Cotton maturity ranges from 2-3 leaf to matchhead square and some fields have multiple stages of cotton.
Fields with squaring plants should be inspected weekly for Cotton Fleahoppers. This can be done visually or by using a small, 2-gallon bucket once the plants are 12 inches tall. Treat fields that exceed an economic threshold of 15 fleahoppers per 100 plants.
Treating fields for cotton fleahoppers prior to squaring is not an effective management practice and will only increase the cost of production without a yield increase. This practice is a waste of insecticide.
Some research I have conducted even questions the value of protecting the first squares from cotton fleahopper. In a 2010 field trial, yield was the same for treating weeks 1, 2, & 3 and only weeks 2 & 3. The cotton fleahopper populations in this trial were very high for the first three weeks of squaring. I have not been able to confirm the results of this trial with another test having high fleahopper numbers in the first week of squaring.
Other insects of concern may include cotton aphids and spider mites. Aphids rarely cause economic damage to squaring cotton and parts of a field with populations over 50 aphids per leaf should be checked again in a few days to determine if the population is crashing.
Spider Mites can be a problem in drought stressed cotton but I have yet to see them at concerning levels.