Dan Egel

Clinical Engagement Associate Professor
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SWPAC

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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…]


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…]


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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I probably spend too much time posting photos of diseased vegetables on-line and presenting vegetable disease symptoms in presentations.   My excuse is that recognizing the symptoms of what might be a disease seems important to me.   However, it might be just as important to recognize symptoms that are not of an infectious disease. See below for some photos of leaves that do not have an infectious disease.   The leaf in Figure 1 is a relatively old leaf.   Older leaves tend to turn yellow with age.   One reason for this is that nitrogen is mobile in the plant.  When newer leaves are formed and need nitrogen, it can be pulled from the older leaf.   This means the older leaf looks yellow and perhaps brown around the edges. It is possible that non infectious problems can be important problems.   However, none of the leaves here have symptoms of a problem[Read More…]


Cucurbit downy mildew has been observed on cucumber and cantaloupe near Wanatah, in La Porte County, Indiana. Downy mildew has also been confirmed on cucumber in St. Joseph County Michigan, just northeast of Elkhart, Indiana as well as on processing pumpkin in central Illinois. Downy mildew of cucurbits has also been reported in southern and central Kentucky and north-central Ohio. All cucurbit growers in Indiana should be scouting and managing for downy mildew. The organism that causes downy mildew of cucurbits doesn’t overwinter in Indiana. It has to be blown in every year. It is common for downy mildew to start the season in the Gulf States and migrate north with the cucurbit crops. Downy mildew apparently overwinters in northern Michigan/southern Ontario in greenhouses where cucumbers are grown year round. Therefore, downy mildew is often found in Michigan before it is found in Indiana. Many cucumber varieties have some resistance to downy mildew. For susceptible[Read More…]


Figure 2. Cross stitch with large lesions.

Cross stitch of watermelons is a physiological disorder (not caused by an infectious disease) first reported in 1990s on watermelon fruit. It received the name because the symptom looks like cross stitch. One or more rows of oval-shaped lesions lie along with the longitudinal axis of the fruit. These lesions are normally more close to the stem end of the fruit (Figure 1). Sizes of the lesions range from a quarter inch to more than 2 inches. When the lesions are small, it normally does not affect interior flesh quality. However, if lesions develop into large gaps, it could lead to fruit rot (Figure 2). Cross-stitch symptom has been noticed in several watermelon production areas, however, causes of the symptom is still largely unknown. In most of the years, this is a minor problem. However, we have received more reports of cross-stitch  on watermelon fruit this year. In one case,[Read More…]


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…]


I have received several calls about pumpkins recently. This article will outline a few steps growers should think about to prevent diseases in pumpkins. Virus diseases – There are several virus diseases that affect pumpkins in the Midwest. The most important diseases include: papaya ring spot, watermelon mosaic and zucchini yellow mosaic virus. Aphids transmit all these diseases. Many of the aphids responsible are carried up from the south each year on winds. Therefore, aphids with virus are more common later in the summer; pumpkins planted later in the season are more likely to be affected with one of the virus diseases listed above. Plant pumpkins by about June 15 to avoid having the fruit set during the period of high virus disease pressure. Powdery mildew – It is nearly impossible to find a pumpkin vine in August without powdery mildew. However, this disease does not have to affect production. The first decision a[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…]


This disease is more likely to develop during periods of heavy rains in relatively poorly drained soils. June started out dry for many areas of Indiana, however recent rains increase the likelihood of Phytophthora diseases. Phytophthora fruit rot of watermelon causes large, soft areas to develop on mature watermelon fruit. These lesions can be several inches across and are often covered with a white mold. The lesions usually form first on the bottom of the fruit, close to where the fruit comes into contact with the soil. Further development of the disease often results in lesions on the top of the fruit as well. The first application of a systemic fungicide for this disease should occur when watermelon are about softball stage. Since Phytophthora does not usually affect the foliage of watermelon, there is no need to apply fungicides for this disease until fruit are present. Applications to small fruit may include[Read More…]