West Texas cotton growers scratched their heads last summer as a “perfect storm” phenomena enveloped fields threatening every boll on the plants. Cotton growers and experts were baffled by plant leaves that mysteriously curled up.

SOUTHWESTERN COTTON RUST causes bright yellow to orange spots on the upper and lower leaves of cotton. Severe infections can cause defoliation and boll dwarfing. The Fort Hancock area is the epicenter of rust outbreaks in West Texas.

“We never had this problem before,” said Salvador Vitanza, Extension integrated pest management specialist, Texas AgriLife Extension Service, Clint, Texas. “One-hundred percent of the fields were affected for two weeks in El Paso and Hudspeth counties; some were worse than others.”

Farmers felt deep-knotted fear because of the unknown culprit. Some suspected viruses and insects. Vitanza consulted with cotton specialists through rapid exchanges of e-mails and photos. Initial thoughts focused on thrips, whitefly, virus, herbicide damage, salt, or a possible pollutant in irrigation water from the Rio Grande River.

Then the group assembled the puzzle pieces and determined that weather was the guilty party.

“We were dealing with a physiological response to irrigation and rainfall after a prolonged dry period coupled with high temperatures and strong winds,” Vitanza says.

Extremely dry and hot weather occurred from April through early July. From April 1 to July 6, the Rio Bravo farm weather station received 0.81 inches of rain and the Tirres Farm reported 0.25 inches. From June 7 to June 28, maximum temperatures reached 100 degrees F or higher.

“The winds were very strong when farmers were irrigating,” Vitanza said. “The new growth was sensitive to heat. The wind was blowing so strong that it damaged the tender tissue of the leaves and caused curling up, especially in the smaller leaves.”

The physiological phenomena similarly affected upland and Pima cotton. The Pima variety that appeared to be most affected by the physiological damage was Deltapine 744, but this may have been because it was the most popular variety in the region. Most Pima grown in Texas is grown in El Paso and Hudspeth counties. About 24,000 acres of cotton were grown in the two counties in 2008 — about three-quarters Pima and one-quarter upland.

Two weeks later the rains returned, soaking fields through July and August. The result was plant damage by Alternaria leaf spot, which is caused by the Alternaria macrospora fungus that infects leaves, bracts, and bolls. Pima cotton (Gossypium barbadense) is more susceptible; upland cotton (G. hirsutum) is fairly tolerant in dry weather.

“The disease usually infects mature plants near leaf senescence without reducing yields,” Vitanza said. Under these conditions, “the cotton plants had healthy, high-producing leaves.” When healthy leaves are affected, the leaves drop and the plant lacks adequate food reserves to feed the bolls.

“When Alternaria leaf spot attacks green leaves the cotton plant is in trouble,” Vitanza said. The disease can be prevented with fungicides including Mancozeb. Alternaria leaf spot is not a problem in most years and if the fungicide is applied and the disease doesn’t show up, the application is wasted, he said.

“Once Alternaria appears it’s too late to make an application. It’s a Catch 22,” Vitanza said.

Growers in Clint had the worst Alternaria leaf spot infestation as irrigation was underway when the rains began. Normal weather from September to harvest allowed some plants to recover with no yield loss. Some growers experienced a 25 percent to 30 percent crop loss from Alternaria combined with cooler weather in July and August and reduced input applications due to higher costs.

Outbreaks of Southwestern cotton rust (Puccinia cacabata) were mild in West Texas last year. The Fort Hancock area is typically the epicenter of rust outbreaks. The most common Southwestern cotton rust symptom is bright yellow to orange spots on the upper and lower leaf surfaces that brown with age. Severe infections can cause defoliation and boll dwarfing.

Southwestern cotton rust is more prevalent in West Texas, Southeastern New Mexico, Southern Arizona, and Northern Mexico. Some growers in the Fort Hancock area lost their entire cotton crop to the rust in 1991, but most growers in Far West Texas lost about 75 percent of the yield.

Factors conducive to fungus development include high humidity after summer rains. The pathogen first develops in grama grass species (Bouteloua spp). The spores are carried by the wind and under the right conditions to cotton leaves.

“The leaf has to have a drop of water on it with spores for about 18 hours,” Vitanza says. “These conditions coupled with repeated spore showers of rust will create a severely infected plant.”

Grama grass grows along the U.S. and Mexico sides of the Rio Grande River. Most grama grass is located in the Fort Hancock area. Spores can travel for miles to cotton, but most severe infections occur when grama grass is within one-quarter mile from the cotton field.

A mild outbreak occurred in West Texas in 2006. Growers worked through the Texas AgriLife Extension Service and the Texas Department of Agriculture to gain Section 18 emergency exemption use of the fungicide Quadris for disease control.

“Some farmers were not strong believers in Quadris but they applied it,” Vitanza said. “Quadris stopped the disease from spreading.”

Cotton insects

Thrips infestations in the seedling stage tend to be light in West Texas. That’s the reverse of the heavy numbers of cotton fleahopper that causes damage from the first to the fourth week of squaring. The cotton fleahopper becomes a beneficial insect after first bloom, consuming bollworm, fall armyworm, and beet armyworm eggs.

Lygus is usually the No. 1 pest in West Texas cotton. The Extension service annually conducts pesticide efficacy trials on lygus. Eleven chemistries were tested in 2007.

The stink bug occasionally causes damage in cotton, while the whitefly and aphid are late-season concerns. The whitefly produces honeydew that causes sticky cotton — a major problem during ginning.

A 2008 Extension cotton insect questionnaire completed by growers in El Paso County during last fall’s harvest indicated that every acre of cotton in the county is enrolled in the Texas Boll Weevil Eradication Foundation’s boll weevil and pink bollworm eradication programs. Growers also pegged 2008 average yields at 1,050 lint pounds/acre (Pima and upland combined).

Pima variety trials

In Pima variety trials conducted last year by Extension in El Paso County, four seed varieties were compared including Deltapine 357 and 744 and PhytoGen 800 and 830. In lint pounds per acre, Deltapine 744 yielded 1,026 lint pounds per acre while the 357 variety produced 1,004 pounds per acre. PhytoGen 830 yielded 870 pounds per acre and 800 produced 776 pounds. Fiber strength, micronaire, and related information are not yet available.

“Deltapine 744 was the best yielding variety. Deltapine 357 wasn’t commercially available in 2008, but it is a very promising variety,” Vitanza said.

Tom Speed, area technology development manager, Delta and Pine Land, Lubbock, Texas, says only carryover 744 seed will be available to growers this year.

“Delta and Pine Land’s three, commercially-available Pima varieties in 2009 will include Deltapine 340, 353, and 357,” Speed said. “Each variety has the same maturity and produces higher yields than Deltapine 744.”

Dow AgroSciences sales representative Greg Alpers says PhytoGen 800 and 830 Pima varieties are commercially available this year.

Vitanza compared 13 varieties of upland cotton in trials last year in Hudspeth County. The top five lint-yielding varieties included: Deltapine 164 B2RF, 1,597 lint pounds per acre; Deltapine 143 B2RF, 1,595 pounds, PhytoGen 375 WRF, 1,590 pounds, Deltapine 161 B2RF, 1,585 pounds, and Dyna Grow 2520B2RF, 1,579 pounds.

Cotton planting intentions

The 24,000 acres of upland and Pima cotton in El Paso and Hudspeth counties last year was down from about 30,000 acres in 2007. The 6,000-acre difference was planted in wheat.

With falling wheat prices, Vitanza predicts the 6,000 acres will be planted equally in wheat and cotton this year to bring cotton acreage in the area to about 27,000.

Results from the National Cotton Council’s latest Early Season Planting Intentions Survey suggest cotton production will fall 14 percent nationally from 2008. Texas cotton production could fall 9 percent this year.

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