Partly cloudy skies. A stray shower or thunderstorm is possible. Low 66F. Winds light and variable..

Partly cloudy skies. A stray shower or thunderstorm is possible. Low 66F. Winds light and variable.

Mary Beth Bennett WVU Extension Agent

Mary Beth Bennett WVU Extension Agent

Tomatoes are members of the Solanaceae or Nightshade family.

Until the late 1800s, the tomato was classified as a fruit to avoid taxation, but this was changed after a Supreme Court ruling that the tomato is a vegetable and should be taxed accordingly.

The tomato has origins traced back to the early Aztecs around 700 A.D; therefore, it is believed that the tomato is native to the Americas.

Today, tomatoes have become a staple item in the kitchen throughout the world. Each area of the world has its own tomato history and how it is used in everyday dining.

Tomatoes are a very popular garden plants, and we get lots of calls when people have problems with their tomato plants.

We see problems with tomato diseases, with people calling and saying their tomato leaves are drying up. Tomato growers across West Virginia may notice a disease which starts as numerous tiny spots on lower leaves that enlarge over time. As they do, the leaf turns yellow and eventually dies. According to Mahfuz Rahman, West Virginia University Extension specialist in plant pathology, this is due to a common tomato disease called Septoria leaf spot (caused by Septoria lycopersici).

Frequent rain, high humidity and dew on tomato leaves lead to rapid disease development. Symptoms start on the lower leaves and then move upward. Septoria leaf spots appear as numerous brown spots (approximately 1/16 to 1/8 inch in diameter) on the leaves with gray or tan centers and dark brown margins. As the spots mature, dark brown pimple-like structures called pycnidia (fruiting bodies of the fungus) appear inside the spots. These pycnidia can easily be seen with a hand lens. Septoria leaf spots generally do not affect stems or fruit, but under high disease, pressure spots may also appear on stems, calyxes and blossoms. Very rarely do they appear on fruit. Leaf loss due to severe disease may expose fruits to sunscald.

Disease cycle: Although the fungus is not a soil inhabitant, it can persist from one season to the next on debris of diseased plants. Tomato seed has been shown to carry spores and produce infected seedlings, but it’s unknown if the pathogen is truly seedborne. The pathogen can also overwinter on solanaceous weeds such as horse nettle (Solanum carolinense), black nightshade (Solanum nigrum), jimsonweed (Datura stramonium) and groundcherry (Physalis subglabrata).

Septoria leaf spot may be confused with early blight, which is caused by Alternaria solani. Early blight is characterized by a few (five to 10) brown, circular spots up to half an inch diameter with concentric rings or ridges that form a target-like pattern surrounded by a yellow halo. As the disease progresses, stem and fruit also become infected forming dark, sunken spots. Dark, sunken cankers with concentric rings may also appear at or above the soil line on stems in case of an Alternaria infection.

How to manage Septoria leaf spot

• Eliminate initial source of infection by removing infected plant debris and weeds and use disease-free seeds.

• If complete removal of plant debris is not possible, destroy by deep plowing immediately after harvest and follow with a one-year rotation with non-solanaceous crop.

• Use a resistant variety. Tomato varieties with complete resistance to Septoria leaf spot are not available. However, the variety Iron Lady with tolerance to the disease is now available, and a WV63 variety with similar tolerance will be available soon.

• Use plastic or other mulch near the base of plant to prevent splashing soil particles that may contain fungal spores associated with debris.

• Use drip irrigation or a soaker hose at the base of the plant instead of watering with a method that gets foliage wet.

• Facilitate quick foliage drying by providing optimum spacing and row orientation for good air movement and sunlight penetration. Water only early in the day. Staking or caging the plants to raise them off the ground should also help in quick drying.

• Remove lower infected leaves from the plant if detected early enough, and bury or burn them immediately. Don’t add infected leaf or debris to the compost pile.

• Fungicidal sprays may still be required in a rainy and humid season. Organic growers may use fixed copper (Champ), Regalia, Serenade or Actinovate on a weekly schedule throughout the growing season.

• Conventional growers may use chlorothalonil (Daconil 2787, Bravo), azoxystrobin (Quadris, Amistar, etc.) or mancozeb (Penncozeb, Dithane, Manzate, etc.). Commercial growers may buy and use more effective fungicides such as Quadris Top, Revus Top, Catamaran or Tanos.

Early blight, caused by the fungal pathogen Alternaria solani, is one of the most common tomato diseases. It brings significant damage to tomato leaves, stems, and fruits almost yearly in West Virginia. Early blight can also affect potato foliage.

How is early blight spread?

Early blight fungus survives the winter on infected plant debris, or it can be brought with infected seeds that initiate the disease in the spring. Any fungal conidia spores surviving in the soil or plant debris are splashed on the lower leaves during rain or sprinkler irrigation. Conidia germinate in the presence of a thin film of water on foliage. Germinated conidia infect tissues if foliage remains wet for another five to 10 hours, depending on the temperature. High humidity and temperatures above 75°F favor disease development.

What are the symptoms of early blight?

Early blight is identified by the appearance of a few (five to 10 in most cases) circular brown spots on a leaf. The spots are up to a half-inch in diameter, with concentric rings or ridges that form a target-like pattern surrounded by a yellow halo. As the disease progresses, spots merge together and may kill the whole leaf. Over time, the stem and fruit may also be infected, showing dark and sunken spots. Cankers with a similar dark and sunken target-like appearance are often found at or above the soil line on the stem

Early blight and closely related diseases

Do not confuse early blight with two other diseases — late blight and Septoria leaf spot.

Late blight spots, caused by the fungus Phytopthora infestans, start out pale green, usually near the edges of tips of foliage, and turn brown to purplish black (Fig. 2B). Under humid conditions, a fuzzy mold appears on the undersides of leaves and may quickly blight the stems and fruits, resulting in a leathery-brown appearance.

Septoria leaf spot manifests as numerous brown spots having a diameter of approximately 1/16 to 1/8 inch on the leaves, with gray or tan centers (Fig. 2C). These spots have a dark brown margin compared with early blight’s yellow halo.

As the spots mature, many dark brown, pimple-like structures called pycnidia (fruiting bodies of the fungus) may appear inside the spots. These pycnidia can easily be seen with a hand lens. Early and late blight spots do not produce pycnidia. Unlike the other two diseases, Septoria leaf spots do not affect stems or fruits, but defoliation caused by more severe disease may expose fruits to sunscald.

How can early blight be managed?

• Use certified seeds from a reputable company or seeds that were kept from disease-free fruits.

• Use resistant varieties such as ‘Mountain Fresh Plus F1’, ‘Juliet F1’, ‘Tommy Toe’, ‘Old Brooks’ or ‘Cabernet F1’.

• Use mulch to prevent soil splash and stake the plant to keep it upright. Because wooden stakes and caging from previous years may be contaminated, do not use them unless they are treated with a 10% bleach solution for 30 minutes.

• Prune lower leaves and stems that are close to the soil surface.

• Grow tomatoes under a well-ventilated plastic tunnel that keeps foliage dry and relative humidity low.

• Use drip tape instead of sprinkler irrigation.

• Keep or let foliage dry during or after a rain or morning fog to minimize the level of infection.

• Space plants and orient rows to allow air to circulate and sunlight to penetrate.

• At the end of the season, remove all plant debris from the garden and burn or bury it by deep plowing.

What should be done if tomatoes have been infected by early blight?

In an area previously having early blight, apply either of the following products on a preventative schedule if rotation is not an option.

• For organically grown tomatoes, use copper hydroxide (Kocide 101) or Serenade on a 10-day schedule, starting pre-bloom or at first sight of blight spots.

• For conventional tomatoes, use chlorothalonil (Daconil 2787) or azoxystrobin (Quadris, Amistar, etc.) if disease is detected and weather remains damp and rainy.

Do not use azoxystrobin more than two consecutive sprays or a total of five sprays in a growing season to keep the fungus from developing resistance.

Information above provided by MM (Mahfuz) Rahman, WVU Extension Service Plant Pathologist

Late blight (Phytophthora infestans) is one of the most serious fungal diseases that can affect tomatoes and potatoes.

Late blight is spread from infected transplants, volunteer potato or tomato plants, and certain weeds botanically related to tomatoes. Spores of this fungus can be airborne and travel great distances in storms. Rain deposits spores onto plants, causing infection. Late blight is favored by cool, wet weather and will cycle repeatedly if weather conditions are favorable.

What are the symptoms of late blight on tomatoes?

Late blight symptoms include leaf, stem, and fruit lesions that have a water-soaked appearance. The lesions eventually turn brown and the plant looks like it has been frost-damaged or blasted by a blowtorch. Unlike early blight, which typically begins infection on the lower leaves of the tomato plant, late blight infections seem to move from the outside of the canopy inward.

Under favorable conditions, all parts of the plant can become infected. Complete infection of a tomato field can occur in a few days. Large rough, brown lesions appear on tomato fruits.

Are there tomato cultivars which are resistant to late blight?

Currently, there are no tomato cultivars with complete resistance to late blight.

How can late blight be prevented or managed?

Since late blight favors wet, cool weather for infection, cultural practices have a relatively small effect on controlling this disease. Bottom-watering via drip irrigation will be beneficial. Plants should be spaced relatively wide within the row to facilitate air movement, and plants should not be handled when the foliage is wet.

Mulching with plastic or an organic material will reduce the development of early blight more than late blight, but these diseases often work in tandem to destroy tomato plants. Staking or caging tomatoes will result in faster drying of the foliage. Before planting, inspect transplants for any symptoms of disease. Avoid planting tomatoes on sites that were previously in potatoes or close to potatoes. Sequential planting or planting several crops of tomatoes over time will reduce the risk of late blight destroying all tomatoes at once.

Spraying fungicides is the most effective way to prevent late blight. For conventional gardeners and commercial producers, protectant fungicides such as chlorothalonil (e.g., Bravo, Echo, Equus, or Daconil) and Mancozeb (Manzate) can be used. Fixed copper products (Kocide) can be used by organic gardeners to prevent late blight infection. Read the label on any fungicide before application. For fungicides that target the fungus specifically, consult the 2009 Commercial Vegetable Production Guide.

If conditions are favorable for late blight development, start a weekly spray application immediately after transplanting. Otherwise, apply protectant fungicides beginning at flowering for control of late blight and other tomato diseases.

What should be done if tomatoes have been infected by late blight?

Continue weekly spray applications to protect plants from further infection. Severely infected plants can be rogued and either buried or burned. Avoid composting diseased plants.

Rotate tomatoes with vegetables unrelated botanically to tomatoes or potatoes. Do not plant these sites with these groups of vegetables for two to three years. Avoid harvesting tomato fruits with visible disease lesions.

Are infected tomatoes safe to eat?

While unblemished fruit from infected plants is safe to eat, the fruit should not be held for any length of time. Also, infected fruit should not be canned or frozen because it can raise the pH of the canning solution and promote further growth of microorganisms.

Information on Late Blight was provided by Lewis W. Jett, WVUES

For more information on tomato diseases, contact Lewis W. Jett, Ph.D., 304-293-2634 (Office) Lewis.Jett@mail.WVU.edu

Other tomato problems we see

Are your tomatoes turning brown on the blossom end? This is called Blossom end rot, and it is a physiological problem not caused by infectious microorganisms but by environmental stresses on the plant. Blossom end rot is a very common problem on green and ripe tomatoes. It first appears as a sunken, brownish black spot ½ to 1 inch in diameter on the blossom end of the fruit. These spots may gradually increase in size. Although blossom end rot itself causes only local injury, secondary organisms frequently invade the lesion and cause complete rotting of the fruit. It often occurs in rapidly developing fruit during periods of hot, dry weather and tends to have the greatest impact on the earliest maturing fruit.

Blossom end rot is caused by a calcium deficiency that is related to wide fluctuations in available moisture. Sometimes, adding calcium will help with this problem. To prevent blossom end rot, maintain a steady rate of plant growth without stress. A consistent and ample supply of moisture can reduce the problem by helping to maintain a steady flow of calcium form the soil to the fruit. Mulching will help by conserving soil moisture. Blossom end rot is more serious when an excess of nitrogen of fertilizer has been applied. Staking and pruning tomato plants may increase the incidence of blossom end rot. If blossom end rot occurs, remove the affected fruit so that later-maturing fruit will develop normally. Mulching and avoiding heavy applications of nitrogen fertilizer may help reduce fruit cracking.

Are your tomatoes cracking? There are two types of cracks that tomato fruit may develop. Radial growth cracks radiate from the stem and concentric cracks encircle the fruit, usually on the shoulders. Similar to blossom end rot, cracking is associated with rapid fruit development and wide fluctuations in water availability to the plant. Fruit that has reached the ripening stage during dry weather may show considerable cracking if the dry period is followed by heavy rains and high temperatures. Tomato varieties differ considerably in the amount and severity of cracking under climatic conditions. Supersonic and Jetstar are two varieties that show relatively low incidence of cracking. As with blossom end rot, mulching and avoiding heavy applications of nitrogen fertilizer may help reduce fruit cracking.

Are your tomatoes misshapen with irregular bulges at the blossom end with bands of leathery scar tissue? This is a term referred to as catfacing. Cold weather at the time of blossom set distorts and kills certain cells that should develop into fruit, resulting in the deformities. The disorder is often observed among first-formed fruit.

Catfacing is most common in the large-fruited “beefsteak” or heirloom types of tomatoes. Although catfacing can cause a tomato to be rather unsightly, most times it is harmless, and the tomato can still be used. Severe catfacing can go all the way through a tomato, rendering it virtually unusable. Just place the severely damaged tomatoes in the compost pile. Hopefully, fruits coming later will develop properly.

These are a few of the tomato problems that we’ve seen in the past.

Due to the high temperatures, we are seeing problems with internal whiting of tomatoes. When you look at the tomato, it looks fine on the outside, but the white appears on the inside when you cut the fruit open. High temperatures during the ripening period seem to trigger this disorder. Adequate potassium fertilization has shown to reduce it but may not eliminate it.

What causes summer vegetables to appear healthy but fail to produce? Shade or too much nitrogen could do this, but in mid-summer, the heat is often to blame. Research has shown that as daytime temperatures rise over 90 to 95°F and nighttime temperatures above 70 to 75°F, fruit set in many vegetables declines and, in some cases, stops. This is partially due to poor pollen or sterile pollen production during high night temperatures and explains why this phenomenon happens more often in areas where nights stay warm.

Without viable pollen, plants cannot set fruit and the flowers abort or drop off. Individual varieties respond to heat differently, so you may notice that one variety of tomatoes continues to set some fruit while another one shuts down entirely. Fruits that do set often ripen very slowly.

The slow ripening is related to the second reason that plants may stop setting fruit during the hottest part of summer and that is water stress during the heat of the day. Plants need water to fill the cells of the fruit being produced. When daytime temperatures reach up into the 90s, many plants have trouble moving enough water into their leaves to keep them from dropping, even when there is enough water in the soil.

When plants can’t keep their leaves full of water, they also don’t have the water to spare for producing fruit such as tomatoes, peppers or beans. In addition, plants under water stress close the stomates or tiny pores in their leaves that allow gas exchange. Closing the stomates or the plant from unrestricted water loss.

But these stomates are also where carbon dioxide is exchanged with the atmosphere. The carbon dioxide is necessary for photosynthesis – the plant process that results in the development of sugars and energy for plant growth. So, plants under water and heat stress have to make a choice – they close their stomates to survive but that means that they are just maintaining rather than growing vigorously and ripening fruit.

Several things can be done to help our gardens be as productive as possible during the summer. First, water consistently to keep soil evenly moist. Do not allow plants to dry out during dry spells and do not over fertilize with high nitrogen fertilizers. Make sure you harvest frequently to keep vegetable plants productive. Leaving fruits on too long reduces the amount of fruit that the plant will set in the future. Be sure to pull large fruit off the vegetable plant before they drain energy necessary for new flower production.

Asian giant hornets, European hornets and cicada killers

According to our WVU Extension entomologist Carlos Quesada, the Cicada killer wasps borrowing activity has started. This makes the cicada killers more visible to people. Female cicada killer can sting to defend themselves. However, they are not aggressive and do not have nest-guarding instincts like honeybees and hornets You can walk through areas where they are active without attracting attention. Below is some information on the difference between the Asian giant hornets, European Hornets and cicada killers.

Asian giant hornet (Vespa mandarinia) was detected for the first time in Washington state and British Columbia, Canada, in 2019. Native to Asia, this wasp belongs to the order Hymenoptera, but media has inaccurately named it the “murder hornet.” Even though Asian giant hornets are not yet present in West Virginia, WVU Extension county offices have received several calls and emails from West Virginia citizens reporting it. European hornets (Vespa crabro) and cicada killers (Sphecius speciosus), on the other hand, are both found in West Virginia and are often confused with Asian giant hornets because of their similar size and color. To facilitate the identification of these wasps, this article describes their patterns on their abdomens. However, there are several other tools and clues used for the identification of the wasps.

The Asian giant hornet is the world’s largest hornet. The insects live in colonies that are built yearly in abandoned underground borrows, in dead hollow tree trunks or within the roots of trees. Because of their social behavior, they will only attack humans to defend themselves, their nest or their food source. They are predators of large caterpillars, beetles and spiders; however, they may attack honeybee hives later in the season when the hornet nest is large and reproductive. The Asian giant hornet can be identified by alternating straight dark and light bands on its abdomen.

European hornet also is an invasive species first reported in New York in 1840. Similar to Asian giant hornets,

European hornets live in colonies and will attack humans to defend their nests. The European hornet diet mainly consists of large insects such grasshoppers, flies, bees and yellow jackets. They also can be considered problematic insects when they feed on fruits like apples. The European hornet is similar in color to the Asian giant hornet; however, they have dark triangular shapes on the abdomen segments closest to the thorax, followed by rows of dark teardrop shapes near the end.

Eastern cicada killers are solitary wasps (live individually) native to the United States, and they build their nests in the ground. While their size can be alarming, they are not aggressive and do not engage in nest-guarding. They are beneficial wasps that help reduce cicada populations. They will only sting to defend themselves. Unlike the other two insects, the yellow color on the cicada killer’s abdomen does not connect to form clear yellow bands across the back

Resource: IPM NEWSLETTER — WINTER 2022 (wvu.edu)

Until next time ...Happy Gardening, Summer, and Farming!

Mary Beth Bennett, Ph.D. is a WVU Extension agent and associate professor. She can be reached at 264-1936, MBBennett@mail.wvu.edu or on the web at http://extension.wvu.edu/berkeley

WVU is an EEO/Affirmative Action Employer — Minority/Female/Disability/Veteran

Mary Beth Bennett WVU Extension Agent

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