Tomato & Capsicum diseases

Discussion in 'Fruit & Vegetable Growing' started by ClissAT, Apr 11, 2018.

  1. ClissAT

    ClissAT Valued Member Premium Member GOLD

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    Please note that this paper was written in USA & also in a time when chemical spraying was the normal method of control. Crop rotation will go a long way to controlling these diseases & general organic growing principles will help as well. But the ability to see what these diseases look like is very helpful to know what you are dealing with & what methods might be successful to control them. I have also found that imbalances in fertilizer types & pH can produce very similar looking problems on these plants.



    The Long List of Diseases Affecting Tomatoes and Capsicums in a Wet Growing Season
    By Thomas A. Zitter
    Cornell University
    (May 2001)

    Introduction

    The 2000 growing season will be remembered for the large number of diseases that could
    be found on both tomatoes and peppers. Some of these diseases are common to both crops, and
    include bacterial leaf spot, Phytophthora blight, and white mold. In this report, we will focus on
    the main fungal (late blight, early blight, Septoria leaf blight, Phytophthora blight), and bacterial
    (spot, speck and canker) diseases of tomato/pepper.

    Tomato Late Blight

    Tomato growers should be aware that late blight infections of this crop are not new in
    New York, but occurrence of the disease has definitely increased during the 1990s with the
    arrival of new immigrant strains of Phytophthora infestans.

    Late Blight of Tomaotes.jpg

    In 1993, U.S.-7 caused widespread losses in home gardens in rural upstate New York,
    with the disease eventually spreading into four counties (Oneida, Herkimer, Madison and
    Oswego).

    In 1996, late blight samples confirmed in the Plant Disease Diagnostic Lab were
    submitted from six counties (Chautaupqua, Ontario, Tioga, Orange, Schenectady and Clinton),
    consisting of U.S.-1, U.S.-8 and U.S.-17. Once again, the infections for the most part were
    limited to home gardens or tomato plantings used for nearby roadside stands.

    In 1997, both commercial and homeowners suffered the greatest losses to late blight
    previously recorded. Tomato late blight was verified by the Diagnostic Lab from samples
    submitted from 12 counties from western, central and eastern New York. Most damage resulted
    from a relatively new genotype of late blight called U.S.-17, which, for tomato, is particularly
    pathogenic. Several other genotypes infecting tomato were recovered (U.S.-8, U.S.-7 or 11,
    U.S.-1, and some unidentified strains), but none were as destructive as U.S.-17.

    In 2000, yet another new strain of late blight was found in eastern New York, causing
    heavy infections in commercial and homeowner settings in Albany, Columbia, Greene,
    Schenectady, Schoharie and Rensselaer counties (Fig. 1). Other occurrences on tomato were
    noted in Genesee, Niagara and Orleans counties. Of equal importance to the occurrence of a new
    strain was the possible linkage with petunias as a source of the initial inoculum. Petunias
    brought into the area from southern states could be carriers of the unwanted inoculum. It is
    unclear where the inoculum is coming from in each yearly incident. Infection may originate
    from infected potato tubers located in the same or nearby home garden setting, from windborne
    spores, from infected tomato transplants, as well as the possibility now from petunias.

    Tomato Early Blight

    This disease occurs every season because the causal fungus, Alternaria solani, can
    overwinter in the soil on infected debris. Primary infection is generally caused by the fungus in
    the soil, and can occur as early as mid-July in upstate locations. Older leaves are infected first,
    and the younger leaves are infected later, after they attain a certain physiological maturity. A
    close linkage occurs between the days to maturity and susceptibility to early blight, with early
    maturing varieties generally being quite susceptible. Following fruit set and development, plants
    become progressively more susceptible (Fig. 2). Long rotations of two or more years out of
    susceptible crops, including potato, are necessary to reduce the amount of overwintering
    inoculum.

    Early Blight of Tomaotes.jpg


    Septoria Leaf Spot of Tomato

    This disease occurs sporadically in New York, but it is particularly severe in years when
    wet weather conditions persist for extended periods, as occurred in the Capital District and
    surrounding counties during the 2000-growing season. The disease is particularly destructive to
    tomato foliage, but the fungus can also infect stems, petioles, and the calyx (Fig. 3). Fruit
    infections are rare. Initially, lesions may be as small (about 2 mm in diameter) as those caused
    by bacterial speck and could also be confused with bacterial spot. However, as Septoria lesions
    mature, they develop dark brown margins and tan-to-gray centers dotted with black, speck-like
    fruiting bodies called pycnidia. When conditions are appropriate and the tissue is succulent, the
    lesions are about 5 mm or 0.2 inch in diameter. The disease spreads upward from the oldest to
    the youngest growth, and if left uncontrolled, can almost defoliate a plant. Septoria lycopersici
    overwinters on infected tomato debris and certain solanaceous weeds such as horsenettle.
    Rotations of two years between tomato crops are recommended.
    Septoria of Tomaotes.jpg

    Phytophthora Blight of Pepper and Buckeye Rot of Tomato


    Even though solanaceous and cucurbitaceous crops are in very different plant families,
    tomatoes, peppers, pumpkins and squashes are all susceptible to infection by Phytophthora blight
    caused by the fungus Phytophthora capsici. P. capsici is a member of the oomycete group of
    fungi, are also known as the “water molds” because they generally grow best under high
    moisture conditions. In fact, the disease is most commonly found in low areas of the field or in
    poorly drained areas where soils remain saturated for extended periods of time. The stems of
    tomato, pepper, and eggplant plants are usually infected near the soil line (Fig.4). At first the
    lesions are dark green in color and appear water-soaked. With time the lesions dry and become
    brown in color. Symptoms also can spread to the upper stems, leaves and fruit. When infections
    occur at ground level the plants can be girdled. These plants will become gray-green in color
    and severely wilted. The fungus can also infect the upper stems and fruit (Buckeye rot) without
    affecting the lower stems, resulting in some wilted leaves and shriveled fruit on an otherwise
    healthy looking plant (Fig. 4.). The fungus survives in the soil and on infested seed. It becomes
    active and infects during warm, wet periods. Recommended control procedures include avoiding
    fields with a history of the disease, planting on well-drained soils, deep plowing to breakup
    hardpans, following crop rotation schedules that avoid other susceptible crops (peppers,
    tomatoes, eggplant, and all cucurbit crops), and the application of fungicides. Raised beds and
    plastic mulch help improve drainage and reduce the amount of spores splashing from the soil
    onto the plant.

    Phytopthora of Tomatoes.jpg


    Bacterial Leaf Spot of Pepper and Tomato

    Bacterial leaf spot (Xanthomonas campestris pv. vesicatoria) remains a problem in
    pepper and tomato fields (Fig. 5). In both instances, starting with clean seed and healthy
    transplants is required. Currently there are eleven races of the pathogen that have been
    identified. Tomato growers must rely upon fungicide sprays (fixed copper mixed with
    mancozeb) for control. Pepper growers should select resistant varieties, which are currently
    available. Commercial pepper varieties are available with resistance to three particular races.
    Named varieties with resistance to races 1, 2, 3, 7, 8 and 9 are: Lafayette, Brigadier and
    Commandant (Syngenta); Aladdin and Red Knight (Petoseed/Seminis); Enterprise, Yorktown,
    Mambo, Intrepid and Corvette (Asgrow/Seminis); Bravo, Orion and Diego (Enza Zaden);

    Boynton Bell (Harris Moran); and Summer Sweet 830 and 890 (Abbott and Cobb).
    Pageant (Syngenta), a sweet banana type, and Ironsides (Petoseed/Seminis), a bell type,
    had fairly good resistance. Many of these varieties may have some spots on the leaves and fruit
    if disease pressure is high, but defoliation is unlikely and yields will not be affected significantly.
    Fungicides used on pepper for BLS control include fixed coppers or a mixture of fixed copper
    and maneb. Following a two-year rotation out of pepper and tomato breaks the cycle of bacterial
    leaf spot carryover on plant debris.

    Bacterial Leaf Spot.jpg


    Bacterial Canker of Tomato

    Bacterial canker, caused by the bacterium Clavibacter michiganensis subsp.


    michiganesis, is one of the most serious diseases attacking tomatoes wherever they are grown.
    The disease has also been found on pepper in New York during the past two seasons, but losses
    on pepper are not as severe as on tomato. Symptoms of canker are first obvious on tomato
    foliage as a marginal necrosis (Fig. 6). A chlorotic area may be seen between the marginal
    necrosis and healthy leaf tissue. Stem cankers may also appear and are commonly found at the
    nodes along the stem. Cutting longitudinally through the stem reveals that the center pith is
    discolored and becomes “mealy.” Fruit symptoms appear as small white lesions with raised
    brown centers giving the appearance of a “bird’s eye spot.”
    The initial source of inoculum is from tomato seed, or if it has occurred previously on the
    farm, from overwintering tomato debris, weed hosts, volunteer plants, and especially from
    contaminated wooden stakes. It has also been reported from greenhouse transplant production
    areas.

    Sanitation is extremely important, since once the plants are infected, it is very difficult to
    control the disease in the field. All tomato seed should be treated with chlorine either by the
    seed provider or by the grower. During transplant production, seedlings can be treated with
    streptomycin before transplanting. Begin sprays once the first true leaves appear. If yellowing
    of the foliage occurs, reduce the rate of streptomycin. In the field, select an area that has been
    free of tomato for two to three years. Shortly after transplanting and once plants have recovered,
    apply a foliar spray of fixed copper and mancozeb several times at 7-day intervals.

    Bacterial Canker.jpg


    Bacterial Speck of Tomato

    Bacterial speck, caused by the bacterium Pseudomonas syringae pv. tomato, was
    common in the Capital District and surrounding counties in 2000. Cool temperatures and high
    moisture favor the disease. Small brown-to-black lesions appear on the foliage, and, with time, a
    yellow halo will develop (Fig. 7). Stems and petioles are also infected, along with the calyx and
    fruit. On fruit the specks are black and rarely larger than 1 mm in diameter, but this is sufficient
    to make them unmarketable. Like bacterial spot and canker, the bacterium responsible for speck

    Bacterial Speck Leaf Infections.jpg


    Editor’s Note: Dr. Thomas A. Zitter is a professor, Department of Plant Pathology, Cornell
    University, Ithaca, N.Y. This presentation was given Feb. 15 as part of the 2001 New York State
    Vegetable Conference Tomato and Pepper Session, held in Liverpool, N.Y.
     
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  2. DarrenP

    DarrenP Well-Known Member Premium Member GOLD

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    While I don't live in an area of a "wet growing season for tomatoes", that is an interesting read.
    Thanks, ClissAT.
     
  3. letsgo

    letsgo Valued Member Premium Member GOLD

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    Wow this post needs to be pinned, so great helpful info :)
     
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