Dan Egel

Clinical Engagement Associate Professor
Dan Egel's website
SWPAC

141 articles by this author

Article List

Many years ago, I was told that to successfully use fungicides on vegetables, one must use high spray pressures and hollow cone nozzles. However, I had trouble finding any research on this topic, just rumors. So, I did my own research. Dennis Nowaskie, Superintendent at the Southwest Purdue Agricultural Center (SWPAC) built a single row sprayer that could be used to vary nozzle types between flat fans and hollow cones and spray pressures from 30 to 150 PSI. We used the sprayer to conduct experiments on Alternaria leaf blight of cantaloupe during three years of field tests. The fungicide we used to try to manage this disease was the contact product chlorothalonil (trade names include Agronil®, Bravo®, Echo® and Terranil®). Phillip Harmon, now a professor at the University of Florida, was my co-author on this paper. Try as we might, we could not find any statistical differences in disease severity[Read More…]


Since there is an article about the application of insecticides in this issue, below I list 10 rules that will help vegetable growers apply fungicides effectively and safely. Apply fungicides prior to the development of disease. Although many fungicides have systemic (“kick back”) action they will not completely eradicate diseases after they have started. And by the time a single disease lesion is observed in the field, many more lesions too small to observe are already working at your crop. Most systemic fungicides move less than an inch toward the tip of the plant or may just move from the upper to the lower side of the leaf. Use shorter spray intervals during weather conducive to plant disease. Each plant disease has its own “personality” and thus prefers different weather. However, most plant diseases require leaf wetness. Therefore, during periods of rain and heavy dews, more frequent fungicide applications are[Read More…]


blah

Bacterial spot of tomato has been observed across Indiana this summer. Leaf spots are usually 1/16 inch, and dark. Where lesions are numerous upon a leaf, the tissue may be chlorotic (yellow) (Figure 1 & 2).  (In contrast, each lesion of bacterial speck is often accompanied by chlorosis whether lesions are numerous or not.) Lesions of bacterial spot on fruit are dark, raised and up to 1/3 inch in diameter (Figure 3). The disease prefers warm, wet weather. Overhead irrigation will also spread this disease. Although much of Indiana has been dry recently, rainy weather earlier in the year has increased the severity of bacterial spot. Bacterial spot is much more common in field tomatoes than in greenhouse or high tunnel tomatoes. This is because bacterial spot requires leaf wetness for infection to take place and rain to spread the bacteria from leaf to leaf and from plant to plant.[Read More…]


Watermelon harvest is in full swing in southern Indiana. At this time, we frequently see many types of leaf symptoms. Some of them are caused by foliar diseases, such as anthracnose, Alternaria leaf blight and gummy stem blight. These diseases require special attention, normally in the form of fungicide sprays, to slow spread of the disease. However, the appearance of a moderate amount of foliar disease in mid-season doesn’t necessarily need an immediate fungicide application. Other leaf symptoms may not be caused by diseases or insects. Here are some examples of leaf symptoms that are not associated with a pathogen. It is important to correctly identify the source of the symptom to prevent unnecessarily pesticide spray. In the article When a yellow leaf is just a yellow leaf, Dr. Dan Egel discussed general rules for determining if the symptom is a disease or not. If you are not certain whether the symptom[Read More…]


The bottom pumpkin leaf has the disease powdery mildew. The top leaf is healthy and has a variegated pattern

Powdery mildew is a common disease of cucurbits in Indiana. This disease is more common on cantaloupe and pumpkin. However, we have observed powdery mildew more frequently on watermelon in recent years. We have also observed this disease on cucumber in high tunnels. If left uncontrolled, this disease can cause loss of foliage, loss of yield and lower quality fruit. This article will discuss the biology and management of powdery mildew of cucurbits. Powdery mildew is relatively easy to recognize; talc-like lesions occur on both sides of the leaf (Figure 1). The fungus that causes powdery mildew, Podosphaera xanthii, does not require leaf wetness for infection of leaves, only high humidity. The optimum temperature for disease development is 68 to 81°F. P. xanthii may survive for a period in crop residue as a resilient fungal structure, but the disease is so easily windborne, that crop rotation is not always a practical control measure. The fungus[Read More…]


Figure 3. Webbing produced on heavily infested cucumber leaves by two-spotted spider mite.

Despite the wet start to the summer that we are experiencing, we have some growers reporting spider mites in field watermelons (Figure 1). This pest is typically associated with hot, dry weather and can be especially problematic in crops grown under protection, such as in high tunnels. Spider mites often move into a field from an adjacent fencerow or rye strip. Two-spotted spider mites (Figure 2.) are most commonly a problem on watermelon and cucumbers in high tunnels, but also affect muskmelons. They can be detected by observing the yellowish discoloration on the upper side of the leaves or using a 10x hand lens and scouting on the underside of the leaf for the pest. Alternatively, you may use a white sheet of paper and tap the leaves above the paper to dislodge the mites; you will see them moving about on the sheet of paper. Because mites often migrate[Read More…]


thumbnail image

The wilted and dead leaves of the watermelon transplants in Figure 1 could have several causes. Above ground symptoms such as wilts and leaf death may be caused by problems underground.  When I investigated the plants in Figure 1, I found that many of the plants had a root rot. The dark area at the base of the stem (technically, the hypocotyl) is caused by a fungus that is growing in the plant (Figure 2). The fungus also can be found on the roots of the plant. This disease is known as black root rot of watermelon. The fungus that causes this disease is Thielaviopsis basicola. This fungus causes a similar disease on carrot, tobacco, pansies and many more crops. The dark area on the base of the stem is actually a ‘sign’ of the disease since the fungus that causes the disease is visible. The wilting and decline of[Read More…]


thumbnail image

This disease has been observed in southern Indiana. Symptoms often begin with dark, wet-looking lesions on the stem (Figure 1). These lesions may extend up the stem and result in the wilt and death of the plant (Figure 2). Occasionally, opportunistic microorganisms invade the stem and produce a disagreeable rotten odor. The conditions that may favor aerial blackleg include dense canopies and warm, wet weather. Overhead irrigation can also be a factor in promoting aerial blackleg. The bacteria which cause aerial blackleg are Dickeya and Pectobacterium spp. These bacteria are often introduced by infected seed potatoes. The bacteria may then spread into the soil and be splashed into wounds or leaf scars.  Conversely, the bacteria have been reported to survive 2 years or less in crop debris. It is important to note that while symptoms of aerial blackleg do not include rot of the seed piece, blackleg may start on[Read More…]


blah

Below, I will briefly discuss a few of the diseases that I have observed on tomatoes recently. Powdery mildew of tomato – Powdery mildew of tomato is not usually a common problem in Indiana. However, in recent years, there have been more reports of this disease than usual. Powdery mildew is more often observed in a greenhouse situation than in a field. The key symptoms of this disease are the talc-like lesions on the upper and lower leaf surfaces (Figure 1). It is important to note that the location of the upper and lower lesions do not correspond with each other. When the lesions are young, it may almost seem as if the lesions can be ‘wiped off’. Few varieties exist with good levels of host resistance, although growers may notice some difference in susceptibility between varieties. It may not be necessary to treat tomatoes affected with powdery mildew with fungicides. If[Read More…]


Figure 1. A cucumber plant grown in a high tunnel died because of bacterial wilt.

Bacterial wilt is one of the most destructive diseases in high tunnel cucumber production. The reason bacterial wilt is so important is because, like other wilt diseases, it ties up with the entire vascular system of a plant, causing systemic effects (Figure 1). The relatively less important roles that other cucumber diseases play also make bacterial wilt the major limitation for high tunnel cucumber production in Indiana. For example, common cucumber diseases such as angular leaf spot, anthracnose and Alternaria leaf blight seldom occur in a high tunnel scenario; improved resistance to powdery mildew was observed in some of the newly developed cucumber varieties; downy mildew in general does not occur in Indiana until end of the high tunnel cucumber production season. The causal organism for bacterial wilt of cucumbers is Erwinia tracheiphila. After the bacteria enter the plant vascular system, it multiplies quickly. As a result, it interferes with[Read More…]