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

221 articles by this author

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Figure 1. Take soil samples at 6 inches deep

This article introduces a new soil test for high tunnel growers. Why is there a need for a new soil test for high tunnel production? Soil tests are valuable tools helping growers decide how much fertilizers and/or other soil amendments to apply for growing a specific vegetable crop. It also helps growers to detect soil fertility-related problems early. The routine soil test and its recommendations for vegetable crops were developed based on research conducted in the open field. When it comes to high tunnel production, the routine soil test and recommendations become less valuable for at least three reasons: Crops growing in high tunnels typically have a much higher yield potential; they require more nutrients than the same crop grown in the open-field with lower yield potential. Therefore the soil test index (low, medium, high) and recommendation for specific nutrients may not apply for high tunnel crops. Since there is[Read More…]


Warm-season vegetables like tomato, cucumber, pepper etc. often receive premium prices if they were sold at farmers’ markets earlier in the season. The same happens on summer squash, with the different fruit shape and color, summer squash provides a great diversity to the market. High tunnels that  are planted with warm-season vegetables are often closed to maintain heat inside the structure in the spring. Growers often hesitate to bring beehives to high tunnels because of the increased production cost and potential worker safety concerns. Under such circumstances, crops that can set fruit without pollination (parthenocarpic) have an advantage for early-season high tunnel production. Previous studies indicated parthenocarpic character exists in some summer squash cultivars. But such information is not always clearly indicated in seed catalogs. Without knowing the information, farmers may miss the opportunity of growing summer squash and targeting for an early harvest in high tunnels. In the spring[Read More…]


Recent studies have suggested that on-farm food safety practices can have unexpected economic and ecological impacts. Despite the potential for negative consequences, limited data is available on the costs and benefits of implementing specific practices. Co-managing farms for food safety and sustainability is further complicated because farms are linked to adjacent environments so that management decisions can have unexpected ecological, economic and food safety consequences. A comprehensive understanding of the links between agricultural and adjacent environments is key to ensuring environmental health, sustainability, and food safety. A new survey, funded by the Atkinson Center at Cornell University, promises to give a clearer picture of these linkages and what this means for growers. Specifically, to meet this need, a new collaborative research project between researchers at Cornell University, the University of California, and the University of Rochester is reaching out to growers in the Eastern United States to fill out a[Read More…]


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Southwest Indiana Melon and Vegetable Growers annual meeting will be held in French Lick, IN on March 13, 8:30 am to 4:00 pm. Participants will learn from Purdue extension specialists about the newly searchable Midwest Vegetable Production Guide; new updates on food safety; watermelon grafting; impacts of pesticide use on pollinator health; weed management; lessons from truck and equipment collision. In addition, Jamie Campbell Petty from the Midwest Hemp Council will give the presentation Hemp as a New Crop. A detailed agenda is attached. The meeting is sponsored by Southwest Indiana Melon and Vegetable Growers Association. Everyone is welcome to participate in the meeting. $15.00 per person will be collected at the time of registration to join or renew your Southwest Indiana Melon and Vegetable Growers Association membership, which includes lunch on March 13, as well as dinner at a winter technical meeting, which will be held in Nov. at[Read More…]


Thanks to the support from NC-SARE, we are going to continue the study of evaluating grafted cucumbers for early season production in greenhouses and high tunnels by collaborating with farmers in 2020. You can find our 2019 on-farm trials’ summary here:  https://ag.purdue.edu/arge/swpap/Documents/Summary%20of%202019%20On-farm%20Grafted%20Cucumber%20Trials.pdf. The same as in previous years, we are going to supply grafted and normal cucumber transplants for free. These plants were grown in a conventional greenhouse using untreated rootstock seeds. What we want from growers is to grow the same number and variety of grafted and normal cucumber plants, and keep track of the performance of the plants and the yields. We will provide a stipend for your efforts in tracking the data. In addition, we encourage farmers to learn grafting technique and produce grafted plants on your own. We will provide you with technical support and help with the process on-site if it is needed. For more[Read More…]


Agricultural producers face a plethora of wildlife issues on the farm, from biosecurity in animal agriculture to food safety requirements for fresh produce farmers. Many wildlife species have social or economic value and may be regulated or protected, constraining timely mitigation strategies. Additionally, research and science-based management recommendations to help farmers address wildlife on the farm are limited, available for some crops and pest species but not others. The last national United States Department of Agriculture (USDA) survey of U.S. wildlife damage to agriculture took place in 2001 and estimated $944 million in losses. At the national level, primary wildlife species resulting in losses to field crops included deer, turkeys, raccoons and waterfowl (collectively 75% of the reported losses), with 22% attributed to other species. For vegetables, fruits and nuts, deer, ground squirrels and other small rodents, crows, raccoons and rabbits were most frequently reported (64%), with other species accounting for 36%[Read More…]


Figure 1. Broccoli grow leaves in the head. A response toward heat stress (Pictures was provided by ANR educator Luis A. Santiago)

Cool nights have finally arrived after the first week of October. Before, we had quite a few days when temperatures were above 90°F. The unusual high temperature has caused problems on early-planted broccoli. Broccoli is a heat-sensitive crop. The critical period for heat sensitivity is when plants shift growing tips from vegetative growth to flower bud initiation. This is about 10 days before the crown is visible. Temperatures above 90°F during the critical period cause injury on the flower buds. As the crown continues to grow, an uneven head becomes noticeable, and these heads are inclined to be affected by pathogens. Another response broccoli often has toward the heat stress is to grow leaves in the head (Figure 1), although it may be less a concern compared to bud damage. Varieties are varied by heat sensitivity, and they may have slightly different responses toward high-temperature. For example, the very popular[Read More…]


Although high tunnels make it possible for Indiana farmers to grow vegetables year-round, many growers may choose to end the production season in the fall. After a busy summer, it is not unusual that off-season management is overlooked. Nevertheless, these good management practices determine the success of the next year. It is an old lessen, but we can never put too much emphasis on the importance of good management practices during the off-season. Terminate plants after final harvest, and remove crop residues out of the tunnel. The worst scenario I have ever seen was a high tunnel full of weeds in late fall, and a few tomato plants still standing in the middle of the weeds. No doubt, the plant materials provide a cozy environment for insect pests to survive the winter. Under the ground, the roots of tomato plants, as well as roots of several weeds continue to feed[Read More…]


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Date: October 26, 2019 8:30 am sign-in Location: Elkhart County Fairgrounds 17746 County Rd. 34, Goshen, IN 46528 Home and Family Arts Building This one-day hands-on workshop will offer a view into aquaculture and aquaponics water quality parameters and considerations. The day will consist of information that will benefit new and established producers. More information about the event and registration: indianaaquaculture.com/shop


This is the final issue of the Vegetable Crops Hotline (VCH) for 2019. Subscribers who receive a paper copy in the mail need to renew. A renewal form is included with this issue. We are providing up-to a three years’ subscription of VCH at a reduced price (1 year for $15, 2 years for $25, and 3 years for $30). You can check the date on the right bottom corner of your VCH envelope to find what year your subscription will last through. You can sign-up for Veggie Texts with the same form. Email subscribers will remain on the subscription list for VCH as long as the email address works. Email subscribers will need to send us an email or call us to sign-up for Veggie Texts. An Indiana Vegetable Grower Association (IVGA) membership form is included here too. IVGA membership no longer automatically includes the VCH subscription. You need to indicate[Read More…]