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

101 articles by this author

Article List

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…]


Figure 1. Fertilizers form insoluble precipitations that clog drip emitters.

When mixing fertilizers, it is important to check fertilizer compatibility before application. If incompatible fertilizers are mixed, they form insoluble precipitations that can clog drip emitters and damage sprayers used to apply foliar fertilizers (Figure 1.). This article discusses a few scenarios for which special attention should be paid on the solubility of mixed fertilizers. Scenario 1. A grower is using 20-20-20, a complete fertilizer to fertigate tomatoes. To prevent blossom end rot, he decided to add calcium nitrate in his fertigation program. However, problems may be caused by the application of these two fertilizers.  The reason is that calcium from calcium nitrate and phosphate from ammonium phosphate in the complete fertilizer may form calcium phosphate, which is insoluble in water. Scenario 2. A soil test indicates that tomato plants are low in magnesium. Epson salt (magnesium sulfate) is recommended to correct magnesium deficiency. The grower should avoid applying Epson[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 and[Read More…]


The Indiana Pesticide Clean Sweep Project is a great opportunity to legally dispose of unwanted chemicals. It is free of charge up to 250 pounds. To dispose of pesticides, complete the 2017 Pesticide Clean Sweep Planning form (the form is attached to the newsletter) and mail, fax or e-mail the completed form to Kevin Neal at Purdue University. 175 South University Street, West Lafayette, IN 47907-2063, (765) 494-4331 (fax) or nealk@purdue.edu no latter than Monday, July 31, 2017. Then bring your labeled, leak free and safe to transport containers to the collection site. Do NOT mix materials. Pesticides will be accepted from 9:00 am to 3:00 pm local time at the following dates and locations: August 15, 2017: LaPorte County Fairgrounds in LaPorte, IN August 16, 2017: Tippecanoe County Fairgrounds in Lafayette, IN August 17, 2017: Grant County Fairgrounds in Marion, IN August 22, 2017: Franklin County Fairgrounds in Brookville, IN August 23, 2017:[Read More…]


After harvest, storing vegetables in optimal conditions is important to ensure the whole season’s hard work has paid off. This article discusses the optimum storage conditions for tomato, pepper, cucumber, watermelon, cantaloupe and sweet corn. Tomato Ideal storage conditions for tomatoes depend on the maturity stage of picking. If tomatoes are picked at mature green, store them in 66 to 70°F with 90 to 95% RH would encourage uniform ripening. Temperatures above 81°F reduce intensity of red color and reduce fruit shelf-life. Green tomatoes are chilling sensitive. If the temperature is below 55°F, fruit may develop chilling injury. Red tomatoes are safe to store at 50°F, however, flavor and aroma may be negatively affected compared to storing them at 55°F. Pepper Optimum storage condition for peppers is 45 to 55°F with 90 to 95% RH. Temperatures lower than 45°F may cause chilling injury. Colored peppers are in general less chilling[Read More…]


Figure 5. Breakdown and death of older cantaloupe leaves caused by manganese toxicity.

Manganese toxicity is a common problem for cantaloupes growing in sandy soils across southwestern Indiana. Because symptom of manganese toxicity can easily be confused with foliar diseases, growers may misdiagnose the problem and waste fungicides by spraying for nonexistent diseases. As we now know that manganese toxicity is a nutrient related disorder caused by low soil pH, it is important for growers to learn the symptom and address the problem in right directions. Manganese toxicity can develop on both cantaloupes and watermelons. But the symptom is more often observed on cantaloupes as they are more sensitive to acid soil conditions than are watermelons. The symptom on cantaloupes is first noticed when light green to yellow color shows between the veins on older leaves (Figure 1). Look at the leaves toward the sun and you will notice the chlorosis is formed by numerous tiny light green to yellow pin-hole type spots growing[Read More…]