76 articles tagged "Plant Disease Management".

Cercospora leaf mold symptoms on the upper leaf surface. Note distinct chlorotic lesions. Photo by Dan Egel.

​ This disease does not typically affect Indiana tomatoes, instead preferring tomatoes grown in tropical and sub-tropical areas. Since Cercospora leaf mold was observed in two different areas of Indiana in the 2015 season, it makes sense for growers to become aware of this disease in case it returns to Indiana in 2016. The two locations where Cercospora leaf mold was observed in Indiana in 2015 were 1) a homeowner garden in southern Indiana and 2) a high tunnel in central Indiana. The fungus that causes Cercospora leaf mold, Pseudocercospora fuligena, normally does not overwinter outside of tropical and subtropical areas. It may be that a wind blew the fungus in from the south in 2015. Symptoms of Cercospora leaf mold are similar to leaf mold caused by Passalora fulva. Both diseases cause chlorotic (yellow) lesions which are visible on the upper side of the leaf. The chlorotic area caused by Cercospora leaf mold is[Read More…]


Anthracnose on watermelon fruit, caused by Colletotrichum orbiculare, is typically round and sunken. (Photo by Dan Egel)

​Late in the 2015 season, I observed some unusual symptoms of anthracnose on watermelon fruit. I wanted to discuss these symptoms, but first a little background of cucurbits. An extension bulletin on this subject may be found at https://www.extension.purdue.edu/extmedia/bp/bp-180-w.pdf. Anthracnose of cucurbits, caused by Colletotrichum orbiculare, is responsible for lesions on leaves, stems and fruit. Crops affected include cucumbers and cantaloupe, however, watermelon is the host most often affected in Indiana. Although lesions on leaves and stems can cause significant loss, it is the lesions on fruit that cause direct yield losses. Lesions on watermelon fruit tend to be close to the ground where the fruit tends to stay wet. These lesions are typically round, sunken and orange to salmon colored (Figure 1). However, the lesions I observed toward the end of the 2015 season differed from the typical. Instead of regular round lesions, the symptoms I observed on the bottom of affected watermelon were[Read More…]


​In 2014 and 2015 blackleg-like symptoms were observed in some U.S. potato growing areas. The presence of a bacterium of the species Dickeya was confirmed by PCR testing. Symptoms caused from this pathogen may include leaf wilts and tuber soft rots which may extend internally up the vascular system of the stem. USDA APHIS PPQ would like to determine if Dickeya spp. are present in Indiana. If you are a potato grower and have observed the symptoms described here, contact Dan Egel.


​When used as a verb, to rogue means to get rid of items that don’t conform to a certain standard. In plant pathology, the word rogue is used to describe a technique whereby diseased plants are removed or rogued to slow the spread of disease. I’d like to describe the practice as it might be used to manage Phytophthora blight of pumpkins. The practice works like this: Under conducive conditions, Phytophthora blight spreads quickly from leaf to leaf and from plant to plant. From a single diseased pumpkin plant, an entire field can become infected. But what if one could rogue the few symptomatic plants at an early stage in the disease epidemic? Would this slow the spread of Phytophthora blight? In theory, yes. If one were able to rogue all of the diseased plants in a field, the disease could be slowed. It would be similar to sending sick children home from a classroom; the disease should[Read More…]


​Downy mildew has been confirmed on jack-o-lantern pumpkins in Daviess and Jasper Counties and on acorn squash in LaPorte County. These are the first confirmed reports of this disease on Cucurbita pepo in Indiana in the 2015 season. There are unconfirmed (but reliable) reports of downy mildew on pumpkins in Parke,  Washington, and White Counties. This disease has also been observed on butternut squash (Cucurbita moschata) in Knox and LaPorte Counties and on giant pumpkins (Curbita maxima) in LaPorte County. Read more about this disease at ag.purdue.edu/arp/swpap/VeggieDiseasesBlog/Lists/Posts/Post.aspx?ID=48.


This disease can be recognized by the light yellow region between veins and

​This disease has been observed in northern Indiana on basil sold as a fresh herb. The fungus that causes downy mildew of basil does not overwinter in Indiana, but must blow in from the south. The fungus that causes downy mildew of basil is not the same fungus that causes downy mildew of cucurbits or soybeans. Leaves may turn a yellow color that is restricted by veins. Brown areas may develop in severe infections. Close examination of the underside of the leaf under moist conditions may reveal a gray ‘fuzz’ which is the spores of the causal fungus. Such leaves may not be marketable. Since the fungus that causes downy mildew of basil does not overwinter in Indiana, fall tillage and crop rotation, although a good idea, won’t help manage this disease. Pruning plants so that leaves dry out sooner may help reduce the amount of infection (many growers may[Read More…]


​Late blight has been reported on processing tomatoes in Cass County Indiana. This is a late blight update from when this disease was reported on potatoes and tomatoes in LaGrange County Indiana. The latter outbreak and some disease management tips are reported in the Vegetable Crops Hotline Issue 603 at ag.purdue.edu/hla/Extension/VegCropsHotline/Pages/Latest-Articles.aspx?article=117 This article was originally published on the veggiediseaseblog.org on August 24, 2015.


Photo by Dan Egel

I have observed this disease in several pumpkin fields this year. It is not clear to me why this disease seems to be more widespread compared to recent seasons. However, it makes sense to review Plectosporium blight here. Plectosporium blight is usually not a serious disease. The occurrence of this disease is usually sporadic. However, when it occurs, it can cause yield loss if left uncontrolled. Older literature may list this disease as Microdochium blight. Plectosporium blight can be recognized from the light tan lesions on stems and leaf petioles. Lesions may also occur on the fruit, although these symptoms are less common. Yield loss is most often caused by lesions on the stem adjacent to the fruit—the pumpkin handle. Yellow squash and zucchini squash are also affected. Lesions are often individually spindle shaped. When these lesions occur in large numbers they can give a light gray or white appearance to[Read More…]


Photo by Dan Egel.

The relatively cool weather Indiana has experienced this summer may be responsible for more observations of northern corn leaf blight (NCLB) on sweet corn than normal. The primary symptom is the cigar shaped lesion that ranges from 1 to 7 inches in length (see Figure 1). The lesions may range from tan to gray in color. Under conditions of high humidity, olive-green fungal spores may be produced on the lesion surface. Symptoms of NCLB are frequently observed late in the season when days become cooler. Yield losses are possible if lesions reach the ear leaf or higher during the two weeks before or after tasseling. NCLB can be managed by a combination of crop rotation, fall tillage, resistant hybrids and fungicide applications. Crop rotation and fall tillage help to minimize crop residue that might harbor the fungus that causes NCLB. Choose hybrids resistant to NCLB when possible. When it is necessary[Read More…]


On July 22, I announced that downy mildew had been observed on watermelon in Knox County in southwestern Indiana. This article in the Vegetable Crop Hotline issue 603, https://ag.purdue.edu/hla/Extension/VegCropsHotline/Pages/Latest-Articles.aspx?article=118, describes the outbreak and management options. Downy mildew has now been reported on cucumber and cantaloupe in Knox and cucumber in La Porte County Indiana and pumpkin in Jasper County. 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. You may follow the development of downy mildew of cucurbits on this website http://cdm.ipmpipe.org/.


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