mosaic diseases are not curable. Remove infected plants and toss them in the garbage. Prevention is a far better course of action. Depending on the specific virus, it may catch a ride into your garden on seeds, tools, aphids, dryberry mites, and other sap-sucking pests. These tips can help reduce the chance of a mosaic disease robbing you of your harvest:
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 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. 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. Horticultural oil spray can also interrupt transmission of this virus but may cause problems of its own. 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. 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. Sometimes plants grow in ways you might not expect. Instead of a nice round stem, you see a flattened ribbon shape. Rather than a regular flower, you get undulating folds. In flowers, it is called cockscomb or cresting. Wherever it happens, it is called fasciation. Fasciation is a relatively rare physiological disorder that can create some beautiful mutations. It can occur anywhere on a plant, but stems and flowers are the most commonly seen examples. How does fasciation occur? In normal plant development, growing tips (apical meristems) focus all their resources on a single point, creating straight or cylindrical stems and flowers. Fasciation elongates the apical meristem, creating a ribbon-like growth. The Latin fascia means band. In some cases, these distortions can create unique bends, twists, odd angles, or unusual clusters of growth that look like a witch's broom. Flowers and leaves growing on these distorted stems may be smaller, more abundant, or have other unique characteristics.
One rare form of fasciation, ring fasciation, has a ring-shaped growing point that creates hollow tubes. What causes fasciation? Plant hormone imbalances, genetic mutations, environmental conditions, or disease can all result in fasciation. It can also occur for no apparent reason. Possible environmental factors include chemical overspray or exposure, mite or other insect infestation, and certain fungi. Exposure to cold and frost can also cause fasciation. Fasciation is not contagious unless caused by bacteria. Plants affected by fasciation Milkweed, nasturtiums, geraniums, dandelions, and ferns may all exhibit fasciation. It also occurs in fruits and vegetables, such as asparagus and broccoli. Some plants are prized and propagated simply because of their fasciation. When most of us hear the word ‘bicarbonate’ we think of baking soda. In this case, we’d only be half right. Baking soda (NaHCO3) is sodium bicarbonate. Potassium bicarbonate is something else entirely.
Unlike sodium bicarbonate, which leaves behind a sodium residue, ammonium bicarbonate (NH5CO3) contain nitrogen, and potassium bicarbonate (NH5CO3) contains potassium, both are important plant nutrients. Organic fungicide Potassium bicarbonate is an organic fungicide used mostly to prevent fungal diseases, such as alternaria blight, apple scab, black spot, blights, botrytis, downy mildews, molds, phytophthora, powdery mildew, and Septoria leaf spot. Once these diseases are in place, they are very difficult to get rid of, though potassium bicarbonate can certainly improve the situation. Research has shown that bicarbonates do, when they cover a leaf completely, slow the growth of and occasionally kill mold spores outright. For potassium bicarbonate to work effectively, it must be in solution. While some people promote the use of homemade mixes that use horticultural oils for this purpose, those oils can lead to phytotoxicity (plant poisoning), oily buildup on the leaves and in the soil, and the mix requires constant shaking to keep the oil and water mixed while applying. The ideal mixture of solution and treatment is sold under the name Ecomate Armicarb "O" 100 Fungicide®.
The fine folks at The Garden Professors Blog Facebook Page directed me towards some good information along the same lines. Bottom line: potassium bicarbonate sprays are an effective prevention and treatment of many fungal diseases. But these mixtures are not something you should be trying to concoct at home. Instead, read labels and buy a product that will protect and not harm your plants.
If you decide to use potassium bicarbonate in your garden, UC Davis recommends no more than 8 treatments a year. Yellow spots on leaves may indicate Septoria leaf spot. This fungal disease is very destructive. It affects celery, chicory, cucumber and other cucurbits, and tomatoes. Like other leaf spot diseases, Septoria reduces photosynthesis and the flow of critical nutrients through the vascular bundles, leaving plants to wither and die.
Warm, wet weather is all these fungi need to set up housekeeping in your garden. And that wetness can be caused by poorly placed sprinklers, leaky hoses, and overhead watering. Temperatures between 60°F and 80°F are ideal for fungal growth. Knowing what to look for can help you protect your plants. Types of Septoria Septoria is a family of fungi. Different subspecies affect different plants. The most common types of Septoria, followed by their host plants and symptoms, include the following:
Symptoms occur first in older leaves. The disease spreads upward into newer growth. As the spots spread, leaves turn yellow, die, and fall off. This leaf loss reduces plant vigor and increases the risk of sunburn damage. Severe infections can result in complete defoliation. Septoria leaf spot lifecycle Septoria fungi travel in the wind and rain, so monitor regularly. Spores land on host plants and send out thready hyphae, which enter plants through cracks and injury sites. Spores overwinter in the soil and on infected plant debris. How to control Septoria leaf spot As with many other diseases, prevention is far easier than treating them. These tips will help prevent Septoria leaf spot in your garden:
If Septoria leaf spot appears, remove infected leaves and throw them in the trash. Also, sanitize any tools that may have come into contact with infected plants. Basil’s fragrant leaves make it a garden favorite. But there is a new disease on the horizon: basil downy mildew. Warm, moist conditions are all basil downy mildew needs to set up housekeeping on your basil plants. First seen in Africa in the 1930s, basil downy mildew (Peronospora belbahrii) came to the U.S. in 2007, probably on infected seeds. It is now a global problem for everyone who enjoys basil and pesto. Downy mildews Like other downy mildews, basil downy mildew is an infection by tiny, algae-like microbes called oomycetes. Oomycetes parasitize vascular plants to complete their life cycle. They do this by collecting on the underside of leaves. From there, these tiny one-celled creatures send out threads that enter the leaf through the stoma and begin propagating. Since the oomycetes cannot pass beyond the leaf veins, the damage from each infection stays between the veins. But when new spores emerge from the stoma, they fall to the soil, waiting to be splashed back up by rain or irrigation water or caught on the breeze for a ride to a new host plant. In addition to water and wind, spores can travel on garden tools, clothing, transplants, and infected seeds. So, how do you know if your basil plants are infected? Symptoms of basil downy mildew Unfortunately, the earliest sign of infection, yellowing leaves, looks like nutritional deficiencies. If you see yellowing between the primary leaf veins, with dark blotchy areas, look at the underside of those leaves. If you see purple or gray powdery spores, it is probably basil downy mildew. Those spores are reproductive bodies. Every infected leaf is a disease factory. Once a plant is infected, it is too late. Harvest any leaves that still look healthy and bury the plant under the soil or in the compost pile to prevent spores from spreading. Generally speaking, these pathogens will not survive in compost or through winter temperatures. We hope. Or, you can bag those diseased plants and throw them in the garbage. Preventing basil downy mildew
To avoid being part of the problem, buy only certified disease-free seeds and seedlings, place all new plants in quarantine, and monitor plants closely. As tempting as it may be, do not replant grocery-store basil plants in your garden. They are guaranteed safe to eat. They are not guaranteed safe to grow. Wet leaves are prone to infection, so provide your basil plants with good air circulation and keep irrigation water at ground level. Skip the watering can. Instead, use a soaker hose or drip system to prevent spores from splashing up onto the underside of leaves. Cut basil plants off at ground level at the end of the growing season and compost them to help break this disease triangle and reduce the chance of things starting again each spring. If you think basil downy mildew has appeared in your garden, please notify your local County Extension Office or Department of Agriculture. You can also use the Basil Downy Mildew Reporting Page to add your contribution to science! Bacterial brown spot is a bacterial disease that causes brown spots on beans, lentils, and other legumes. Overhead watering spreads bacterial brown spot infections, plus it provides the bacteria with needed moisture, so don’t do it. Use soaker hoses, drip lines, or simply hold your garden hose closer to the ground as you water.
At the end of the growing season, remove host plant debris and add it to the compost pile. Crop rotation and fixed copper sprays can also reduce the risk of bacterial brown spot. These lesions interfere with photosynthesis, weakening plants and reducing your crop. Rather than allowing infection to spread, it is better to remove infected plants and toss them in the trash. Preventing bacterial brown spot Start out with certified disease-free plants and seeds. If you buy plants, put them in quarantine until you are certain that they are healthy.The bacterium responsible for bacterial brown spot is called Pseudomonas syringae pv. syringae. This bacteria is already found on the leaves of many different plants. Wind, rain, overhead watering, or coming into contact with infected seeds and plants can cause bacterial population explosions in snap beans, pole beans, peas, lima beans, and other legumes. Bacterial brown spot can also infect orchids, so be sure to wash your hands and sanitize your tools. The pathogen enters through stoma and points of injury, usually when temperatures are below 85°F, and during the rainy season. Before long, symptoms will appear. Bacterial brown spot symptoms Bacterial brown spot is frequently confused with halo blight 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. Halo blight lesions tend to stay small and they have prominent light green halos, hence the name. Bacterial brown spot lesions have narrow light green borders and the centers tend to dry out and look tattered. The spots may overlap, creating an even more tattered appearance. Pods infected with bacterial brown spot become distorted. Lesions are also seen on stems. Mottles are symptoms of viral disease. Mottles are irregularly colored, spotted, or blotched areas. These discolored areas are usually yellow, but not always. Mottles often indicate viral mosaic disease. Viral families
Several families of viruses cause mottling in plants. And each of these families causes dozens, maybe hundreds, of diseases. There are even sub-viral agents that lack the genetic instructions needed for replication. Because of this, they use helper viruses to set up households in plant victims. The more we learn, the stranger the world gets. Diseases that present as mottling When plants are struggling, many normal behaviors are interrupted. The discoloration associated with mottling can indicate any of the following diseases:
Mottling can also occur in response to cold temperatures. Or it may indicate a zinc deficiency. Air pollution can also cause mottling. In the case of mottle-leaf in citrus, it gets confusing. The jury is still out on whether this condition is from too much nitrogen, insufficient nitrogen or organic matter (SOM), or mineral deficiencies or toxicities. Yes, assessing poor plant health can be challenging. But the more you know, the better you can help them grow. Mottle or mosaic? Mottling is a symptom. Mosaics are diseases. And mottling can be a symptom of a mosaic disease. Bottom line, if you see uncharacteristic coloration on leaves or fruit, take a closer look and consider what might be causing it before a full-blown infection wipes out your crop. Armillaria root rot is a soil borne that attacks the roots and trunks of many fruit and nut trees. It is also the largest living fungi in the world. In Oregon’s Malheur National Forest, there is a mushroom colony that covers 2.200 acres. That colony is believed to be a single entity, all growing from the same network of fungal mycelium. By itself, that's impressive. In your tree, it's a deadly fungal disease. Trees vulnerable to Armillaria root rot Also known as honey fungus, shoestring fungus, or oak root fungus, Armillaria root rot (Armillaria mellea) is a deadly disease that infects avocado, cherimoya, cherry, chestnuts, conifers, kiwifruit, kumquat, lemons and other citrus, pomegranate, stone pine, and walnuts, along with the mighty oak. If that weren’t bad enough, trees weakened by Armillaria root rot become more susceptible to serious pests, such as Pacific flathead borers. Armillaria root rot symptoms Everything starts out looking fine. Your tree is growing nicely and you suspect nothing. Suddenly, you notice downward cupping leaves, chlorosis (yellowing), dieback of upper limbs, and leaf drop. You may also see a variety of mushrooms growing nearby. Your tree is dying. Young trees die quickly, while older trees make take longer, but the end result is nearly always the same. Armillaria root rot diagnosis If your tree shows the above mentioned symptoms, take a closer look at the base of your tree. You may be able to see fan-shaped fungal growth rising up the trunk from the soil level. Use a sharp knife and cut away a section of bark at the base of the tree, so you can see the cambium layer. If you see white fungal threads (mycelia) and can smell a strong mushroom odor, your tree is in serious trouble. If you see reddish brown streaks or patches, or water-soaked areas, the infection is more likely to be Phytophthora root and crown rot, rather than Armillaria, though that isn't any better news for your tree. If you have easy access to the tree’s roots, cut one open. Infected roots are darker than normal and have a cottony center. You may also see black rhizomorphs, called ‘shoestrings’, on the surface of infected roots. How Armillaria spreads
As a soil borne disease, Armillaria mycelia can remain viable in the soil for many years. It isn’t until a healthy root comes into contact with infected wood, roots, stumps, or other wood fragments. Then, the fungus enters the healthy tree and begins to populate the cambium layer, eventually killing the tree. Infected nursery stock can also carry this disease, so always quarantine new plants. Preventing Armillaria root rot Good drainage, sunburn protection, and proper (not excessive) irrigation can all help protect your trees against Armillaria root rot. Once infection occurs, the tree should be completely removed and the area should only be planted with crops that are not vulnerable to Alternaria root rot. |
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