Crop insect guru Dan Johnson spoke about the importance of good sampling techniques at the Farming Smarter summer Field School in Alberta recently. As Tim Kalinowski reports in the Lethbridge Herald, Johnson, who is a pioneer in the field of crop insect forecasting and a world respected specialist in grasshoppers and potato psyllids in particular, said the key to good assessment within a farmer’s field is understanding the difference between “accuracy” and “precision.”
Johnson provided two diagrams of a testing target circle to explain this point. The first diagram reflected accuracy with samples taken all throughout the target circle area, and even outside, with counts from the sweeps varying across the different sample points. However, the complete summary of all the sweeps gives a pretty accurate picture of how many insects might be in that field.
The other diagram Johnson produced showed a narrow sample area to one corner of the field which precisely charted how many insects were in that sample. Johnson said both types of procedures have their place in research, but only the “accurate” target gives the complete picture of the field, and thus better enables farmers to decide whether an expensive chemical intervention is warranted or not.
Johnson said another factor which hasn’t been much considered in the past, but has become much more important now is the presence of natural enemies, beneficial insects, in fields. He isn’t aware of too many wide-ranging studies in Canada at present which have actually tried to survey how many of these natural enemies are present in ratio with known crop pests, and what that might mean to natural controls of these pest species.
“For 20 or 30 years we have recommended it, and done research on it, but it hasn’t been a formalized survey very often,” he said. “Field Heroes are working on at least drawing attention to them.” Johnson said it is a much different story in New Zealand where they count both the number of pests present in a given field and the number of natural enemies present at the same time.