Agronomy Handbook

Illinois Agronomy Handbook

Several chapters of the Illinois Agronomy Handbook were updated in 2021 and are available for free download.

Managing Insect Pests

By: Nick Seiter

Insects can reduce crop yield and quality, either by feeding directly on the marketable portion or by indirectly stressing or killing the plant. Many insects can be considered pests of alfalfa, corn, soybean, or wheat; however, only a relative few are frequently encountered at economically significant densities in Illinois. This chapter considers “key” pests, which should form the basis of insect management strategies for these crops, as well as some “occasional” pests that, while frequently encountered, rarely cause economic damage. | Read the chapter.


Managing Diseases

By: Nathan Kleczewski and Chelsea Harbach

There are many pathogens that can cause disease in field crops grown in Illinois. However, diseases are not problematic in every field in every year. This is because several factors are required for a disease to occur. The plant disease triangle outlines the three conditions that are needed in order for disease to occur: a virulent pathogen, a susceptible host, and a conducive environment. The longer these three conditions remain together, the more disease will occur. Disease will not occur when these components are not simultaneously present. | Read the chapter.



By: Chelsea Harbach and Nathan Kleczewski

Nematodes are roundworms, similar to the animal parasites encountered in livestock and pets. Soil-dwelling nematodes are both beneficial and harmful in crop production. The good nematodes, which don’t get much press, feed on fungi, bacteria, other nematodes, and other creatures that live in the soil and thereby recycle the nutrients contained in it. The presence of some of these types of “good” nematodes can be used as an indication of soil health. Tens of millions of mostly beneficial nematodes live in each square meter of cropland; however, a few of these microscopic roundworms—the plant-pathogenic nematodes—give all nematodes in crop production a bad name. This chapter addresses the most important plant-pathogenic nematodes in Illinois agriculture. | Read the chapter.


Water Management 

By: Richard A. Cooke and Laura E. Christianson

A superior water management program seeks to provide an optimal balance of water and air in the soil, which allows full expression of genetic potential in plants. The differences among poor, average, and record crop yields generally can be attributed to the amount and timing of the soil’s water supply. Indeed, a large part of getting agriculture “right” involves getting the water “right.” When there is not enough water, one irrigates and when there is too much water, one can improve land drainage. | Read the chapter.


Water Quality

By: Laura E. Christianson and George F. Czapar

Water quality can be evaluated in many ways: color, odor, temperature, turbidity, and the presence or absence of bacteria. Pharmaceuticals and personal care products have also been identified in many of the lakes, rivers, and streams in the United States. Current water quality issues in Illinois generally relate to drinking water safety and the need to reduce nutrient loss from agricultural fields. This chapter is organized around those two themes. | Read the chapter


Weed Management 

By: Aaron Hager

Numerous plant species are considered weeds in agronomic cropping systems. Weeds have many attributes undesirable to crop producers, not the least being the ability to reduce crop yields through competition for resources such as sunlight, water, nutrients, and space. Weeds also may harbor insects and provide a host for certain plant pathogens. Some weed species, such as wild garlic and eastern black nightshade, can reduce the quality of the harvested crop. Eliminating or reducing the deleterious effects of weeds on agronomic crops is the ultimate goal of weed management. Integrated weed management includes all practices that enhance a crop’s competitive ability and decrease weeds’ ability to reduce yield. |  Read the chapter


Cropping Systems and Alternative Crops

by Phillip Alberti, Talon Becker, Jennifer Jones, and Nathan Johanning; adapted from the previous version of this chapter written by Emerson Nafziger

Two crops—corn and soybeans—have come to dominate the cultivated area of Illinois over the past 70 years, moving from around 60% of cropped
acres in 1950 to more than 90% in recent years. This has been, in large part, due to increases in soybean acreage, which increased from around 20% of total harvested acres in 1950 to around 45% of total harvested acres in recent years. In 2000, Illinois corn and soybean acreage were near equal, with approximately 11 million harvested acres and 10.5 million harvested acres, respectively. In the following decade corn acreage saw a large increase, peaking in 2007 at about 13 million acres. This increase in corn acreage and movement away from the relatively even split of corn and soybean acreage coincided with a large increase in domestic ethanol production due to increases in gasoline prices and the adoption of federal bioenergy policies. | Read the chapter.


Weather, Climate, and Agriculture

by Trent Ford and Jim Angel

The key atmospheric and land variables that impact crops are solar radiation, air temperature, humidity, precipitation, and soil moisture. The day-to-day variability of these variables can be described as weather. Weather extremes at critical periods of crop development or phenology can have dramatic influences on productivity and yield. The long-term average temperature and humidity, total solar radiation and precipitation, and average soil moisture over a crop’s growing season can be described as the climate. It is the climate that, in the absence of weather extremes, determines the realized yields for a given region. Additionally, Illinois’ climate has changed over the past century and models project continued change to the end of this century. These changes have had tangible impacts on agriculture. Read the chapter.


Nitrogen Management for Corn

by Emerson Nafziger

Approximately 78% of the air is nitrogen (N)—that’s nearly 34,800 tons of N above every acre of land. Nitrogen exists in the air as N2—two N atoms bound tightly together. This bond is so strong that plants can’t break it, so can’t make use of this N. One of the few natural ways that N is released from the air is through lightning bolts, which produce small amounts of N that may reach the soil with rainfall. Plants contain more N than any other element besides those that come from the air or water (carbon, hydrogen, and oxygen), and N is the most limiting nutrient in growth of nonleguminous crops, including corn, in most farming systems. Finding ways to provide the right amount of plant-available N to corn remains a major challenge in most parts of the world where corn is grown. | Read the chapter.


Chapters Under Revision

The following chapters are under revision. Previous editions are available on the Extension Crop Science website.