72 articles tagged "Tomato".

For many vegetable growers, the season is in full swing. All that hard work in season preparation, planting and maintenance is paying off with harvest. One of the on-going season maintenance issues is applying fungicides. In other articles, I have described how and when to spray. In this article, I want to address when to stop. To limit the scope of this article, I will concentrate on tomato, cantaloupe and watermelon crops. These are crops where the fruit is consumed, not the foliage. For most vegetable crops, there is no need to apply a fungicide shortly before the final harvest. Foliage needs to be protected to preserve fruit quality. A plant with reduced foliage will produce a smaller fruit and/or fruit that have fewer sugars and other desirable compounds. I don’t know how much foliage needs to be reduced to affect fruit size or quality. However, I do know that for many foliar diseases, symptoms will not be obvious[Read More…]

Southern blight of tomato thrives under hot, dry conditions. Usually, such conditions are more common in August than early July. However, 2016 has been relatively hot and dry in southwest Indiana. Perhaps for this reason, I have observed this disease in my own tomato plots. This article will discuss the symptoms, biology and management of southern blight of tomato. Southern blight has a wide host range affecting many vegetable, field and ornamental crops. Tomato is the most important host. The disease is caused by the fungus Sclerotium rolfsii. This fungus is related to the one that causes white mold. The first symptom one is likely to observe of southern blight is plant wilt. At the base of the plant, one is likely to notice a canker with sclerotia that may be as large as a sesame seed (Figure 1). These sclerotia are survival structures for the fungus and allow the disease to occur[Read More…]

Figure 1. Hornworm feeding on tomato leaves in a high tunnel.

Hornworms can be pests of tomato and pepper in field grown crops, but for some reason seem to be particularly severe in high tunnels. Hornworms are very large caterpillars, measuring up to 4 inches long (Figure 1), and they can consume large quantities of foliage and will also feed on green fruit (Figure 2). In fields, hornworm damage is usually localized and tolerable, although treatment is sometimes required. In high tunnels, hornworm damage, particularly to tomato, is often severe (Figure 3) and will require several applications of insecticides. In field situations, the treatment threshold is one hornworm per two plants. Since the infestations are often localized, it may not be necessary to treat the entire field. In high tunnels, there is no established threshold, so my recommendation would be to treat as soon as you seen caterpillars or their damage. The good news is that hornworms are fairly easy to control.[Read More…]

Below, I will briefly discuss four diseases that I have observed on tomatoes recently. White mold of tomato – Perhaps the most common symptom of white mold of tomato is the light brown area on the lower stem (Figure 1). This brown area is essentially dead and will result in the wilt and death of the tomato plant above that point. Either on the outside of this dead area or inside the stem, dark, irregularly shaped fungal bodies can usually be found. These fungal bodies (known as sclerotia) are diagnostic of white mold. The fungal spores responsible for white mold are released early in the spring from a very small mushroom (several mushrooms could fit on a dime). The spores will enter a plant where tissue is dead or senescent, such as old flower petals. Fortunately, white mold, once established, will not spread from tomato to tomato plant. However, growers may observe more symptoms as later[Read More…]

We have received a number of reports of outbreaks of spider mites, primarily in watermelons in the field and cucumbers in high tunnels. Spider mite damage can be recognized by the chlorosis often observed on older leaves (Figure 1).  Plus, the underside of leaves affected by spider mites often appears ‘dirty’ due to the debris caught by the webbing (Figure 2).  The problems in high tunnels are not unexpected because one of the primary causes of mortality in mite populations is rainfall washing them off the plants and, of course, that is lacking completely in high tunnels. In addition, the warmer temperatures present in high tunnels allow mites to complete generations faster so populations can build to high levels quickly. The hot weather recently is helping to drive population increases in fields as well. In both scenarios, we don’t really have treatment thresholds for mites. Generally speaking, if populations are increasing,[Read More…]

Last week, the highest temperature reached 110°F for a few successive days inside of our high tunnels. As a result, we observed some blossom drop on tomatoes. More information on high temperature effects on tomato fruit set can be found here. In addition to blossom drop, high temperature and high light intensity contribute to sunscald injury, uneven ripening, and cracking of tomato fruit. To protect tomatoes from damage caused by excessive heat, we placed 30% black shade cloth on top of the high tunnel. By installing the shadecloth, we expect there will be less cracking and more uniformly ripe tomatoes. Tomato marketability will increase. However, using shade cloth also has some negative effects. In this article, we review the effects of high temperatures on tomatoes, and discuss positive and negative aspects of using a shade cloth. Excessive high temperature (above 100°F) lasting for a few hours for successive days could cause tomato flower abortion and affect[Read More…]

Figure 1. Colorado potato beetle larvae found on high tunnel tomatoes.

Last week we had a report of an infestation of Colorado potato beetle larvae on tomatoes in a high tunnel (Figure 1). Potato beetles are a pest of most of the solanaceous crops (potato, tomato, eggplant, pepper), but they rarely become a serious problem on tomato in Indiana. In addition, we have not seen them in high tunnels before, so this is a new problem for us. There are a number of insecticides that are labeled for use on Colorado potato beetles, but that list gets much shorter when the problem is in a high tunnel. Remember that in Indiana, a high tunnel is considered a greenhouse, so insecticides that are prohibited in greenhouse cannot be used in high tunnels. The effective products that could be used in this situation are Admire Pro®, Intrepid®, Entrust® and Exirel®.

Figure 1. Aphids on tomatoes in a high tunnel (Photo credit Wenjing Guan)

We have begun to receive the first reports of aphid outbreaks in high tunnels on tomato, pepper, and cucumber (Figure 1). Aphids are a very common problem in high tunnels because the covering excludes rainfall, which is a major mortality factor for small insects like aphids. Some growers are interested in using biological control in their high tunnels because the ability to contain natural enemies within the tunnels increases the likelihood of achieving control. Based on our experience, we believe that lacewing larvae hold the greatest promise for successful biological control of aphids in high tunnels. Because they don’t fly, they are less likely to leave the high tunnel than many other biological control agents. There are a number of biological control suppliers who can provide lacewing larvae for growers. For growers interested in chemical control, some of the insecticides that could be expected to provide good control and are[Read More…]

I have observed leaf mold of tomato in greenhouses and high tunnels recently. This article will discuss this disease and management options. In the last issue of the Hotline, I discussed Botrytis gray mold. I noted how gray mold is favored by the cool, cloudy weather we experienced earlier this spring. The warmer and sunnier weather we have experienced more recently should favor leaf mold over gray mold. Leaf mold is caused by the fungus Passalora fulva. Cercospora leaf mold of tomato is rare in Indiana and is discussed here (https://vegcropshotline.org/article/cercospora-leaf-mold-of-tomato/). The first symptom of leaf mold one is likely to notice is a pale yellow lesion on the top side of the leaf (Figure 1). When the leaves are turned over, the fungal mold that gives the disease its name becomes evident (Figure 2). Leaf mold often becomes a problem under humid conditions (85% humidity or greater) and temperatures between 71 and 75°F, although leaf[Read More…]

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We recently published an article in the Hotline about gray mold of tomato.  That article and more details about this disease can be found here. In this short note, we want to share examples of the relationship of gray mold and tomato plant injury. In the figure 1 above, a pruning injury of tomato in a commercial greenhouse has become necrotic and a gray mold infection is starting. Figure 2 is from our research high tunnel.  In the photo, one can see where there was an abrasion, probably due to tying the plant in the greenhouse. This injury allowed the gray mold fungus to begin to grow.  Not only will this infection cause a die-back, but the spores produced may cause the disease to spread.  We clipped off this branch to stop the spread of the disease. The photo is taken outside of the greenhouse for better lighting. The lesson here is[Read More…]

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