Texas Cotton: Lygus Season Fast Approaching Hale County
With the high heat came some calmer days that has given much of the area cotton a respite from the winds and a chance to recover from any damage. Even the most damaged cotton has taken advantage of the respite and is developing better. Cotton that had escaped much of the damaging events seems to be jumping through its self.
Our scouted fields this week ranged from 2nd true leaf stage to nearly ½ grown squares. Fields at pinhead to match head squares exhibiting 3 to 6 squares per plant were much more common. Insect pressure remains very light.
Thrips have become an afterthought for all but the latest cotton fields. The thrips seem to have found other, more preferred host plants. Even in our latest fields, we did not see any economic populations this week. Our highest thrips count came from northwestern Hale County with a population of 1.6 thrips per plant on a pinhead square stage field. Every field situation will be different and can change often. I recommend that we continue to check for thrips until these fields reach pinhead square stage. The economic threshold remains at 1 thrips per true leaf stage until we start seeing those pinhead squares.
Cotton comes under risk from fleahopper damage with the development of the first pinhead square. We began scouting for fleahoppers last week and to this date we have not found any economic populations. We began finding some spotty pressure and fleahopper nymphs just out from the egg about mid-week. This indicates to me a likelihood of future problems developing in pockets where fleahoppers are reproducing. Fleahoppers at this age are very hard to find as they are only about the size of a grain of sand.
Our highest population was in a northwestern Hale county field where fleahoppers had infested 10% of the cotton plant population that had experienced a 5% square drop. Our predator counts have also been pretty high so far and I would estimate that there is a moderate to good chance they may control some of the potential fleahopper issues for us.
The economic threshold for fleahoppers is at 25 to 35% plant infestation with square drop considerations. For those of you making use of drop cloths, and do not know the plant population of the field being scouted, this translates into roughly 1 fleahopper per 1.5 to 2 ft. with the same square drop considerations.
Many area producers and entomologist, myself included, have come to the conclusion that the Lygus complex is the most damaging insect pest for most season on our area cotton. Several area cotton fields are quickly nearing the dreaded ‘Lygus season.’
There are multiple species of Lygus bugs that haunt our area crops, but all belong to the Lygus genus, giving them their lumped common name. Almost all of these species of Lygus share a pest status and exhibit many similar behavior patterns which thankfully allow us to generally speak about “the Lygus problem” without troubling producers too much about species identification. The prevalent species in our area vary slightly in color but are usually a pale green base color and about a quarter of an inch long.
Lygus bugs can look similar to cotton fleahoppers at first glance, but they will be notably larger and often exhibit a distinct triangle or V prominently on their backs. The nymphs are more similar to cotton fleahopper nymphs when very young, but the Lygus nymphs will have five dark, distinct spots on their backs, while fleahoppers will not. Lygus are primarily attracted to wild succulent plants as well as alfalfa, clovers, potatoes or vetch, but will feed on cotton squares and bolls almost as readily.
In cotton, their feeding pattern is similar to fleahoppers, only potentially much worse as they are proven to cause damage to medium sized cotton bolls. Lygus are also capable of traveling distances with impunity. Lygus are generally larger and more robust than fleahoppers. They can cause square drop and blackened lesions or dents in bolls, as well as deformities within the bolls. These insects start moving into cotton around the time it is squaring, and will hang around for the rest of the growing season.
There are dozens of acceptable host plants Lygus can feed upon, but alfalfa seems to be a favorite. Even though Lygus adults can move regularly, they tend to stay in or near an abundant food source. However, if that food source is disturbed, Lygus adults have proven to move quickly and ‘set up shop’ in cotton, devastating yield potential remarkably fast.
Cotton fields within three to five miles of any alfalfa field should be watched a little more cautiously with every alfalfa cutting. Fields adjacent to highway medians and ditches that contains large amounts of clover, etc. should also be on high alert when the medians are mowed as should producers with fields near weedy CRP fields that get bailed or cattle turned onto them.
The damage from heavy populations of adult Lygus alone can be quite serious, but it is the damage from high numbers of nymphs that is generally a larger concern. Once adult Lygus are forced to, or decide to, feed on a cotton field, they will generally stay in that field or nearby lending them to reproduce within the field. Once a more preferred host becomes available, the adults have the ability to leave the field at will, and often times, they do.
This often mitigates the longevity of potential adult Lygus damage. The wingless nymphs have no such option; therefore, the nymphs have much more potential to damage cotton. Combined populations of Lygus adults and nymphs at economic populations can be disastrous.
With the potential for damage to Lygus so great, I recommend extreme vigilance when scouting for this pest. Scouting procedures are very similar to fleahopper and often make use of drop cloths and / or beat buckets and / or sweep nets. The most common utilized economic threshold for Lygus is 1 per 2.5 to 4 ft. with square drop, fruit loss, and fruiting stage considerations.
We have not seen any in the field yet, but quite a bit of the area’s cotton is getting just the right size for them to be moving in. Area conditions are right for much of their most preferred host to be drying down, or otherwise disturbed, leaving our irrigated cotton as a very attractive food source for the Lygus. These small green bugs can reduce yield in cotton very quickly, so please keep an eye out for them!
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