The Heat is on to Monitor for Lygus in Valley Cotton Fields

With more hot weather predicted in the Valley this week, it’s a sure bet that cotton plants will flourish. And so will the bugs.

“Cotton likes hot weather. I wouldn’t be surprised if cotton plants grow three inches in a week,” field scout Damien Jelen says, noting the return of triple digit temperatures over the next few days in the Valley. Last week, the Valley recorded two days of 100-degree spring weather. Forecasters are predicting more sizzling weather Tuesday and Wednesday – good cotton growing weather you might say.

A cotton square is damaged by lygus bugs.

Of course, there’s a flip side to the pre-summer heat and it’s lurking in the hay ready to explode in numbers. That’s lygus bugs.

“I’m starting to see lygus in cotton,” Damien says. His observation raises the red flag because cotton is in the vulnerable time of development – the early squaring period. The square is part of the developing cotton plant and becomes the flower that eventually turns into cotton.

Lygus can threaten cotton until the final boll set in the summer. The pest pierces the square and damages the tissue. Smaller squares can shrivel and drop from the plant. Larger ones may not fertilize. If too many squares drop, the cotton plant may experience too much vegetative growth, resulting in tall, spindly plants and reduce yields, according to UC Integrated Pest Management.

Lygus populations will increase steadily through the end of this month.  To monitor the pest in cotton, Damien and other scouts will take a sweep net and canvass the field. The thresholds for growers to consider treatment are low this time of year – one bug for every 50 passes of the sweep net through mid-June and two per 50 from June 15 to 30, UC IPM says. 

Lygus bugs prefer to live in alfalfa fields rather than in cotton.

Cotton isn’t the first choice as a home for lygus. The bug actually prefers to live in crops such as alfalfa, safflower, beans, potatoes and tomatoes. “As these crops are prepared for harvest, winged adults migrate out of the field in search of new hosts. Careful management of these crops can reduce the migration of lygus bugs into cotton fields during cotton's most vulnerable period: mid-May through late July. Watch closely cotton fields that are downwind from these crops by sampling the cotton and surrounding fields often,” UC IPM says.

Around the Valley, it’s common to find alfalfa growing close to cotton fields.  Moreover, alfalfa is harvested almost monthly, meaning lygus populations will flock to find new homes in nearby cotton fields.

One way to keep lygus in alfalfa is to leave small sections of the field uncut during harvest.  This will leave a habitat for lygus and keep the pest from migrating into neighboring cotton fields. We’ll talk more about this practice in the future.

 “I haven’t seen much strip cutting so far,” Damien says. With more high temperatures coming up, “I’m going to get high lygus counts.”