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

106 articles by this author

Article List
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 


The Midwestern Regional Climate Center, the USDA Midwest Climate Hub, and National Drought Mitigation Center (NDMC) are partnering to determine data needs and develop additional tools, educational resources and other information for producers to better adapt to a variable and changing climate. Changing climatic conditions are having a wide ranging impact on agriculture in the Midwest including changes in crop yields, season length, and soil health. To meet these changes, we will host several workshops with specialty crop producers and extension staff to determine specific data and tool needs as well as climate change education needs this coming winter. To decipher what specialty crop producers are currently using, and to facilitate the adaption and creation of new tools, the following survey (https://ssp.qualtrics.com/jfe/form/SV_0vtKm5WhOdoKawZ) has been created to help gather information. From the results of this survey, we will be inviting producers to workshops in December, 2017. Please visit our website for more information and printable PDFs of our goals[Read More…]


Figure 1. Galling of tomato roots infested by root-knot nematode.

In a recent grower visit in southwest Indiana, we saw a severe root-knot nematode infestation on high tunnel tomatoes. Soil fumigation is by far the most effective approach to control nematodes, but many soil fumigants are not labeled for greenhouse (high tunnel) use. In addition, the types of equipment that used for soil fumigation are often hard to fit into high tunnels. Considering the constraints, this article focuses on cultural practices to control root-knot nematodes that can be easily adopted by small-scale, high tunnel growers. Root-knot nematodes are small, colorless roundworms that dwell in the soil. They penetrate into plant root in the juvenile stage. Once they find a favorable location in plant tissues, they stop moving. Infested root cells start swelling and form galls that are the characteristic symptom of root-knot nematode infestation (Figure 1.). Infested roots fail to absorb water and nutrient resulting  in stunted growth, yellowing and[Read More…]


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Southwest Purdue Ag Center High Tunnel Tour Date: Thursday, August 10, 7 p.m.- 9 p.m. (EDT) Location: Southwest Purdue Agricultural Center, 4669 North Purdue Road, Vincennes, IN, 47591 Registration: Visit http://tinyurl.com/yc5lqvez or call (812) 886-0198 For more information, contact: Wenjing Guan at guan40@purdue.edu or Dan Egel at egel@purdue.edu During the evening event at Southwest Purdue Agricultural Center, attendees will see demonstrations of soil solarization, end-of-season clearance of soil covers, sprayers used for small-scale plots, and an innovative season-long low tunnel system for growing tomato and pepper. Attendees will also learn how to ID tomato diseases by walking in the field with a plant pathologist. You are also welcome to bring your own disease samples for identification. A NRCS representative will share the insights about high tunnel cost-share program. We will also discuss issues relating to how to choose, locate and make pre-construction decisions for a high tunnel. Pinney Purdue Vegetable[Read More…]


Figure 3. Broccoli ready to harvest.

A fall broccoli trial was conducted in a high tunnel at Southwest Purdue Ag Center in 2016 to test the potential of growing broccoli in high tunnels after tomatoes. This article describes what we found from the trial. Broccoli is a cool-season, frost-tolerant crop. The harvest portion of broccoli is the compact, slightly dome-shaped head that is comprised by numerous immature flower buds. Broccoli that forms a single large head and thick stalks requires 50-70 days to harvest. Vegetative growth occurs over a wide range of temperatures, but high-quality head development requires temperatures in the range of 54-68 ºF. If temperatures are below 41ºF, plant growth is significantly reduced. In Indiana, fall production of broccoli in an open-field can be challenging because of the relatively long growing season. But with increased heat accumulation in high tunnels, it is possible to have a second crop of broccoli following tomatoes. Broccoli can[Read More…]