What is this? A review on galled flower clusters in your vineyard
By Michela Centinari
Denise Gardner, Penn State’s Enology Extension Associate, visited the Southwest region of Pennsylvania on June third. Several growers showed her some strange looking clusters (Figure 1), asking for guidance on what pest can cause the damage and how it should be managed. Additionally, I had received inquiries from growers in the southeast corner of Pennsylvania earlier this year concerning these oddly deformed clusters. In the below blog post, you can find some information on the insect responsible for these galls, what damage it causes to grapevines and how to manage it in the vineyard.
What is it? What it does to your grapevine?
Galls of various shapes can occur on leaves, tendrils, and flowers of grapevine (Figures 1; 2; 3). These galls are caused by the larvae of a small fly known as grape tumid gallmaker (Janetiella brevicauda Felt) . Grape tumid gallmaker is native to the northeastern United States and southeastern Canada. It infests only grapes (Vitis spp.), both wild and cultivated species. Some varieties (e.g., Traminette, Niagara) are more sensitive than others.
Midges (adults) produce from one to three generations per year. The life cycle begins with the adult flies laying eggs within the unfolding bud or shoot tip. Larvae hatch from these eggs, enter vine tissues, and as they begin to feed the galls start to emerge. When the larvae are fully grown, they leave the galls and fall to the soil . For detailed information about this insect and its life cycle please check: IPM_CornellCooperativeExtension_GrapeTumidGallmaker.
The galls are usually 3.2 to 6.4 mm (1/8 to ¼ in.) in diameter. Galls on flower clusters can cause deformed fruit clusters or complete loss of berries . Galls occurring on leaves could be confused with phylloxera symptoms (Figure2). However, if you look carefully you will notice that grape tumid gall maker galls are smooth and round, whereas phylloxera (Daktulosphaira vitifoliae F.) galls are rough and bumpy . Heavy infestation can result in reduction of vine vegetative growth and shoot breakage. However, infestations are generally spotty both within vineyards and within infested vines; the insects are not usually present in sufficient numbers to cause significant harm to grapevines.
What should you do?
Grape tumid gallmaker infestations do not usually represent an economic threat. It is recommended to remove the galls by hand and destroy them to reduce future populations. In most situations, pesticide application is not required and is not economically justified unless the infestation is heavy [1; 3]. In vineyard with a history of tumid gall problems Movento (spirotetramat) may be used (Table 1; see also pre-bloom section in the Pest Management Guide for Commercial Vineyards). Another approach suggested is to bury the pupae by mounding up the soil beneath the vine early in the season (end of April) .
If pesticide application is needed it should be timed to kill adults of the overwintered generation as they emerge. The overwintered generation is the most dangerous because the offspring can heavily damage the young leaves and flower clusters early in the season (Figure 1). However, adults are small, measuring 2.5 mm (1/10 in.) long and difficult to detect. Therefore, “it may be most feasible to base control measures on the first sign of larval entrance into vine tissues, the small white scar, or on the first indication of gall formation” .