I received last week some pictures of these very interesting larvae within their casing made of grass blades and twigs (Figs. 1 and 2). The casings are about 6-12mm long with some pieces of grass being longer than the actual casing. These larvae are of the common bagworm moth (Psyche casta) which is a nocturnal moth species of which the female is a grub-like wingless moth (Fig. 3). They were introduced from Europe in the 1930s. The larvae feed on birch, willow, poplar, Vaccinium, grasses, lichens, and decaying vegetable matter. They look for places to pupate in May and June and may attach themselves to tree trunk, foliage, wooden fences and are quite hard to dislodge. They are not considered a pest in grape and have only been reported occasionally around this time of year.
Some reports came in as well of grape plume moth larvae (Fig. 4) being found on grapes. It is indeed the time of the year to see these feeding and webbing grape leaves. These are usually of no significant concern and rarely if ever reach economic threshold levels. Vines with up to 20% of shoots infested with grape plume moths did not show any reduction on yield. The best option in cases of light infestations would be to hand pick the caterpillars and place them in soapy water. If you find a severe outbreak, Danitol for conventional and Pyganic for organic production systems should help control this pest. For more info on this insect, see this previous article.
Finally, grape phylloxera continue to develop at the West Madison Agricultural Research Station (WMARS), causing more galls on grape leaves (Fig. 5). If you experience or have a history of heavy gall infestations, it is recommended to target the first generation in early summer as the crawlers may cause 40-50 galls per leaf. The timing can be determined by using a Degree Day (DD) model which uses a biofix date of the time at which the first leaves unfurl and a base temperature of 43ºF. From there, calculate DD each day by taking the average daily temperature and subtract 43ºF, this will give you a DD for each day from the biofix and you can accumulate these DD values each day. Minnesota extension recommends to start scouting once you reach 450DD and that the 2nd generation crawler emergence will occur at 500-800DD. Chemical control for conventional production include Danitol, Movento, Platinum, Assail or Scorpion. Movento works as a systemic insecticide that will be translocated throughout the plant and reach the insects within the galls and will have long lasting activity on gall forming insects, including grape tumid gall maker. More information on Movento can be found here. In organic production, Azera (azadirachtin) and Pyganic may provide adequate control of grape phylloxera.
And to end on a more uplifting note, Andi Nelson took a nice picture of a lady beetle on the grapes at WMARS (Fig. 6), likely to be a spotted pink lady beetle (Coleomegilla maculata), native to North America. As we all know, lady beetles are beneficial insects that feed on soft-bodied pest insects, such as aphids, and should be fostered in our agroecosystems and biocontrol agents.
Thank you to Andi Nelson for scouting the vineyards.
Happy growing season!This article was posted in Grapes, Insects and tagged bagworm, bagworm moth, Christelle Guédot, grape phylloxera, grape phylloxera galls, grape plume moth, Grapes, insects, lady beetle.