Aphids on hops reported in significant numbers
As harvest approaches, growers should continue to scout for a number of pests and diseases, including aphids.
Like 2013, as harvest approaches growers are reporting high numbers of aphids in their hopyards, warranting management. At this time, Michigan State University Extension has not confirmed the species as Damson hop aphid (Phorodon humuli), but based on the prevalence and importance of this pest, that is likely the case. Damson hop aphid is one of the primary pest species in hop production in the northern hemisphere and can cause major damage and economic losses. Aphids generally thrive under greenhouse conditions and can be moved to new locations via nursery stock. Regardless of the species of aphid present, growers should be managing to prevent plant and cone damage.
The following information is summarized from the publication, “Field Guide for Integrated Pest Management in Hops.”
Damson hop aphids are small, 0.05-0.1 inches, pear-shaped, and soft-bodied insects that may be either winged or wingless. Wingless aphids are pale white to green and are typically found on the underside of leaves. Winged aphids are dark green or brown with black markings on the head and abdomen. Aphids have two cornicles or “tailpipes” at the end of the abdomen.
Aphids remove nutrients and moisture from leaf and cone tissue with their piercing and sucking mouthparts. Damaged leaves may curl and wilt, heavy infestations can cause defoliation. Cone feeding can cause wilt like symptoms in the cones and browning. When feeding, aphids secret sugary honey dew that can support the growth of secondary fungi and bacteria, most notably sooty mold. Sooty mold reduces photosynthesis and can make cones unsaleable. Aphids can also transmit viruses.
Damson hop aphids overwinter as eggs on Prunus species – genus of trees and shrubs, which includes plums, cherries, peaches, nectarines, apricots and almonds – which are prevalent in agricultural settings and the landscape in Michigan. In early spring, eggs hatch into stem mothers that give birth to wingless females that feed on the Prunus host. In May, winged females are produced and travel to hop plants where additional generations of wingless females are produced. As many as 10 generations may occur in a season with each female producing 30-50 offspring in her lifetime. Aphids do not reproduce as quickly in hot and dry weather, preferring more moderate temperatures and moisture levels. As cold weather approaches, winged females and males are produced and move back onto a Prunus host where they mate and lay eggs before winter. We expect that this migration off of hops and onto plants in the Prunus genus will occur sometime in September in Michigan.
Monitoring for aphids should begin when daytime temperatures exceed 58-60 degrees Fahrenheit and continue through harvest. Aphids are not tolerated after flowering because cone infestations are very difficult to treat. Growers experiencing aphid infestations should consider that excessive nitrogen application and large flushes of new growth favor outbreaks. Ideally, growers would apply early season controls to limit population growth over the season.
Pymetrozine, such as Fulfill, is commonly recommended in the Pacific Northwest because it is effective and helps preserve beneficial insects. Additionally, products containing imidacloprid (Admire Pro, Provado), spirotetramat (Movento) and thiamethoxam (Platinum) are all labeled against aphids. Organic products labeled for aphids in hop include azadiractin (Azadirect, Ecozin Plus), azadiractin+pyrethrins (Azera), potassium salts of fatty acids (Des-x insecticidal soap, M-pede), Chromobacterium subtsudgae (Grandevo), Beauvaria bassiana (Mycotrol O), mineral oil (Omni Supreme spray, Purespray green, SuffOil-X), pyrethrins (Pyganic), neem (trilogy) and Potassium silicate (Sil-matrix). Products containing synthetic pyrethroids (beta-cyfluthrin, bifenthrin, or cyfluthrin) and organophosphates (Malathion) are also labeled on hops for aphid management, but are generally avoided due to the negative effect on beneficial mites.