Cabbage aphid protections coming

Although they must still cope with few controls for occasional outbreaks of several pests, cole crop growers may be in line for some new materials to deal with cabbage aphid in the near future.

Bill Chaney, Monterey County farm advisor, said cabbage aphid, largely because of a protective waxy compound on its body, escapes many predators that feed on other aphid species.

Parasites, on the other hand, are not deterred by the wax and lay eggs in the cabbage aphid. This results in mummies no less objectionable on fresh produce than live aphids.

Chaney, who has researched several compounds for aphid pests, said one group, neonicotinoids, is promising.

Among new-generation neonicotinoids, Bayer's imidacloprid twins, Admire (soil applied) and Provado (foliar applied), were the first to be labeled. Similar products, active against sucking insects, will be coming to the marketplace within the next several years, Chaney predicted.

These products typically have low water-solubility, and once the materials are in place they tend to remain. While advantageous in avoiding groundwater contamination, they require on-target placement.

“An interesting feature of labels for these materials will be the wide range in amounts of active ingredient, from only 19 grams per acre to twice that amount in some newer materials,” said Chaney, reminding that they can be expected to perform differently at different rates.

Broad spectrum

Neem products, based on neem oil or other botanical extracts, tend to be broad spectrum on insects and safe for humans and other mammals. Depending on their active ingredients, they may be active as insect growth regulators, repellents, or suffocants. Although not potent, “clean-up” materials, they will provide some suppression of aphids.

Hopefully, he said, in the meantime growers will be able to retain use of the organophosphates MSR and Orthene, long the backbone of aphid control.

The carbamate Aphistar has been in trials for a decade but has not been registered in California.

He said several years ago he encountered cauliflower root infestation by turnip aphid, normally a foliar pest. In trials he applied Aphistar to the foliage and destroyed the root feeders. He learned that when applied to the soil, it also will control foliar aphids.

Pirimor, another carbamate, also has no clearance for California but is a standard for aphid control elsewhere. Although effort is being made to secure a registration for it, progress has been slow.

The naturalyte class is active on worms and leafminers and one example is Dow's Success, a relatively safe material that is registered in California. It has been successful on diamondback moth.

“It was promoted early for being a very selective material, but the data coming out lately shows it may not be as selective as we earlier thought,’ Chaney said.

Its effect on beneficials may be offset by performance against multiple pests, such as worms, thrips, and leafminers.

“An interesting feature of labels for these materials will be the wide range in amounts of active ingredient.”

Chaney observed Success on lettuce aphid and peach aphid in trials last season and detected flaring of aphid populations after Success was applied.

He attributed that to the material's significant impact on syrphid fly populations that were controlling a portion of the aphids. The impact was greater when syrphid fly larvae contacted wet spray but less when they contacted dried residue.

In a brief account of other cole crop insect pests, Chaney said root maggots, mainly cabbage maggots, are one of the chief potential problems for both transplanted and direct seeded fields. They occur mostly underground but will occasionally appear on the soil surface on non-cole crops.

“It is worst when a population is established before a cole crop is planted, but it can also be a problem in a clean field because the adult flies are very mobile. Eggs laid on the soil hatch, and the larvae go to the roots,” he said.

Few alternatives

Chaney said if organophosphates are removed from the market after Food Quality Protection Act review, cole crop growers will have no chemical alternatives for control of root maggots.

“This is a example of a pest that we really have to make a case for in an FQPA scenario because we also have very few biological and cultural alternatives.”

Bulb mites build up on broccoli crop residue and create problems for a following crop of lettuce. The tiny mites devour seed, causing loss of stand.

Lygus, some on transplants before they leave the greenhouse, feed on broccoli plants, injecting a toxin that destroys growing points, resulting in blank plants. Insecticides can be effective controls, but timing to avoid lygus migrations from drying hillsides are critical to prevent frequent treatments.

Leafminers, customarily of minor concern to cole crops, occasionally will go to cauliflower transplants in the greenhouse and lay eggs in cotyledons. Larvae destroy cotyledons and move into the stems of plants. Damage may not be obvious until transplants are put into the field and stressed. Infested plants can collapse.

The miners also feed on the leaves of older plants. Although they may not be a problem on an existing crop, when it is harvested they can cause problems for surrounding or subsequent lettuce or spinach crops.

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