86 articles tagged "Cucurbits".

Figure 2. Squash bug nymphs (photo credit John Obermeyer)

Squash bug is the most consistent insect pest of squash and pumpkins and is the most difficult to control (Figure 1 and 2). The key to management is early detection and control of the nymphs. The adults are extremely difficult to kill. Foliar insecticides should be applied to control the nymphs when you have more than an average of one egg mass per plant. When you find egg masses, mark them with flags and check every day or two to see when they hatch. When many of the egg masses are hatching, that is the time to begin application. Since eggs are laid and hatch over an extended period of time, several applications may be required. Brigade®, Mustang Max® and Warrior® have provided excellent control.

Figure 1. Stripped cucumber beetle (Photo by Wenjing Guan)

Populations of the overwintering generation of striped cucumber beetles are just about at their peak levels right now (Figure 1.). For muskmelons and cucumbers, this generation is the one that we worry the most about in terms of transmitting the pathogen that causes bacterial wilt. As a result, our spray threshold is relatively low, 1 beetle per plant. Watermelons and most squashes and pumpkins are not susceptible to bacterial wilt so we use a higher threshold, 5 beetles per plant. The pyrethroid insecticides provide excellent control. Because these insecticides are harmful to pollinators, growers should wait until late afternoon or evening when the flowers have closed and the pollinators have left the field before spraying.

Cantaloupe, watermelon and pumpkin growers can use information in the Midwest Vegetable Production Guide for Commercial Growers (ID-56) to help determine what fungicides to apply. The MELCAST system (see accompanying article in this issue) can be used to help to decide when fungicides should be applied. I have developed two fungicide schedules that I hope will help growers determine the sequence of fungicides. One fungicide schedule is for cantaloupe and watermelon growers and the other one is for pumpkin growers. Growers who are interested in obtaining a copy of these fungicide schedules should contact Dan Egel using either the email or the phone number listed above. I look forward to getting feedback about the usefulness of these schedules.

Figure 1. Grafted Fascination plants were grown on the right bed, ungrafted plants were grown on the left bed. The field were naturally infested with Fusarium wilt.

Watermelon production is threatened by Fusarium wilt, a widely distributed soilborne disease that can cause yield losses up to 100%. Currently, there are no watermelon varieties that are completely resistant to all races of Fusarium wilt. One way to control the disease is through grafting. The grafted plant combines a watermelon cultivar with a squash rootstock that has resistance to Fusarium wilt. In a study conducted at Southwest Purdue Ag Center (SWPAC), we found grafted watermelons significantly reduced disease incidence, and more than doubled watermelon yield in a Fusarium wilt infected field (Figure 1). In addition to controlling Fusarium wilt, grafted watermelons often show substantial advantages in early watermelon production due to cold tolerance from rootstocks. In a study conducted in Arizona, grafted watermelons that were transplanted in the field two months before soil temperatures reached 70 °F had twice as much yield as ungrafted watermelons grown in the same[Read More…]

Many cantaloupe and watermelon growers have transplanted seedlings to the field. Soon, these growers will have questions about what and when to apply fungicides. The article below in this issue of the Vegetable Crops Hotline will address what fungicides to apply (Fungicides schedules for cucurbits). This article discusses when to apply fungicides with the MELCAST system. 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[Read More…]

One of the most damaging pests in cucurbit production are cucumber beetles and the bacterial pathogen they transmit (Erwinia trachephila), leading to bacterial wilt.  In the recently released video, Dr. Laura Ingwell from Purdue Entomology demonstrates how to install insect exclusion screens on high tunnels. Such screens are effective at excluding cucumber beetles and the pathogen they transmit from high tunnels. 

Figure 1. Seedcorn maggot in a melon stem

I received my first report of seedcorn maggot damage on cantaloupes last week (Figure 1 and 2). A grower in northern Indiana reported losing 90-95% of his plants. Given the cool, wet growing conditions, it wouldn’t be surprising to see more reports of this type for a number of crops, including melons, beans, corn, onions, and crucifers. Some of these crops have insecticide alternatives that can be used at planting but other, like melons, have no such option. The best approach for melon growers is to either wait for warmer weather or cover the young plants with row covers to physically exclude the flies from laying eggs. If you have had plants killed by maggots, wait at least 3 days before replanting in the same holes to give the maggots time to complete their development. See the article from Issue 625 (published on April 13, 2017) for more details.

Many cantaloupe and watermelon growers are either growing transplants in a greenhouse or are expecting delivery of transplants in the next few weeks. Either way, growers should inspect transplants for disease before planting in the field. Below I will describe several common transplant diseases of cantaloupe and watermelon as well as management options. Gummy stem blight on transplant seedlings may be recognized by the water soaked area of the stem near the seed leaves (Figure 1). (A water soaked area near the soil line is more likely to be damping-off.) The water soaked area may eventually turn brown and woody. A closer look at the woody area may reveal the small, dark fungal structures of the gummy stem blight fungus. Medium brown, irregular lesions may also be observed on true leaves. The fungus that causes gummy stem blight (Didymella bryoniae) may survive in crop debris, thus overwintering in the field[Read More…]

Figure 2: We often observe Fusarium wilt in transplant trays in a clustered distribution. We believe that Fusarium wilt may spread from plant-to-plant within a transplant tray, perhaps by soil splash or spores that have been observed on diseased seedlings.

Fusarium wilt is one of the most serious diseases of watermelon in the Midwest. The disease often causes a one-sided wilt 2-3 weeks after transplanting. Whether a plant is affected, and to what degree, depends on the population of the long-lived spores in the soil that the roots contact. However, Fusarium wilt of watermelon is not known to spread from plant to plant in the field. This is in contrast with a disease such as anthracnose which can spread from plant-to-plant rapidly in one season. Occasionally, Fusarium wilt can be observed affecting commercially produced watermelon transplants in new trays and virgin soilless mix. The most likely explanation for such outbreaks is the introduction of Fusarium wilt on seed. The distribution of Fusarium wilt from seed should appear random. However, we often observe a clustered distribution of affected seedlings as seen in Figure 1. We conducted an investigation to determine whether[Read More…]

As part of a multi-state effort being headed by Dr. Ian Kaplan at Purdue University in the Department of Entomology, we are investigating how to best manage insect pests on cucurbits, in our case watermelons, while having the least possible impact on pollinators. The research is being funded through the USDA/NIFA Specialty Crop Research Initiative. The premise of this research is based on the fact that neonicotinoid insecticides, which are a versatile and powerful pest management tool, have been implicated as a factor contributing to pollinator declines. Thus, farmers growing pollinator-dependent crops—including watermelons—are confronted with a potential trade-off between two competing aspects of crop production: effective pest suppression and successful pollination. Our objective here is to identify insecticidal management strategies that simultaneously optimize pest suppression while minimizing non-target exposure to cucurbit pollinators. To achieve this objective, we are currently looking for producers to collaborate with members of the Entomology Department[Read More…]

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