Friday, July 1, 2016

Southern Plains of Texas: Time to Look for Fleahoppers

Suhas Vyavhare and Blayne Reed, Texas A&M AgriLife Extension Service

The high temperatures, high humidity, and the passing of light cotton showers over the last couple of weeks have been very conducive for rapid crop growth and development. Most cotton fields on the Southern High Plains are past the 5th true leaf stage and are sporting pinhead through ¼ grown squares.  This should mean they are no longer vulnerable to economic damage by thrips. There are some late fields and re-planted fields which can still be injured by thrips, however, and we should continue to scout these fields for thrips. With the high temperatures potential for rapid plant growth, and a lessening thrips pressure in general these field might be able to escape from any serious thrips damage.

As the crop is approaching reproductive phase, we should be looking for fleahoppers—many of us scouting regularly in the field are already seeing a few on squaring cotton.  There are already a small handful of regional fields reaching an economic level for this pest.  If you see the smaller and freshly adorned squares turning brown and dropping to the ground, and / or missing from the plant, the problem could be physiological or weather related but most likely the damage was caused by fleahoppers. Fleahoppers can be found in abundance on their preferred weedy hosts like silver leaf nightshade, woolly croton and horsemint. Although cotton is not the primary preferred host, it is a choice secondary host that fleahoppers will move to once weeds are killed by herbicide application, mechanical cultivation, or physical hoeing .

The adult fleahopper is about 1/8 inch long, pale green, and have piercing and sucking mouthparts which they use to suck proteins and other nutrients from the developing squares. Their bodies are flat with an elongated, oval outline and prominent antennae. As their name suggests, they do slightly resemble a whitish or yellowish-green flea, mostly due to the appearance of their hind legs looking much like the hind legs of a common cat flea.  Nymphs resemble adults but lack wings and are initially almost white in color or sometimes pinkish until they feed. After feeding, the immature stage is pale green with prominent, often reddish eyes.

Both adults and nymphs suck sap from the tender portion of the plant, often targeting the smaller squares (immature flower buds).  Matchhead, pinhead, and even smaller size squares are the preferred cotton feeding sites even after the plant develops larger squares.  Unfortunately the all-important first squares put on the plant are at the most risk.  While cotton has the ability to replace some level of early fruit loss, losing too much early fruit set will affect cotton’s growth patterns causing rankness and could impact fiber quality by the end of the season via fruit maturity. When fleahoppers are abundant, heavy early fruit loss may occur. Cotton is particularly susceptible to cotton fleahopper damage during the first three weeks of squaring but remains at risk until the second week of blooming when blooms become widely abundant throughout the field.  At that time, fleahoppers will feed upon readily and easier accessible pollen and be of no economic importance.  Later in the season, fleahoppers are known to even feed upon a few bollworm eggs and small larva as a predator, but early season economic populations should not be ‘saved’ for any beneficial potential. 

The 1st week of squaring economic threshold for fleahoppers in match head stage cotton is 35% infested plants with 90% square set or worse.  This percent fleahopper infested plant calculation can be made via whole plant inspection or beat bucket methods.  As plants get older, many entomologists prefer to scout for fleahoppers with drop cloths or sweep nets.  This allows the field scout to check dozens and hundreds more plants over the same period of time scouting in the field.  The 35% infested economic threshold and treatment level translates into roughly 1 fleahopper / 1.5 – 2.5 row feet for the drop cloth or sweep net method with the same percent square set calculation. 

As cotton plants develop, higher levels of fruit loss to fleahoppers becomes acceptable.  Given sufficient time and if early losses were not heavy enough to impact plant development, cotton is often able to compensate for lost squares during the pre-bloom period with little impact on yield, up to a point.  Thankfully, quite a bit of research has gone into finding those levels.

Cotton fleahopper action threshold is 25-30 cotton fleahoppers/ 100 terminals with:
Week of squaring
Square set
1st week
<90 percent
2nd week
<85 percent
3rd week to 1st bloom
<75 percent
After 1st bloom
Treatment is rarely justified