Mile-a-minute vine (photo courtesy forestryimages.org)
(by Steve Kallesser, CF, vice chair)
Recently, I had the pleasure of speaking with Mark Mayer of the NJ Department of Agriculture’s Phillip Alampi Beneficial Insect Laboratory (PABIL). The Laboratory is one of the nation’s leaders in the discovery, research, and rearing of beneficial insects for traditional agricultural lands and forests. We started by discussing mile-a-minute weed, and the weevil (Rhinoncomimus latipes) that the Laboratory is rearing to assist in mile-a-minute control. As many of us are aware, mile-a-minute appears to be expanding at an exponential rate in forests following “superstorm” Sandy. It was initially surprising to hear that many of the weevils are sent out-of-state. However that is only because most of the known infestations of mile-a-minute are already being attacked by the weevil and funding for the program is provided by the USDA-APHIS and the USFS for the express purpose of sending weevils outside of the state. The biocontrol program is a classical biological control program where the beneficial is established; then once established the need for further releases is reduced. pabil still releases weevils in areas where the weevil populations may need a boost.
This is a similar situation to the Laboratory’s huge success in the biocontrol of purple loosestrife. Today, almost all of the purple loosestrife predators are sent out-of-state providing additional operational funds for PABIL, because there is no area of New Jersey where those predators are not present. The rearing space for the loosestrife beneficials within the lab has been reduced from what it was years ago. The biocontrol of purple loosestrife has been a true victory for PABIL, as the predators have reduced the average height of the plant by more than half, reduced its vitality and the amount of shade it casts on native wetland plants. Thus, native wetlands plants are able to compete successfully with the purple loosestrife, making the monocultures many of us remember virtually extinct in New Jersey.
Mile-a-minute predator weevil (photo courtesy 2.bp.blogspot.com)
Time will tell whether similar success will be had with mile-a-minute. The initial weevil release sites in NJ showed a dramatic reduction in the percent cover, number of seedlings and an increase in the number of species of other plants at the sites. At some sites, the plant is gone. Although reducing loosestrife height from 6 feet to 3 feet has been a great improvement, it remains to be seen if reducing mile-a-minute vine growth from 20 feet/year to “only” 7-10 feet/year is meaningful. As with all biocontrol programs, you have to be patient with the ultimate goal of reducing the carrying capacity of the plant over time. Mile-a-minute can grow 20 feet in a year on a good site in full sun. In a forested situation with full or partial shade, that potential drops to 7-10 feet per year, possibly less. However, presence of weevils on mile-a-minute under such shade conditions may not materially affect the plant. Dr. Hough-Goldstein of University of Delaware also has data that shows that the weevils have delayed the onset of the berries by one month which has also been observed by PABIL field staff. This, combined with the rapid spread of mile-a-minute despite weevil prevalence is difficult to stomach. It will get worse before it gets better.
Still, the Laboratory is asking foresters to report new infestations of mile-a-minute, so that surveyors can look to see if weevils are already present. Indications of weevil presence include many small holes in leaves, and cracked or reddish discoloration on nodes along the stem. If no weevils are present, then the site will be placed on a priority list for weevil introduction. Mr. Mayer can be contacted at email@example.com. There is no charge for beneficial insects reared by the lab for releases within New Jersey.
We discussed the recent Verticillium wilt of Ailanthus epidemics from central Pennsylvania, through the West Virginia panhandle, and into northern Virginia. He mentioned that there is a weevil under development for Ailanthus control, as well. Lastly for the exotic invasive plant front, he mentioned that Cornell University and the University of Rhode Island have a proposal under consideration to search for beneficial organisms for future biocontrol of Japanese stiltgrass, however even if such an insect is found the earliest that a product could become available would be 5-10 years from now.
Hemlock wooly adelgid infestation (photo courtesy USDA Forest Service)
This brought us to Eastern hemlock, once an important component of ravine forest stands and northern exposures in the ridge and valley and highlands provinces. Due to hemlock wooly adelgid, and reports of biocontrol failures in other states, many foresters have written this tree off. The Laboratory says not so, and Mr. Mayer is personally optimistic for the future of the species in eastern forests. Why such optimism? A relatively new beetle (Laricobius nigrinus) that the lab was rearing was released near the Delaware Water Gap several years ago. Today, the beetle is found up to 7 ½ miles east and 18 miles north from the original sites in NJ. The beetle is throughout the Delaware Water Gap National Recreation Area in NJ and PA, and is present in Stokes State Forest and High Point State Park. Also, the beetle was unaffected by the exceptionally severe winter of 2013-14. Similar releases were also conducted in the mountains of North Carolina, and preliminary results there are suggesting increased health of Eastern hemlock trees in areas that have the beetle.
Meanwhile, at least one, possibly two stands of adelgid-resistant Eastern hemlock have been confirmed in the ridge and valley province of New Jersey according to work done in conjunction with University of Massachusetts and University of Rhode Island. (Mr. Mayer will not say where!) The resistance to the adelgid appears to be related to a variation in the chemistry of certain terpene hydrocarbons within the subject trees. The prospect of beetles protecting Eastern hemlock regeneration and possibly remnant trees, and a seed source for adelgid-resistant Eastern hemlocks should be a cause for optimism for foresters throughout the east.
New Jersey Division SAF thanks Mr. Mayer for his time in passing along this information.