Potato Leaf Hoppers on Hops

Author: 
Dr. Gerald Brust

I do not usually look at hops very much as only a few farms have them, but they are becoming a bit more common in the last 10 years (Fig. 1). Visiting two farms withy hops I saw marginal leaf damage (Fig. 2) on some leaves (found some thrips too) and then marginal leaf scorch on others (Fig. 3). When looking on the underside of these leaf-scorched damaged leaves, I found many potato leaf hopper nymphs (no adults) (Fig. 4) on one farm and only a few on the other. Potato leafhoppers prefer warm, dry conditions and are common in southern states where they overwinter; leaf hoppers do not overwinter in our area. Potato leaf hoppers (PLH) move into our area via storm systems from the south. PLH are generally seen in early to mid-May, but are arriving on average in our area 7-10 days earlier than it was just 20-30 years ago. Females lay one to two eggs per day in the leaf stems or veins of hops and 1 week to 10 days later nymphs emerge. Nymphs reach maturity in about 2 weeks. Leafhoppers are capable of very rapid population increases so scouting is important to control the pest to avoid damage to hops. Alfalfa is the primary host for the potato leafhopper and once the first cutting of that forage is done, PLH will move into other susceptible crops such as potato and hops.

Figures 1, 2 and 3. Hops vine, hops leaf with the start of hopper/thrips damage and leaves with severe hopper burn.

Figure 4. Potato leaf hopper nymphs on hops leaf

Damage: The most obvious symptom of potato leafhopper feeding is hopper burn. Hopper burn is the yellowing of the leaf margin usually starting near the tip of the leaf (Fig. 3). This damage is followed by leaf curling and necrosis. Hopper burn occurs because potato leafhoppers feed by sucking the juices out of leaf veins and blocking the veins with a toxin in their saliva.

Monitoring and Management: Because potato leafhoppers can have very rapid population growths, it is important to scout and control them before major damage can occur. While there is no agreed upon threshold for leafhoppers in hops, most recommendations have a threshold at 2-3 PLH per leaf. Fields should be scouted weekly by checking the undersides of 5-10 leaves per 10–20 plants. If the average number of leafhoppers per leaf is at or above the threshold, then a control is needed. Because hops are a newer crop in our area states may differ in what they allow to be used, so be sure to check the label to see what your state will allow to be used on hops for PLH control. In general, neonicotinoids, pyrethroids, or spinosyns could be used. Organic growers could use spinosad or pyrethrins that are OMRI approved for potato leafhopper management. If PLH are more of a consistent problem for you one suggestion is to plant red clover in drive rows as the potato leafhoppers prefer to feed on the red clover than the hops.

 

Maintained by the IET Department of the College of Agriculture and Natural Resources. © 2017. Web Accessibility