William G Johnson

Professor

Department: Botany and Plant Pathology
Phone: 765.494.4656
Fax: 765.494.0363
Office: Lilly Hall, Room G-313
E-mail: wgj@purdue.edu

Area of Expertise: Weed Science - Biology and management of economically important weeds in agronomic crops; interactions between weed management tactics, insects and diseases

Rationale

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:

Biology, Management, and Distribution of Glyphosate Resistant Horseweed, Giant Ragweed, Volunteer Corn, and other Weeds.
Interactions Between Weeds and Other Plant Pests Such as Soybean Cyst Nematode, and Western Corn Rootworm.
Management of Weeds Common to No-Till Systems.
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.

- Recent Publications

Krupke, C., P. Marquardt, W. G. Johnson, S. Weller, & S. P. Conley (2009). Volunteer corn presents new challenges for insect resistance management. Agronomy Journal, 101, 797-799.

Johnson, W. G., W. M. Davis, G. R. Kruger, & S. C. Weller (2009). Influence of glyphosate-resistant cropping systems on weed species shifts and glyphosate-resistant weed populations. European Journal of Agronomy, 31, 162-172.

Davis, V. M., G. R. Kruger, J. M. Stachler, M. M. Loux, & W. G. Johnson (2009). Growth and seed production of horseweed (Conyza canadensis) populations resistant to glyphosate, ALS-inhibiting, and multiple (glyphosate + ALS inhibiting) herbicides. Weed Science, 57, 494-504.

Mock, V. A., J. E. Creech, V. M. Davis, & W. G. Johnson (2009). Plant growth and soybean cyst nematode response to purple deadnettle (Lamium purpuream), annual ryegrass, and soybean combinations. Weed Science, 57, 489-493.

Davis, V. M., K. D. Gibson, T. T. Bauman, S. C. Weller, & W. G. Johnson (2009). Influence of weed management practices and crop rotation on glyphosate-resistant horseweed population dynamics and crop yield – years III and IV. Weed Science, 57, 417-426.

Kruger, G. R., V. M. Davis, S. C. Weller, J. M. Stachler, M. M. Loux, & W. G. Johnson (2009). Frequency, distribution, and characterization of horseweed biotypes with resistance to glyphosate and ALS-inhibiting herbicides. Weed Science.

Davis, V. M., K. D. Gibson, V. A. Mock, & W. G. Johnson (2009). In-field and soil-related factors that affect the presence and prediction of glyphosate-resistant horseweed (Conyza canadensis) populations collected from Indiana soybean fields. Weed Science, 57, 281-289.

Johnson, W. G., M. D. K. Owen, G. R. Kruger, B. G. Young, D. R. Shaw, R. G. Wilson, D. L. Jordan, & S. C. Weller (2009). Farmer awareness of glyphosate resistant weeds and resistance management strategies. Weed Technology, 23, 308-312.

Brown, L. R., D. E. Robinson, D. B. Young, M. M. Loux, W. G. Johnson, R. E. Nurse, C. J. Swanton, & P. H. Sikkema (2009). Response of corn to simulated glyphosate drift followed by in-crop herbicides. Weed Technology, 23, 11-16.

Shaw, D. R., W. A. Givens, L. A. Farno, P. D. Gerard, D. Jordan, W. G. Johnson, S. C. Weller, B. G. Young, R. G. Wilson, & M. D. K. Owen (2009). Using a grower survey to assess the benefits and challenges of glyphosate-resistant cropping systems for weed management in U.S. corn, cotton, and soybean. Weed Technology, 23, 134-149.