Many cotton fields are generally beyond the stage requiring fleahopper control as they have reached the second week of bloom. However, younger fields susceptible to fleahopper damage exist in the region.
The heaviest cotton fleahopper infestations have been in the El Campo area in one of our fleahopper control studies. As the wind began to blow from the north, adult fleahopper numbers rapidly increased on Friday, May 28 at 7 days after treatment number two and since we were delayed in treating, their numbers continued to increase through 10 days after that second treatment (May 31).
We finally treated on June 1; it will be interesting to see what happens in the plots over the next 2 week period and later determine how much was lost to these high numbers. Several things to note in the study:
• The Orthene rate being used is 8 ounces per acre.
• (2) We were still seeing statistically fewer fleahoppers in the treatments even with the high numbers.
• (3) The fewest number of fleahopper (numerically) at 10 DAT-2 was in the Centric treated cotton. It may turn out that we are achieving better control than indicated by the high numbers. Plant mapping and the yield data should tell the final story if all goes well with the production year.
Spider mites had been observed in fields where extremely dry conditions existed, but rainfall the night of June 2 should help reduce that threat. It has always been difficult to know when to apply a miticide since at the time their numbers become alarming, the infestations often begin to decline. We treated at the Research and Extension Center one year and left areas with no treatment. There were no differences in look of the cotton about a week later or yield at the end of the season.
Leafminers also present a problem in that just as they reach alarming numbers the infestation abruptly ends due to high parasitism rate. This parasitism occurs even where insecticides have been used. To determine parasitism I have to examine leaves under a microscope to see if the parasites are there. The leaf miner is another pest that I have no real feel of how to handle with insecticide.
Cotton aphids will probably increase in numbers as they do every year about this time. My advice it to watch the population build to at least 50 per leaf on average and do not consider control until the infestation is at that level and building for over 10 to 14 days.
Even after becoming alarmed at their numbers, never treat on that day. Wait 48 hours and then determine if numbers have begun to decline. Look for parasitized aphids (mummies), presence of predators, or the start of the fungus that takes out aphids. If the mummies have exit holes where the adult parasitic wasp has emerged the aphid infestation is usually over. Where about 20 percent of the aphids are mummies, it has been my experience that a very rapid decline will be observed in aphid numbers.
I have had only one field study where aphids caused a clear yield decrease. In that case the infestation persisted for 20 days in cotton during the heavy bloom period. More than 200 pounds of lint per acre was gained in that case with 0.6 ounces per acre of Intruder.