Vegetable Production Update- June 22, 2018
From Dr. Amanda Strayer-Scherer (Postdoctoral Research Scholar, Plant Pathology, Tomatoes) and Inga Meadows (Extension Associate, Plant Pathology Specialist)
Background: The information presented in this vegetable production update contains a summary of the details discussed in the one-hour, biweekly vegetable production conference calls entitled Veggie Calls. These open forum sessions were developed to allow extension personnel (agents, area specialized agents [ASAs], and specialists) to discuss challenging cases, seek advice on recommendations, report emerging issues, and share training opportunities related to vegetable production. These calls are hosted by Inga Meadows, Dr. Amanda Strayer-Scherer, and/or Dr. Lina Quesada-Ocampo every two weeks throughout the vegetable production season.
Attendees (description) of the June 22 Veggie Call: Minda Daughtry (Extension Agent, Lee County), Craig Mauney (Extension Area Specialized Agent, Commercial Vegetables & Fruits), Inga Meadows (Extension Associate, Vegetable and Herbaceous Ornamental Pathology), Daniel Overcash (NCDA Agronomist), and Amanda Scherer (Postdoctoral Research Scholar, Plant Pathology).
Vegetable Production Updates: Overall, there has been a lot of rain over the last couple of weeks, which has increased disease incidence. Due to heavy rains and flooding, there have been several calls about replant periods in flooded areas.
- Powdery Mildew has been reported on zucchini in three counties from Western and Central North Carolina.
- Tomato spotted wilt virus (TSWV) has been reported on field tomatoes in three counties from Western and Central North Carolina.
- Bacterial wilt has been reported in greenhouse tomatoes Central North Carolina and in field tomatoes in Western North Carolina.
- Southern blight was reported on tomatoes in Western North Carolina. Sclerotia, a sign of the disease, were present.
- Bean Rust has been reported on pole beans in Western North Carolina.
- Damping-off has been reported on tomato transplants in North-Central North Carolina.
- In Western North Carolina and Northern Georgia, there has been a steady stream of reports of Phytophthora nicotianae and capsici causing stem and leaf lesions on peppers and tomatoes. Lesions look very similar to late blight, but P. nicotianae and P. capsici move only locally (within a field) and is not easily spread by wind and air currents like P. infestans. Producers are advised to put late blight products on (they are effective for all Phytophthora) at least until the weather turns warmer and drier. Most of these cases were due to heavy rains that caused flooding in fields and plants to be under water.
- Collar rot (Alternaria linariae, the same pathogen that causes early blight) has been reported on field tomatoes three counties in Western North Carolina. In one field, about 90% of the plants were affected. Inoculum comes from the greenhouse, and the pathogen will cause the stem to girdle and can kill the plant. If it is caught early, then you can build up soil around the stem lesions and the plants can recover.
- Bacterial canker has been reported on field grown tomatoes, var. Mountain Majesty, at two farms in Western North Carolina.
- There are reports of horn worms on tomatoes in Western North Carolina. Horn worms haven’t been seen in years and the producer had not sprayed any insecticides.
- Holes in eggplant, tomato, and pepper leaves have been reported in Central and Western North Carolina. The holes could be due to pest or hail damage.
- Cucumbers in Western North Carolina are exhibiting symptoms of chemical burn. The plants were sprayed with Quadris and Manzate on a hot and humid day at 10 am. However, the new growth appears to be fine and is growing out of it.
- Copper deficiencies have been reported on tomatoes in Central North Carolina. Copper deficiency symptoms in tomato include stunting, wilting, distortion of the youngest plant leaves, and necrosis of growing points. Copper is a micronutrient and only 4-6 ppm of copper is required for plant growth. Copper deficiency is rarely observed in commercial production as most soils contain adequate amounts of copper.
- Overall, there have been several reports of nutritional deficiencies and soil issues in vegetable production areas in several counties from Central and Western North Carolina. For example, several producers in Western North Carolina have reported tip burn, burning of cotyledons, and a reduction in root growth due to high soluble salts in the soil. Producers are recommended to send soil to the NCDA for testing.
- In experimental field trials at MHREC, reports of spotty mortality in tomato transplants. The transplants show no signs of disease, but they were extremely tender from being in the greenhouse under shady weather. Transplants were planted on a hot and sunny day onto black plastic. The heat from the plastic and sun likely caused some plants to burn and die shortly after.
- Although not a vegetable production issue, apple cedar rust and fire blight have been reported on apples in Central North Carolina.
- Mountain Research Station Field Day on Thursday, July 19, 2018, at 2:00 pm (research updates, trade show, entertainment, and more!) (Waynesville, NC).
- 3-In-1 Alternative Crops and Organics Day on Wednesday, July 25, 2018, from 8:30 am to 6:00 pm at the Mountain Research Station (Waynesville, NC).
- Mountain Horticultural Crops Research and Extension Center 2018 Tomato Field Day August 16 (field tours, lunch, research initiatives, taste tests, and more!) (Mills River, NC).
Pest News and other Announcements:
- Inga Meadows (Extension Associate, Vegetable and Herbaceous Ornamental Pathology): Explained to the group that we plan to publish summaries of the Veggie Calls with important pest information in the NCSU Extension Pest News and will keep track of the names of the attendees to give them credit in the published summaries. These published summaries will be accessible to vegetable producers, ASAs, county extension agents, extension specialists, and researchers with an interest in North Carolina’s vegetable production industry.
- Amanda Scherer (Postdoctoral Research Scholar, Plant Pathology): Amanda is a new postdoctoral research scholar with Inga Meadows at the Mountain Research Station in Waynesville, NC. Part of her research is to look at the pesticide sensitivities of the bacterial spot and early blight of tomato pathogens.
- For bacterial spot, they are focusing on tomato transplant producers and are asking for help from extension agent in collecting greenhouse tomato samples with bacterial spot symptoms.
- For early blight, they are focusing efforts on collecting tomato samples with early blight symptoms from commercial fields in North Carolina.
- These samples will help provide us with valuable information on how to better advise growers in North Carolina to manage these two diseases. If you are interested or available to help them with this project, then they can send shipping labels and simple instructions for collecting samples. Please contact Amanda (firstname.lastname@example.org) or Inga (email@example.com) for more information.
Additional Information on the Vegetable Plant Pathogens Mentioned in this Vegetable Production Update:
Bacterial Canker is caused by the vascular, bacterial pathogen Clavibacter michiganensis subsp. michiganensis. Although bacterial canker epidemics occur only sporadically, infection can be devastating as the disease can cause up to 100% yield loss. It is one of the most economically important diseases that occurs on greenhouse tomatoes. Infections originate from contaminated seed and can cause severe symptoms on seedlings. Other sources of inoculum include plant debris, weed hosts, and volunteer tomatoes, along with contaminated wooden stakes, flats, and benches. In tunnels and greenhouses, the disease can easily spread between plants via pruning and clipping transplants, contaminated equipment, and worker’s hands. Warm temperatures (75 to 90 ℉) and high moisture or relative humidity (≥ 80%) favor disease development. Bacterial canker can also occur on pepper, but it is only economically significant on tomato.
- Symptoms: Symptoms will vary with plant age, type of infection, environmental conditions, and other factors, which can make the disease difficult to diagnose based on symptoms alone. In seedlings, small, white, raised spots can form on leaves and open cankers may form on the stem. Seedlings can be stunted and wilted in appearance and will eventually die. In the field, the outer edges of leaves will brown and have a think yellow boarder. Yellow to tan patches will form between dark, sunken leaf and petiole veins. When the stem in cut open, brown streaks can be seen in the vascular tissue. Long, brown cankers will also form on the stem. The lower leaves may also wilt and may only occur on one side of the plant. Fruit lesions are usually small (0.25 in), creamy, white spots with tan or brown centers (also called “birds-eye” spots) on green or red fruit. The entire plant may collapse and die.
- Signs: When squeezed, a yellow, sticky fluid may emerge from a cut stem of an infected plant. Bacterial streaming can be under a light microscope from the margins of a leaf, stem, or fruit lesion. Bacterial streaming will not be observed in lesions caused by fungal pathogens.
- Management: Once a plant becomes infected, the disease is extremely difficult to manage. Only plant certified pathogen-free seeds or sanitize seed with hot water, bleach (sodium hypochlorite), or hydrochloric acid. Also, only use clean or disease-free transplants. Scout plants daily and destroy and remove infected plants. Clean and disinfect all tools and farm equipment prior to working with transplants or plants. Spraying with copper-based bactericides alone or in combination with mancozeb in the greenhouse has been shown to effective in managing the disease. The pathogen can survive in a field as long as there is infested crop debris present. It is recommended to rotate with a non-host (avoid pepper, eggplant, and tobacco) for 3 to 4 years before replanting with tomato. Remove weeds and volunteer tomato plants prior to planting. There are very few chemical options for managing bacterial canker.
- Grabowski, M., and Orshinsky, A. 2018. Bacterial Canker of Tomato. University of Minnesota Extension Publication. Retrieved on June 28, 2018.
- Lewis-Ivey, M. L., and Miller, S A. 2018. Bacterial Canker of Tomato. The Ohio State University Vegetable Disease Fact Sheets. Retrieved on June 28, 2018.
- Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 50-53). St. Paul, MN: APS press.
Bacterial Wilt is caused by Ralstonia solanacearum, which has a wide host range of more than 200 cultivated plant and weed species in 50 different plant families. Some of the most economically important hosts include tomato, potato, tobacco, and eggplants. The primary inoculum source is infested soil, but other sources also include irrigation water, weeds, farming equipment and operators, and diseased plant material. In the field, bacteria are more concentrated in lower areas with water accumulation.
- Symptoms: R. solanacearum colonizes and multiplies in the vascular (xylem) tissue of the plant, which causes wilting of infected plants. The first visible symptoms consist of the wilting of the youngest leaves at the end of branches. Wilting will be most visible on hot days and plants may seem to recover at night when temperatures are cooler. Eventually, the entire plant may wilt quickly and dry out leading to plant death. In the field, plants may also become stunted or visually healthy plants may wilt suddenly when fruits are expanding rapidly.
- Signs in tomato: Cross sections of infected stems may show brown discoloration in the vascular tissue. When a freshly cut stem is suspended in water, a white, milky stream of bacterial cells will flow from the vascular tissue within 3 to 5 minutes.
- Management: Due to its wide host range and ability to persist in the soil, bacterial wilt is difficult to control. There are no chemical control methods available for bacterial wilt. It is important to use pathogen-free soil, irrigation water, and transplants to exclude primary inoculum sources. Crop rotation and planting cover crops of non-susceptible plants (corn, beans, cabbage, etc.) can reduce soilborne populations of R. solanacearum. Fields should not be overirrigated because excess soil moisture favors disease.
- Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 58-60). St. Paul, MN: APS press.
- Vallad, G., Pernezny, K., and Momol, T. 2004. A series on diseases in the Florida vegetable garden: tomato. University of Florida Plant Pathology Department and IFAS Fact Sheet. PP-200. Retrieved April 17, 2018.
- Meadows, I. and Henson, M. 2017. Southern Bacterial Wilt of Tomato. North Carolina State University Extension Publications. Retrieved April 17, 2018.
Bean Rust is caused by the obligate fungus Uromyces appendiculatus. The disease occurs worldwide but is most common in humid tropical and subtropical areas. Moderate temperatures (70 to 85 ℉) and moist conditions such as prolonged periods of water (10 to 18 hours) are favor disease development.
- Symptoms: Spots will first appear as small, yellow or white raised spots on the upper and/or lower leaf surfaces. As spots enlarge, they will form reddish-brown pustules. (uredinia pustules). As the pustules enlarge, they may be surrounded by a yellow halo. Rust colored-spores will be released from the pustules and give plants and anything they touch a rusty appearance. Severe infections will cause leaves to curl, dry up, turn brown, and drop prematurely. Severe infections can also cause reductions in pod set, pod fill, and seed size. A severely infected field will appear scorched. Near the end of the season, pustules will turn brownish-black in color due to the production of overwintering spores (teliospores).
- Signs: Uredinia pustules (1-2 mm or larger in diameter) will contain rust-colored spores called urediniospores (20-33 x 18-29 µm) that can be seen with a light microscope. The rust-colored spores will give plants a rusty appearance and will rub off unlike other foliar diseases. Near the end of the season, the pustules will contain teliospores which are nearly black, thick-walled spores that are 24-35 x 20-29 µm in size.
- Management: Implementation of an integrated pest management strategy (IMP) is critical for managing bean rust. It is recommended to rotate with nonhost crops, remove or burry plant debris, change irrigation times to avoid wet foliage at night, and modify planting dates to reduce late-season exposure to high inoculum levels and favorable disease conditions. Most older bean varieties are susceptible to bean rust, but some resistant varieties are available for many classes of beans such pinto, great northern, small white, red kidney, and black beans. Scout fields frequently during late vegetative or early pod development for rust pustules. Fungicides can be applied to help manage the disease. For the latest fungicide recommendations for bean rust see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
- Harveson, R. M., Chwartz, H F., and Steadman, J. R. 2013. Rust of Dry Bean. University of Nebraska-Lincoln Extension. Retrieved on July 2, 2018.
- Hall, R. 1991. Compendium of Bean Diseases (pp. 96-97). St. Paul, MN: APS press.
Collar Rot is caused by Alternaria linariae (formerly known as A. solani), which also the pathogen that causes early blight of tomato. Early blight is more commonly observed in the field, but greenhouse tomato seedlings can be affected by collar rot. A. linariae can cause disease occurs in humid climates and semiarid climates with frequent dews that provide enough moisture (≥ 90% relative humidity or greater) conducive for disease development.
- Symptoms: On seedlings, stem lesions are small, dark, and slightly sunken. As they enlarge, they will form circular or elongated lesions with pronounced concentric rights with light centers. Once the infected seedlings are planted in the field, the lesions will continue to enlarge around the gourd line causing the plants to girdle. If the infection girdles the stem, the seedling will wilt and die.
- Signs: Mycelia are septate and branched and become dark with age. Conidia (asexual spores) are beaked, muriform (multicelled), dark, 12-20 x 83-117 µm in size, and can be borne singly or chains of two.
- Management: If it is caught early, then you can build up soil around the stem lesions and the plants can recover. Although there are no early blight resistant varieties, it is recommended to use varieties that are more tolerant to early blight and maintain plant vigor with adequate fertilization to reduce susceptibility. Remove volunteer weeds that cans serve as a source of inoculum. For the latest fungicide recommendations for early blight, please consult the 2018 Southeastern US Vegetable Crop Handbook.
- Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 39-40). St. Paul, MN: APS press.
- Meadows, I. 2015. Early Blight of Tomato. North Carolina State University. Plant Disease Fact Sheet. Retrieved May 16, 2018.
- Grabowski, M., and Orshinsky, A. 2018. Early Blight of Tomato. University of Minnesota Extension Publication. Retrieved on June 28, 2018.
Damping-off is the death of seedling before or shortly after emergence that is caused by the decomposition of the roots or lower stem. Damping-off is primarily caused by the presence of fungal or fungal-like pathogens such as Rhizoctonia and Pythium species in the soil. The disease can occur on both greenhouse and field tomatoes and can cause plant losses and uneven stand establishment.
- Symptoms: Infection of tomato by Pythium spp. can occur at any stage of seed germination. Infected seeds develop a soft, mushy rot before the radicle emerges causing a reduction in seedling emergence. Most commonly, however, germinating seedlings develop dark-brown or black, water-soaked lesions that spread rapidly. Seedlings infected by postemergence damping-off develop dark-colored, water-soaked lesions on the roots that extend up the basal stem to or above the soil line. If dark-colored, soft lesions develop around the major portion of the stem, then the seedling will fall over, desiccate, and die. Before emergence, seedlings infected with R. solani will rot after the pathogen kills the growing tips. Germinating seedlings will have tan to reddish brown lesions. After emergence, seedlings will have brown, reddish-brown, or nearly black lesions near the soil line. The stem will become constricted and soft causing the plant to fall over and die.
- Signs: Moldy fungal or fungal-like growth may be seen on infected plants at the soil line. All Pythium spp. produce white, rapidly growing, coenocytic mycelia. They produce sporangia of various sizes and shapes depending on the species.
- Management: Seed can be treated with a broad-spectrum fungicide to control R. solani and other seedborne diseases and soilborne pathogens. In the greenhouse, potting media should be sterilized, and containers should be disinfested with hot water, steam, or with a 10% sodium hypochlorite solution before use. Workers should clean their hands and tools before handling healthy plants. Plant seeds at proper planting depth and soil temperature to assure rapid emergence and growth. Treating soil with a broad-spectrum fumigant to solarization can reduce inoculum levels in the soil. Transplants should be planted in well-drained soil.
- Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 96-97). St. Paul, MN: APS press.
- Meadows, I., Sharpe, S., and Henson, M. 2017. Damping-off in Flower and Vegetable Seedlings. North Carolina State University. Plant Disease Fact Sheet. Retrieved June 28, 2018.
Powdery Mildew is caused by the fungal pathogens Podosphaera xanthii and Erysiphe cichoracearum. Disease can occur on all cucurbit crops. However, due to the incorporation of resistance genes, most commercial cucumber and melon cultivars are less susceptible. High-humidity (50-90%), moderate temperatures (68 to 80 ℉), dense foliage, and low light conditions favor disease development. However, dry conditions favor colonization, sporulation, and dispersal of the pathogen.
- Signs and Symptoms: White, powdery fungal growth first appears on older or shaded leaves and on the underside of leaves. Yellow spots may form on upper leaf surfaces opposite of powdery mildew colonies. The white, powdery growth can also appear on stems and petioles. Infected leaves will senesce (deteriorate) early, and fruit yield and quality can be affected. Due to plant stress induced by powdery mildew infections, speckling of fruit can occur in some cucurbits.
- Management: Provide adequate spacing between plants and remove any debris, weeds, and volunteers that can harbor the pathogen. When possible, the use of resistant cultivars is recommended. Fungicides should be applied to protect the crop from infection. For the latest fungicide recommendations for cucurbit powdery mildew see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
Southern Blight (also known as southern wilt and southern stem rot) is caused by the soil-born fungus Sclerotium rolfsii. The disease was first reported on tomato, but it occurs on hundreds of other plant species of economically important vegetable, ornamental, agronomic crops. Host crops include bean, cantaloupe, carrot, pepper, potato, sweet potato, tomato, watermelon, and others. High temperatures (77 to 95 ℉), aerobic and moist conditions, and acidic soil favor disease development. In North Carolina, the disease will appear in “hot spots” in fields in early to mid-summer until cooler, dryer conditions prevail.
- Symptoms: The most common symptom occurs on the stem, which has contact with the soil. A brown to black lesion usually develops on the stem near the soil line. The lesion will develop rapidly and can completely girdle the stem, which will cause a sudden and permanent wilt of all above ground parts. Young plants may fall over at the soil line. If fruit comes into contact with infested soil, then the fungus can easily penetrate the epidermis. Lesions will initially appear as sunken and slightly yellow areas that later become water-soaked, soft, and star-shaped spots. The fruit will collapse within 3 to 4 days and white mycelium and sclerotia can fill the lesion cavity.
- Signs: Under moist conditions, white mycelium can develop on stem lesions and can sometimes extend several centimeters up the stem of the plant. After a few days, tan to reddish-brown, spherical sclerotia (1 to 2 mm in diameter) can appear on the mat of mycelia. After fruit lesions collapse, white mycelium and sclerotia can fill the lesion cavity.
- Management: Management of southern blight is difficult when inoculum density is high under conducive conditions for disease development. Avoid fields that have S. rolfsii. Rotate tomato crops with non-susceptible grass crops such as corn, wheat, and barely to reduce inoculum levels in the soil. Modify planting dates to avoid conditions that favor disease development. Remove diseased plants and weed populations. Avoid injuring plants and adopt wider plant spacings (dense canopies increase disease incidence). Inoculum levels can be reduced by burying infected plant debris and sclerotia via deep plowing (at least 20 cm) with a mold-board extension to invert the soil. Plastic mulch and row covers will provide a barrier between plants and the soil and reduces disease severity. For the latest fungicide recommendations for southern blight see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.
- Jones, J. B., Zitter, T. A., Momol, T. M., and Miller, S. A. (Eds.). 2014. Compendium of tomato diseases and pests(pp. 96-97). St. Paul, MN: APS press.
- Meadows, I., and Henson, M. 2017. Southern Blight of Vegetable Crops. North Carolina State University. Plant Disease Fact Sheet. Retrieved June 28, 2018.
Tomato Spotted Wilt Virus (TSWV) is a member of the genus Tospovirus and has one of the widest host ranges of any virus. It is estimated to infect 800 plant species in more than 80 plant families including tomato, pepper, potato, celery, lettuce, legumes, annual and perennial ornamentals, and several weed species. It is transmitted in a propagative manner by seven species of thrips such as western flower thrips (Frankliniella occidentalis) and tobacco thrips (F. fusca).
- Symptoms: Symptoms can vary among hosts. In most cases, young leaves will turn bronze and later develop numerous, small dark spots. Stunting is also a common symptom and is more severe in young plants. Half or the entire plant maybe stunted. Tomatoes that are infected early may not produce any fruit. On plants infected after fruit set, may produce fruit with chlorotic ringspots. On green fruit, fruit may have slightly raised areas with faint, concentric rings. On ripe fruit, these rings are more obvious and can become red and white or red and yellow.
- Signs: Virus particles are 80 to 110 nm in diameter and membrane bound.
- Management: Due to the wide host range of TSWV and its vectors, management of this disease can be difficult. Do not grow ornamental plants in the same greenhouses as vegetable transplants started from seed. An integrated pest management strategy using UV reflective mulches, a plant activator (acibenzolar-S-methyl), and insecticides can provide some control.
- Sherwood, J.L., German, T.L., Moyer, J.W. and D.E. Ullman. 2009. Tomato spotted wilt. The Plant Health Instructor. APS Press. Retrieved May 30, 2018.