Herbicide alternatives better for grapes than other crops Surflan is in short supply this season, but California grape growers can handle weed problems with a combination of alternatives until the long-used, soil-residual herbicide is back in production, hopefully by the fall of 2001.
In discussing available stand-ins at a gathering of growers in Madera, Kurt Hembree, Fresno County farm advisor, reminded that any weed control program depends on proper identification of weeds present to match them with effective herbicides.
Fortunately, alternatives among registered herbicides are more numerous for grapes than other tree and vine crops, Hembree said. Registered for bearing and non-bearing grapes and other tree and vine crops, Dow AgroScience's Surflan acts by causing root tip swelling and preventing microtubule formation in weeds.
The least volatile of the dinitroanaline class of herbicides, it is translocated through the plant after being absorbed by roots or shoots. It can remain on the soil surface for about three weeks before it must be incorporated by rainfall or sprinkler irrigation.
Alternatives likely will not work in all the same situations where Surflan was successful. However, by considering materials on the basis of their efficacy against the target weeds, and the irrigation system and soil type of the vineyard, substitutes can be found.
See and record Hembree recommends monitoring weeds, just like insect pests, at several locations in a vineyard at least twice a year. "Don't try to do it from the window of your pickup. Get out and see what's going on and start a record of what you see."
Chose from the alternatives to cover your spectrum of weeds and not your neighbor's. Keep an eye out for species that might be escaping treatments and check for things such as timing of applications, rates, or sprayer problems. Map the problem areas.
"Adjust your program on a yearly basis, and change the rates upward, or downward, depending on what you see, and maintain good records on what you do."
If a grower can't identify a weed in any of several references available, he can seal it in a plastic bag and get it to an Extension office for identification.
When it comes to selecting alternatives, Hembree said growers need to know if the material is registered for grapes and whether the weeds they have are susceptible to it?
Also important is knowing the way the material works, both in the soil and inside a weed. Growers can't necessarily expect the same results when they use alternatives in the same fashion as Surflan.
The type of irrigation system in the vineyard has much to do with performance of soil residual herbicides. Surflan isn't apt to leach rapidly and does not rapidly volatilize. It is incorporated by rainfall or sprinkler irrigation.
On the other hand, Karmex tends to leach down quickly under drip irrigation and tends to work best under flood or basis irrigation where moisture carries it to the top two inches of soil.
No less important is the timing involved in incorporation of the herbicide. Surflan needs to be incorporated within a three-week period, yet Devrinol must be incorporated within four days following application.
Sorption and solubility are only two of several herbicide physical properties, Hembree said. He has prepared a sheet that groups herbicide physical properties for growers. Gallery T&V, even though it is non-volatile, its low sorption and relatively high solubility make it prone to leaching in sandy soils.
Knowing the vineyard's soil texture is essential, since many alternative materials have distinct leaching properties. Most soil residual herbicides can be used on heavy, fine textured soils, and Surflan can be used on all textures. On light, coarse soils, Princep should not be used, and Solicam, Karmex, and Kerb, along with Gallery T&V, should be used with caution.
For postemergence control of a couple of major problem weeds, Hembree said hairy fleabane is tough to control once it has 18 to 20 leaves Roundup at the 1/2-quart rate will control it at the 3- to 8-leaf stage, but the 1-quart rate is needed at the 19-leaf stage.
For yellow nutsedge, the best timing is before the 5-leaf stage with treatments at 20 to 28 days during March through September.
Hembree also listed tillage and rainfall management guidelines to prevent movement of herbicides downward through the soil profile and in runoff water, including:
- Try to treat dry soil prior to mild rain.
- Plant cover crops and incorporate plant residues where possible.
- Use conventional tillage to disrupt soil macropores, so less water is moved downward.
- Maintain good soil organic matter to help increase sorption and herbicide degradation.
In other sound management practices for pesticides, Hembree suggested implementing IPM strategies to minimize the amount of herbicides used. These include tillage or mechanical control, monitoring and mapping of problem areas, use of the least toxic and least mobile herbicides, reduction of spray pattern, and crop rotation.
Dow AgroSciences spokesmen say the Surflan shortage came about as a result of an explosion late last summer in Michigan at a nearby plant of a contract manufacturer of the herbicide's active ingredient. The blast damaged the wastewater treatment portion of the Dow plant.
Although the production process itself was not damaged, Dow officials decided not to operate the plant until the wastewater treatment component was repaired.
Dow AgroSciences marketing manager in Indianapolis, Jim Parker, said production of Surflan is scheduled to resume in the fall of 2001, although whether growers will have all they might want remains to be seen.