80 articles tagged "Plant Disease Management".

Figure 2: A tomato with tomato spotted wilt virus has necrotic ring spots.

While many virus diseases affect pepper and tomato plants, in the Midwest, the most common virus diseases of these two crops are tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus (INSV). These diseases are usually observed in greenhouse or high tunnel situations. The two viruses, TSWV and INSV are closely related. In fact, at one time, they were both considered TSWV. Therefore, the symptoms, biology and management of these two diseases are similar. This article discusses the symptoms, biology and management of these two diseases. Both TSWV and INSV affect many hosts, including vegetables and flowering ornamentals. Symptoms vary according to host, stage of plant affected and environmental conditions. Both diseases can cause stunting, yellowing, necrotic rings, leaf mottle and more. Figure 1 shows a tomato leaf with necrotic rings caused by TSWV. Figure 2 shows a pepper transplant with ring spots caused by INSV. Additional symptoms may[Read More…]


Figure 1. Powdery mildew causes talc-like lesions on pumpkin leaves.

Powdery mildew is a foliar disease of all plants in the cucurbit family.  The talc-like symptoms on leaves are relatively easy to identify  (Figure 1).  More about powdery mildew of cucurbits can be found at this link https://vegcropshotline.org/article/powdery-mildew-of-cucurbits-2/.  The remainder of this article is an update. There are several systemic fungicides which are recommended for powdery mildew of cucurbits. These include:  Aprovia Top®, Fontelis®, Luna Experience®, Merivon®, Procure®, Quintec®, Rally® and Torino®.  Recently, fungicide resistance to the product Torino® was discovered in eastern New York. I don’t know if the strains of the powdery mildew fungus we have in Indiana are resistant to Torino® or not.  Growers should scout their fields for the effectiveness of Torino® and other products. It is always best to alternate systemic fungicides for the management of powdery mildew of cucurbits. If possible, alternate between 3 or 4 products that have different modes of action. Not only[Read More…]


The Midwest Vegetable Production Guide for Commercial Growers 2018 described above is a good way to keep up with what fungicides are recommended and their proper use. Last year, I developed a fungicide schedule to help growers schedule when fungicides are applied. These fungicide schedules seemed to be popular, so I have updated the fungicide schedules and made them available again. There are two fungicide schedules- one for cantaloupe and watermelons and a second for pumpkins. You can find the schedules at this URL: https://ag.purdue.edu/arge/swpap/Pages/SWPAPPresentationFiles.aspx. Or call (812) 886-0198.    


Figure 3. With damping off, multiple factors usually occur to cause seedling death, both before and after germination. These factors include improper watering, poor water quality, poor seed health (e.g., old seeds, improperly stored seed), or cool temperatures all impact seedling germination, emergence, and growth.

This is the time of year when growers begin planting seed—whether you are child planting a few seeds in Dixie cup for a school project, home tomato growers, or professional horticulturists. Unfortunately, one problem you may share in common is damping-off. Damping-off describes the death of seeds or seedlings and includes all of the following phenomena: Seeds that rot before they germinate, the newly emerging root (radicle) or shoot (cotyledons) of the seedling rots before emergence, or stems of seedlings (cotyledon) are attacked near the soil line, causing the young plants to collapse. Damping-off is caused by several fungi, including Botrytis spp and Rhizoctonia solani, and fungal-like organisms such as Pythium spp. and Phytophthora spp. These microbes are found in practically all soils and pose a large threat to plant propagation. Almost all species of plants can be infected, and these organisms also cause new cuttings to rot, as well.[Read More…]


he round lesions on this watermelon are caused by Phytophthora blight. Note that the Phytophtora blight fungus can be seen sporulating on the lesion under moist conditions.

This disease was a serious problem in much of the state this past summer.  As a result, I have had many questions about managing this disease.  The questions I have been asked have ranged from what do I spray to how does this disease work? Therefore, I have written an article about the symptoms, biology and management of Phytophthora blight. I will concentrate on Phytophthora blight of cucurbits, but this disease is also a very serious problem on peppers. In the following article, I will outline some of the information I think it is important to know about this important disease. Phytophthora blight-biology Phytophthora blight is caused by a fungus-like organism known as Phytophthora capsici. Even when I was in graduate school in the 1980’s, my professors told us that we would discuss Phytophthora and related organisms in our fungus taxonomy class even though these organisms are more closely related to brown[Read More…]


Earlier in August, downy mildew was reported on all cucurbit species in LaPorte County in northwest Indiana and on pumpkins in Starke County (just south of La Porte County). More recently, downy mildew was reported on cucumbers and butternut squash in Knox County in southwestern Indiana. In addition, downy mildew is strongly suspected on cucumbers in Jefferson County. Growers in nearby areas should take care to manage downy mildew if they have valuable cucurbit crops. However, this late in the season, it is unlikely that there will be widespread losses. Management of downy mildew of cucurbits is discussed in the Midwest Vegetable Production Guide for Commercial Growers 2017 mwveguide.org and in the extension bulletin Downy Mildew of Pumpkin https://www.extension.purdue.edu/extmedia/BP/BP-140-W.pdf.  Note that downy mildew of cucurbits and downy mildew of soybeans are not caused by the same organism.  Please call Dan Egel if you have questions or concerns.


Figure 1: Cercospora leaf spot of garden beet causes bray/brown lesions with reddish margins.

This disease was observed in southern Indiana recently. Cercospora leaf spot affects table beets and swiss chard. Symptoms include circular leaf spots that may have a reddish margin. The center of the lesions may start off a light brown and turn to gray after the fungus (Cercospora beticola) begins to sporulate. Under conditions conducive to disease, the lesions can coalesce and result in loss of foliage. Yield and quality of the crop can be reduced. Cercospora leaf spot is favored by rainy weather or overhead irrigation and temperatures from 77 to 95°F.  The spores are readily dispersed in rainy, windy weather. Resistant cultivars are available. Fall tillage and crop rotations of 2 to 3 years should help to lessen disease severity. Several fungicides are listed in the 2017 Midwest Vegetable Production Guide for Commercial Growers including copper compounds, some of which may be allowed in organic certifications. Synthetic fungicides include:[Read More…]


Figure 1. Powdery mildew causes talc-like lesions on pumpkin leaves.

Powdery mildew is a common disease of cantaloupe and pumpkin in Indiana. Occasionally, I observe this disease on watermelon as well. Recently, I have noticed more powdery mildew than usual on watermelon. 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 with an emphasis on watermelon. Powdery mildew is relatively easy to recognize; talc-like lesions occur on both sides of the leaf (Figure 1).  (This article https://vegcropshotline.org/powdery-mildew-symptoms-vs-variegated-leaves/ has additional information about powdery mildew symptoms. ) 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[Read More…]


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One of the most common diseases of pumpkin in Indiana is powdery mildew.  Growers are naturally anxious to observe whether the fungicide they have been applying for this disease has been effective.   Therefore, many pumpkin growers scout their fields for disease. Although powdery mildew is relatively easy to recognize, it is possible to become confused.   Figure one shows two pumpkin leaves.  The bottom leaf has the white, sporulation of the powdery mildew fungus in colonies randomly scattered across the leaf.   The top leaf, has silvery coloration primarily along the vein.  This latter leaf is a healthy variegated leaf.   Some pumpkin varieties show this type of variegation more than others. It may be a good idea to study the photo shown here so that one can tell the difference between a pumpkin leaf with the disease powdery mildew and a healthy leaf that is merely variegated


Southern blight causes red-orange pustules primarily on the upper surface of sweet corn.

Southern rust of corn is normally a disease of tropical areas. During summer months, however, the fungus which causes southern rust, Puccinia polysora, often moves into southern areas of the U.S. This summer, southern rust has been observed in at least 11 Indiana counties. Symptoms of southern rust include raised structures called pustules. If rubbed with a finger, the spores in rust pustules will come off leaving a stain on one’s hand. Southern rust develops rust pustules primarily on the upper leaf surface (Figure 1). Common rust typically has rust pustules on both upper and lower leaf surfaces. In severe cases, southern blight can cause rust pustules on ear husks and leaf sheaths. Late in the summer, dark pustules may be formed which are called telia. It is possible to confuse southern rust with other diseases, therefore, a confirmation by the Purdue University Plant and Pest Laboratory is advised. The[Read More…]


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