Upon arriving in Louisiana in 1981, Tim decided that his main research focus would be to try to develop a solution to the problems caused by the occurrence of red rice in rice fields. Red rice is a weedy relative of cultivated rice. Since commercial rice and the weedy red rice are extremely similar genetically, no herbicide could be found that would do a good job of killing the red rice growing in a rice field without also killing the commercial rice planted by the farmer. Tim felt that the solution to this problem might lie in attacking the problem from another direction. Instead of hoping for the development of a new herbicide, this alternative approach would involve changing the rice plant so that it became immune to a herbicide that would normally kill it, as well as red rice. A plant with immunity to this weed killer could then be used to develop rice crops that could be sprayed with this herbicide, killing the weedy red rice but not injuring the commercial rice. If such a herbicide-resistant commercial rice plant could be found, it had the potential to solve one of the biggest problems that rice growers were facing.

While Tim started working towards this goal immediately, rapid success proved elusive. Hoping to find an existing rice variety that was just fortuitously resistant to herbicide, Tim's first approach was to plant and spray thousands of rows of different rice lines from all over the world. However, none of the existing rice lines proved to be resistant. He then implemented a very extensive laboratory program to try to develop laboratory-derived plants that were resistant to herbicide, but after years of extensive effort this too proved fruitless. Meanwhile, Tim implemented a year-round greenhouse program for soaking millions of rice seeds in a herbicide solution, in the hope that one of the seeds might have a slight genetic change that made it resistant. Years of doing this also failed. So Tim expanded his approach to an even larger scale. On acres of land he planted tons of rice seed that had been soaked in a chemical that could encourage miniscule genetic changes, in the hope that this would yield a plant with the desired resistance to herbicide. At this point Tim's program was easily the largest and most comprehensive research project of this type in the world. Even after more than a decade of work with no success, Tim continued with and even increased his effort on this project. He felt that finding the herbicide-resistant plant would be of such benefit to rice producers that he shouldn't let failure deter him from continuing to pursue this goal.
Finally, after 17 years of persistence, Tim finally found the plant he was looking for. He was able to obtain patents on this new discovery, and now has 12 U.S. patents and over 100 patents either issued or pending in foreign countries. The new herbicide-resistant rice was licensed to BASF by LSU, and is now in wide commercial production under the name Clearfield rice. Most of the rice grown in the U.S. today is Clearfield rice, and it continues to increase in acreage. Louisiana, with its severe red rice problem, already plants about ¾ of its rice acreage in Clearfield rice. So when you buy a bag of rice at the grocery store now, it's probably Clearfield rice.
While working at the LSU Rice Research Station, the Croughans were also active in Crowley community activities. Tim served as President of several organizations, including the Crowley Rotary Club, the Acadia Division of the American Heart Association, and the Crowley Town Club. He also served on the Board of Directors of the Crowley Chamber of Commerce. Sue was state-wide treasurer of the Louisiana Division of the American Association of University Women, and treasurer of Crowley's Solitic Club. She also served as captain of the Krewe de la Dames where she edited and help produce a cookbook for the Crowley Town Club. The Croughans have three children – Pete, who is pre-med at Yale University, Carolyn, who is pre-vet at Warren Wilson College, and Bill who is entering the honors math program at Carnegie Mellon University this fall. Since retiring, Tim and Sue have completed several half marathons, and Tim completed his first full marathon last year at the age of 60.