Published on
Viticulture News, Week of 19 May 2025
Columbia, MO
Contents:
- When vines experience sudden death
- Cumulative Growing Degree Days for the Seven Grape Growing Regions of Missouri from April 1 to May 12, 2025
When vines experience sudden death
In the middle of summer and often when drought conditions prevail some grapevines experience a rapid wilt. The impacted vine(s) appeared healthy a day or week ago and now the leaves are turning pale grey-green, and the clusters are wilting. The term to describe this condition is apoplexy (sudden loss) and is often associated with grapevine trunk diseases (GTD). The common GTD often associated with apoplexy is esca. Esca is complex disease that can be caused by three fungal species including Phaeomoniella chlamydospora, Phaeoacremonium minimum. and Fomitiporia mediterranea. Besides GTD other grapevine disorders can also result in death of grapevines although the onset seldom appears so sudden.
In Missouri, death of grapevines can also result from Crown gall Agrobacterium vitis, Grapevine vein clearing virus, winter cold-damage, and grape scale Diaspidiotus uvae. All these biotic and abiotic disorders have key diagnostic clues. Determining the causal agent(s) is the first step in any IPM program prior to applying management strategies.
At this time of year, I will focus on grape scale Diaspidiotus uvae Comst.
The grape scale is not new to Missouri. The earliest record of grape scale is from St. Louis, MO in 1875 (Zimmer 1912). A few years later, 1888, grape canes from Kirkwood, MO were reported to be infested with grape scale. Since these early reports the grape scale has been reported on several plant species, but most notable are species within Vitaceae and include Ampelopsis sp. cultivated grape, European grape (Vitis vinifera) and wild grapes (Vitis spp.) as reported by (Zimmer1912).
There is limited research on the incidence of grape scale within vineyards of most states. However, grape scale has been reported in many states. The lack of grower reports is likely the result of the grape scale spending much of its lifecycle hidden from plain view.
The grape scale like mealybugs are seldom seen in the vineyard without a bit of detective work. Grape scale is very well adapted to concealment by remaining hidden under the grapevine bark. To determine if grape scale is present in your vineyard start peeling back bark starting near the grapevine crown. The young scales often settle in longitudinal rows (Figure 1). These scales can be male or female. The females are wingless whereas the males have wings (Figure 2). The females have piercing sucking mouthparts and feed on the grapevine sap within the phloem. The male is winged and looks very different compared to the female-this is called sexual dimorphism. The males are short lived and do not feed on the grapevine. The female scales produce 30 to 50 crawlers by live birth (viviparous). This alone suggests that grape scale populations can increase very rapidly.
The economic damage to grapevines can be dramatic and result in grapevine death. Whitehead (1963) reported that many Arkansas vineyards were abandoned after 1950 because of widespread grapevine death resulting from grape scale. Historical reports suggest that liquid lime sulfur was effective in managing grape scale (Zimmer 1912). In most instances these liquid lime sulfur applications were applied to dormant vines to avoid phytotoxicity during the growing season. With the advent of chlorpyrifos (Lorsban Advanced), grape growers had a new tool to manage grape scale. However, Lorsban Advanced and generics containing the active ingredient chlorpyrifos can no longer be used in food crops.
To manage the grape scale there are various management strategies. First be aware that scale insects have a large contingent of other insects that attack and kill them. It is important to preserve these natural enemies by selecting pesticides that are not broad spectrum. Superior oil can be applied prior to bud break to the trunks and cordons. The application of Superior oil needs to saturate the trunks and cordons. Superior oil is efficacious by reducing oxygen uptake and disrupting the cellular membranes of the scales. Superior oil preserves the natural enemies.
The next strategy for controlling the grape scale is to apply an insecticide when the first instar or crawler stage is present. The first-generation crawler or spring generation begins to emerge at 274 degree days (DD) (base 50 F) with peak crawler emergence at 356 DD (base 50 F) with DD being accumulated from April 1. The second-generation crawler or summer generation begins to emerge at 1,166 DD (base 50 F) with peak crawler emergence at 1541 DD (base 50 F) with DD being accumulated from April 1 Johnson et al. 1999). Besides monitoring degree days, apply double sided tape around trunks of grapevines that have grape scale to monitor for crawlers. Insecticide application timing that targets the crawler stage of the grape scale is critical.
The following insecticides, Applaud 70DF, Carbaryl 4L, Movento, Admire Pro, and Assail 30 SG should control grape scale crawlers but the label does not specifically list grape scale. Additionally, the pyrethroids (Baythroid, Mustang Max, Danitol and others) should control grape scale crawlers. Knack (Pyriproxyfen) is an insect growth regulator that suppresses embryogenesis of insect eggs and has no activity on adult insects. The Knack label states applications should be made when scale crawlers first emerge.
In summary, managing grape scale requires the following:
- First, determine if the grapevines are infected with grape scale by removing bark and determining the presence or absence. Early infestations are often sporadic and infected grapevines will be scattered throughout the vineyard. Advanced infestations often results in most grapevines being infected
- Second, monitor vines for grape crawler emergence
- First generation emergence 274 DD (base 50)
- Second generation emergence 1,166 DD (base 50)
- Apply insecticide for grape scale crawlers
- Prior to bud break apply Superior oil
References cited
Johnson, D.T., B.A. Lewis and J.D. Whitehead. 1999. Grape scale (homoptera: Diaspididae) biology and management on grapes. J. Entomol. Sci. 34:161-170.
Whitehead, J. D. 1963. The biology and control of the grape scale, Aspidiotus uvae (Comstock) in northwestern Arkansas. M.S. Thesis, Univ Arkansas, Fayetteville.
Zimmer, J.F. 1912. Papers on deciduous fruit insects and insecticides: The grape scale. USDA Bureau of Entomol. Bull. 97, Part VII.
Cumulative Growing Degree Days for the Seven Grape Growing Regions of Missouri from April 1 to May 12, 2025.
1Growing degree days at base 50 from April 1 to May 12, 2025. Data compiled from U2U Decision Support Tools – Corn GDD
To determine the number of growing degree days accumulated in your area since April 1. Use this tool.
Please scout your vineyards on a regularly scheduled basis in an effort to manage problem pests. This report contains information on scouting reports from specific locations and may not reflect pest problems in your vineyard. If you would like more information on IPM in grapes, please contact Dean Volenberg at 573-473-0374 or volenbergd@missouri.edu