Lygus Sweeping into Cotton while Mites Hitting Almonds

The uber-hot weather greeting the start of summer in the Valley is triggering a big uptick in lygus bugs populating cotton fields.

Field scout Damien Jelen is snaring four to five lygus for every 50 passes of his is sweep net. In one field, he recorded eight pests per 50 sweeps. In comparison, the count was one to two lygus bugs the previous week, which is about normal for this time of year.

“The lygus numbers are up. Growers are monitoring it. They do not want it to go on too long,” Damien says.“The hot weather is contributing to the increase.”The triple-digit temperatures along with harvesting of nearby alfalfa fields have combined to boost the lygus numbers in cotton.

Sweep nets snaring lygus bugs in cotton.

Here is the lygus threshold from UC Integrated Pest Management:

·  June 15-June 30:  more than two lygus bugs per 50 sweeps

·  Mid-Squaring (1st flower - 1st mature boll, beginning of July):  seven-10 lygus bugs (at least one nymph) per 50 sweeps and expected or better fruit retention. If retention is higher than expected you may be able to wait and monitor again that week before making a treatment decision. If retention is lower than expected and lygus bugs are present, consider treating.

·  Late Squaring (after 1st mature boll): 10 lygus bugs/50 sweeps, including the presence of nymphs

“The above thresholds are guidelines to be used with square monitoring, depending on the particular weather patterns. For example, during warm springs they are very reasonable, because cotton is setting fruit early and has high retention potential.

Moreover, UC IPM adds: “In contrast, late plantings, vigorous cotton, and high plant populations promote lower fruit retention and therefore thresholds will be lower. Additionally, duration of fruit retention may vary according to the cotton cultivar present in the field. The longer the fruit is retained, the longer it will be attractive to lygus bug populations. Finally, success in retaining early squares will greatly determine the final yield; therefore protecting cotton during the early square formation period (June) is critical. Protection during the early season is very complex. Factors such as low lygus bug numbers, high susceptibility of cotton, and variability in sampling require the grower to be extremely vigilant and ready to act at an instant.”

Lygus numbers have increased in cotton fields.

Damien is passing along his findings to growers, who will compare those numbers to the counts from their pest control advisers. It’s good to have a second pair of eyes monitoring the fields.

“If there is a spike by the end of the week, growers may order spraying,” Damien says. Growers should look at using reduced-risk materials.

There are two options for spray timing - during early fruiting  when monitoring indicates lygus densities are low and square retention is only slightly off (5 percent), re-inspect the field again in three days if square retention continues to be slightly off normal. Use product that preserves natural enemies. When population densities of lygus are high and potential for repeated and sustained invasion, may needed quicker acting.

Here are some chemical options: There is some resistance to organophosphate, carbamate and pyrethroid insecticides. Suggested chemicals to use are Carbine, Belay,Steward, Diamond, Brigade, Baythroid or Warrior.

Damien reminds growers with alfalfa fields adjacent to their cotton to leave uncut strips of alfalfa during harvest. This will provide a habitat for lygus – which prefer to live in alfalfa than cotton – when the alfalfa is cut.

Almond growers are concerned about mites in their orchards.

Meanwhile, the heat also is causing a spike in mites in almond orchards. “Growers have been spraying the edges of the orchards to control mites,” field scout Jenna Mayfield says. “Mites are pretty much the pest issue right now.”

UC IPM notes that “mites damage foliage by sucking cell contents from leaves. The damage begins with leaf stippling. Leaves can turn yellow and drop off. High numbers of mites cover tree terminals with webbing. Crop reduction and reduced vegetative tree growth shows up the year after damage occurs.”
Jenna says almond hulls are starting to split in most orchards. “If growers have not done their hull split spray yet, it’s on their agenda.”

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Alfalfa Growers Can Make the Cut as Good Neighbors to Valley Cotton Farmers

American author Emily Post espoused about the importance of proper etiquette during the 20^th century. These words certainly ring true in farm country: “To do exactly as your neighbors do is the only sensible rule.”

In our last post, we reported field scout Damien Jelen started to find lygus bugs in cotton fields, a habitat that these pests don’t find attractive. However, lygus do love to live in nearby alfalfa fields. But alfalfa harvesting drove them out to find a new landing spot in adjacent cotton fields, which are starting to develop their buds.

Harvesting alfalfa will disturb the habitat for lygus bugs.

 Damien said he hadn’t seen growers leaving uncut strips of alfalfa as a habitat for lygus. This practice is a neighborly thing to do to keep this pest from threatening the developing cotton squares.

Alfalfa is harvested many times during the season – on average about once a month. That means lygus can be on the move roughly every 30 days.

By leaving uncut strips of alfalfa during harvest, lygus will flock to this habitat and stay there until the next irrigation cycle. The bugs will then go back to the larger alfalfa field as the plants start growing again.

A grower leaves uncut strip of alfalfa grown adjacent to cotton.

UC Integrated Pest Management advisers say leaving uncut strips is vital from June to July because that time period is a crucial stage for cotton development.

Here are strip-cutting tips from UC IPM:

•         Leave a 10- to 14-foot wide uncut strip adjacent to every other irrigation border (or levee). At the subsequent harvest, these strips are cut with half of the alfalfa strip going into one windrow and the other half going into a second windrow to give a 50:50 blend of new and old hay. These windrows are then each combined with a windrow of newly cut (100 percent new) alfalfa making a blend of 25 percent old hay and 75 percent new hay. This technique minimizes quality problems from the older hay. Specific blends of old and new hay have been found not to significantly impact forage quality compared to 100 percent new growth alfalfa in most cases.
•         At the following cutting, uncut strips are left adjacent to the alternate irrigation borders. As an alternative, uncut strips of alfalfa may be left adjacent to the crop to be protected, such as cotton or dry beans.

This practice should be followed for alfalfa fields that are within a two mile radius of a cotton field. Lygus bugs can easily go that far after their habitat is disrupted.

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.”

These Bugs Benefit Cotton Growers and the Environment

 For the first time this season, field scout Damien Jelen took his pest-catching sweep net to the fledgling cotton fields across the Valley.

Sweep, sweep, sweep … he went snagging whatever bugs were hovering around the cotton plants, which have reached the third true leaf stage in development.  (After the cotton seed is planted, cotyledons form and poke through the soil surface. A bud above the cotyledons will enlarge and serve as the foundation for the true leaves and branches to develop.)

Well, Damien caught plenty of bugs.  The good news, he reports, is his catch werebeneficial insects – the good bugs that gobble up the bad bugs that can damage the crop.

“I caught a lot of beneficials,” Damien said, noting most of the good insects have been big-eyed bugs. “The bug pressure is low because the weather is not super hot yet.”

Researchers say some 50 bugs are potential crop-damaging pests in cotton. Aphids, whiteflies and spider mites are common pests that can be controlled by beneficial insects. An unsprayed cotton field can host several million beneficials per acre, according to one report.

Aphids populate a cotton plant leaf.

You can call beneficial insects the farmer’s best ally. They are a free source of natural pest control, meaning growers can save money while protecting our land, water and soil from pesticides.  It’s called biological control – using nature’s good bugs to manage bad bugs in the field and orchards.

Who are these unsung heroes? 

  

Here are a few of the common good bugs: green and brown lacewings, minute pirate bugs, lady beetles, assassin bugs, six-spotted thrips and parasitic wasps. Three cheers to these beneficials.

A minute pirate bug gobbles up an aphid.

Meanwhile, Damien reports alfalfa growers are preparing for their second cutting of the season. (A few early birds are getting ready for the third harvest.) He says pest pressure is low in alfalfa as well.