European grapevine moth (aka European grape berry moth; (Lobesia botrana) was recently found in Napa County, a first known find for California. The insect has the potential to cause great economic harm to California’s diverse grape industries. The moth was trapped in Napa County’s, famous Oakville grape growing region known for high valued wines. Common to Europe and the Mediterranean, European grapevine moth has been intercepted from across the US where international travelers, cargo or mail disembark from planes originating from overseas. Currently, the Napa County Agriculture Commissioner is working with the CDFA and USDA to survey the area where the moth was first located in an attempt to detect additional European grapevine moths.
European grapevine moth identification
European grapevine moth can be confused with American grape berry moth (Endopiza viteana) native to the eastern United States or European grape berry moth (Eupoecilia ambiguella). Wings of the invasive European grapevine moth, L. botrana, have a mosaic shaped pattern with black-brown, cream, and gray-blue ornamentation (Fig. 1). Larvae tend to develop a purple cast after feeding and will often be found inside the berry. Samples should be taken to a trained university or state entomologist for proper identification and documentation. It is important to note that samples should be enclosed in a sealed container, jar, or vial if found prior to moving the insect (all stages) from an infested site.
Damage
Damage can be seen to both grape flowers and developing fruit. Larvae feed on flowers prior to bloom and continue through bloom. As bloom peaks, larvae protect themselves by producing webbing around the damaged flowers and feeding on neighboring flowers and parts. Second and third generation larvae feed on berries hollowing and contaminating them with excrements (Fig. 2). Cultivars that naturally have tight clusters—like Chardonnay, Pinot noir and Zinfandel—will suffer the most damage. Much like infestations from other worm pests, feeding damage will lead to infections by bunch rot fungi. Raisin and table grape cultivars will also experience damage, especially when bloom is prolonged due to weather, making flowers less responsive to applications of gibberellic acid used for bloom thinning. Table grape cultivars with tight clusters have the least tolerance for the moth due to fruit feeding damage and contamination with webbing, excrements and rot. All life stages can be found in vineyards infested with European grapevine moth but larvae from the second and third generations have been found to be the most damaging when fruit is maturing.
Host range
The host range for European grapevine moth is diverse. In addition to Vitis vinifera (cultivated grape), they also feed on other important agri
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Erineum mite populations seem to be exploding this season. In the past two weeks, a half-dozen samples have been dropped off at my office for inspection. Normally, a few samples are brought in from backyard vineyards, which I expect. However, the most recent samples and calls have been from commercial wine grape vineyards with concerns that it is downy mildew. First, let me assure you that it is not downy mildew. The Valley has not experienced an outbreak of downy mildew since the mid-90’s when a few table grape vineyards were identified with the disease after optimal weather; rain and warm temperatures. The recent erineum mite outbreaks in commercial vineyards are easily explained by a reduction in sulfur use for powdery mildew. Winegrape vineyards tend to experience more frequent outbreaks when wineries request a reduction in sulfur dust so it does not interfere with fermentation. Below is a summary of erineum mite life cycle.
Have you recently removed an old vineyard that had treated grape stakes and now have piles sitting on your property and don’t know how to get rid of them? The Natural Resources Conservation Service (NRCS) is offering financial assistance to California grape growers to help properly dispose of chemically-treated wooden stakes. Treated grape stakes are typically treated with preserving chemicals that protect the wood from insect attack and fungal decay. Chemicals added to preserve wood and known to be toxic or carcinogenic include arsenic, chromium, copper, creosote, and pentachlorophenol. Burning treated grape stakes is prohibited by law.
With the passing of bloom, table grape growers are turning their attention from managing fruit set to maximizing berry size. One practice that increases berry size is girdling, removing a thin strip of bark from around the vine trunk. The girdle disrupts the flow of carbohydrates from the vine's canopy to its roots; the young berries grow fat on the extra sugar that would otherwise have been consumed by the roots.
Special double-bladed knives are used to make the girdles. Keeping the blades sharp makes the task go much easier. Some knives also have a single blade on one end of the handle. I prefer such knives as the single blade is a handy tool for removing loose bark that interferes with girdling. However, an experienced colleague prefers to remove the loose bark by hand.
Some trunks, especially on old vines, develop grooves and folds from which it is hard to remove the bark strip with a double-bladed knife.
If the bark is not removed from these places, the effectiveness of the girdle is diminished.
Within five or ten minutes, any remaining phloem (sugar-transporting tissue of the bark) will become brown colored. If any such tissue is seen, it should be scraped away. However, the girdles should not cut any deeper into the trunk than is necessary to remove the phloem, as deep cuts into the wood can disrupt water supply to the shoots, which may injure or even kill the vine. Proper girdles, applied at the right time, can increase berry size by 10% to 30%.
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