84 articles tagged "Plant Disease Management".

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…]


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…]


The Purdue MELCAST system allows growers to apply foliar fungicides according to weather conditions instead of using a calendar-based system.

MELCAST is a weather-based disease-forecasting program that helps growers schedule foliar fungicides. MELCAST stands for MELon disease forCASTer. This program, designed by Dr. Rick Latin, Professor of Plant Pathology at Purdue University, keeps track of weather conditions so that cantaloupe and watermelon growers can apply foliar fungicides to their crops when they are most needed. The foliar diseases that MELCAST was designed for are Alternaria leaf blight, anthracnose and gummy stem blight. In a typical year, MELCAST will save growers 2 to 3 foliar applications of fungicides without sacrificing yield. MELCAST works by having growers apply fungicides at specific Environmental Favorability Index (EFI) values instead of using a calendar-based schedule. The extension bulletin “Foliar Disease Control using MELCAST” BP-67 describes this program in more detail. To use MELCAST, follow these steps: Apply your first foliar fungicide application when vines first touch within a row or earlier. Find a MELCAST site[Read More…]


blah

I recently encountered some lesions of Tomato Spotted Wilt Virus (TSWV) that appeared relatively large and had a ring-like structure.  I was able to confirm the presence of the virus, but at first glance, the lesions could be mistaken for a very common tomato disease: early blight. This article will describe how the foliar lesions of these two diseases might be distinguished. First, a bit about the symptoms of these diseases. Early blight is perhaps the most common foliar disease of tomato in Indiana. One might first notice that the older leaves turn necrotic. If left uncontrolled, the diseased lesions appear to ‘move’ up the plant. A closer look at early blight lesions may reveal the bull’s-eye lesions of this disease (Figure 1). These lesions may also be described as having concentric rings similar to a target. (Early blight is not the only disease to have concentric rings.) I usually[Read More…]


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.


Vegetable Crops Hotline - Department of Horticulture and Landscape Architecture 625 Agriculture Mall Dr. West Lafayette, IN 47907

© 2018 Purdue University | An equal access/equal opportunity university | Copyright Complaints | Maintained by Vegetable Crops Hotline

If you have trouble accessing this page because of a disability, please contact Vegetable Crops Hotline at guan40@purdue.edu.