Last season saw the introduction of two new aphid species to the Salinas Valley. After some early confusion, it was determined that there were two new aphids being found in lettuce, celery, and radicchio. Of these, the more important appears to be the lettuce aphid, Nasonovia ribis-nigri. The other species, Aulacorthum solani, is commonly called the foxglove aphid. Although both species appear very similar to each other and both may infest inner portions of lettuce, they are different species.
The lettuce aphid appears as though it will be the more important of the two. In Europe, Canada, and South America, where this pest has been established for some time, it is considered to be one of the most important pests, if not THE most important pest of lettuce. It had never been found in California until last year. The foxglove aphid can also be damaging, and in each of these other areas that deal with lettuce aphid, the foxglove aphid can also be found. One very important difference is that the foxglove aphid is a vector of lettuce mosaic virus, while transmission of LMV by the lettuce aphid has not been proven.
Unlike the lettuce aphid, some records do indicate that Aulacorthum solani has been collected from the Salinas Valley years ago. However, most entomologists agree that Aulacorthum solani may actually be used to refer to more than one species, and clearly there are different races or biotypes of this species. I believe that the foxglove aphid we saw last year was indeed a new biotype (or perhaps species) and not the same one that had been collected years ago that never became a problem. Of the two, only the foxglove aphid has been found to infest celery.
Both of these aphids have very short life cycles, and populations can build quite rapidly. The lettuce aphid has an interesting life cycle in Europe and Canada. In these cold climates, it migrates to the black currants and some other members of the genus Ribes, which are its primary hosts. There it overwinters on the roots after passing through a sexual generation. There are reports from more mild areas of South America that this aphid overwinters on secondary hosts without going through this sexual stage. This winter we were unable to find this aphid on the roots of any of the wild gooseberries (Ribes spp.) growing in the foothills of the Salinas Valley.
The lettuce aphid has several different color forms, ranging from green to orange to deep pink. It also produces a high percentage of winged adults in comparison to most aphid species. Although it can be difficult to distinguish from the foxglove aphid, they can be separated from green peach or potato aphids easily using a hand lens.The key distinguishing characteristic, however, is where it attacks the plants. In all of the crops it attacks, it moves to the youngest tissues near the center of the plant. This is a characteristic common to both the lettuce and foxglove aphids.
Any questions to whether these new aphids would survive the winter in the Salinas Valley have been answered. Several fields have already been found that have lettuce and/or foxglove aphid infestations in 1999. Some of these fields are pretty heavily infested considering the early stage of both the crop and the season. Control tactics are still being investigated for both conventional and organic growers.
To date these aphids have not been found in the Santa Maria or Lompoc Valleys. Anyone finding aphid infestations that do not conform to typical green peach or potato aphid activity should submit specimens to the Agriculture Commissioner or the Cooperative Extension office for specific identification. We need to know when and where these aphids are found, so that control strategies can be immediately implemented.
Colored photos of the lettuce aphid have been published in the Jan.-Feb. issue of California Agriculture. Persons wanting a copy of these photos should contact the Santa Maria Cooperative Extension office (805/934-6240).
Two reports have recently appeared in the print and broadcast media, which again attempt to scare the reader/listener into thinking their food supply is unsafe due to plant health product residues. One report was issued by Consumer Report, and the other appeared in the San Francisco Chronicle in the Opinion Section. The latter piece was published on the 10th anniversary of the Alar on apples scare. The Consumer Report piece had to do with residues on fruits and vegetables particularly as they relate to children.
Both of these press releases have been reviewed by Carl Winter, Ph.D., Toxicologist and Director of the Food Safe Program, Department of Food Science and Technology, University of California, Davis. He discusses the manipulation, misuse, and misinterpretation of data for the purpose of producing "scary" headlines. These are the standard tactics used by the folks who want to ban plant health product use.
If you would like copies of Carl's two reviews, contact me at 805/934-6240 with your request.
P.S. Eat Apples - Give up Junk Food and Junk Science!
Tolerances have been established for the herbicide sethoxydim (Poast) on the leafy vegetable crop group and the tuberous and corm vegetable subgroup. The establishment of the group and subgroup tolerances will extend tolerances to include all the commodities in that group.
The label for use has not yet been issued, but will probably be forthcoming. Look for it in the future. The tolerances established will extend to the following commodities:
| Leafy Vegetable Group |
| Amaranth (leafy amaranth, Chinese spinach, tompale) |
| Arugula (Roquette) |
| Cardoon |
| Celery (previously registered) |
| Chinese celery |
| Celtuce |
| Chervil |
| Chrysanthemum, edible-leaved |
| Chrysanthemum, garland |
| Cilantro |
| Corn salad |
| Cress, garden and upland |
| Dandelion |
| Dock (sorrel) |
| Endive (Escarole), previously registered |
| Fennel, Florence (firenchio) |
| Lettuce, head and leaf (previously registered) |
| Orach |
| Parsley |
| Purslane, garden and winter |
| Radicchio (red chicory) |
| Rhubarb (previously registered) |
| Spinach (previously registered) |
| Spinach, New Zealand |
| Spinach, vine |
| Swiss chard |
| Tuberous and Corm Vegetable Subgroup |
| Anecacha |
| Arrowroot |
| Artichoke, Chinese |
| Artichoke, Jerusalem |
| Beet, garden |
| Canna, edible |
| Cassava, bitter and sweet |
| Chayote (root) |
| Chufa |
| Dasheen |
| Ginger |
| Leren |
| Potato (previously registered) |
| Potato, sweet (previously registered) |
| Tanier |
| Turmeric |
| Yam bean |
| Yam, true |
Call your PCA or BASF representative for details about the use of this product in your operation.
A new pest poses a serious new threat to California's grape industry and efforts to reduce pesticide use. The vine mealybug was found this past summer in the San Joaquin Valley.
"If the vine mealybug spreads in California, it will be a very serious problem," says Walter Bentley, UC integrated pest management entomologist. "And everybody expects it to spread."
As the vine mealybug feeds on vines and grape stems, it produces tremendous amounts of sticky honeydew, promoting sooty mold and rendering the grapes inedible. It also transmits grape viruses. To date, scientists in the United States and other parts of the world have not been successful controlling the pest with its natural enemies.
The vine mealybug was first found in the United States 4 years ago in the Coachella Valley. It was identified in a tablegrape vineyard south of Arvin in June 1998. Since then small populations have been detected at two other nearby vineyards. A native of the Black Sea area and an established pest of grapes, date palms and figs in South Africa, Egypt, India, and Israel, the vine mealybug is a separate, and much more damaging, species than the grape mealybug already found in the San Joaquin Valley.
Since the pest prefers warmer, non-freezing areas, Bentley said the renowned wine producing vineyards of Napa, Mendocino and Sonoma counties, plus those in the mild Central Coast counties of San Luis Obispo, Santa Barbara, and Monterey are threatened by the possible spread of vine mealybug.
New or unusual mealybug activity in vineyards should be given immediate attention. Strange mealybug activity should be reported, so that area grape growers can be alerted and control strategies implemented.
Information adapted from Cal. Ag. J., Jan.-Feb. 1999 issue.