Early season hop yard in the Yakima Valley, WA (image via Wikipedia: http://en.wikipedia.org/wiki/File:Yakima-Valley-Hop-Yard.jpg)
There's been a noticeable buzz about hops in NC lately, and I have been receiving more questions about pests and management. I am typically conservative when comes to recommending that growers plant a crop about which we still have a lot to learn (from culture to market demand), but several small growers have vines in the ground and have seen pests appear this season. If these growers persist and other join them, I'll be ready with as much help as I can provide. The biggest challenge for many of these growers will be their desire to produce hops organically--there are good market reasons for this decision, but many of the pests of hops will be particularly hard to manage organically.
Fortunately, a friend at WSU works some on hops and has been an early resource, but as he pointed out in our first conversation about hops--we have this thing here called humidity that they don't content with in the high desert. Because NC growing conditions are so different from the places where hops are typically produced, we need to be careful when adapting management recommendations from Washington and Idaho. We may have pests they don't and visa versa.
I do have a sense of what was out there this year based on clinic submission and emails, and some them are the usual suspects. A short list of what to watch for on hops:
Twospotted spider mites: TSSM (as I like to call them) are polyphagous pests. This means they feed on lots of plants from strawberry to tomato and from Japanese maple to hops. Mite feeding causes leaf stippling and yellowing with severe infestations resulting in defoliation. This leaf injury then can impact yield. Idaho recommendations suggest treating when mites reach 1-10 per leaf. Because organic materials behave differently, I would err on the more conservative side. I hope to gather some data on predatory mites in hops next summer, and I think these may be a viable option. I am not aware of any work done on pred. mites in hops, so I can't say what they real benefit would be yet. Organic pesticides are marginal against mites and their use will be challenging with the large hop canopy (an air cannon sprayer would be a good investment for the serious grower).
Hop aphid: Hop aphids do occur in NC, and they are a pest both because they vector disease (it's unclear how big an issue these diseases will be here) and because they feed in hop flowers--the harvested part of the plant. Aphids and the sooty mold they produce render cones unmarketable, which makes them a very serious pest. Aphid feeding behavior also makes them very hard to control completely in an organic system (there are very effective conventional controls). Biological control agents typically only move in when aphid populations are established and do not provide sufficient control. Organic pesticides need to contact aphids to kill them, since they do no move within the plant. I suspect the plan for organic aphid management will be to "treat early, and treat often"--a situation we typically try to avoid.
Leafhoppers: I have heard lots of complaints of early season leafhopper populations in hops, but I haven't seen any samples. This mean that I don't know what species we're dealing with or the damage it's creating (if any). Leafhopper do not appear to be hop pests in the western US (where most commercial hops are grown), so this a problem we will have develop information on here.
I'm keeping an ear to the ground to see where hops go in NC, and I'll keep posting.