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William G Johnson

Botany and Plant Pathology 

  • Professor
Lilly Hall Room 1-361


The estimated average monetary loss caused by weeds in field crops grown in the U.S. is over 4 billion dollars each year. Weed management expenses are one of the largest variable costs incurred by growers annually. Weeds growing on cropland are like crop plants themselves, drawing upon the soil and air for essential elements. Unfortunately, weeds obtain essential elements at the expense of adjacent crop plants. The result of inadequate weed control is a reduction of crop yield and quality. Traditionally, weed management practices have included preventative, cultural, mechanical, biological, and chemical tactics. However, with the rapid increase in the number of effective herbicides in the 1960-1990's, weed management techniques have become more reliant on herbicides in the last 20 years. In any biological system, strong dependence on any single tactic results in selection pressure for species (weeds, insects, and/or diseases) which can exploit the niche left by the single tactic. As a result of overdependence on herbicides, the number of herbicide-resistant weeds has grown from less than 10 in the 1960's to over 200 in 2009. Additionally, there are over 1000 non-indigenous plant species which can potentially infest crop production systems if given the opportunity. Therefore, production of food for humans and livestock and the economic well being of Indiana farmers depends heavily on effective, integrated management of weeds and other plant pests.

My Program Objectives
  1. Develop weed management systems that are economically and environmentally sound, integrate cultural practices with judicious herbicide use, improve efficiency of production, and minimize selection pressure for herbicide-resistant weeds.
  2. Promote grower acceptance of these weed management systems through education efforts targeting growers, crop consultants, input suppliers, industry representatives and extension educators in Indiana and surrounding states.
To that end, my efforts are focused on the following topics:
  1. Biology, Management, and Distribution of Glyphosate Resistant Horseweed, Giant Ragweed, Volunteer Corn, and other Weeds.
  2. Interactions Between Weeds and Other Plant Pests Such as Soybean Cyst Nematode, and Western Corn Rootworm.
  3. Management of Weeds Common to No-Till Systems.
  4. Evaluation and Management of New Weed Management Tools and Transgenic Events such as 2,4-D Resistant Crops, Dicamba-Tolerant Soybeans, and Optimum GAT Crops.

Awards & Honors

(2016) Advisor - NCWSS Outstanding Graduate Student (Travis Legleiter). North Central Weed Science Society.

(2016) Advisor - Dept. of Botany/Plant Pathology Outstanding Graduate Student (Pratap Devkota). Purdue University Dept. of Botany and Plant Pathology.

(2014) Advisor - NCWSS Outstanding Graduate Student (Jessica Schafer). North Central Weed Science Society.

(2014) Outstanding Graduate Educator Award. Purdue University College of Agriculture.

(2014) Purdue College of Agriculture Outstanding Graduate Educator. Purdue University College of Agriculture.

(2014) Purdue University Seed for Success Award. Purdue University.

(2013) Outstanding Graduate Educator Award. Purdue University Dept of Botany and Plant Pathology.

(2013) Seed For Success Research Award (for a grant exceeding $1,000,000). Purdue University.

(2012) Advisor - NCWSS Outstanding Graduate Student (Paul Marquardt). North Central Weed Science Society.

(2012) Outstanding Graduate Educator Award. Purdue University Dept of Botany and Plant Pathology.

Selected Publications

Johnson, W. G. (n.d.). Impact of Inoculum Concentration on Goss’s Wilt Development in Corn and Alternative Hosts. Plant Health Progress, 20(3), 155-159. doi:

Johnson, W. G., & Devkota, P. (2016). Effect of carrier water hardness and ammonium sulfate on the efficacy of 2,4-D choline and premixed 2,4-D choline plus glyphosate. Weed Technology, (30), 878-887. doi:10.1614/WT-D-16-00040.1

Freije, A., Ikley, J. T., Wise, K. A., & Johnson, W. G. (2015). Diseases of Corn: Goss’s Wilt on Grass Hosts. (BP-88-W). Retrieved from

Giesler, L., Bradley, C., Chilvers, M., Freije, A., Johnson, W. G., Legleiter, T., . . . Young-Kelly, H. (2015). Scouting for Soybean Seedling Disease and Disorders. (CPN 1009).

Dobbins, C. L., Langemeier, M. R., Nielsen, R. L., Vyn, T. J., Casteel, S. N., Johnson, W. G., & Wise, K. A. (2017). 2017 Purdue Crop Cost & Return Guide. Purdue Extension, (ID-166-W), 3. Retrieved from

Patton, A. J., Weisenberger, D. V., & Johnson, W. G. (2016). Divalent Cations in Spray Water Influence 2,4-D Efficacy on Dandelion. Weed Technology, 30(2), 431-440. Retrieved from

Bledsoe, L., Buckmaster, D., Camberato, J. J., Creswell, T. C., Krupke, C. H., Johnson, W. G., . . . Wise, K. A. (2015). Forage Field Guide Third Edition. (ID-317), 314.

Brouder, S. M., Camberato, J. J., Casteel, S. N., Creswell, T. C., Faghihi, J., Gerber, C., . . . Young, B. G. (2017). Corn & Soybean Field Guide. Purdue Extension, (ID-179), 313.

Robinson, A. P., Simpson, D. M., Yau, K., Canada, S., & Johnson, W. G. (2015). Aryloxyalkanoate Dioxygenase-12 Soybean Protein Expression. Weed Science, 63(1), 229-234. Retrieved from

Brouder, S. M., Camberato, J. J., Carpenter, B. N., Casteel, S. N., Creswell, T. C., Faghihi, J., . . . Young, B. G. (2017). Soybean Field Scout - 2017 edition. Purdue Extension.

Botany and Plant Pathology, 915 West State Street, West Lafayette, IN 47907 USA, (765) 494-4614

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