When a detective is called to a crime scene, he doesn't wait for the evidence to disappear.

Growers with crop problems shouldn't wait, either. They should take notes all season long.

"Trying to conduct a diagnosis after harvest for a problem that occurred in midsummer is often impossible," points out Purdue University agronomist Robert Nielsen. "Invariably, the factor that most limits a good crop-problem diagnosis is inadequate cropping records."

The first step: Get out and walk your fields, particularly early in the season.

"Diagnose the problem as soon as possible, because the evidence often disappears as seeds or plants rot away," says Nielsen. "For example, wireworm damage to a corn kernel is impossible to diagnose after the kernel has rotted away."

Alan Madison, a Walnut, IL, grower, is a veteran field-note taker. He usually takes "notes" on a tape recorder to create a map for each field.

"The first notes we take are at planting time," says Madison. "We keep track of planting date, hybrid or variety, air and soil temperature, soil conditions, wet spots and weeds."

His second note-taking trip comes soon after the crop is up. Madison records germination rate and plant stand, plus weeds and any evidence of insects. He uses a clean map of a field each time he scouts it.

Madison's third set of notes are made when he sprays or sidedresses. He records air temperature, wind speed and direction, humidity, soil conditions, weeds and their stage of growth and any insects or diseases.

>From then on, he checks fields periodically to note anything that may affect plant growth.

"One of the best aids you can have for checking fields is the weekly pest bulletin put out by your state extension service," says Madison. "It keeps you posted on what's happening in general with insects, diseases and weeds, tells you what to look for, provides guidelines on whether to treat, and suggests products if treatment is called for."

Independent crop consultant Bill Craig, Carlinville, IL, urges clients to write down as much historical information on each field as they can recall. Data on previous crops, tillage, manure applications, etc., can stay part of a field's permanent record. For the current year, he suggests growers make note of all wet spots, since those areas can become pockets of compaction.

"As a crop consultant, I keep track of small soil-type changes that may not show up on a soil map," says Craig.

Purdue agronomist Don Griffith adds: "Scouting fields for problems during the growing season not only helps explain what a farmer sees in the fall, but also provides a basis for correcting problems before the next crop."