Four new herbicides for use in celery, two now on the horizon and two others still several years distant, are moving toward registration in California.

Steve Fennimore, University of California, Davis Extension vegetable specialist at Salinas, reported on his evaluations of the materials during a recent meeting of celery growers there.

Application for a Section 24c special local needs registration for Dual Magnum has been submitted to the California Department of Pesticide Regulation. The Syngenta product is effective on numerous weeds in celery and has a federal tolerance.

Goal 4F, a new, microencapsulated formulation of the Dow AgroSciences compound used on various crops for several years, has a federal label for celery and is expected to gain California registration for that crop later this year.

Meanwhile, Valent's Chateau and Bayer Crop Science's Define have far to go. They have been submitted to the IR-4 Program at Davis for residue tolerance field trials, which will require four to five years to complete.

“Although celery growers now have choices in herbicides, in our search for new materials,” Fennimore said, “the main need is for control of yellow nutsedge.”

The standby herbicide, Caporal, applied to nearly three of every four acres of celery in California, is quite safe for the crop but also has little effect on yellow nutsedge.

Lorox and Treflan are also widely used in celery for several weeds, but their control of persistent, pea-sized yellow nutsedge tubers is also limited, particularly during cool, fall weather.

Could lose product

What's more, he continued, “Just because you have a good material like Caporal today, there's no reason to assume you will have it tomorrow.”

Given the protracted process for registration of new herbicides, growers need to consider a long-term timeline for even the most promising herbicides.

Goal 4F and Chateau are among the new class of protox inhibitors that act against chlorophyll synthesis in weeds, breaking down lipids and creating the same effect as freezing temperatures.

“The good thing about this class of herbicides,” Fennimore said, “is no weed resistance to it has been found anywhere in the world. That's contrary to the resistance found in almost every other classical herbicide chemistry, including that of Lorox and Caparol.”

In trials on celery transplants at Oxnard and Salinas during the past three years, Fennimore compared several new herbicides with Caporal and Lorox, both known for their effectiveness on purslane and hairy nightshade. The new compounds also were screened for their control of yellow nutsedge.

Dual Magnum, an intensified version of the well-established Dual product, is active in the soil, inhibiting growth of roots and shoots of grasses and sedges. In Fennimore's trials it showed broad-spectrum activity, including good control of purslane and fair control of hairy nightshade, although higher rates may be needed for heavy nutsedge.

Plusses, minuses

Define showed fair control of nutsedge and purslane but had little effect on hairy nightshade.

Goal 4F performed well against purslane, but hairy nightshade and nutsedge escaped it.

Chateau gave good control on purslane and hairy nightshade but “basically doesn't do anything to nutsedge,” he said.

The new materials generally did little harm to the celery crop in trials with populations ranging from 32,000 to 45,000 plants per acre. Weights of marketable stalks indicated the products had no significant effect on yields. In another presentation during the celery gathering, Bill Chaney, entomology farm advisor for Monterey County, said among several aphid pests, the foxglove aphid has been the most harmful to celery recently.

“According to the literature, foxglove aphid has been in the Salinas Valley for a long time, but I suspect when the lettuce aphid was introduced several years ago we also got foxglove aphid. In Europe, where we think the lettuce aphid came from, both species are always found together.”

Several products can control foxglove aphid, distinguished by its green color when in celery. The neonicotinoid group of compounds he tested, Chaney said, worked well until they started to break down 10 to 14 days after application.

Leafminers

Leafminers have returned to Salinas Valley celery fields after an absence of several seasons and continue to be of more concern in celery than in other crops. He said the standard compounds, Trigard and Agri-Mek, give good control of leafminers on celery.

Several plant bug species attack celery, but usually most losses come from lygus that accumulate on native hillside vegetation. As the hillside cover dries, they invade celery and other crops.

Another plant bug, Calocoris, inflicts similar feeding-site damage. When immature forms of it or lygus infest celery, they cause twisting of plant hearts.

Chaney said although other compounds have residual effects on lygus and other plant bugs, neonicotinoids knock down the pests when applied but then lose potency once sprays have dried.

Recalling the increased damage to celery by western flower thrips in 2003, he said, ”We had numbers like we have not seen in a very long time. They are both a source of direct damage to the crop and a contaminant.”

Taiwan and other Pacific Rim destinations for California celery exports have zero tolerance for the tiny insects that leave scars on stalks.

Another vegetable pest in higher numbers last year was root maggot, which normally remains beneath the soil surface. Last year it damaged some celery fields above ground.

Extended periods of cool, wet conditions during the winter, Chaney explained, caused adult females to lay eggs at the base of plants rather than underground. Larvae then remained on the plant to feed.

Three species in the maggot group, cabbage, seed corn, and onion, occurred in various combinations to damage celery mostly in the Santa Maria and Oxnard areas.

Chaney said since the egg laying coincided with the celery-free period in the Salinas Valley, root maggot damage on celery there was less.