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

100 articles by this author

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Figure 1. Breakdown of young leaf tissues in the heart of a celery plant

Blackheart of celery is a physiological disorder that causes significant crop loss in major celery production areas. It is characterized by the breakdown of young leaf tissues in the heart of the plants (Figure 1). The affected young tissues turn black, which give it the name “blackheart”.  The cause of blackheart of celery is related to calcium deficiency in the fast expanding tissues, similar to the cause of blossom-end rot of tomato and tip-burn of lettuce. The symptom is more severe as plants approach maturity. Fluctuation in soil moistures; excessive soil fertility, especially nitrogen and potassium; and high soil salinity favor the development of blackheart. Varieties may show different tolerance to the physiological disorder. In addition, the problem can be prevented by avoiding wide fluctuation of soil moisture and over-fertilization. Drench application and foliar spray of soluble calcium direct to the heart of the plant may help to prevent the[Read More…]


Figure 2. Demonstration soil solarization in a high tunnel.

Soil solarization can be used as a tool for soil disinfestation. It is accomplished by covering moist soil with transparent polyethylene film for 4 to 6 weeks in the summer. During this period, soils are heated to temperatures that are lethal to many soil pathogens, nematodes and weed seeds. This summer we conducted a demonstration trial in one of the high tunnels at Southwest Purdue Ag Center. The high tunnel was divided into three parts that were covered with 6-mil plastic, 1.5-mil plastic, and no plastic. The 6-mil plastic is the old covering of the high tunnel, and the 1.5-mil plastic was purchased from a paint store. Air temperature and soil temperature at the depth of 12 inches were recorded. We saw little difference between temperatures of the soils covered with 6-mil plastic and 1.5-mil plastic, which indicated that the old coverings of high tunnels are as good as thin[Read More…]


Beginning Farmer East Regional Workshop Date: Oct. 28, 2017, 8:30 am – 4 pm Location: Randolph County Fairgrounds, 1885 U.S. Route 27, Winchester Attendees for this workshop can learn about: Business planning Pasture management Fruit and vegetable pest management Pastured poultry Greenhouse and high tunnel management Marketing products Purdue Extension experts will be available to discuss and answer questions. Cost is $10 and lunch will be provided. To register or find more information about the next four regional workshops, go to www.conf.purdue.edu/BegFarmerTours. Southwest Indiana Melon and Vegetable Growers’ Technical Meeting Date: November 21, 2017 5:00 pm to 8:00 pm (EST) Location: Southwest Purdue Ag Center (SWPAC), 4369 N. Purdue Road, Vincennes, IN The meeting will start at 5:00 pm for board members to discuss topics for the March meeting, which will be held in French Lick, IN. Any member who wants to participate in the discussion is welcome. At 6:00 pm, dinner will be served.[Read More…]


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Hydroponics Workshop II Date: Sep 8, 2017, 7:30 am – noon. Location: WSLR 116, Horticulture & Landscape Architecture 170 S. University St. Purdue University West Lafayette, IN 47907 Registration: http://tinyurl.com/yb4dnwrh For further questions contact Lori Jolly-Brown, ljollybr@purdue.edu, (765) 494-1296 In this workshop, you will learn about: LED lighting for winter produce in greenhouses Things to know about successful production in ‘vertical or indoor farms’ Biological control of insects Fertilizer recipes and injectors Ongoing research in our greenhouses Beginning Farmer East Regional Workshop Date: Oct. 28, 2017, 8:30 am – 4 pm. Location: Randolph County Fairgrounds, 1885 U.S. Route 27, Winchester. Attendees for this workshop can learn about: Business planning Pasture management Fruit and vegetable pest management Pastured poultry Greenhouse and high tunnel management Marketing products Purdue Extension experts will be available to discuss and answer questions. Cost is $10 and lunch will be provided. To register or find more information about the next[Read More…]


Figure 2. Multi-leaf lettuces grown in a high tunnel (photo credit: Liz Maynard)

Winter farmers markets are becoming more and more popular. Lettuce is a primary type of vegetables grown for the market. As we are finishing up summer crops, it is a good time to learn and refresh knowledge about lettuce. This article discusses some of the basics of growing lettuce in high tunnels, as well as the lessons we learned from a trial conducted at Southwest Purdue Ag Center in fall 2016. Lettuce Types Lettuce has multiple morphological forms major types include crisphead (iceberg), butterhead (bibb), romaine (cos), Batavian (summer crisp), and multi-leaf lettuce (salanova). The first decision about growing lettuce is whether to harvest full-size heads of lettuce, or to harvest ‘baby-leaf’ lettuce (Figure 1). These harvest methods require very different production practices. Full-size heads are harvested one time as a single head of leaves. Baby-leaf lettuce is first harvested when single leaves reach about 4 to 5 inches, and[Read More…]


Figure 1. Tomatoes are grown under a retractable tunnel system.

Tomato foliar diseases such as early blight, Septoria leaf blight, bacterial spot and speck that are commonly seen in the field are often less common on tomatoes grown in greenhouses and high tunnels. It is also true that high tunnel tomatoes have smoother skins than tomatoes grown in the fields. An important factor that determines this difference is rainfall. Pathogens that cause foliar diseases require leaves to be wet in order for infection to occur and rely on rain for spread. In addition, heavy rains cause tomato physiological disorders such as rain check. It is great that greenhouse and high tunnel structures prevent tomato canopies from direct exposure to rainfall, however, a significant initial investment is required for building the structures, and it is hard to relocate them after they are built. This summer, we used a retractable tunnel to grow tomatoes and peppers in the field (Figure 1). The tunnels[Read More…]


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It got my attention recently that the newest USDA planting map is shifted northward compared to the one before. The planting map is based on the coldest winter temperatures of the past 30 years’ record. The most recent map is generated from data in 1981-2010, the prior one is based on data from 1971-2000. Planting zones were changed from Zone 5 to Zone 6 in several places in middle and northeast Indiana. In the map before, green areas are where planting zones have been changed. Undoubtedly, these changes will make a difference in plants that could survive in these areas in the winter. It may also affect vegetable production in the state, especially winter and protected cultural productions. Want to know which zones you are located? Check this site http://noaa.maps.arcgis.com/apps/MapSeries/index.html?appid=5f617f338eb5431eb3700e8685eccaf7

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Organic Vegetable Seed Production & Varietal Selection Workshop Date: August 22, 2017, 9:00 am – 3:00 pm. Location: Daniel Turf Center, 1340 Cherry Ln, West Lafayette, IN, 47907. Registration: http://tinyurl.com/y7da7dsh Topics include Seed biology fundamentals; Harvesting, processing, and storing seed; Population size and isolation requirements; Managing pathogens during seed production and after harvest; On-farm variety trialing and participatory breeding techniques. Registration fee is $15 including workshop and lunch.  Hydroponics Workshop II Date: Sep 8, 2017, 7:30 am – noon. Location: WSLR 116, Horticulture & Landscape Architecture 170 S. University St. Purdue University West Lafayette, IN 47907 Registration: http://tinyurl.com/yb4dnwrh For further questions contact Lori Jolly-Brown, ljollybr@purdue.edu, 765-494-1296 In this workshop, you will learn about: LED lighting for winter produce in greenhouses Things to know about successful production in ‘vertical or indoor farms’ Biological control of insects Fertilizer recipes and injectors Ongoing research in our greenhouses  Midwest Mechanical Weed Control Field Day Date: Sep 26,[Read More…]


Farmer Rancher Program Farmers and ranchers are invited to submit grant proposals to explore sustainable agriculture solutions to problems on the farm or ranch. There are three types of competitive grants: individual grants ($7,500 maximum), team of two grants for two farmers/ranchers from separate operations who are working together ($15,000 maximum), and group grants for three or more farmers/ranchers from separate operations who are working together ($22,500 maximum). Projects may last up to 24 months. Interested applicants can find the call for proposals online as well as useful information for completing a proposal at http://www.northcentralsare.org/Grants/Types-of-Grants/Farmer-Rancher-Grant-Program. Proposals are due on December 7, 2017 at 4 p.m. CST. Partnership Program The Partnership Grant program is intended to foster cooperation between agriculture professionals and three or more farmers or ranchers to catalyze on-farm research, demonstration, and education activities related to sustainable agriculture. Partnership Grants are funded for up to 24 months. Up to $30,000[Read More…]


The U.S. Department of Agriculture is currently accepting nominations from qualified fruit and vegetable industry members to fill 10 seats on the Fruit and Vegetable Industry Advisory Committee. This Committee is composed of 25 members from every commercial capacity within the fruit and vegetable industry including growers, distributors, processors, farmers market managers, food hubs etc. The committee provides advice and recommendations to the Secretary of Agriculture on issues related to the programs and services that USDA provides to the produce industry. Nomination is end on Sep 1, 2017. More information about nomination and serving on the committee can be found at https://content.govdelivery.com/accounts/USDAAMS/bulletins/1b13cdd