105 articles tagged "Cucurbits".

Cucurbit downy mildew has been observed on cucumber in La Porte County and LaGrange Counties, Indiana. Downy mildew of cucurbits has also been reported in southern and central Kentucky. All cucurbit growers in Indiana should be scouting and managing for downy mildew. The organism that causes downy mildew of cucurbits doesn’t overwinter in Indiana. It has to be blown in every year. It is common for downy mildew to start the season in the Gulf States and migrate north with the cucurbit crops. Downy mildew apparently overwinters in northern Michigan/southern Ontario in greenhouses where cucumbers are grown year round. Therefore, downy mildew is often found in Michigan before it is found in Indiana. Many cucumber varieties have some resistance to downy mildew. For susceptible cucumber varieties or other types of cucurbits, specialized systemic fungicides will help to reduce the severity of downy mildew. Unfortunately, many of the most effective systemic fungicides for downy mildew are not[Read More…]


Watermelon harvest is in full swing in southern Indiana. At this time, we frequently see many types of leaf symptoms. Some of them are caused by foliar diseases, such as anthracnose, Alternaria leaf blight and gummy stem blight. These diseases require special attention, normally in the form of fungicide sprays, to slow spread of the disease. However, the appearance of a moderate amount of foliar disease in mid-season doesn’t necessarily need an immediate fungicide application. Other leaf symptoms may not be caused by diseases or insects. Here are some examples of leaf symptoms that are not associated with a pathogen. It is important to correctly identify the source of the symptom to prevent unnecessarily pesticide spray. In the article When a yellow leaf is just a yellow leaf, Dr. Dan Egel discussed general rules for determining if the symptom is a disease or not. If you are not certain whether the symptom[Read More…]


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…]


Figure 3. Webbing produced on heavily infested cucumber leaves by two-spotted spider mite.

Despite the wet start to the summer that we are experiencing, we have some growers reporting spider mites in field watermelons (Figure 1). This pest is typically associated with hot, dry weather and can be especially problematic in crops grown under protection, such as in high tunnels. Spider mites often move into a field from an adjacent fencerow or rye strip. Two-spotted spider mites (Figure 2.) are most commonly a problem on watermelon and cucumbers in high tunnels, but also affect muskmelons. They can be detected by observing the yellowish discoloration on the upper side of the leaves or using a 10x hand lens and scouting on the underside of the leaf for the pest. Alternatively, you may use a white sheet of paper and tap the leaves above the paper to dislodge the mites; you will see them moving about on the sheet of paper. Because mites often migrate[Read More…]


Figure 1. A cucumber plant grown in a high tunnel died because of bacterial wilt.

Bacterial wilt is one of the most destructive diseases in high tunnel cucumber production. The reason bacterial wilt is so important is because, like other wilt diseases, it ties up with the entire vascular system of a plant, causing systemic effects (Figure 1). The relatively less important roles that other cucumber diseases play also make bacterial wilt the major limitation for high tunnel cucumber production in Indiana. For example, common cucumber diseases such as angular leaf spot, anthracnose and Alternaria leaf blight seldom occur in a high tunnel scenario; improved resistance to powdery mildew was observed in some of the newly developed cucumber varieties; downy mildew in general does not occur in Indiana until end of the high tunnel cucumber production season. The causal organism for bacterial wilt of cucumbers is Erwinia tracheiphila. After the bacteria enter the plant vascular system, it multiplies quickly. As a result, it interferes with[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…]


Entomologists are looking for growers willing to participate in research examining the detection and distribution of striped cucumber beetles. We would like to visit your fields on multiple occasions this year to count the number of cucumber beetles we encounter in your crop. If you grow slicing cucumbers in the field, and are interested in helping to improve our sampling recommendations for this pest, please contact Dr. Laura Ingwell at (765) 494-6167 or lingwell@purdue.edu


This article provides more detailed information about this herbicide. How does Chateau® herbicide work Chateau® is a group 14 mode-of-action herbicide. Compounds in this group are most active on broadleaf weeds. Before Chateau® became available,  no other preemergence herbicide with the same mode of action was labeled for use in watermelons and cantaloupes. The active ingredient of Chateau® herbicide, flumioxazin, controls susceptible weeds by inhibiting propoporphyrinogen oxidase (PPO), an enzyme that controls chlorophyll synthesis. Because of chlorophyll production inhibition, a chain reaction occurs within the plant that causes cell membrane disruption. Chateau® herbicide can assist in the postemergence control of emerged weeds. It is taken up by roots, stems, or leaves of young plants. It kills weeds through direct contact. There is usually little or no translocation of the herbicide within plants. Foliage necrosis can be observed after 4 to 6 hours of sunlight following the herbicide application. Susceptible plants[Read More…]


Chateau SW® herbicide now has a 24(c) special local needs label for cucurbits. This product is produced by Valent, but the label is held by the Indiana Vegetable Growers Association (IVGA).  To obtain a label, one must be a member of the IVGA, pay an annual $100 processing fee, read and understand the ‘conditions for use’ and have the appropriate forms signed and notarized. One cannot use Chateau SW® without completing these forms and obtaining a label. This process must be repeated every year. Chateau® can only be used in row middles between raised plastic mulch beds that are 4 inches higher than the treated row middle. The mulched bed must be at least 24 inches wide. The application must be directed between rows with a shielded sprayer. Chateau® cannot be applied post-transplant. Do not apply more than 4 oz. of Chateau® per acre at a broadcast rate during a single application.[Read More…]


Figure 3. A cucumber beetle on the 0.7 x 1.0 mm screen (photo credit: John Obermeyer)

One of the most problematic insect pests that organic vegetable growers have to deal with is the striped cucumber beetle. The insect feeds on all the cucurbit crops, but can be particularly devastating to muskmelons and cucumbers because those two crops are susceptible to bacterial wilt of cucurbits, which is caused by a bacterium carried by the beetles. The only way to avoid this devastating disease is to prevent the beetles from feeding on the plants. There are no effective organic insecticides for managing striped cucumber so we have to look for alternative methods. Row Covers: Row covers can be used to physically prevent beetles from feeding on the plants. To be effective, these need to be placed over the plants immediately after transplanting or before direct seeded crops emerge. The edges of the row covers should be sealed with soil to prevent the beetles from crawling under the fabric[Read More…]


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