How to Sample
After the first open boll, you can stop sampling for spider mites but continue to take a combined sample for aphids and whitefly at least once a week.
Beginning at least 50 paces into the field, choose a sample plant at random and select the 5th mainstem node leaf from the terminal. Using a hand lens, turn the leaf over and check for insects on the underside (these are called leaf-turns). Record monitoring results.
| Aphids | Count and record number and color (yellow or black). |
|---|---|
| Whitefly adults | If 3 or more are found, count the leaf as infested |
| Whitefly nymphs | Place a quarter-sized ring between the central and left-side main veins and check for presence or absence of large nymphs (3rd or 4th instar). |
Repeat these leaf-turn samples on 10 plants in this area of the field, walking at least 20 paces between sample plants. Then move on to another area, repeating the procedure in a total of 4 areas of the field. Be sure to check the edges of the field for whiteflies migrating in. Also check for natural enemies of aphids and whiteflies including bigeyed bugs, minute pirate bugs, lacewing larvae, syrphid fly larvae, lady beetles as well as parasitized aphids and whiteflies.
Treatment Thresholds
(See aphid and whitefly sections for more details on thresholds and treatment options.)
| Aphids | Between open boll to preharvest, treatment threshold is as low as 5 to 10 aphids per 5th mainstem node leaf because of honeydew deposition on lint. |
|---|---|
| Whitefly adults | 40% leaves with at least 3 adults. If using insect growth regulators (IGRs), nymphs must also be present to justify treatment. If high numbers of adults are at field edges, but no nymphs, an edge treatment with a non-IGR may be required. |
| Whitefly nymphs | 40% leaves infested with large nymphs. |