2005 Year in Review

Fighting Plant Disease without Chemicals

Source: Darin Eastburn (217) 244-9632; eastburn@uiuc.edu; Author: Debra Levey Larson

Evelyn Riebe owes her sanity to organic foods. "When I was 20 years old, I lost my mind," she said. "Finally my doctor figured out that I was allergic to petrochemicals. Once I started eating all organic foods, my mind was clear again."

Today, Riebe is an organic farmer. She farms almost 200 acres about 10 miles west of Pontiac, Illinois. On Short Point Organic Farm, she grows certified organic oats, corn, food grade soybeans and blue corn. She also has a small vegetable garden for her personal use.

Riebe was in attendance at a sustainable agriculture tour at the University of Illinois hoping to pick up some strategies to fight off plant diseases and kill weeds without using chemicals. Her latest concern is Canada thistle. The way she treats it now is by using deep tillage that gets at the roots, then going down the field rows with a hoe, individually digging them out.

"When you are certified organic, you can't usually use a rescue treatment with a chemical. There are a few products approved for use in organic systems, but the options are very limited and should be considered as a last resort. So the best thing to do is to focus on prevention," said University of Illinois plant pathologist Darin Eastburn.

Eastburn says you can control diseases by changing variables in one or more of four areas: the host or crop; the pathogen, which could be a fungus, bacterium, virus or nematode; the environment; and time.

"For example, if you use crop rotation, the pathogen cannot survive because you keep changing the host," he said. "Another way is to plant varieties that are resistant to disease. You need to know your crop and keep good records to know which varieties to plant."

Another strategy is to make the environment unattractive to the pathogen. "About 80 percent of plant diseases are caused by a fungus of some sort," said Eastburn. "And most fungi do best under high humidity. Dense crop canopies provide shade and restrict air movement which promotes higher humidity, so spreading out the plants can help make the environment less conducive to fungal growth."

He explained that another way to change the environment is to irrigate in the morning rather than at night. "If you irrigate in the evening, the crop stays moist through the night and the conditions are more favorable for fungi to grow. But if you water in the early morning, the sun dries off the plants more quickly making the environment unsuitable for the pathogen to grow."

The saying, "Timing is everything" can apply to controlling plant diseases as it refers to planting dates. "If you plant early, the crop may already be well established by the time a particular pathogen is trying to emerge. Or you might delay planting until after the most favorable period for infection has past."

Eastburn and graduate student Shin-Yi Li are a part of a larger organic research project at the U of I. Their portion of the research is looking at soil pathogens such as sudden death syndrome, brown stem rot, charcoal rot and Phytophthora root and stem rot of soybeans. Li gathers soil samples from the organic plots, takes them to the greenhouse, adds pathogens to the soil and evaluates the amount of disease that develops.

On the field plot, they've added compost in three different levels -- zero, 15 tons per acre and 30 tons per acre to evaluate the effects of adding organic matter on root disease development. "We purposely planted a soybean variety that's susceptible to a number of diseases. It's a liberty you can take with research that no farmer would want to do," said Eastburn.

He said that adding organic matter to the soil is thought to stimulate the microorganisms in the soil that suppress plant pathogens. "Our hypothesis is that the highest level of compost (30 tons per acre) will have the lowest incidence of disease." Similar studies on other crops have found that adding composts to soil results in less infection by soil borne pathogens. "We want to find out if the same thing will occur in this system which is in the transition process of organic certification. We hope that our findings will be useful for growers in Illinois who are trying to figure out the best way to transition from conventional to organic agriculture."

Eastburn’s study is in the third year of a five-year study.

by  Editor, theCity1.com
July 11, 2005