76 articles tagged "Plant Disease Management".

There are large areas of this watermelon field that appear brown from the disease anthracnose.  No amount of fungicide will cause these areas to turn green.  Growers should assess the likelihood that fungicides will be effective before spending large amounts of money on an application.  (Photo by Dan Egel)

​Protecting vegetable crops from foliar disease involves many factors. Crop rotation and fall tillage will help to lessen disease severity. Choosing a resistant or partially resistant variety can lower the amount of disease. Purchasing seed that has been tested for seed borne disease is also an important factor. Most growers, however, find it is also necessary to apply fungicides to manage foliar diseases. This article will discuss when such applications are productive-and one case where they may not be.  Foliar fungicides are most effective when applied before infection of a plant disease takes place or early in the disease epidemic. That is, it is best to apply fungicides before one observes disease and at regular intervals. Fungicides are designed to protect healthy foliage from disease. Applications of fungicides will not change plant tissue that has been turned brown (necrotic) from disease into green healthy tissue.  Figure 1 shows a watermelon[Read More…]


(Photo by Shubin K. Saha)

​Tomato growers who utilize high tunnels to reach early markets often find that there are few economic alternatives to tomato. Therefore, many growers grow tomatoes after tomatoes instead of rotating to a different crop. The repeated cropping of tomato in the same area can lead to disease problems such as Fusarium crown rot and white mold (timber rot). Soil solarization takes advantage of solar radiation to heat the soil to temperatures that are lethal to many fungal pathogens, nematodes, and weed seeds. In Indiana, soil solarization is not always practical for field use since the period where soil solarization would be useful, summer, is also the period where most growers must produce crops. The use of soil solarization in high tunnels, however, may be more practical since these crops are produced earlier than field crops. Additionally there is chance for greater heating of the soil if the high tunnel vents[Read More…]


Late blight can cause brown necrotic lesions on tomato leaves that may be surrounded by growth of the causal fungus under moist conditions (Photo: Tom Creswell).

​Late blight has been reported on potatoes and tomatoes in LaGrange County.Potato and tomato growers in northern Indiana should follow the management recommendations listed below and in the Midwest Vegetable Production Guide for Commercial Growers 2015 (ID-56). Late blight thrives under cool, wet conditions. The disease can easily spread from plant to plant. Under ideal conditions, the disease can spread rapidly, causing symptoms on all above ground plant parts (Figure 1). The lesions may be green to brown and under moist conditions may be ringed with white fungal growth. Affected tomato fruit may have large brown lesions. The fungus-like organism that causes late blight does not usually overwinter in Indiana. Therefore, the disease must be blown or brought into Indiana. All strains of the fungus-like organism that affect tomato will cause disease on potato. However, not all potato strains will affect tomatoes. It is best for tomato and potato growers[Read More…]


Downy mildew causes bright chlorotic lesions on pumpkin leaves that are limited by veins. Lesions eventually become necrotic. (Photo by Dan Egel).

​On July 22, I announced that downy mildew had been observed on watermelon in Knox County in southwestern Indiana. This article https://ag.purdue.edu/arp/swpap/VeggieDiseasesBlog/Lists/Posts/Post.aspx?ID=48 describes the outbreak and management options. Below, I will discuss the whereabouts of additional downy mildew outbreaks on cucurbits.  Downy mildew has now been reported on cucumber in Knox and La Porte County Indiana. Downy mildew has been observed on pumpkins in Mason County in central Illinois. In addition, several counties in Kentucky and Michigan have reported downy mildew, primarily on cucumbers. A photo of downy mildew on pumpkin is shown here for reference (Figure 1). You may follow the development of downy mildew of cucurbits on this website http://cdm.ipmpipe.org/.


Leaf lesions of Botrytis gray mold are often a light gray or brown color and the sporulation of the causal fungus can be seen on the leaf margin.

​Gray mold of tomato is one of the more common diseases of greenhouse-produced tomatoes. Although it is often a minor problem, if left unchecked, gray mold can cause yield loss. Gray mold, or more properly, Botrytis gray mold, often causes a light gray or brown necrotic lesion on leaves (Figure 1). The lesions on leaves are sometimes wedge shaped on the margin of the leaf. Stem lesions are a similar color and may encircle the stem, causing the death of the upper portion of the  stem. Occasionally, gray mold may cause the rot of tomato fruit. Whether on leafs, stems or fruit, the gray fungal sporulation is often easily seen, thus the name. It is a rare symptom, but when fungal spores land on tomato fruit that is wet, the spores may germinate, causing a symptom known as a ghost spot (Figure 2). Botrytis gray mold can cause disease on many different host plants, enabling[Read More…]


Magnesium deficiency in cantaloupe often occurs in high

​I have observed many fields of cantaloupes with magnesium deficiency or manganese toxicity. Watermelon plants may exhibit similar symptoms, but not as frequently as cantaloupe. Both disorders are related to acid (low pH) soils and usually occur in clusters in a field. Magnesium deficiency usually appears on sandy ridges and can be recognized by interveinal yellowing and death of tissues on older leaves (Figure 1). Manganese toxicity also first occurs on older leaves but appears in heavier or darker sands, often in low areas of the field. The diagnostic feature of manganese toxicity are the tiny pin-hole type lesions with yellow halos clustered between the veins (Figure 2). Leaves are best viewed when held up to the sun. These disorders can easily be confused with an infectious disease. In particular, magnesium deficiency has been confused with Alternaria leaf blight. Symptoms may seem to “spread” from areas of the lowest pH[Read More…]


Downy mildew of watermelon causes dark brown or black lesions often surrounded by a yellow halo.

This disease has been observed on watermelon in Knox County. The following article will discuss the symptoms, biology and management of downy mildew of cucurbits. Symptoms. The symptoms of downy mildew vary depending on the host.    On watermelon, the lesions start out as chlorotic (yellow) areas that become round and necrotic (brown/black) areas surrounded by a chlorotic halo. Lesions may be limited by veins (Figure 1). Note that leaf lesions of gummy stem blight may have dark fungal structures (pycnidia) present that are lacking with downy mildew. Also, whereas gummy stem blight will affect stems and petioles, downy mildew will not.  Pumpkin lesions also start out chlorotic and are often angular. Eventually, the chlorotic lesions become necrotic. Lesions may be more common along a vein. Lesions on muskmelon often have poorly defined margins and are not as angular as described above for pumpkin.   Cucumber lesions start out chlorotic and very[Read More…]


Powdery mildew of tomato is easily recognized from the sporulation of the white fungus on the leaves.

​This disease has been reported near West Lafayette and in Wanatah Indiana. Powdery mildew of tomato can be recognized by the white fungal colonies on both leaf surfaces (Figure 1). Occasionally, stems may also be infected. Severely affected tomato plants may have leaves that turn chlorotic and necrotic. Fruit will not be directly affected. The causal organism has been tentatively identified as Pseudoidium neolycopersici, formerly Oidium neolycopersici. This fungus may survive as resting structures on host material. The spores are easily wind dispersed to additional tomato plants. Development of this disease is favored by temperatures below 86°F. As with most powdery mildew diseases, high humidity allows the disease to develop; leaf wetness is not necessary. Since high humidity favors powdery mildew of tomato, greenhouse environments often favor the disease. Reports of powdery mildew on tomato are not common in Indiana. There is no data on yield loss from this disease on tomato. Nevertheless, if this disease is present, management options should be considered. Several systemic[Read More…]


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​Burrs and Cones. Both of the trellises in the Boiler Hopyard have begun flowering and coning. The primary shoots were pruned at the top of the net on the dwarf trellis in order to promote lateral growth. The pruning took place on May 19 and again on May 28. The bines on the dwarf trellis have been flourishing with flowers and now cones. Out of the six cultivars in the hopyard, Galena was the first to reach the top of the dwarf trellis and begin flowering. The tall trellis began flowering in early June along with the dwarf trellis, but after adding the last dose of nitrogen the plants in the tall trellis began putting on more vegetative growth, including lateral branches. This appeared to delay flowering and allowed for more lateral growth development. The plants in the tall trellis are now in full bloom and appear to be several[Read More…]


These lesions may be covered with a white mold during moist conditions. (Photo by Dan Egel)

​Most growers first notice this disease when large, soft areas 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 (see Figure 1). Conditions that favor Phytophthora fruit rot include warm, rainy weather such as occurred recently over much of Indiana. Water that stands in pools also favors severe disease symptoms. Overhead irrigation may help the disease to spread. Phytophthora fruit rot can spread rapidly when conditions are favorable. The organism that causes Phytophthora fruit rot of watermelon is Phytophthora capsici. This organism is more closely related to algae than to fungi. Therefore, P. capsici is sometimes referred to as a fungus-like[Read More…]


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