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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

(2011) Coach - 1st Place Graduate Team - 2011 Weed Olympics. Weed Science Society of America.

(2011) NCWSS Fellow – presented by North Central Weed Science Society. North Central Weed Science Society.

(2010) Advisor of WSSA Outstanding Ph.D. Student. Weed Science Society of America.

(2010) Eric G. Sharvelle Distinguished Extension Specialist Award. Purdue University Cooperative Extension Service.

(2010) Outstanding Extension Specialist Award. Weed Science Society of America.

(2009) Advisor of Outstanding Ph.D. Student - Greg Kruger. Dept. of Botany and Plant Pathology.

(2009) CropLife Educator of the Year. Mid American CropLife Association.

(2009) Outstanding Graduate Educator Award. Dept. of Botany and Plant Pathology.

(2008) Advisor of Outstanding M.S. Student - Valerie Mock. Dept. of Botany and Plant Pathology.

(2008) Coach - 1st Place Graduate Team at NCWSS Weed Science Contest. North Central Weed Science Society.

Selected Publications

Marquardt, P. M., Terry, R., & Johnson, W. G. (2012). Competitive effects of volunteer corn on hybrid corn growth and yield.. Weed Science, 60, 634-640.

Chahal, G. S., & Johnson, W. G. (2012). Influence of Glyphosate or Glufosinate Combinations With Growth Regulator Herbicides and Other Agrochemicals in Controlling Glyphosate-Resistant Weeds.. Weed Technology, 26, 638-643.

Terry, R. M., Marquardt, P. T., Camberato, J. J., & Johnson, W. G. (2012). Influence of nitrogen application timing and rate on volunteer corn interference in hybrid corn. Weed Science, 60, 510-515.

Mock, V. A., Creech, J. E., Ferriss, V. R., Faghihi, J., Westphal, A., Santini, J. B., & Johnson, W. G. (2012). Influence of winter annual weed management and crop rotation on soybean cyst nematode (Heterodera glycines) and winter annual weeds: years four and five.. Weed Science, 60, 634-640.

Schafer, J. R., Hallett, S. G., & Johnson, W. G. (2012). Response of giant ragweed (Ambrosia trifida), horseweed (Conyza canadensis), and common lambsquarters (Chenopodium album) biotypes to glyphosate in the presence and absence of soil microorganisms.. Weed Science, 60, 641-650.

Loux, M. M., Dobbels, A. F., Johnson, W. G., & Young, B. G. (2011). Effect of Residual Herbicide and Postemergence Application Timing on Weed Control and Yield in Glyphosate-resistant Corn. Weed Technology, 25, 19-24.

Mithila, J., Hall, J. C., Johnson, W. G., Kelly, K. B., & Reichers, D. E. (2011). Evolution of Resistance to Auxinic Herbicides: Historical Perspectives, Mechanisms of Resistance, and Implications for Broadleaf Weed Management in Agronomic Crops. Weed Science, 59, 445-457.

Brabham, C. B., Gerber, C. K., & Johnson, W. G. (in press). Fitness of glyphosate-resistant giant ragweed (Ambrosia trifida L.) in the presence and absence of glyphosate. Weed Science, (59), 506-511.

Henry, R. S., Wise, K. A., & Johnson, W. G. (2011). Glyphosate’s effect upon mineral accumulation in soybean.. Crop Management, 2011. Retrieved from doi:10.1094/CM-2011-1024-01-RS.

Davis, V. M., Kruger, G. R., Hallett, S. G., Tranel, P. J., & Johnson, W. G. (2010). Heritability of glyphosate resistance in Indiana horseweed (Conyza canadensis) populations. Weed Science, 58, 30-38.