New aphid controls effective, costly Materials active against the lettuce aphid, including insect growth regulators, show efficacy in trials in the Salinas Valley by University of California researchers.
Bill Chaney, Monterey County farm advisor, said pressure from the insect, Nasonovia ribis-nigri, this year was spotty: relatively light early in the season and then heavy toward the end.
Reporting on his projects at the recent meeting of the California Lettuce Research Board at Seaside, he said the battery of 10 products used in his trials includes both new and old.
"To look at the list of materials, you might think we are in pretty good shape," he said, "but several of the materials are not currently registered."
Likely more expensive Chaney also warned that although products from "new chemistry" may perform on a par with older materials, the new ones likely will be more expensive.
Among organophosphates are the standbys MSR and Orthene; carbamates include Aphistar and Pirimor, neither registered in California; and the trials also looked at a group of products having unconventional modes of action.
A new naturalyte compound, Dow's Success, has some activity on worms, thrips, and leafminers.
Neem-oil compounds have various modes of action, most commonly as insect growth regulators (IGRs), but also as repellants or suffocants. Chaney worked with neem-based Neemix, AZA-Direct (formerly GWN 1535), Ecozin, and Agrineem.
He said the label rates for the neem compounds have a wide range, from 2 to 22 ounces per acre. "So if you wonder why we see differences between these products that have similar chemistries, it may be because of the amount of actual ingredient we are putting out."
He said the neem products mostly tend to slow down population growth. "You have to keep that in mind if you are considering them in a program. They do not kill and clean up big populations."
Success, which showed effect on leafminer trials, showed relatively poor performance in lettuce aphid trials. However, Chaney said, further investigation showed wet sprays of Success, although not its dried residue, knock out larvae of the syrphid fly, a predator of the lettuce aphid.
This underscores, he added, the value of conserving syrphid fly populations in the field. "If natural enemies are in the field at the time you apply some of these materials, they will knock out the beneficials. But once the spray residue has dried, you'll probably see reinfestation by the natural enemies if conditions are right."
Chaney said he hopes to find ways to observe the effects of the compounds on syrphid fly adults, which cannot be reared in sufficient numbers for release in the field and are difficult to collect for testing. He does plan bioassays with lacewing larvae, which are available and being used by several growers.
A parasite of the lettuce aphid has been found but not yet classified. "We do not have a species for it, but we do think we know which genus it belongs to, but parasites don't play a role in lettuce aphid management," Chaney said.
Must be careful "We really have to be careful to take advantage of syrphid fly larvae and some of the native lacewing larvae in deciding which insecticides to use."
Among the neonicotinoid class of insecticides, the imidicloprid products, soil-active Admire and foliar Provado, both registered, may be followed by the newer Platnum/Actara, Assail, and Calypso.
The class is mostly active on sucking insects, most compounds have lower LD-50 ratings than other products, and most are water soluble. Actara and Assail have twice the active ingredient, and twice the residual control, of Provado. All have good activity, although only for the short term, Chaney noted.
In the pyridine class, Novartis' Fullfil could be registered soon, he said. It paralyzes the sucking apparatus of aphids, causing them to starve.
Chaney cautioned that none of the new compounds coming along, except for the unregistered Aphistar, has the effectiveness growers have come to expect from MSR.
However, he added, the availability of MSR for head lettuce makes obtaining Section 18s for new materials for it more difficult. It is easier to make a case for registration of new materials for leaf lettuce, which has no alternatives.
Turning to another of his board-funded projects, management of leafminers, Chaney said pressure during the fall was higher than most people anticipated, and that likely can be attributed to weather patterns. "It was not as high as about three or four years ago but more than the last couple of seasons."
Chaney said the Central Coast Vegetable IPM Project, a limited-term effort financed by a Pew Charitable Trusts grant, is winding down and valuable data has been collected and published in newsletters.
Its original target was better management of the pea leafminer on lettuce and celery, but direction was later shifted to add lettuce aphids and other pests of head and leaf lettuce and celery.
The purpose of the CCVIPMP was to develop IPM practices without economic loss of crop quality and quantity. Project director Lynn Wunderlich has accepted a position as a farm advisor in El Dorado County.