89 articles tagged "Cucurbits".

I have observed very few foliar diseases of cucurbits this season. However, I have had several worried phone calls about these diseases, so here is an update. Alternaria leaf blight-this disease is caused by a fungus that survives in crop residue. It usually is not an important disease. However, Alternaria can cause brown lesions with a ring-like structure in them. This disease is more important on cantaloupe. I have not observed this disease in 2017. Anthracnose-after some effort, I have been able to start this disease in my own plots. Look for jagged, brown lesions on leaves and stems and pitted lesions on fruit. Except for my own experiments, I have not observed this disease in 2017. Gummy stem blight-this disease does not seem to occur as often as anthracnose. However, this disease showed up uninvited in my research plots. I have not observed this disease in commercial fields. The[Read More…]


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In southern Indiana, we are between generations of striped cucumber beetles. That doesn’t mean there are none out there, but numbers are lower than they were and lower than they will be. The second generation should be coming out soon. Northern areas are a little behind. The biggest concern we have with the first generation or overwintering cucumber beetles is their ability to feed on seedlings and to transmit the pathogen that causes bacterial wilt to cantaloupes and cucumbers. For the second generation, we are less concerned about bacterial wilt and more concerned about feeding damage to the fruit, particularly watermelons and cucumbers. If you are seeing beetle feeding on fruit, you should probably apply an insecticide to protect the fruit. If not, you are probably safe not spraying. For later planted pumpkins, the biggest concern is feeding on the plants in the seedling stage. Once the plants get larger,[Read More…]


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

It is that time of year again, when the two-spotted spider mites (Tetranychus urticae; TSSM, Figure 1), and other mite species, show up in full force and wreak havoc on fruit and vegetables. These pests are very inconspicuous and often go unnoticed until the resulting damage appears. For TSSM this includes the webbing produced on heavily infested leaves or to the more trained eye, the characteristic yellow speckles or mottled symptoms on the upper surface of the leaves (Figure 2 and 3). The mites can be found on the underside, feeding with their sucking mouthparts. Cucumber, especially in organic production, can be the most susceptible. However, this pest feeds on a wide range of plants including tomatoes, melons, peppers, strawberries, apples, pears and grapevines, as well as flowers and field crops. Regardless of your production technique, an intervention is almost always necessary to control TSSM. In high tunnels in particular,[Read More…]


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.


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