Research in vegetables at the West Side Research and Education Center suggests fine-tuning of rates and application methods can improve herbicide performance under San Joaquin Valley conditions, says Kurt Hembree, Fresno County farm advisor.
Hembree, discussing his findings during a recent field day at the center near Five Points, said the herbicide Chateau worked well in experiments as a pre-emergence, postplant material through chemigation for annual weeds in onions and garlic on loamy soils common to the west side of the valley.
“Rather than spraying with the rates of 2 to 12 ounces per acre of Chateau typical in other crops,” Hembree said, “we used rates of only one-fourth- and one-eighth-ounce per acre. Of course, that would be difficult for a grower or an applicator to precisely mix for a sprayer, so we decided to chemigate with two applications. It worked well on the spectrum of winter and summer weeds.”
He said he is working on the method with the manufacturer, Valent, and an advantage would be to package the product in small amounts so it could be easily and accurately used in a sprayer or sprinkler system.
However, he cautioned, the rates are critical on sandy-textured soils. Similar studies on such soils in Southern California desert areas showed the one-eighth-ounce rate was quite successful and had good selectivity, but the one-fourth-ounce rate killed both the weeds and the crop.
Turning to Chateau and garlic, he said the herbicide, when tank-mixed with Prowl, performed quite well in summer weed control in trials off the station this year.
“We need a pre-emergence, postplant treatment with Chateau for garlic, but the problem has been the existing registration groups onions and garlic together. To get the registration, it had to be for a postemergence application. It could be a year or two before a new, separate registration for garlic can be approved.”
Goal Tender label
In another project, Hembree is collaborating with other farm advisors and Dow AgroSciences to develop data leading to a label for Goal Tender (4F) at 6 to 8 ounces for use on onions at the one-leaf stage. This would enable earlier treatments instead of waiting until the two-leaf stage and applying Goal 2XL.
Citing his data this year on direct-seeded, red fresh-market onions, Hembree said “We are finding about twice the safety factor with the Goal 4F formulation. It is less volatile than 2XL, holds to the soil better, and gives a slightly better weed control. There is a little initial injury to the crop, which we expected, but the onions came out of it pretty quickly.”
For several years, Hembree and several of his colleagues in other counties have also pursued ways to get more out of Roundup treatments to control bindweed, a long-standing problem species for research projects at the station. The material on its own does not give sufficient control.
One approach was undercutting the deep-rooted weed, combined with herbicide treatments, but the labor costs proved to be excessive.
An obstacle on a portion of the station is a shallow water table. The bindweed roots are so deep, it is difficult to deliver enough herbicide to kill them.
The researchers mixed Roundup at several rates with phenoxy herbicides and various other materials in trying to manage the weed. The trial with the best control of bindweed this year was an experimental combination of the 3- to 5-pound rate of Roundup Ultramax with Indicate 5, a buffering agent containing adjuvants and surfactants.
“Within about seven days after application, the bindweed was smoking,” he said. “So now we will re-irrigate the plot to check on regrowth.” Although details on the product's composition are sketchy, Hembree said he plans to learn more about it and do more research with it.
The Indicate 5 product, he added, is said to enhance the effect of insecticides, herbicides, fungicides, and other products. When added to spray water before other chemicals, it adjusts the pH, a dark red color in the water showing 4.5 to 5 and lighter shades indicating movement toward neutral.
Tom Trout, supervisory agricultural engineer with USDA-ARS at Parlier, told the field day assembly of progress with another project aimed at taking guesswork out of irrigating vegetable crops.
Trout is using a lysimeter and weather data equipment to refine scheduling irrigations for pepper and lettuce crops by relating their irrigation crop coefficients with the amount of soil covered by crop foliage.
Briefly defined, a lysimeter measures the amount of water that percolates through a certain depth of soil. As Trout put it, “it is essentially a large flower pot sitting on a scale.” Housed in an underground vault, the 7 by 7-foot bin filled with soil about 6 feet deep is set flush with the surface and planted with the same grass as the surrounding four acres of subsurface drip-irrigated turf. The scale registers the amount of moisture in the soil. Another similar device is installed in the field used for the vegetable crops.
The weight of the bin is monitored hourly as it is irrigated practically continuously to replace water lost to the atmosphere. That data is collected by a computer and compared with data from the CIMIS weather station and an evaporation pan on the turf site to confirm the evapotranspiration rate.
New watering guide
“Instead of using days after planting as a guide, we are looking at the percentage of crop cover or the shaded area to develop a relationship between it and the crop coefficient,” he explained.
“That way, no matter when you plant or at what density you plant, you should be able to have a way to schedule your irrigations.”
While substantial research of this kind has been done on irrigation of major crops such as corn, cotton, and wheat, Trout said little has been done on lettuce, peppers, onions, and other specialty vegetables.
This season he is observing peppers watered with surface drip, subsurface drip, and furrow irrigation, each at four different rates: 50 percent, 75 percent, 100 percent, and 125 percent of the needed water as indicated by the lysimeter. He monitored harvests of the peppers to find the amount of water and method of irrigation for maximum yield.
As the early data was compiled for the 2005 season, Trout said, they learned furrow irrigation was not nearly as efficient as the drip systems in getting the optimum amount of moisture to the crop.
Even when twice the amount was applied by furrow, the plants did not get as much moisture as with drip. What's more, he added, with short moisture, the amount of culls increased, plants were smaller and became sunburned, and peppers tended to turn red too early.
Previous trials have been with lettuce, both fall and spring, and the next crop will be garlic or onions.
Trout said the findings from the project will be applicable not only for vegetable crops on the Westside but also for those elsewhere in the world. “The basic equations are universal, and if we can understand enough about the solar radiation, humidity, wind, and temperature, they should apply everywhere. In fact, the basic manual for this type of research was prepared for the United Nations.”