Dan Egel

Clinical Engagement Associate Professor
(812) 886-0198 egel@purdue.edu
Dan Egel's website
SWPAC

127 articles by this author

Article List

Ethylene Damage on Tomato Plants

January 18, 2017 - From Issue:
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These tomato plants are exhibiting epinasty or a downward growth of the leaves in response to ethylene produced from a malfunctioning heater in a greenhouse. The topmost leaves are growing normally because the plants were removed to a separate greenhouse after exposure to ethylene. (Photo by Dan Egel).

Almost every year, I have a greenhouse tomato grower or two call me about tomato plants that are distorted and don’t seem to be growing right. The problem often turns out to be ethylene damage. This year, I have decided to write an article about it before I get those calls. Tomato plants with ethylene damage often have leaves that are curled down and stems that are twisted (Figure 1). Stems or leaves that are curled downwards are said to have epinasty (in botanical terms). Epinasty is a common symptom of ethylene damage. Ethylene is a common by-product of incomplete combustion of several different types of fuel. Incomplete combustion is often the result of heaters that are not working efficiently. Tomatoes are very sensitive to ethylene damage; however, other crops may also show ethylene damage. The tomato plants in figure 1 also have yellow seed leaves. Ethylene damage does not include yellowing.[Read More…]

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Anthracnose of Gourds

November 23, 2016 - Veggie Extras Article
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As Thanksgiving approaches, I have noticed that the gourds I set out before Halloween are starting to rot. But before I throw them away, what is causing the lesions? The circular lesions that can be seen in Figure 1 and 2 are symptoms of anthracnose of gourd.   That is, the pathogen that is causing the lesions in the accompanying figures is Colletotrichum orbiculare.   This is the same pathogen as the one that causes anthracnose on other cucurbits such as watermelon. (It is possible that the anthracnose is caused by a different species of Colletotrichum. Even if the pathogen is C. orbiculare, I am not sure of the race. More research would be required.)     A second question is how the pathogen contacted the gourd sitting in a basket in my house since early October.   This is a harder question to answer.   My guess is that the pathogen contacted[Read More…]

The Results are in: Pesticide Residues in Produce

November 15, 2016 - From Issue:
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Vegetable growers are familiar with pesticide labels that specify how much of a product may be applied. As commercial growers, we usually think about such instructions as telling us how much pesticide is the right amount to apply to a crop to be effective. While such an interpretation is correct, there is more to the labeled rates of a pesticide. While many researchers (including myself) are involved with experiments to try to manage pests with pesticides, others are involved in trying to determine the pesticide concentrations that may safely exist in the produce we all eat. The latter is known as the pesticide tolerance. Both efficacies of the pesticide and human safety are involved in determining the label rates and timing of each pesticide. Indeed, some pesticides are not labeled for certain crops for reasons of safety. There is mostly good news in the just released 2015 Pesticide Data Program. Each year, the USDA’s[Read More…]

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Alternaria Leaf Blight of Carrot

November 15, 2016 - From Issue:
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Last fall, my lab received a carrot sample with disease-like lesions (Figures 1 and 2). There are at least 3 carrot diseases that may appear similar. These diseases are: Alternaria leaf blight (late blight), Cercospora leaf spot (early blight) and bacterial leaf blight. Often an examination in the laboratory is necessary. My examination revealed the characteristic spores (conidia) of Alternaria dauci, causal agent of Alternaria leaf blight. Figure 1  shows a stand of carrots with several leaves that appear chlorotic (yellow) and necrotic. A closer examination reveals small lesions on the leaves (Figure 2). Loss of leaves may lead to fewer or smaller carrots. Sometimes severe infections can lead to the premature separating of the leaves and root. Alternaria leaf blight can be rapidly spread between plants by the conidia that are produced on the plant surface. I could easily find these spores on the surface of the carrot leaves brought to my lab. The conidia may[Read More…]

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Fall Clean and Sanitize

October 13, 2016 - From Issue:
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As Indiana growers finish up the 2017 season, it is important to remember to clean and sanitize equipment and tools. In this article, I would like to discuss the importance of and how to sanitize. Bacteria and fungi that cause plant disease may survive on some types of equipment. Examples include: stakes, transplant trays, shovels, greenhouse benches etc. Equipment can be contaminated by diseased plants in close contact with the surfaces. For example, a tomato with bacterial canker may rub up against a wooden stake, transferring some of the bacteria to the stake. Such bacteria may cause disease problems next year. A transplant tray of cantaloupe with a damping-off problem may have the same disease next year if the tray is not properly cleaned and sanitized. It is important to clean the equipment of crop debris or soil prior to the use of one of the sanitizers described below. Equipment free of crop[Read More…]

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MW Vegetable Guide for 2017

October 13, 2016 - From Issue:
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Usually I wait until January before releasing information about the Midwest Vegetable Production Guide for Commercial Growers (ID-56).   For two reasons, however, I would like to talk about the 2017 ID-56 now. This year, we welcome Michigan growers and Michigan State University to the Midwest Vegetable Production Guide The Guide is now an 8-state publication. We expect the ID-56 to be available in mid-December this year, instead of the beginning of January. Read below to find many new changes to the 2017 ID-56. New and Revised Sections We added a chapter for Celery with the help of MSU. We added a section called Selected University Diagnostic Laboratory Services, which includes contact information for each state. We revised the organic section to list certifiers on a regional basis. The Soils and Fertility section has been modified and updated. Disease Management We updated the Disease Management section. We updated the Orondis® products[Read More…]

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Downy Mildew of Cucurbit Update

September 15, 2016 - From Issue:
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Downy mildew has now been observed on butternut squash, jack-o-lantern pumpkins and cucumbers in Knox County. The list of cucurbits observed in Porter County has been updated to include butternut squash and giant pumpkin. All cucurbit growers should assume that downy mildew is present nearby and may attack any cucurbit crop. However, it is not clear what affect downy mildew may have on cucurbit crops this late in the season. Pumpkin growers who expect to harvest in the next few weeks may not need to take any management steps at this time. Downy mildew affects only leaves; stems and fruit are unaffected. Indirect effects of downy mildew in fruit are unlikely to be observed in a few weeks. Another article in this Hotline issue discusses the question of when to stop managing diseases in pumpkins. If the decision is made to apply fungicides, this article https://vegcropshotline.org/article/cucurbit-downy-mildew-watch/ or the Midwest Vegetable Production Guide mwveguide.org will help to select a[Read More…]

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Late Season Pumpkin Disease Management

September 15, 2016 - From Issue:
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Several pumpkin growers have asked me when to stop managing for pumpkin diseases. That is, when should a pumpkin grower stop applying fungicides? I cannot provide a definitive answer for this question; every grower will have to make his or her own decision. Below, however, are some factors to consider. Estimate the crop yield – walk through the field and evaluate the yield of pumpkins that are ready to harvest. Be sure to only consider fruit of marketable quality. If the yield is at or above what is expected, it may be time to put the sprayer away. Estimate when harvest will take place – Pumpkins that are scheduled for harvest in the next week or two are less likely to need any fungicide treatment. A longer period to final harvest may indicate that there is time for immature fruit to ripen. For example, pumpkins that are to be picked by the consumer up to Halloween may[Read More…]

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Preharvest Intervals

September 1, 2016 - From Issue:
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Late summer is a time when vegetable growers spend much of their time harvesting produce. Many growers, however, also find it is necessary to apply pesticides. All pesticides label state a preharvest interval (PHI) on the label. This is the amount of time, in days, between the time the fruit is sprayed with a pesticides and the time it can be harvested. That is, after a pesticide is applied to a vegetable crop, a specific amount of days must pass before the fruit is harvested. This article will breifly describe how PHIs are determined, give some examples of PHIs and list a couple of questions about PHIs. I have used examples of vegetable crops and fungicides, however, the same concepts apply to apply to all pesticides and all produce. The reason the US EPA determines PHIs is to ensure that produce that is consumed does not have unsafe pesticide residues. The first step in determining a[Read More…]

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Pumpkin Fruit Set

September 1, 2016 - From Issue:
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Figure 3. The fungus on this senescent female pumpkin flower (Choanephora sp.) is growing on a flower which did not develop properly.

There has been some concern about poor fruit set in pumpkin fields that otherwise have healthy vigorous vines. This summer we have experienced above normal temperatures for much of the pumpkin fruit set season and I suspect that has played a role. This article will consider temperature as well as other factors that influence pumpkin fruit set. In order for fruit set to take place, male and female flowers must be open on the same day, pollinating insects must be active, the plant must not be too stressed and it must have an adequate level of carbohydrates. Growers can influence some of these conditions. High temperatures promote death of female pumpkin flowers while still in the bud stage. Varieties differ in the their sensitivity to high temperatures. To determine whether flowers have died early in development requires close inspection of the pumpkin vine. An aborted bud often dries up and[Read More…]

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