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Japanese Beetle, Steely Beetle and Grape Rootworm

Can you tell the difference between the feeding patterns of these three pests? In a number of Concord vineyards we are seeing feeding on the leaves from all three pests on a single vine and often times more than one of these pests on a single leaf.

Japanese beetle feeding is perhaps the most distinctive of the three. In Concords, early feeding consists of small punctures in the leaf with brown edges spaced randomly within an area of the leaf as seen in Figure 1. As feeding continues more green tissue is removed and it appears that a pattern might be taking shape. With extreme feeding pressure, a majority of the green tissue between the major veins can be removed creating a leaf with a lacy appearance (Figure 2). Feeding typically takes place along the top wire or the upper half of the canopy.

The smooth-leaved wine varieties are much more susceptible to feeding from Japanese beetle and removal of leaf surface by this pest can reach economically important levels much faster than in the native varieties. Japanese beetle can also be a major problem in young vineyards, or in replant situations where grow tubes are being used. Make sure to check inside the tubes to determine if the Japanese beetle are taking advantage of the protection of the tubes while they are feeding.

Steely beetle is typically a concern only at the bud swell to 1-inch of shoot growth stage when the adults are hollowing out buds. However, the larvae of this secondary pest feed on the leaves and while I have never seen a situation where I have recommended a spray specifically for Steely beetle larvae, knowing what the damage looks like will be helpful when scouting for grape rootworm or Japanese beetle. Figure 3 shows typical feeding pattern by the steely beetle larvae. The feeding is done earlier in the season than that of Japanese beetle and grape rootworm so there is the appearance of the feeding area being pulled apart as the young leaf has expanded and matured. Location of feeding damage from this pest is typically up in the canopy toward the base of the shoot. You can find this damage early in the season.

Grape rootworm feeding is often described as a chain-like feeding pattern (Figure 4). The feeding pattern is less random on the leaf than the previously mentioned pests and the feeding does not reach a level where damaged areas converge to cover a large area of the leaf (Figure 5). Feeding damage from this pest is most commonly seen on sucker leaves or leaves of the lower canopy. Damage will start to become noticeable around the end of June, beginning of July.

Keep in mind that rootworm foliar feeding is going to be the best indicator that there is a problem in your vineyard. Grape rootworm spends most of its lifecycle underground in the larval stage where it does the most damage by feeding on grape roots.

If you are seeing a decline in vine vigor in some vineyard blocks, now would be a good time to get out and take a closer look to see just what pests are feeding on your vines leaves (and possibly the roots).