Early Blight and Sunscald on Tomatoes

“What are the best varieties for the low country of South Carolina?  I have problem with what appears to be early blight and due to the heat, sun scalding.  I want hybrids and fungicides I can use.

thanks for your help,

ron”

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Hi Ron,

Thank you for the email regarding your tomato problems.

First of all, no matter what tomato variety you select, you are going to want to make sure that it is a variety with a good range of disease resistance.  One of the easiest methods to combating Early Blight and Sunscald is making sure your plants are as healthy as possible.

Seed companies don’t sell any tomato varieties that are particularly noted for having wonderful Early Blight resistance, and there are a couple of reasons for that.  First of all, research really hasn’t been done at the level of seed development for the home gardener in that respect.  Plant breeders have been gear more towards late blight because it is a more devasting disease and there are few cultural options for controlling it.

However, don’t be discouraged.  The solution to lowering your risk of having Early Blight starts right in your garden.  Early blight tends to get off to an early start in the spring when wet weather is experienced soon after transplants are set. These type of conditions are ideal for infection of young tomato plants by the early blight fungus.

Growing a crop in the same area for several years often leads to increased disease problems.  Early Blight control is based on crop rotation, removal and destruction of crop debris from previous crops, staking, mulching, and timely application of fungicides.  What I do at the end of the gardening season is pick up every stem, leaf, and fruit (no matter how small) and burn
them or put them in a garbage bag for the dump.

Staking and mulching are important in an Early Blight control program, since staking keeps foliage and fruit from contacting the soil surface, and mulching cuts down on “soil splash” onto lower parts of the plant. Since soil particles often contain the early blight fungus, this is a good way of keeping the fungus from invading plants. Plastic, or organic mulches (pine straw or even newspapers) are equally effective.

Application of fungicides is also generally needed for Early Blight control, if you are into that kind of thing.  Field tests have shown that chlorothalonil, maneb, and mancozeb fungicides –
all available at gardening supply stores under a variety of trade names –  provide effective early blight control when used according to label directions and applications are started early in the season. As an added plus, any of these fungicides may be “tank mixed” with an insecticide such as malathion or Sevin (or newer formulation, Eight), thus allowing a single application for control of disease and insects.

Begin fungicide applications as soon as possible after transplants are set out and continue at 7 to 10-day intervals throughout the season. Also, applications should be made after a rain. Other leaf diseases such as leaf mold, gray leaf spot, and Septoria leaf spot are controlled by these fungicides.  Make sure to read and follow label directions concerning rates, application intervals, and the number of days required from the last application until fruit can be harvested.

As for the sunscald, this comes from not having enough leaf cover over the tomato as it is developing.  UV rays damage the pigments inside the tomato — just like it does to human skin.  In turn, the ‘pigment initials’ for lycopene and other carotenoids that are present in a ripe tomato to give it color are damaged enough that they will not have color.  Natural enzymes and plant hormones ripen the tomato so it is soft and deteriorate the chlorophyll so it is the ripe color.  However, with no lycopene or other carotenoids there, it’s just whitish and lacking pigment.  Controlling the
Early Blight so you are not losing foliage and staking your plants will aid in controlling the sunscald.

As for some varieties that are good for South Carolina, I recommend:

–Large:  Better Boy, Better Bush, Big Beef, Celebrity, Early Girl II, Park’s Whopper
–Cherry:  Juliet (these are the best I’ve had against Early Blight in my garden and they are really good with Late Blight too), Small Fry, Super Sweet 100, Sweet Million, Tomatoberry Garden
–Plum:  Viva Italia

I hope this information helps you out.  If you have any other questions, please feel free to ask.

Oozing Gel: Peach Tree Borer or Cytospora Canker?

“My peach trees are oozing gel. What is wrong with them? Thanks, Gary”

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Hi Gary,

Thank you for your question.  Oozing gel could be one of two things.  If the gel has fine sawdust on it, you have Peach Tree Borer.  If not, the other problem the tree could have is cytospora canker.

The peach tree borer (also called the peach crown borer) is the most destructive insect pest of peach, cherry, plum and other stone fruits (Prunus spp.). The insect feeds under the bark of the tree, where it cuts deep gouges. When abundant, peach tree borers seriously weaken and even kill trees.

The entire life cycle of the peach tree borer requires one year to complete. The immature (larva) stage produces tree damage. Upon hatching from the eggs, young larvae immediately tunnel into the sapwood of the tree, usually through cracks and wounds in the bark. Larvae continue to feed and develop until the onset of cold weather. Most activity occurs a few inches below ground on the trunk and larger roots. The Insects spend the winter as partially grown larvae below ground under the bark.

With the return of warmer weather in early spring, the larvae again feed on the tree. Injury is most extensive at this time because the maturing Insects feed more. The larvae finish feeding and change to the pupal stage in late May through early July. Pupation occurs in a cell made of silk, gum and chewed wood fragments located just below the soil surface.

The pupal stage lasts almost one month. Adult borers then emerge. They often pull out the pupal skin in the process. This skin may be seen at the base of the tree. Adults are a kind of clearwing moth that fly during the day and superficially resemble wasps. Adult activity may begin as early as mid-June but primarily occurs during July and August. After mating, the female moth lays up to 400 eggs on the bark of the lower trunk and in soil cracks near the tree base. Eggs generally hatch in about 10 days.

External evidence of peach tree borer tunneling is a wet spot on the bark or the presence of oozing, gummy sap. The sap is clear or translucent and often dark from the sawdust-like excrement of the insect. Most injuries occur along the lower trunk beneath the soil line. Lower branches rarely receive injuries.

Peach tree borer can be difficult to control because insecticides cannot reach the damaging larvae after they move under the bark. The most effective controls are preventive insecticide applications at the vulnerable egg and early larval stages, while the insect is on the tree bark.

Egg laying occurs during the middle of the growing season. It may begin July 1 and continue into September. In general, peak egg laying occurs from mid-July to mid-August.

As a general guideline, apply preventive trunk sprays the first or second week in July and again in August if flights continue. Better determination of egg-laying occurrence is possible using pheromone (sex attractant) traps that capture adult Insects. Pheromone traps are available through some garden supply catalogs.

Peach tree borer is controlled in commercial orchards by insecticides that contain permethrin (Pounce, Ambush) or esfenvalerate (Asana). Insecticides containing these active ingredients (permethrin, esfenvalerate) are recently becoming available in some garden centers. Perhaps more widely available is carbaryl (Sevin). Some formulations of this insecticide allow use on fruit-bearing trees.

Paradichlorobenzene (PDB) moth crystals, used as a fumigant, may help control infestations of peach tree borer within a tree. After clearing away leaves and other debris from around the tree base, place the crystals in a band 1 to 2 inches from the base of the tree trunk. Cover the crystals with enough soil to create a 5- to 10-inch packed mound around the plant. The crystals release a gas at temperatures above 60 degrees F. The gas penetrates the trunk to kill peach tree borer larvae. Applications of PDB crystals are best made in late September or early fall but also can be applied in late spring.

PDB can injure plants. To avoid plant injury, follow these precautions:

1.    Do not allow the crystals to touch the tree bark.

2.    Adjust the amount of crystals used by tree size. Use 1/4 ounce on a first-year tree, 1/2 ounce on a 2-year-old tree, 3/4 ounce on a 3- to 5-year-old tree, and 1 to 2 ounces on a large, well-established tree.

3.    Remove the soil mound three weeks after the application.

With some effort, many larvae can be dug out of the tree or killed by puncturing them with a strong, thin wire. Be careful with these methods because they may cause more mechanical injury to the tree than the borer itself.

Maintaining tree vigor through proper tree care (water, fertilization, pruning, etc.) can greatly affect how well the tree can tolerate borer injury. Avoid any unnecessary wounding around the lower trunk; this area is often attacked. Extra care of already damaged trees is particularly important.

The use of insect parasitic/predator nematodes has given inconsistent control of peach tree borer larvae. If they are used, it is suggested that they be applied in a large volume of water to adequately moisten the soil. Also, use them only if soil temperatures are at least 50 degrees. insect parasitic nematodes are available through many nursery catalogs and some local nurseries.

Cytospora canker is a destructive disease of tree fruits. Although most common on stone fruits, the disease can be encountered on apple. Also known as peach canker, perennial canker, and Valsa canker in some areas, the disease occurs wherever stone fruits are grown. The disease is general in occurrence in peach, nectarine, prune, plum, and sweet cherry orchards. Cytospora canker is associated with winter-injured or mechanically wounded twigs, trunks, and scaffold branches.

Cytospora canker is caused by either of two fungi species, Cytospora leucostoma or Cytospora cincta. These two fungi are very similar morphologically and can be definitively separated only by microscopic examination of the sexual fruiting structures. These structures, called perithecia, are not frequently found.

The Cytospora fungi are vigorous wound invaders that grow throughout the bark and cambium and to a lesser extent into the structural wood of the tree. Common infection sites are bark that has been killed or injured by low winter temperatures or sunburn, pruning cuts, or insect damage. Winter injury is frequently an important predisposing factor to infection. Once established in dead or weakened tissue, the Cytospora fungi will invade adjacent healthy tissue, causing dieback and stem cankers.

As cankers enlarge, the fungus produces pinhead-sized, black, pimplelike, spore-producing structures, called pycnidia. These structures produce millions of spores, called conidia. During wet weather, spores ooze out of the spore-producing structures in reddish to orange colored gelatinous masses. Spores are carried to other infection sites (that is, wounds on the same or nearby trees) by splashing and windblown rain, insects, or people. These spores are not adapted to wind dispersal. Spores germinate at wound sites, resulting in infection and eventual cankering. Spore-producing structures ultimately form in the new cankers, producing more spores for subsequent infections. The spore-producing structures generally form 4 to 6 weeks after a cankered branch dies. The fungus overwinters in diseased tissue of living hosts and in stem debris on the ground.

If cankers are allowed to remain for several years, a second spore-producing structure, the perithecium, develops in the diseased tissue and produces ascospores. Ascospores are wind-disseminated; infection can result if moisture is present when ascospores are blown against wounded host tissue.

Infection can occur anytime during the year, except during very hot and dry, or cold weather. In Idaho, most infections occur during spring and early summer when temperatures are mild and moisture from rainfall is high.

Usually, the first symptoms of infection are dead twigs and dieback. Leaves above stem infections droop and discolor through shades of green to various shades of brown, and often remain attached, sometimes through the winter. These “flags” are caused by stem invasions and girdling or near-girdling cankers immediately below the flag.

Cankers are dark and depressed areas of dead bark and wood on main leaders and branches. Canker margins are sharp and distinct on the bark and discolored wood. Cankers are frequently perennial and may assume a zoneate appearance. Young cankers usually exude gum at the margin and may have a sour, sap odor. The surface of the cankers may develop raised pinhead-sized pycnidia in the bark. The spore-forming structures are rarely produced on cherry stems. After rainy weather, tendrils of dried reddish-orange ooze are sometimes visible coming from pycnidia.

Small at first, cankers slowly enlarge elliptically; sometimes they streak rapidly up and down the stem without girdling it immediately.

There is currently no cure for infected trees. Prevention and sanitation practices are the best management approaches. Use the following three steps concurrently.

1. Minimize injuries. Winter injuries are the most common infection sites. Painting tree trunks white before winter has reduced Cytospora infections. Take other measures to reduce winter injury and maintain good tree vigor.

2. Remove and destroy infected wood. Prune out infected branches, flags, cankers, and maintain good orchard sanitation. Cytospora has been isolated from apparently healthy tissue on cankered branches. Make pruning cuts at least one foot below the infected area.

3. Prune correctly. Make cuts that leave a raised collar of tissue at the branch junction rather than flush cuts or cuts that leave a stub. Pruning in the spring when wounds heal most rapidly has effectively reduced disease incidence in some areas.

Do not establish new orchards close to badly diseased orchards. Treetop or other hedgerow pruning and overhead irrigation favor the disease. Maintain trees in good vigor, but with maximum hardiness. Trees under water stress or grown in potassium-deficient soil are susceptible to infection. Weakened trees easily become victims of the Cytospora fungi.

I hope this information helps you out.  If you have any other questions, please feel free to ask.

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2014. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

 

Rose Rosette Disease

“I purchased 10 Dream Come True grandi roses last Summer.  I had a wonderful summer/fall with them last year.  Several of them succombed to rose rosette disease this summer.  Do you have any suggestions to prevent any other plants from getting it or what to do?  I live in Virginia.  I just learned about this disease today, I will remove the diseased roses and bag them for trash.  Help is appreciated! ~J.”

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Thank you for contacting me in regards to your roses.  Rose rosette disease (RRD), a disease believed to be caused by a virus, has been spreading through much of the wild rose population of the midwestern, southern and eastern United States for years, and has now been confirmed in cultivated roses in Virginia. This disease is of great concern to the nursery industry and to many home gardeners because it is known to be lethal to the wild multiflora rose (Rosa multiflora) and it is potentially lethal to many ornamental rose species and cultivars.

Symptoms of rose rosette disease are highly variable, depending on the species or cultivar of rose affected. This variability can complicate diagnosis. Some of the more recognizable symptoms include rapid elongation of new shoots, followed by development of witches’ brooms or clustering of small branches.  Leaves in the witches’ broom are small, distorted, and may have a conspicuous red pigmentation, although red pigmentation is not a consistent symptom. Canes on some species or cultivars develop excessive growth of unusually soft and pliable red or green thorns, which may stiffen later. When this symptom is present, it is diagnostic for rose rosette disease. Symptomatic canes may also be noticeably thicker than the parent cane from which they emerged or they may grow in a spiral pattern. Flowers
may be distorted with fewer petals than normal, and flower color may be abnormal. For example, flowers that are normally a solid color may be mottled. Buds may abort, be deformed, or be converted to leaf-like tissue. Infected rose plants often die within one to two years.

When all of the above symptoms are present, diagnosis is relatively straightforward. However, a diseased plant may exhibit few of these symptoms, especially in the early stages of the disease. By the time symptoms are severe and recognizable, the disease is likely to have already spread to neighboring plants.

Some symptoms, such as leaf coloration, may be subtle. Although some diseased plants develop very obvious red pigmentation, others exhibit a less striking reddish pink color on leaf undersides or along the margins of otherwise green leaves. Since the new leaves of many rose cultivars normally have reddish pigments, it may be difficult to determine whether the reddish color is abnormal or not. Therefore, it is important to continue to monitor symptoms on suspect roses. On RRD-infected plants, the reddish color does not go away, whereas on healthy plants, the reddish color usually disappears as the leaf matures. Witches’ brooms on some diseased plants may be an unusual color of green that can be mistaken for symptoms of a nutrient deficiency. However, nutrient deficiency should affect the whole plant. If these symptoms appear only on parts of the plant, they are probably not due to nutrient deficiency, and RRD is more likely.

The witches’ broom symptom itself is not necessarily diagnostic for rose rosette disease. This symptom can also occur in response to certain types of herbicide injury. For example, if glyphosate, the active ingredient of the herbicide Roundup, contacts green tissue of rose plants in the fall, it is translocated to the buds, and symptoms do not become evident until those buds emerge the following spring. Witches’ brooms with yellow, narrow leaves on clusters of shoots are typical of glyphosate injury. The commonly used broadleaf herbicide 2,4-D can also cause leaf distortion on roses. Unless plants are injured again, symptoms of herbicide injury should disappear by the following year.

Other symptoms of RRD that may be expressed include blackening and death of the canes on some cultivars, short internodal distances, blind shoots (shoots that do not produce a flower) that remain blind, and greater sensitivity of reddish purple tissue to frost. Leaves of diseased plants may have a roughened, “pebbly” texture. Plants with RRD also have increased susceptibility to the fungal disease, powdery mildew. This is especially evident when nearby roses known to be highly susceptible to powdery mildew do not develop signs of this disease.

Symptoms that were undoubtedly due to rose rosette disease were described in the United States as early as 1941. Spread of the disease in the United States was intimately tied to the history of the multiflora rose, an exotic plant that was introduced from Japan in 1866 as a rootstock for ornamental roses. During the 1930’s through 1960’s, planting multiflora rose was recommended for erosion control, as a bird sanctuary and food source, as a living fence for cattle, for strip mine reclamation, and as a crash barrier on highways. This recommendation ultimately backfired. Multiflora rose can produce a million or more seeds per plant and can propagate itself vegetatively as well. It quickly spread and is now declared a noxious weed in several states.

Multiflora rose is highly susceptible to rose rosette disease, so much so that the disease was initially considered a potential biological control for multiflora rose. Even now, some people suggest introducing infected plants into areas with multiflora rose to control this weed. Most rose growers, however, are very wary of this recommendation because rose rosette disease can spread quickly from multiflora rose to cultivated roses.

Rose rosette disease is caused by a virus or virus-like pathogen yet to be characterized. Because the exact causal agent has not yet been identified, there is currently no laboratory test for confirming rose rosette disease. The disease is diagnosed based on a preponderance of characteristic symptoms or by grafting suspect plant material onto known healthy roses and demonstrating transmission of symptoms after a period of weeks to months.

The disease is known to be transmitted by the eriophyid mite Phyllocoptes fructiphylus or by grafting. The wild multiflora rose (Rosa multiflora) is very susceptible to the disease and is a common source of inoculum. Cultivated roses planted downwind of infected multiflora rose are especially at risk because the mite vector travels on wind currents from infected to healthy plants. Some growers have observed symptoms on previously healthy plants within four weeks of being planted downwind from diseased multiflora rose.

The causal agent of rose rosette disease is not soil-borne, so it is possible to successfully plant healthy roses in beds where diseased plants have been removed; however, the pathogen may persist in old root pieces that remain in the soil from previous diseased roses. If plants regrow from these old root pieces, as multiflora rose is apt to do, they can serve as an inoculum source for healthy plants. Therefore, it is important to remove old plants thoroughly and ensure that infected plants are not allowed to regrow from old, infected root pieces.

No effective control is available for rose rosette in existing, diseased rose plants, but the disease may be prevented from spreading to healthy plants by using a combination of the following approaches.

R. multiflora is the species that appears to be most susceptible to rose rosette disease. However, many species and selections of cultivated roses are also highly susceptible, and no cultivars have been proven to be resistant. Although the native species Rosa setigera is reported to be resistant to the disease, one grower has reported increased susceptibility
to powdery mildew on plants of R. setigera, which could indicate some level of infection by the RRD pathogen. A species called the McCartney rose, which exists as a weed in Texas, is susceptible to RRD but resistant to feeding by the mites that transmit the disease. It may be possible, through breeding techniques, to incorporate this mite resistance into cultivated roses in the future. In the meantime, it would be wise to assume that all cultivated roses are potentially susceptible to the disease and to be on the lookout for symptoms of rose rosette.

Early detection of the disease is the key to effective cultural control. Any suspect roses should be removed and destroyed immediately or monitored for continued symptoms and removed as soon as presence of RRD is ascertained. In some areas burning is permitted and can be used to destroy diseased plants. If burning is not allowed in your area, plants should be bagged and removed. Diseased plants that have been uprooted should not be allowed to remain in
the vicinity of healthy roses as they can continue to serve as a source of inoculum.

If possible, R. multiflora plants, which frequently serve as the source of inoculum, should be eliminated from the immediate vicinity (100-meter radius) of rose nurseries and gardens. Locations where individual multiflora rose plants have been removed should be monitored for regrowth and any regrowth should be removed and destroyed. Multiflora rose over larger areas is, however, difficult to control and complete removal may not be practical. To prevent infection of new transplants, avoid planting cultivated roses on hilltops or downwind of known multiflora rose plantings where the cultivated rose transplants are more susceptible to invasion by the mites. Space plants so that canes and leaves do not touch each other. Eriophyid mites do not have wings and must crawl from plant to plant. Proper spacing makes it more
difficult for the mites to move within a planting.

Although there is no compound that will control the causal agent of rose rosette directly, effective control of mites with certain miticides can reduce the risk of spread. Be aware that miticides registered for control of spider mites do not control the eriophyid mites that transmit rose rosette disease. Some researchers have obtained reasonable control with Sevin; however, mites are very small and it can be difficult to get complete coverage. Also, use of Sevin to control eriophyid mites can lead to outbreaks of spider mites. The insecticide, Avid, is registered for control of both eriophyid and spider mites on roses.

Use of miticides in the absence of cultural controls is not recommended. One way to use a miticide as an additional tool in a control program is to focus sprays on plants that surround spots where diseased plants have been removed. These are the most likely plants to which mites from within a planting would have moved. Spraying every two weeks from April until September should significantly reduce the mite population and the risk of transmission. Additional sprays may be needed during hot, dry weather when eriophyid mites are most active.

 

 

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2011. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

Rhubarb Insect Control: Rhubarb Curculio

“Hi Edelweiss,

I get bugs eating on my rhubarb stems each year.  It looks like eggs under the leaves, but I’ve never seen any bugs to identify.  What are they and what can I do? Colorado potato beetles?  Sevin?

Thanks,

Ben”

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Hi Ben,

Thanks for contacting Horticulture Talk through our Facebook page.  To be honest, there are not a lot of insect pests that affect rhubarb — because it is acidic and because of the oxalate crystals in the leaves.  However, based on your description, it sounds like you have Rhubarb Curculio (Lixus concavus).

The leaf stalks of the rhubarb may show exuding sap and partial decay from late-May through early summer, due to the feeding and egg laying punctures of the rhubarb curculio.  Feeding injury appears as notches in the stem and on the leaf edges. Sap exudes from wounds of either type and collects as glistening drops of gum when fresh. Fortunately, the eggs of this insect do not hatch when deposited in rhubarb.

The rhubarb curculio (or rhubarb weevil) is a large snout beetle, about 1/2 inch long. It is dark colored, with a yellow powdery material dusted on its back. The yellowish covering easily rubs off when the insect is handled.  The head has a downwardly curved snout, at the end of which are the mandibles (the chewing mouth parts). The eggs are oblong and yellow- white in color (similar to Colorado Potato Beetles). The mature larva is a legless grub about 3/4 inch in length, with a brown head.

The curculio overwinters as an adult, in piles of debris or in other protected places near the rhubarb planting. In about mid-May the adults appear, and are seen resting on the stalks and leaves of rhubarb, dock, thistle or sunflower. They soon begin laying eggs. Eggs are deposited singly in cavities about 1/8 inch deep in the stalks of host plants, and hatching occurs in a week to ten days, in all plants but the rhubarb. The rhubarb curculio survives in weeds in or near the garden. Eggs deposited in rhubarb do not hatch, but are killed by the actively growing plant tissue, which crushes them. In other hosts the newly hatched larva begins burrowing its way down through the stalk, so that when it reaches maturity in eight to nine weeks, it has reached the bottom of the stalk just below the soil surface. Usually one grub reaches maturity in a host plant. Pupation occurs in a cavity at the base of the host plant, and within a few weeks the adult beetles emerge. The adults feed for a short time, and then seek out protected places to spend the winter. There is only one generation of this insect a year.

The only direct method of control is to hand pick the beetles from the plants during early summer and destroy them. When the beetles first emerge they are easily picked from the vegetation on which they are resting. Their large size aids in finding them and helps make them easy to handle. The removal of all wild plants in which the beetles breed (dock, thistle, and sunflower) growing in or near the planting during July, while the curculio larvae are still in them, will also be helpful.

 

 

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2011. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

It’s Not Too Late: Controlling Early Blight on your Tomatoes

“Dear Horticulture Talk Blogger,  I have noticed that I have a lot of blight starting on my tomato plants.  It is early blight, not late.  Is it too late to do something about it?  Love your column and would love to know your thoughts on this. Thanks, ~T.”

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Attention home gardeners — it’s not too early to start your control program for tomato early blight!

Early Tomato Blight (Alternaria solani) is generally one of the most severe tomato problems faced by home gardeners each season.  Early blight shows up as a leaf blight on the lower part of plants. The disease moves upward, and by early to mid-summer, early blight has caused a “firing-up” of foliage over most of the tomato plants in the garden.  As the disease progresses, leaves turn yellow, wither, and drop from plants. Tomato plant severely infected by early blight produce low yields of undersized fruit. Generally, fruit are also show signs of sun-scald since leaves aren’t present to protect fruit from direct sunlight.

Early blight tends to get off to an early start in the spring when wet weather is experienced soon after transplants are set. These type conditions are ideal for infection of young tomato plants by the early blight fungus. But probably the most important reason this disease is so common has to do with the tremendous popularity of tomatoes in Southern gardens.

For top yields of high quality fruit, early blight control is essential. Since early blight-resistant tomato varieties aren’t available, gardeners have to use a combination of practices to keep this disease in check.

As experienced gardeners know, growing a crop in the same area for several years often leads to increased disease problems.  Early blight control is based on crop rotation, removal and destruction of crop debris from previous crops, staking, mulching, and timely application of fungicides.

Staking and mulching are important in an early blight control program, since staking keeps foliage and fruit from contacting the soil surface, and mulching cuts down on “soil splash” onto lower parts of the plant. Since soil particles often contain the early blight fungus, this is a good way of keeping the fungus from invading plants. Plastic, or organic mulches (pine straw or even newspapers) are equally effective.

Application of fungicides is also generally needed for early blight control. Field tests have shown that chlorothalonil, maneb, and mancozeb fungicides — all available at gardening supply stores under a variety of trade names — provide effective early blight control when used according to label directions and applications are started early in the season.

As an added plus, any of these fungicides may be “tank mixed” with an insecticide such as malathion or Sevin (or newer formulation, Eight), thus allowing a single application for control of disease and insects.

Begin fungicide applications as soon as possible after transplants are set out and continue at 7 to 10-day intervals throughout the season. Also, applications should be made after a rain. Other leaf diseases such as leaf mold, gray leaf spot, and Septoria leaf spot are controlled by these fungicides.

Make sure to read and follow label directions concerning rates, application intervals, and the number of days required from the last application until fruit can be harvested.

For more information on Early Blight Resistant Tomato varieties, click here.

 

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© Mertie Mae Botanics LLC and Horticulture Talk!, 2010. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.