Over-top application tolerance sought for herbicide: Broccoli trials send Goal 4F to IR-4

After field trials in the Salinas Valley, a request has been made for further testing by the IR-4 program for a tolerance for “over the top” application of Goal 4F herbicide on broccoli.

The trials were done this spring and summer on lettuce, broccoli, and spinach near Chualar and Castroville by Steve Fennimore, University of California Cooperative Extension weed specialist, and Richard Smith, Monterey County farm advisor.

Lettuce and spinach were very sensitive to the treatments, but “broccoli came up a winner,” particularly with respect to control of malva and purselane, in the trials, Fennimore said.

Dacthal, which returned to the market in 2000 after a four-year absence, and topically applied AN-20 fertilizer, in use since the early 1980s, are foundations for weed control on broccoli in the valley. However, AN-20 cannot be applied during the winter due to the thin, sensitive cuticle of the crop at that time.

Dow AgroSciences' Goal 4F is a new, flowable, micro-encapsulated formulation that might have a place in post-emergence control where pre-emergence treatments are less than satisfactory. The company suggested to Fennimore that the trials be done.

Vegetable growers are handicapped without the variety of herbicides available for other crops, so anything new has significant interest, Fennimore said.

“The stream of new conventional herbicides now is really slow, and one theory is because Roundup Ready soybeans have taken $100 million to $200 million out of the value of the herbicide market. So the incentive for chemical manufacturers to screen for herbicides is pretty low.”

Goal 4F, he added, is shielded for a time before the tiny coatings degrade, and this allows it to be watered without immediate loss of effectiveness.

Fennimore and Smith say Goal 4F sprayed at a 0.063-pound rate on broccoli at the two- to three-leaf stage performed best in their evaluations. They observed it in the main broccoli-growing season in the spring and summer months but say its performance during the winter remains to be seen in additional trials.

Fennimore applied for the IR-4 testing in July. The IR-4 program at UC, Davis is a federal-state-industry agency that does extensive residue testing to determine tolerances required for registration of chemical and biological control agents on so-called “minor crops.” It is especially important for California vegetables and other specialty crops whose relatively small acreage discourages manufacturers from performing the tests.

Factors in favor

Smith expects it could take from two to four years before a tolerance for the over-the-top use could be cleared. “But the proposal has several things in its favor. The manufacturer is behind it, the use and the safety are evident, the need is there, and there's already a pretransplant tolerance for Goal on broccoli.”

Once a tolerance for a product is granted by the IR-4 authorities, it still has to pass evaluations by EPA and the California Department of Pesticide Regulation before it can be marketed.

Hopefully, Smith said, tolerances for Goal 4F on other vegetables such as cabbage and green onions might be developed in the future.

Although their tests focused on weed control efficacy, they say the Goal 4F product, with its tiny encapsulation, is likely to be safer for surrounding crops because it is more readily trapped in the soil and its breakdown is delayed.

Smith explained that the phenomenon of “lift off,” distinct from drift, is always an issue with herbicides. It occurs when materials volatilize into the air and then, even in the absence of wind, fall to the ground in erratic patterns. “This is very important in the Salinas Valley where there is so much sensitive lettuce.”

Lettuce deformities

In a separate project, Smith continues to search for the cause of deformed, unmarketable heads of romaine lettuce. Several reports of the problem came from PCAs in the summer of 2001.

The symptoms, he said, were two or more young leaves “glued together” near their margins. “Subsequently, as these leaves expanded, they were not able to unfold normally, which restricted the head from expanding normally and caused the twisting and deformity.”

After eliminating any connection with known lettuce viruses, Smith reasoned that the cause appeared related to cultural practices or was chemically induced.

He found reference to 1959 University of California research on a similar problem, known as spiral heads, in head lettuce. Due to a uniting of leaves, heads deformed into a spiral shape during summer months. Researchers duplicated the symptoms by binding heads with rubber bands or staples and concluded that too close spacing of plants was the cause of the problem.

Smith tried all sorts of chemicals, herbicides, insecticides, fungicides and even micronutrients, in his trials. He found the chemical treatments caused other symptoms, but neither the chemicals nor binding the heads with rubber bands produced the conical shape.

Planting depth

He did, however, observe deformity, but without the glued leaves, in the summer of 2002 in transplants set an inch to one-and-a-half inches deep.

“It appears that during the summer months, deep planting alone can cause deformed and unmarketable heads. The exact cause of the glued and twisted leaves seen in 2001 remains the subject of continuing evaluations,” Smith said.

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