Cotton Likes It Hot – But Only Under Certain Conditions

Some like it hot. Others not.

“It’s brutal,” field scout Carlos Silva says about the scorching 100 degree-plus weather that enveloped the San Joaquin Valley much of last week.Like many others who work outdoors, Carlos isn’t looking forward to another scorcher this week.

On the flip side, some do like it hot. Take cotton plants.

Cotton can thrive in really hot weather.  You might say it’s in the genes – cotton originated in hot, tropical climates and can live in very high temperatures, especially irrigated cotton.

Here’s a little science: The optimum air temperature range for cotton photosynthesis is 77 to 113 degrees. Photosynthesis, in short, is the foundation of plant life in which the sun’s rays are captured by the plant to create sugar necessary for growth.

The impact of high air temperatures on cotton really depends on the plant tissue. Like humans, cotton plants let water evaporate from its tissue – we call it sweat in humans – to stay cool. Well-water cotton plants have been found to be 10 degrees cooler than the air temperature, according to scientists. One study measured plant canopy temperature at 88 degrees on a blistering 121-degree day in Arizona.

Interestingly, the evaporative cooling of cotton in July can provide the same cooling output as up to 100 average home air conditioners, according to a July 1990 article by Kater Hake and Jeff Silvertooth in a National Cotton Council publication, Physiology Today. (The title is “High Temperature Effects on Cotton.) The key, they note, is maintaining an ideal tissue temperature range of 74 to 90 degrees. Another important factor is providing adequate water for the plant to use to cool itself.

The authors point out that yield and quality are tied to temperatures. By understanding the effects of hot spells on cotton, growers can make the timely adjustments on the production practices to maintain yield and quality. Dry soil, high humidity, bright sunny days, plant diseases and high night temperatures can play a role in tissue temperatures.

Checking moisture content in cotton.

Without adequate moisture, the plant can’t stay cool enough and that will impact yield.  “Hot” cotton is not good.

Quality, though, is less susceptible to hot temperatures, which often cuts short the boll setting process. That means fewer, poor quality late-set bolls.

During high temperatures, growers should keep the moisture high and surface soil moist. Too much water, though, will create waterlog conditions and can cause cotton to wilt and die. Growers need to keep an eye on fruit retention during hot weather, which will spur growth.

The bottom line advice: use frequent light irrigations during hot, hot weather.

Meanwhile, in the fields and orchards, Carlos and almond field scout Jenna Mayfield report relatively low pest pressures. They had anticipated a surge because of the heat wave.

Jenna says many orchards are showing signs of hull split. Carlos says the hot weather has spurred cotton and alfalfa growth this past week. Look for growers to start cutting alfalfa within the week.

In cotton, fruit retention remains good. But lygus bugs are still showing up in some fields and fruit drop is evident there. Growers will have to decide whether to treat, Carlos points out.

The exciting news is cotton plants are at first bloom. Soon we’ll start seeing cotton fields come alive with colorful flowers.

Keeping Cool Essential in a HOT, HOT San Joaquin Valley

Hot, hot, hot, hot…

That’s the weather forecast this entire week in the scorching San Joaquin Valley. Tripled-digit temperatures are on tap over the next nine days with little relief in sight. What a way to mark the first week of summer.

Now that’s tough for farm workers and others that spend their day outdoors. 

Workers will need to be careful about heat illness this week.

“You want to protect yourself,’’ says field scout Carlos Silva, who spending his days scouting cotton and alfalfa fields. During these hot times, Carlos makes sure he loads up with plenty of water for the road, brings a hat and wears a long-sleeve shirt before heading out early in the morning.

“I’ve seen workers wearing sweaters in the field,” Carlos says.  

For almond field scout Jenna Mayfield, the thick orchard canopy serves as a natural sun shade during his rounds.  But Jenna has to cope with the humidity trapped under the orchard canopy.She gets out early and finishes early in the afternoon to avoid the peak high temperatures.

It’s important for farmers and their workers to prevent heat illness.  

Grower Joe Del Bosque has been an advocate for grower safety.  For years, he has been heavily involved with AgSafe, a nonprofit dedicated to preventing injuries and illnesses to farm workers. 

 “We should value our farm workers more. It’s very important to me being able to work in a fair and safe environment,” he says.

Here are some heat safety from the Occupational Safety and Health Administration (OSHA) and the Carle Center for Rural Health and Farm Safety:

• Acclimate to heat slowly over 5 to 7 days. For new workers, increase the amount of time in the heat by 20% per day. If you’re already used to hot conditions, you can increase your exposure more quickly, but if you’re away from the heat for 4 days or more, you’ll need to build up your tolerance again.
• Drink lots of water before, during and after work. OSHA recommends 4 cups of water per hour. Drink water every 15 minutes, even if you don’t feel thirsty, and avoid sweetened or caffeinated beverages.
• Adjust the timing of certain activities, if possible. Cut back exposure to the sun between 10 a.m. and 4 p.m. Avoid confined spaces during the hottest hours. Consider putting hay in the barn the morning after it’s been baled, or later in the evening when temperatures cool off.
• Take breaks in the shade or a cool environment. Taking 5-minute breathers as needed not only cuts down on heat stress, but also makes everyone more productive. Use machinery with cabs or shades, but don’t skip breaks – farm equipment generates a lot of heat, too. Set up simple tents in fields and other unsheltered areas to create needed shade. 

Taking these precautions will help everyone survive the heat. “You don’t want to be in the middle of nowhere and pass out,” Carlos says.

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Spring Humidity Can Trigger Rust in Almond Trees

We’re all familiar with rust. You see it on old tin cans, aging pipes and junkyard cars. 

   

Merriam-Webster Dictionary defines rust as reddish substance that forms on iron or some other metal usually when it comes in contact with moisture or air.”

In the plant world, it’s another story: “A disease that causes plants to develop reddish-brown spots.” That can be bad news for farmers.

As scientists officially bid farewell to the fizzled El Niño weather pattern last week, the spring rains coupled with hot weather has transformed almond orchards into canopy-covered steam rooms. That creates ideal conditions for rust to develop up in almonds.

“It has been usually humid this year compared to past years,” says Field Scout Jenna Mayfield. “Rust has been a problem around the Valley.”

Rust spots are showing up on leaves. - UC IPM photo

During her rounds through almond orchards, Jenna has spotted evidence of rust in trees. She’s finding small, yellow spots under leaves and on the fruit. The rust-colored spores are spread through the air. If left unchecked, “it can defoliate the tree.”

Rust is most often found in orchards near rivers or streams or other areas with high humidity during the late spring or summer, according to UC IPM. The rust fungus survives from one season to the next through infected leaves.

Almond leaves on the ground because of rust problems.

 To manage this disease, UC IPM recommends for orchards with a history of rust:  “Apply sulfur or maneb five weeks after petal fall and follow four to five weeks later in late spring and summer with a Quinone outside inhibitor fungicide (FRAC Group number 11) to control leaf infections. Two or three applications may be needed in orchards that have had severe rust problems. To be effective, fungicide must be applied before rust symptoms are visible.”

“When zinc sulfate (20-40 lb/acre) is applied in late October to early November to hasten leaf fall, rust inoculum is prevented from increasing. Otherwise, the inoculum may build up, overwinter on the trees, and infect leaves the following spring,” UC IPM says.
Meanwhile, Jenna says growers are out of the woods at this moment for stink bugs and leaffooted plant bugs. They become problematic again at hull split. “We’re waiting for the mites to come up later this month,” she says.

Field Scout Carlos Silva says alfalfa growers have wrapped up their third cutting of the season.  He continues to discover “a ton of lygus”  in alfalfa. Again, now’s the time for growers to leave strips of uncut alfalfa to provide a habitat for lygus bugs and keep them from migrating to nearby cotton fields.

The first post-planting irrigation has started in cotton fields.

Cotton plants continue to develop their first squares with some plants showing four to five squares. Carlos is still finding lygus bugs in some fields. Growers are irrigating the crop for the first time since planting. Overall, things are looking good so far for cotton.

How to Be a Good Neighbor: Strip-cut Your Alfalfa Fields

While making his rounds around the Valley last week, field scout Carlos Silva noticed a grower had just harvested his field of golden brown alfalfa.

The freshly-cut alfalfa lay drying on the sun-baked field, waiting to be collected and formed into bales. Nothing usual about that sight. Still, one thing stood out: “There were no strips of uncut alfalfa in the field,” Carlos says. It was surprising because a cotton field was right next door.

There are lots of lygus bugs living in alfalfa fields right now.

You might ask why this is a surprise. Well, lygus bugs are plentiful in alfalfa right now and this pest is a threat to cotton, especially now that the plants are developing their early squares – the flower buds of the cotton plant.

Around the Valley, you’ll often find cotton and alfalfa planted in neighboring fields. Lygus bugs prefer alfalfa over cotton as a home. But when their habitat is disturbed every month or so when alfalfa is harvested, the bugs literally bug out and set down in the cotton fields.

Already, Carlos is discovering lygus bugs in some cotton fields. His sweep net is gathering one to three bugs for every 50 sweeps. Lygus will be a big worry for cotton growers until final boll set later this summer.

Here is an example of a cotton square with lygus bug damage.

Here’s what UC Integrated Pest Management says about the destruction the pest can have on cotton: “Lygus bugs pierce squares and damage anthers and other tissues. When squares are less than 0.2 inch (5 mm) long, they shrivel, turn brown, and drop from the plant. Damage to larger squares may be to anthers, styles, and stigma, and may interfere with fertilization. If many squares drop, the plant may put its energy resources into vegetative growth, resulting in tall, spindly plants and reduced yields. Lygus bugs also feed on and destroy terminal meristems, causing bushy plants. If these bugs pierce the wall of young bolls (typically less than 10 days old) and feed on young seeds, these seeds may fail to develop. Lint around the injured seeds is stained yellow and may not mature normally.”

Carlos reports some instances of squares falling off. It’s unclear if the drop is due to lygus bug damage or other stress. One thing is for certain, cotton growers have a near zero tolerance for the pest. UC IPM suggests treatment until mid-June at one bug per 50 sweeps of the sweep net and two bugs per 50 through the end of this month. Spraying, however, can be harmful to beneficial insects. That’s why cultural controls are preferred pest management strategy at the outset.

So here we come full circle to back to alfalfa fields and leaving a habitat for lygus and reducing the migration to cotton. Here are strip-cutting tips from UC IPM:

·         Leave 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% new) alfalfa making a blend of 25% old hay and 75% 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% 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. 

A grower leaves a strip of uncut alfalfa near a field of cotton.

 Carlos says this practice should be followed for alfalfa fields that are within a two mile radius of a cotton field. Lygus bugs can easily travel that far after their habitat is disrupted.Carlos will be reminding growers that strip cutting is the neighborly thing to do.