Field crop production practices continue to change as growers evaluate new techniques and technologies to increase productivity. Plant diseases, unfortunately, present a challenge to producers by continuing to limit yields in soybeans, corn, wheat, and alfalfa in Ohio. There are a multitude of crop production management decisions that producers must make throughout a growing season. Many of these decisions can influence the impact of plant diseases on yields. This bulletin describes many of the management options available for field crop producers in Ohio and how these management options influence crop disease development.
Proper cultural practices that favor the development of vigorous seedlings and hardy, mature plants will help manage diseases or lessen their detrimental effects. Disease management is also aided by good agronomic practices such as proper seeding rates and seeding dates, balanced fertility, crop rotation, tillage, and weed control. In other words, the healthier a plant is, the better able it is to still be productive, even in the presence of plant pathogens. Many disease-management decisions are made before planting. In most farming systems, the producer can do little once a disease becomes severe in his field. Therefore, prevention is the first, and usually the only, line of defense against disease. It is rarely economical to treat acreages with fungicides. The primary fungicide application method in field crops is seed treatment, where extremely low rates of active ingredient per acre are applied directly on the seed before planting in the soil.
Diseases are not mysterious things that occur for no reason. They are the direct result of three critical factors coming together at one time. Disease occurs when a pathogen attacks a susceptible plant under environmental conditions that favor the infection and growth of the pathogen within the plant. The most common disease-causing agents, or pathogens, are fungi, bacteria, viruses, and nematodes. The most critical environmental factors are soil and air temperature, moisture as rain or dew, relative humidity, soil fertility, and pH. Serious disease can occur on susceptible cultivars when environmental conditions are right for the spread of an aggressive pathogen. For instance, the fungus that causes leaf rust of wheat produces severe yield losses on susceptible varieties when spores are blown in on wind currents from the southern states. Infection and rapid spread occurs in late May or early June when the day and night temperatures are between 60 degrees F and 72 degrees F and at least six hours of leaf wetness occurs for several days each week. Susceptible varieties may have as much as a 50 percent yield loss, whereas resistant varieties may have little or no yield loss.
The cornerstone to successful disease control is correct identification of the disease problems on your farm. Producers facing specific disease problems can fine-tune their disease-control strategies to those few diseases encountered each year. Those with little experience identifying diseases should seek help from competent sources. Disease samples can be submitted to the C. Wayne Ellett Plant and Pest Diagnostic Clinic for diagnosis at The Ohio State University. Clinic forms and information on proper packaging of plant material can be obtained from county Extension offices. Submit plant samples to the following address:
C. Wayne Ellett Plant & Pest Diagnostic Clinic
The Ohio State University
Room 110, Kottman Hall
2021 Coffey Rd.
Columbus, OH 43210
This Extension bulletin outlines the most effective control procedures for the major field-crop diseases. No attempt is made to cover all diseases or to present detailed information on disease cycles or symptoms. Several recent Extension publications provide color photos of the major diseases and complete descriptions of factors affecting their development. These publications are available from your local Extension office. Ohio State University Extensions' web site Ohioline (http://ohioline.ag.ohio-state.edu) provides up-to date resources on diseases in the form of fact sheets, bulletins, and newsletters.
Although not all diseases are described in this bulletin, the management practice summaries following each crop section provide comprehensive disease management strategies for specific crops. To achieve adequate disease control, producers should follow a comprehensive disease-management program. Most of these disease-management procedures are also excellent agronomic practices. The major disease-control practices to be followed for most field crops are listed with Table 1. Specific control procedures are outlined in each crop section.