Posts Tagged ‘tomato’

Late Blight on Tomato Confirmed in Baltimore County, MD

Monday, August 20th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Late blight on tomato is now confirmed in Maryland (Baltimore County). We do not yet know what strain or genotype it is. Until additional information is available, growers should assume that both tomatoes and potatoes are at risk. The pathogen is very aggressive and can complete its life cycle and sporulate in as little as 7 days. Tomato growers should scout their crop aggressively and modify their spray program. Conventional growers should add translaminar fungicides, which can move into and through leaves are more effective than a protectant only program. The following are some fungicides that have performed well on tomato in our region. Growers should apply them with a protectant and rotate among them based on rotation of products that are in a different FRAC grouping.

  • Curzate–3.2 to 5.0 oz 60DF/A
  • Forum–6.0 fl oz 4.18SC/A
  • Presidio–3.0 to 4.0 fl oz 4SC/A
  • Previcur Flex–1.5 pt 6F/A
  • Ranman–2.10 to 2.75 fl oz 400SC/A
  • Reason–5.5 to 8.2 fl oz 500SC/A
  • Revus Top–5.5 to 7.0 fl oz 4.16SC/A
  • Tanos–8.0 oz 50WG/A

The best option for organic growers is an OMRI approved copper product. While research results indicate that copper is the best available option in organic production, remember that it is a protectant. That means it must be present on tissue to work. Keep protecting plants with repeated applications as new tissue forms.

Different products are available on potato. Please refer to Maryland, Extension Bulletin 236 (in Delaware, Extension Bulletin 137) for additional information.

Because this disease can spread rapidly by air, advise home gardeners with infected plants to use fungicides – or to kill their plants and bag them or place them under a tarp. This will avoid allowing the spores to spread to neighboring farms.

Stink Bugs are Bad in Some Tomato Fields – But it is Not BMSB

Friday, August 17th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

I have seen a great deal of stink bug damage to tomato fruit this year-more than usual (Fig. 1). The fruit has the characteristic white spots that when peeled back reveal spongy white areas. As the fruit turns red these white areas turn yellow (Fig. 1). When adults, or especially nymphs, feed on the fruit they create a star burst pattern in the surface of the fruit. I guess the surprise is that I have found very few if any Brown marmorated stink bugs (BMSB) in any of these tomato fields. Almost all of the stink bugs have been brown stink bugs (Euschistus spp), although lately (last 2 weeks) I have seen more green stink bugs. There have been very few reports or observations of BMSB being much of a problem so far this year in vegetables. Adult brown stink bugs are grayish-yellow to light brown with dark punctures on their back (Fig. 2). They DO NOT have two white spots on their antenna as do BMSB. Adults overwinter in woods, fence rows and under the bark of trees. A female oviposits a total of about 60 eggs over the summer. The nymphs, which are pale green, develop through five instars and require about one month for development. Because the adults are strong fliers they rapidly can move between hosts. Brown stink bugs are very difficult to scout for and often the only thing that is seen is the damage they cause to large green or ripening fruit. Stink bugs are difficult to control even when found as it takes several applications of insecticide to reduce their numbers (see the Commercial Vegetable Production guide for recommendations). Some of the most heavily fed upon fruit had very dark areas that when cut into appear as a dry rot (Fig. 3). What microorganisms are in this dry rot area is something we are looking into. It appears that our native stink bugs can inject microorganisms almost as readily as do BMSB when they feed.

Figure 1. Stink bug feeding on tomato, yellow areas when cut reveal spongy white cells

Figure 2. Brown stink bug, Euschistus, spp.

Figure 3. Internal dry rot caused by very heavy stink bug feeding

Odd Year for Some Pests in Tomatoes and Cucumbers

Friday, August 10th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

This has been a very hot dry summer so far and we would expect to see pests such as twospotted spider mites and their damage to be common, which we have. However, I have been surprised by the amount of worm (Lepidoptera larvae) damage in tomatoes. Usually worms are a problem in a few fields every summer where they do some damage, but the amount of damage they have done in some fields this year is much greater, around 15-20% of harvestable fruit in several instances. The biggest culprit seems to be yellow striped armyworm (YSAW) Spodoptera ornithogalli (Fig. 1). As the name implies the larvae have two bright yellow stripes on the upper part of the worm running the length of its body. The yellow stripe is often flanked towards the inside with black triangular-shaped markings. This worm species tends to feed on the foliage of many plants, but most of the damage I have seen this summer has been on the fruit with little feeding on the foliage. The fruit damage usually appears as surface feeding (Fig. 1) or feeding holes that are very shallow and do not penetrate too deeply into the fruit (Fig. 2). This often leads to a dry type of damage as opposed to the smaller, deeper holes that often lead to a wet rot (Fig. 2). The YSAW overwinters as pupa in the soil and becomes active in late May or mid-June in our area. This year it has become active much earlier than it normally does and has built its population earlier too. We usually do not see this much damage until late August. Management must take place early when larvae are small; once larvae become large they are difficult to control.

 Figure 1. Yellow striped AW and feeding damage on tomato

Figure 2. Yellow striped AW damage to ripening tomato fruit. Dry (yellow arrows) and wet damage.

Another surprise is that bacterial diseases are turning up in many tomato fields. Moist weather and splashing rains are most often needed for spreading bacteria. Maybe the presence of bacteria in the field is not too surprising, but what is surprising is the widespread nature of the bacterial spot, speck and sometimes canker diseases. Most tomato fields I have looked at in the last two weeks seem to have at least some if not a considerable amount of bacterial disease, usually on the lower leaves (Fig. 3) that in some cases has moved up to the pedicels of the fruit (Fig. 4). Infection of the flower or pedicel with bacterial spot is serious, causing early blossom drop (Fig. 5). From the pedicel the next stop for the bacteria, after a heavy thundershower, will be the fruit. A weekly mixture of mancozeb plus fixed copper or ManKocide should help with bacterial spot or speck, but once in the field, bacterial diseases are difficult to control. If a grower has an older tomato field that has bacterial spot in it that field should be plowed under as soon as possible as it will act as a nursery for spreading the disease to the younger tomato fields.

 Figure 3 Bacterial spot or speck on tomato

Figure 4. Tomato pedicels and blossoms with bacterial spot

Figure 5. Blossom drop due to bacterial infection (yellow arrows) and the start of a flower being aborted (red arrow).

The last ‘surprise’ pest has been the seemingly sudden appearance of downy mildew in cucumber fields (Fig. 6). This disease usually needs cooler weather that we have had little of this summer. But on the 21 of July we had a cool wet period when several areas in the mid-Atlantic set a record low for the daily high (77o F). Right after this brief cool down the downy mildew seemed to explode. Many of the cucumber fields I visited in southern and central Maryland that had been harvested at least once had downy mildew. Once it starts it can defoliate a patch of cucumbers very quickly leaving any fruit to sunburn (Fig. 7).

Figure 6. Downy mildew on cucumber leaf

Figure 7. Cucumber plants defoliated due to downy mildew resulting in sunburned fruit

Hot Year Means More Blossom End Rot

Friday, July 20th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Blossom end rot (BER) is showing up again this year in peppers and tomatoes. BER is a disorder where developing fruits do not have enough calcium for cell walls, cells do not form properly, and the fruit tissue at the blossom end collapses, turning dark in color. Calcium moves through cation exchange with water movement in the fruit, so the end of the fruit will be the last to accumulate calcium. Larger fruits and longer fruits are most susceptible. With fruits, the rapid cell division phase occurs early in the development of the fruit and if calcium accumulation in the fruit is inadequate during this period, BER may occur. While it may not be noticed until the fruit expands, the deficiency has already occurred and cells have already been negatively affected. We most commonly see signs of blossom end rot on fruits many days after the calcium deficiency has occurred.

Understanding blossom end rot also requires an understanding of how calcium moves from the soil into and through the plant. Calcium moves from the soil exchange sites into soil water and to plant roots by diffusion and mass flow. At plant roots, the calcium moves into the xylem (water conducting vessels), mostly from the area right behind root tips. In the xylem, calcium moves with the transpirational flow, the movement of water from roots, up the xylem, and out the leave through stomata. Calcium is taken up by the plant as a divalent cation, which means it has a charge of +2. It is attracted to negatively charged areas on the wall of the xylem, and for calcium to move, it must be exchanged off the xylem wall by other positively charged cations such as magnesium (Mg++), potassium (K+), ammonium (NH4+), or additional calcium cations (Ca++). This cation exchange of calcium in the xylem requires continuous movement of water into and up through the plant. It also requires a continuous supply of calcium from the soil.

In general, most soils have sufficient calcium to support proper plant growth. While proper liming will insure there is adequate calcium, it is not the lack of calcium in the soil that causes blossom end rot in most cases. It is the inadequate movement of calcium into plants that is the common culprit. Anything that impacts root activity or effectiveness will limit calcium uptake. This would include dry soils, saturated soils (low oxygen limits root function), compaction, root pathogens, or root insect damage. In hot weather on black plastic mulch, roots can also be affected by high bed temperatures. Low pH can also be a contributing factor. Calcium availability decreases as pH drops, and below a pH of 5.2 free aluminum is released, directly interfering with calcium uptake. Again, proper liming will insure that this does not occur. Applying additional calcium as a soil amendment, above what is needed by normal liming, will not reduce blossom end rot.

In the plant, there is a “competition” for calcium by various plant parts that require calcium such as newly forming leaves and newly forming fruits. Those areas that transpire the most will receive more calcium. In general, fruits have much lower transpiration than leaves. In hot weather, transpiration increases through the leaves and fruits receive lower amounts of calcium. High humidity will reduce calcium movement into the fruit even more. Tissue tests will often show adequate levels of calcium in leaf samples; however, fruits may not be receiving adequate calcium. In addition, in hot weather, there is an increased risk of interruptions in water uptake, evidenced by plant wilting, when transpirational demand exceeds water uptake. When plants wilt, calcium uptake will be severely restricted. Therefore, excess heat and interruptions in the supply of water (inadequate irrigation and/or rainfall) will have a large impact on the potential for blossom end rot to occur. Proper irrigation is therefore critical to manage blossom end rot.

As a positive cation, there is “competition” for uptake of calcium with other positive cations. Therefore, if potassium, ammonium, or magnesium levels are too high in relation to calcium, they can reduce calcium uptake. To manage this, do not over-fertilize with potassium or magnesium and replace ammonium or urea sources of nitrogen with nitrate sources.

Applying additional soluble calcium through irrigation, especially drip systems, can reduce blossom end rot to some degree if applied prior to and through heat events and if irrigation is applied evenly in adequate amounts. Foliar applications are much less effective because fruits do not absorb much calcium, especially once a waxy layer has developed, and calcium will not move from leaves into the fruit (there is little or no phloem transport).

In conclusion, the keys to controlling blossom end rot are making sure roots are actively growing and root systems are not compromised, soil pH is in the proper range, and irrigation is supplied in an even manner so that calcium uptake is not interrupted. Supplemental calcium fertilization will only marginally reduce blossom end rot if water is not managed properly.

Another calcium disorder that is found in peppers is called “stip”. These spots on peppers occur later in the year, commonly in the late summer or fall, during cool, humid conditions. Under these conditions, calcium movement into the fruit is uneven, leading to localized collapse of cells, causing the spotting. Again, making sure adequate calcium is moving in the plant is critical to control stip.

Tomato Pollination and Excessive Heat

Thursday, July 12th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

The extreme heat we had will play havoc on tomato fruit that was just flowering or ripening, causing problems in fruit development due to poor pollination. Constant exposure of a tomato plant to high temperatures (day/night temperatures of 95/80°F) significantly reduces the number of pollen grains produced and released per flower and decreases the pollen’s viability. Most pollen is shed between 10:00 a.m. and 4:00 p.m. and 3-hours or more at 103oF on two consecutive days can cause fruit set failure. Temperatures at night may play a more important role in determining whether or not pollination takes place than day time temperatures. This is because ideal fruit set occurs within a very narrow range of night temperatures (60°-70° F). If tomato plants experience night temperatures above 75°F, interference with the growth of pollen tubes can occur preventing normal fertilization and causing blossom drop (Fig. 1). Prolonged high humidity (>80%) also will hinder good fruit set as the pollen either will not shed freely or the pollen grains may bind together, resulting in poor pollination. Poor pollination may result in under-size fruit that looks ‘normal’ but is just a great deal smaller. Other problems include poor development of the gel inside the fruit. This causes the fruit to appear angular and soft when squeezed (Fig. 2). When this type of fruit is cut in half, open cavities can be seen between the seed gel and the outer wall (Fig. 2). High temperatures during the ripening period additionally can cause ‘internal whitening’ in tomato fruit (Fig. 2). This white tissue only is noticeable when the fruit is cut. The hard, white areas tend to be in the vascular tissues in the outer and center walls of the fruit. Low potassium levels are also associated with ‘internal whitening’. There is not a great deal that can be done about any of the environmental problems other than to be sure to water enough and do not over fertilize during these extreme conditions. Although growth regulating chemicals can be used sometimes to help fruit set under cooler than ideal conditions there is no growth regulator that will induce normal fruit development under high temperature conditions.

 

Figure 1. Blossom drop (arrows) in tomato due to high night temperatures

Figure 2. Angular sides of fruit due to poor pollination. When cut open you can see the lack of gel resulting in pockets inside the fruit as well as ‘internal whitening’–spots in the outer wall.

Sunburn in Fruits and Fruiting Vegetables

Friday, July 6th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

High temperatures, clear skies and high light radiation, and long daylengths are a recipe for developing sunburn in fruits and fruiting vegetables. We commonly see sunburn in watermelons, tomatoes, peppers, eggplants, cucumbers, apples, strawberries, and brambles (raspberries and blackberries).

There are three types of sunburn which may have effects on the fruit. The first, sunburn necrosis, is where skin, peel, or fruit tissue dies on the sun exposed side of the fruit. Cell membrane integrity is lost in this type of sunburn and cells start leaking their contents. The critical fruit tissue temperature for sunburn necrosis varies with type of fruit. For cucumbers research has shown that the fruit skin temperature threshold for sunburn necrosis is 100 to 104°F; for peppers, the threshold is 105 to 108°F, and for apples the critical fruit skin temperature is 125-127 °F. Fruits with sunburn necrosis are not marketable.

The second type of sunburn injury is sunburn browning. This sunburn does not cause tissue death but does cause loss of pigmentation resulting in a yellow, bronze, or brown spot on the sun exposed side of the fruit. Cells remain alive, cell membranes retain their integrity, cells do not leak, but pigments such as chlorophyll, carotenes, and xanthophylls are denatured or destroyed. This type of sunburn browning occurs at a temperature about 5°F lower than sunburn necrosis (115 to 120° F in apples). Light is required for sunburn browning. Fruits may be marketable but will be a lower grade.

The third type of sunburn is photooxidative sunburn. This is where shaded fruit are suddenly exposed to sunlight as might occur with late pruning, after storms where leaf cover is suddenly lost, or when vines are turned in drive rows. In this type of sunburn, the fruits will become photobleached by the excess light because the fruit is not acclimatized to high light levels, and fruit tissue will die. This bleaching will occur at much lower fruit temperatures than the other types of sunburn.

Genetics also play a role in sunburn and some varieties are more susceptible to sunburn. Varieties with darker colored fruit, those with more open canopies, and those with more open fruit clusters have higher risk of sunburn. Some varieties have other genetic properties that predispose them to sunburn, for example, some blackberries are more susceptible to fruit damage from UV light.

Control of sunburn in fruits starts with developing good leaf cover in the canopy to shade the fruit. Fruits most susceptible to sunburn will be those that are most exposed, especially those that are not shaded in the afternoon. Anything that reduces canopy cover will increase sunburn, such as foliar diseases, wilting due to inadequate irrigation, and excessive or late pruning. Physiological leaf roll, common in some solanaceous crops such as tomato, can also increase sunburn.

In crops with large percentages of exposed fruits at risk of sunburn, fruits can be protected by artificial shading using shade cloth (10-30% shade). However, this is not practical for large acreages. For sunburn protection at a field scale, use of film spray-on materials can reduce or eliminate sunburn. Many of these materials are Kaolin clay based and leave a white particle film on the fruit (such as Surround, Screen Duo, and many others). There are also film products that protect fruits from sunburn but do not leave a white residue, such as Raynox. Apply these materials at the manufacturer’s rates for sunburn protection. They may have to be reapplied after heavy rains or multiple overhead irrigation events.

UMD Researchers Seek Tomato and Leafy Greens Farm Participants

Friday, June 22nd, 2012

Sasha Marine, UMD Postdoctoral Research Associate; scmarine@umd.edu

In recent years, outbreaks of Salmonella, Listeria and E. coli in fresh vegetables and the resulting public concern over food safety has prompted regulators to re-evaluate production and post-harvest practices. Research has demonstrated the importance of Good Agricultural Practices (GAPs) and Good Hygienic Practices (GHPs) for preventing contamination and the subsequent growth of pathogenic microorganisms. As a result, protocols (referred to as “metrics” by the food industry) have been established by specific commodity groups and retailers, as well as by state and federal organizations. However, knowledge gaps remain as to the risk factors and adaptability of these protocols to different climates, regions and types of farming operations. It is important that any protocols be suited to implementation on small- and medium-sized farms, which are typical to Maryland and Delaware.

Thanks to a multi-state grant from the USDA National Institute of Food and Agriculture, University of Maryland researchers Kathryne Everts and Christopher Walsh will be collecting data from several small- and medium-sized farms in Maryland and Delaware to examine the influence of water sources and environmental parameters on the microflora on tomatoes and leafy greens. The scientific and technological knowledge gained from the 3-year project will be used to develop, refine and defend national food safety protocols for domestic and imported produce. Data generated from this project will also be incorporated into an upper-division undergraduate course being developed by Walsh and faculty at the University of Delaware and the University of Florida.

Farmers wishing to participate in this project may contact Sasha Marine (scmarine@umd.edu).

Pruning Tomatoes

Friday, June 8th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Commercial determinate tomatoes may require pruning of “suckers”, those shoots that develop at lower nodes. Removal of one or more of these shoots up to the first fork, just below the first flower cluster, can improve fruit size, quality, and marketable yield on some varieties. Varieties that are very vigorous and tall with a lot of foliage such as BHN589 are the best candidates for pruning. Pruning will increase fruit size, increase early set, and reduce disease pressure by improving air movement and spray coverage. However, fruit numbers will be reduced. Pruning is best carried out prior to first stringing when shoots are small (2 to 4 inches long). They can be removed by bending the shoot backward where it easily snaps off. Later pruning with larger shoots may require the use of hand pruners to avoid excessive tearing. A second trip through the field after stringing may be required to remove late developing suckers. Always prune when foliage is dry to avoid spreading diseases. The amount of pruning required will vary by variety. Some varieties require little or no pruning or removal of ground suckers only (those coming from the cotyledon node); vigorous varieties may require the removal of ground suckers plus two additional suckers. Check with your seed-persons for pruning recommendations for the varieties you are using. Over-pruning can result in reduced yields and increased sunburn, blossom end rot, fruit cracking, and catfacing.

Managing Diseases of High Tunnel Tomatoes

Friday, June 1st, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

I have received several questions about timber rot caused by Sclerotinia sclerotiorum, leaf mold caused by Fulvia fulva, and gray mold caused by Botrytis cinerea over the past week for greenhouse and high tunnel tomatoes in Maryland and Delaware.

Timber rot is common where tomatoes (or another susceptible host) have been planted in ground beds in the past. The fungus Sclerotinia sclerotiorum causes disease on hundreds of plant species. Therefore rotation is difficult. Even when a high tunnel is moved between seasons, the disease can be severe because the fungus overwinters both in and around the tunnels. Usually the primary source of inoculum is outside of a high tunnel. In the spring when the soil is moist, the fungal fruiting bodies emerge and spores (ascospores) are released. These ascospores will be released continually throughout the spring and are carried on wind into the doors or raised sides of nearby high tunnels. Ascospores are usually carried or dispersed less than 330 feet. Therefore it is important to use sanitation within 330 feet of a high tunnel. No plants, leaf clippings, potting mix, or soil from the tunnels should be discarded within this area.

There are some practices that will help reduce timber rot pressure, such as minimizing the length of time that the soil stays wet. The biocontrol, Contans has been effective in managing Sclerotinia diseases in the field. Contans, which is a formulation of the fungus Coniothyrium minitans, parasitizes the survival structures of S. sclerotiorum. If it is sprayed on the area around the high tunnel and watered into the soil, it may help reduce ascospore formation in future years. Because the product is a live organism, it must be handled carefully to preserve its effectiveness. Contans would be a good choice for fields or areas around high tunnels, which are used repeatedly for a susceptible crop. See the Contans label for additional information. Other products labeled for Sclerotinia timber rot are Endura, which is labeled for field use, and Botran, which is labeled for greenhouse use.

Leaf mold and gray mold are both favored by high humidity and therefore improving air flow can reduce the extent of disease spread. There are several fungicides that are labeled for greenhouse use that will help reduce disease. These include Scala for leaf mold, Mycostop and Decree for suppressing gray mold, mancozeb products such as Dithane F-45, and copper. In addition to timber rot, Botran has activity on gray mold.

Spray to Prevent Late Blight on Potato and Tomato

Thursday, May 24th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Late blight has been found on potato in central New Jersey. The grower was applying preventative fungicides, however lesions occurred in a part of the field that the sprayer missed. All potato and tomato crops are susceptible to this disease. Growers should scout and apply preventative fungicides to protect their crops. Chlorothalonil, mancozeb or Polyram can be applied to potato and chlorothalonil, Gavel, or mancozeb can be applied to tomato. Complete coverage of the field is extremely important. Once late blight has been found close to a grower’s field, switch to a fungicide that is late blight specific. More information on available fungicides for this disease can be found at http://ag.udel.edu/extension/vegprogram/publications.htm#vegrecs.

Controlling late blight in organic systems is extremely difficult. Organic growers should apply a protectant such as copper to their crop. Serenade, Sonata and Sporatec are OMRI listed, and labeled for late blight. (However, there are very few research trials on efficacy of these products). It is critical to apply these materials with adequate coverage and at short spray intervals.