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

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We recently published an article in the Hotline about gray mold of tomato.  That article and more details about this disease can be found here. In this short note, we want to share examples of the relationship of gray mold and tomato plant injury. In the figure 1 above, a pruning injury of tomato in a commercial greenhouse has become necrotic and a gray mold infection is starting. Figure 2 is from our research high tunnel.  In the photo, one can see where there was an abrasion, probably due to tying the plant in the greenhouse. This injury allowed the gray mold fungus to begin to grow.  Not only will this infection cause a die-back, but the spores produced may cause the disease to spread.  We clipped off this branch to stop the spread of the disease. The photo is taken outside of the greenhouse for better lighting. The lesson here is[Read More…]


Figure 2. Wilt cucumber plants in a high tunnel

  Last week, we were called by a few watermelon growers who reported their newly planted watermelon seedlings were dead (Figure 1 ). After closely inspecting the affected plants, we did not find any pathogens. This reminded us of what happened to our cucumbers back in early April in our high tunnel. We will review the cucumber story first, and rethink what might have happened to the watermelons. Cucumbers were planted on March 30 in a high tunnel located at Southwest PurdueAgricultural Center (SWPAC), Vincennes, IN. The lowest air temperature after planting was recorded at 37.5°F inside the high tunnel, which should not be low enough to cause frost damage. However, we lost 40% to 80% of the newly planted cucumbers depending on varieties. The symptoms were similar to water deficiency-caused plant wilt (Figure 2 ). Most of the dead plants had intact stems, however, we did find wire worms[Read More…]


Beginning Farmer Tours June 25, 2016: Silverthorn Farm, Rossville. Organic fruits and vegetables, pastured pork and working with restaurants. July 14, 2016: Melon Acres, Oaktown. Community-supported agriculture and agritourism. Sept. 29, 2016: River Ridge Farm, Roann. Four-season vegetable farming, operating an on-farm store, and farm-to-school programs. The tours are free, but registration is required. Registration at https://mdc.itap.purdue.edu/wk_group.asp?wk_group=BeginFarmer For more information about the Beginning Farmer and Rancher program, or the farm tour schedule, contact Kevin Gibson at (765) 496-2161 or kgibson@purdue.edu.   Hops Field Day Location: Crazy Horse Hop Farm. 8781 S. County Road 925 West Knightstown, IN 46158 Date: June 4 2016, 1:00 pm to 3:00 pm EST Learn about irrigation management, hilling in hops yards, petiole test for nutrients, pruning lower foliage for mildew management and insect identification (bring specimens). Please register at http://bit.ly/1rkkciw or at The Purdue Extension – Monroe County Office at (812) 349-2575 or afthompson@purdue.edu. Registration deadline is June 1.


Recent cool weather increases the occurrence of zippering on high tunnel tomatoes. We observed at least 20% of developing fruit (most on the first and second flower clusters) on the variety Mountain Spring showed the zippering symptoms in our high tunnel. A typical symptom of the disorder is a thin, brown, necrotic scar that starts from the stem end and extend fully or partially to the blossom end. The reason the symptom is called zippering is because transverse scars are along with the longitudinal scar that looks like a zipper (Figure 1). In more severe cases, the scar is open and reveal locule (Figure 2). In the initial stage, zippering is often observed with anthers adhering to the fruit (Figure 3), the attached anthers is believed to disturb fruit development and cause the symptom. Zippering symptom is more noticeable with cool weather. Optimum temperatures for tomato fruit set are 60-75°F (night) and 60-90°F[Read More…]


The recent cool and cloudy weather has influenced conditions in the field as well as in greenhouses and high tunnels. I have observed more Botrytis gray mold of tomatoes in greenhouses this spring than usual. This is due in part to the weather. This article will discuss this disease on tomatoes and some management options. Gray mold is caused by a fungus that attacks many types of vegetables and ornamentals. The fungus is not a strong pathogen and often starts on weakened or senescent tissue such as old flower petals. The gray mold fungus, Botrytis cinerea, may be a weak pathogen, but it is a good saprophyte, growing well on old crop debris and organic matter until a good plant host is available. Figure 1 shows a tomato leaf on which a flower petal has fallen. Since the gray mold fungus is sporulating on the flower petal, there is a[Read More…]


Beginning Farmer Tours May 26, 2016: South Circle Farm, Indianapolis. Urban agriculture, organic farming and key tools for managing small-scale farming operations. June 25, 2016: Silverthorn Farm, Rossville. Organic fruits and vegetables, pastured pork and working with restaurants. July 14, 2016: Melon Acres, Oaktown. Community-supported agriculture and agritourism. Sept. 29, 2016: River Ridge Farm, Roann. Four-season vegetable farming, operating an on-farm store, and farm-to-school programs. The tours are free, but registration is required. Registration at https://mdc.itap.purdue.edu/wk_group.asp?wk_group=BeginFarmer For more information about the Beginning Farmer and Rancher program, or the farm tour schedule, contact Kevin Gibson at (765) 496-2161 or kgibson@purdue.edu. Hops Field Day Location: Crazy Horse Hop Farm. 8781 S. County Road 925 West Knightstown, IN 46158 Date: June 4 2016, 1:00 pm to 3:00 pm EST Learn about irrigation management, hilling in hops yards, petiole test for nutrients, pruning lower foliage for mildew management and insect identification (bring specimens). Please register at http://bit.ly/1rkkciw or at The Purdue Extension – Monroe County[Read More…]



In a recent visit to a high tunnel, we observed a severe salinity problem on tomatoes. Approximately one month after planting , most tomato plants in the affected area had not sent out any new leaves. Roots did not grow at all (Figure 1).  After conducting a soil test, very high soluble salt level explains these symptoms. This article reviews the basics of soil salinity. Salinity describes salt content in the soil. Virtually all fertilizer materials are salts, but they vary in their effects to increase salt concentration in soil solutions. In a field situation, precipitation in the form of rain and snow tend to leach salts.  Since high tunnels exclude rain and snow, elevated salt levels are a common concern for high tunnel vegetable growers. Table 1 are the salt indexes of common fertilizers. If you are using a premixed fertilizer such as 12-12-12, check the fertilizer components on[Read More…]


Soil temperatures are critical for seed germination and are closely related to occurrences of some early season soilborne disease and pest problems on vegetable crops. Plant vegetable crops after the soil is warm enough ensure good seed germination and fast crop establishment. The figures below show daily average soil and air temperatures at  recorded at six locations (Figure 1) in Indiana from April 25 to May 8 that maybe helpful in assessing soil conditions for planting across the state. More information regarding recommended soil temperatures for vegetable planting can be found in the articles https://www.hort.purdue.edu/ext/ho-186.pdf  and https://vegcropshotline.org/article/seedcorn-maggots-and-wireworms/      


Every year since 1980, we have conducted watermelon and cantaloupe variety trials at Southwest Purdue Agricultural Center. In 2016, our variety trials include 44 standard seedless watermelons, 12 cantaloupes, 4 mini-sized seedless watermelons, and 5 seeded watermelon varieties. Seeds have already been planted in the greenhouses and our target date for transplanting in the field will be the week of May 9th. The fruit will become ripe around the middle of July. If you are interested in observing how each variety performs during the season, don’t hesitate to come to visit us and witness the plots first hand. We will continue to present the results of our variety trials, as in the past, at the annual meeting held at the Southwest Purdue Ag Center in late November or early December but don’t miss the opportunity to visualize them during the growing season. In the winter meeting, we will discuss yield[Read More…]