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
|
|
