75 articles tagged "Plant Disease Management".

Gummy Stem Blight – this fungal disease causes dark brown leaf spots, however, the diagnostic feature of this disease is the water soaked lesion that is often formed under one of the seed leaves (cotyledons). Such lesions often start at the point where the seed leaf joins the stem (hypocotyl) and do not extend to the soil line (Figure 1). In time, these lesions turn a light brown in color and appear ‘woody’. If one inspects the woody stem closely, it is possible to see dark specks imbedded in the stem—these are fruiting bodies of the fungus and will exude numerous spores when wet. Gummy stem blight affects both cantaloupe and watermelon. The fungus that causes gummy stem blight may be seed borne. The fungus may also survive on the residue left on contaminated transplant trays, the greenhouse floor or bench. Gummy stem blight may spread rapidly from plant to[Read More…]


Recently, this disease was observed in a greenhouse in Indiana. This article will serve as a review of this important disease. The symptoms of bacterial canker vary considerably. In most cases, the edges of the leaves may turn yellow and/or brown. That is, the margins of the leaves may become chlorotic and/or necrotic (Figure 1). This symptom, which is sometimes known as ‘firing’, may be more common in a field situation than in a greenhouse. Tomato plants may wilt as a result of bacterial canker. The inside of the stem of affected plants may be discolored brown (Figure 2). The fruit may have bird’s-eye spots-this symptoms is more common in field outbreaks.  In the greenhouse where this disease was recently observed, adventitious root development was observed on the stems of affected plants. That is, the stems may develop a ‘bumpy’ appearance where extra roots are starting to develop. However, this symptom may also develop from stresses[Read More…]


I have never had as many questions about how to use MELCAST as I did in 2015. The interest in this program is growing both here in Indiana and nationally. Read on to find out how to apply fungicides according to the weather and perhaps save money in the process. MELCAST (MELon disease foreCASTer) is a weather-based disease-forecasting program for cantaloupe and watermelon growers developed By Dr. Rick Latin at Purdue University. Instead of using a calendar based fungicide application program where one applies fungicides every 7 to 14 days, the MELCAST program lets growers apply fungicides when the weather is most conducive to disease. The diseases for which MELCAST may be used for are: Alternaria leaf blight, anthracnose and gummy stem blight. Details are listed below or in the extension bulletin, Foliar Disease Control Using MELCAST, BP-67-W. Download the bulletin at http://www.extension.purdue. edu/extmedia/BP/BP-67-W.pdf or contact Dan Egel for a[Read More…]


The symptoms of lettuce drop include a white mold that covers much of the plant and the dark, irregular sclerotia that are observed here. (photo: Wenjing Guan).

Cool season crops such as lettuce are becoming a more popular crop among Indiana greenhouse/high tunnel growers. One of the most important diseases of lettuce is known as lettuce drop. The symptoms of lettuce drop are often noticed after the thinning stage, early in the crop development. The early symptoms may include browning of leaves. Later on in the crop development, the outer most leaves of the lettuce plant may wilt. As the disease become more severe, inner leaves may become infected. Eventually, the entire plant may collapse. The plant often has white mold on the leaves and dark irregular fruiting bodies may be observed (Figure 1). The dark fruiting bodies are known as sclerotia. Two different organisms may be responsible for lettuce drop. Sclerotina sclerotiorum and S. minor. Lettuce drop caused by S. sclerotiorum requires a chilling period (52 to 59° F) for the sclerotia to turn into mushrooms smaller than a[Read More…]


Updates to the MW Vegetable Production Guide for Commercial Growers 2016 (ID-56)-The table below gives the changes that have been made to the on-line version of the ID-56 as of this date.  If you have purchased, or will purchase, a hard copy of this guide, please make these changes.  If you use the  ID-56, these updates will already have been incorporated. Note, many of the changes have to do with the newly registered Orondis® products from Syngenta.  Please contact me with any questions.   Page Comment 42 Move Oberon® from the label prohibits greenhouse use to the column label silent on greenhouse use. 43 Move Quintec® from the column label silent on greenhouse use to label prohibits greenhouse use. 74 Add row… Orondis Opti® /oxathiapiproplin (U15); chlorothalonil (M)/medium-high/U15, M 74 Add row…. Orondis Ridomil Gold SL®/oxathiapipropilin (U15); mefenoxam (4); /medium-high/U15, 4 74 Modify row… Orondis Ultra®/oxathiapipropilin (U15); mandipropamid (40)/U15, 40 74 oxathiapipropilin under common name, is one word.  Same row[Read More…]


New fungicide – I would like to announce the release of a new fungicide, Orondis® from Syngenta. It is a good product and should help commercial vegetable growers in combating downy mildew of cucurbits, Phytophthora blight of cucurbits, peppers and tomato, Buckeye rot of tomato and late blight of potato and tomato. However, I also want to discuss Orondis® because of the complicated way in which it is being released. Be advised that the listing for Orondis® in the MW Vegetable Production Guide for 2016 (ID-56) is incorrect. Please see the on-line version of the ID-56 for the most current information. Orondis® has a new active ingredient which does not appear in any other fungicide and a novel mode of action, FRAC code U15. But you will not be able to purchase Orondis® on its own. It will be available as 3 different multi packs or co-packs. Each multi-pack will contain two jugs, each with a[Read More…]


The last two summers, I have had pretty good fungicide trials for powdery mildew of pumpkin. Since all of the products trialed are now labeled or close to being labeled, I thought it was time to share this information with vegetable growers of Indiana. First, a bit of background about this disease. In Indiana, powdery mildew affects primarily pumpkin and cantaloupe.  The disease is easily recognized by the talc-like lesions on both sides of the leaf. (This article will help with diagnosis.) If left uncontrolled, the disease can cause loss of foliage, loss of yield and lower quality fruit. 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 in crop residue as a resilient fungal structure, but the disease is so easily windborne, that crop[Read More…]


In a separate article in this issue, I discussed management of powdery mildew with conventional fungicides.  Here I would like to talk about powdery mildew management of cucurbits with organically approved products.  I will describe two studies, one with all organically approved products and a second with a combination of organic and conventional products.  All studies were conducted at the SW Purdue Ag Center in Vincennes, IN. The organic products discussed are defined as organic since they appear on the Organic Material Review Institute (OMRI).  There are other certifying agencies.  Be sure to check with your certifying agency before using any fungicide product.  As an example, the Champ DP® product used in 2010 is listed by OMRI as approved.  However, Champ WP® is not. In the 2010 study shown below, zucchini of the variety Raven F1 were planted in the certified organic plot managed at the SW Purdue Ag Center.  Organic products[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…]


A grafted tomato plant growing in a high tunnel. (Photo by Wenjing Guan)

​You might have heard about tomato grafting, or you might even already have tried the new technique. Yes, it has multiple benefits: control of soilborne diseases, enhanced tolerance to abiotic stresses, and increased productivity. It works for some growers, but not all. Why? There are several reasons. First, effects of grafting on controlling soilborne diseases depend on the presence of the disease that the rootstock is designed to control. For example, grafting might not be very helpful for white mold, because current commercial rootstocks do not have resistance to white mold. However, grafting might work if the primary problem is Fusarium crown and root rot, as most commercial tomato rootstocks have resistance to this disease. With that said, it is very important to look at the disease resistance profile before deciding on the rootstocks. Second, grafting effects on improving yield depend on factors such as scion and rootstock cultivars, cultural[Read More…]


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