Wenjing Guan

Vegetable Crops Hotline Editor & Clinical Engagement Assistant Professor
Department of Horticulture and Landscape Architecture
Area(s) of Interest: Commercial Vegetable and Melon Production
Wenjing Guan's website

142 articles by this author

Article List

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…]


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Southwest Purdue Ag Center High Tunnel Tour Date: June 13, 2018 7:00-9:00 pm Eastern Time Location: Southwest Purdue Agricultural Center, 4369 North Purdue Road, Vincennes, IN, 47591 The SWPAC high tunnel tour will be held on the evening of June 13, 2018. Attendees will have the opportunity to see a wide range of research projects being conducted in high tunnels at SWPAC. Topics that will be discussed include: Grafting cucumbers for season extension; Seedless cucumber and summer squash variety evaluations in a high tunnel; Different pruning and trellising systems for growing cucumber, tomato and pepper in a high tunnel; Grafting tomatoes for improved yield; Cucumber beetle management; Annual plasticultural strawberry production with an innovative low tunnel system. Registration will begin at 6:30 pm. The tour is free, to register please call (812) 886-0198, for more information please contact Wenjing Guan (guan40@purdue.edu). This event is sponsored by North-Central Sustainable Agriculture Research[Read More…]


I have recently received a number of calls from growers about how to prune determinate tomatoes in a stake and weave system. Although this is relatively easy compared to how to prune indeterminate tomatoes with a trellis system, there are a few things I would like to call to your attention. What to prune  The common practice is to prune the suckers at the bottom of tomato plants. The benefit of this practice is to improve airflow which may help to control foliar diseases. Shoots of determinate tomatoes stop growing once they set a terminal bud. Most of us understand that if suckers are pruned too much, plants may have reduced yield.  However, there is confusion about exactly what to prune. Normally, the bottom 6-7 suckers should be pruned until the first flower cluster. But it is important to note that the sucker just below the first flower cluster develops a[Read More…]


Figure 1. Strawberries were covered with straw mulch and row cover. Picture were taken in Jan. 9 2018.

Although strawberry plants can be quite cold hardy, they need protection to survive the winter. In North Carolina, growers use floating row covers to protect strawberries in the winter. In Indiana, straw mulch is a more traditional way of winter protection for strawberries grown in a matted row system. After two relatively mild winters in 2015 and 2016, I heard successful stories about growing strawberries with the plasticulture system and using row covers for winter protection in Southern Indiana. Can the system also be successful in a colder winter, like the one that just passed? Our ongoing strawberry study will provide the answer. This article provides an update from this project comparing strawberries covered with straw mulch (about 4-inch thick) and row covers (two layers of 1.5-oz/yard2 row cover laid on wire hoops) this past winter (Figure 1). Temperature Between Dec. 27 to Jan. 6, we had the coldest nights[Read More…]


Figure 2. Plants died in the second day after average soil temperature was 54 °F

Growers start to plant tomatoes in unheated high tunnels around the end of March in southern Indiana. Around that time, there may still be a few light frosts, or even heavier ones, like the one we just experienced in the past week. With additional help from row covers inside of high tunnels, temperatures normally can be maintained above 32°F. Tomatoes typically do not have problems with the short-term low temperatures. However, this may not be the case for cucumbers. Although they are both warm season crops, Cucurbits (cucumbers, cantaloupes, and watermelons) are much more cold sensitive than Solanaceous crops (tomato, pepper). From a temperature perspective, this article discusses important considerations for deciding the time for planting cucumbers in a high tunnel. The best condition to grow cucumbers is when soil temperatures are above 70°F. This situation may not happen until the middle of May inside of the high tunnels, according to our[Read More…]


Southwest Purdue Ag Center High Tunnel Tour Date: June 13, 2018 7:00-9:00 pm Eastern Time Location: Southwest Purdue Agricultural Center, 4369 North Purdue Road, Vincennes, IN, 47591 The SWPAC high tunnel tour will be held on the evening of June 13, 2018. Attendees will have the opportunity to see a wide range of research projects being conducted in high tunnels at SWPAC. Topics that will be discussed include: Grafting cucumbers for season extension; Seedless cucumber and summer squash variety evaluations in a high tunnel; Different pruning and trellising systems for growing cucumber, tomato and pepper in a high tunnel; Grafting tomatoes for improved yield; Cucumber beetle management; Annual plasticultural strawberry production with an innovative low tunnel system. Registration will begin at 6:30 pm. The tour is free, to register please call (812) 886-0198, for more information please contact Wenjing Guan (guan40@purdue.edu). This event is sponsored by North-Central Sustainable Agriculture Research[Read More…]


Renew now! Vegetable Crops Hotline (VCH), is Purdue Extension’s newsletter for people in the business of growing vegetables. We have fifteen issues throughout the 2018 growing season. The first two issues of the year are being sent to all who subscribed to VCH via US-mail in 2017 as well as new subscribers for 2018. To continue receiving future copies through US-mail, renew your Hotline subscription using the form attached to this issue. Your subscription year may be found on the bottom right of the envelope your copy of the hotline was mailed in. If your envelope says 2017, this will be your last issue unless you renew. If you receive notification of a new issue through email, you will continue to receive notice of the newsletters being published. In addition, you will receive emails if there are articles or announcements that need your immediate attention. These articles will be posted under Hot Topics and be included in the next issue. All[Read More…]


Figure 3. A Japanese type cucumber grown in a high tunnel.

Cucumbers are produced with very different production systems. The ideal cucumber variety for process pickling production is not the variety used for greenhouse production. Choosing the suitable variety for a specific production system then becomes important. Where do you find recommended cucumber varieties for high tunnel production in seed catalogs? Some of the seed catalogs have a category called Greenhouse or Protected culture. Varieties listed in this category are recommend for greenhouse or high tunnel production. Other seeds catalogs may call this group Parthenocarpic hybrid or European slicer. Cucumbers listed under these names are also suitable for greenhouse or high tunnel production. A few technical words (parthenocarpic, monoecious, gynoecious) occur frequently in the descriptions of high tunnel-grown cucumbers. Understanding their meaning is important in choosing the right varieties. Parthenocarpic means that the plant can set fruit without pollination. Since pollinators are not required in this case, parthenocarpic is a desirable characteristic for cucumbers grown in protected[Read More…]


Food Safety Modernization Act Produce Safety Rule Training A series of Food Safety Modernization Act produce safety rule training and registration information can be found on the website https://ag.purdue.edu/extension/safeproduce/Pages/FSMA-Training.aspx. The curriculum is designed to meet the needs of growers. Modules 1 through 6 align with sections outlined in the Food Safety Modernization Act (FSMA) Produce Safety Rule.  Module 7 is focused on helping growers develop a written farm food safety plan. The farm food safety plan is not required by the FSMA Produce Safety Rule, it is included in the curriculum because growers expressed a need for a plan.   eOrganic Webinars eOrganic provides a series of great webinars in organic farming practices and research. The upcoming webinars that might interest vegetable farmers include Conducting on-farm variety trials to manage risk for organic and specialty crop production (March 20 and April 11); Organic tomato foliar pathogen IPM webinar (March 21). Registration and more information about the[Read More…]


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This article is my response to a grower’s question about lowering soil pH in a high tunnel. The soil test indicated pH of the soil in his high tunnel was 7.7. The high pH could be partially caused by alkaline water he used to use for irrigation. The grower has changed the water source, but high soil pH is still a concern. ‘I have soil sample from the high tunnels if I could have your input on them I would appreciate it. I am concerned with the pH, should I use sulfur to bring it down, if so, how much?’ Following is my response to the grower’s question. My response is mainly based on the publication ‘Lowering Soil pH for Horticulture Crops‘. Purdue Extension HO-241-W. We have a few choices to reduce soil pH. Adding elemental sulfur is one way to do it. If you want to reduce soil pH[Read More…]