Thursday, July 23, 2009

Peach disease field day

Today, Botond Balogh, PhD. ('Bo') from the Connecticut Agricultural Experiment Station, and Lorraine Los, of UConn Fruit IPM, visited the UMass Cold Spring Orchard in Belchertown, MA in search of bacterial spot of peaches (picture). Bo has a particular research interest in using bacteriophages to control bacterial diseases, and has worked in citrus (Florida) and vegetables in the past. We were also joined by Dan Cooley.

Indeed we found bacterial spot in two sub-acid stone fruit varieties from the Zaiger breeding program out of California -- in Honeykist nectarine (foliage and fruit) and Country Sweet peach (foliage and fruit). Now, I knew these varieties are susceptible to bacterial spot, no big surprise. The reason being is California does not have much rain, which is essential to spread the disease, so the breeding program does not necessarily screen for this disease. Peaches and nectarines from east coast (Rutgers) or Michigan (Paul Friday and Stellar) breeding programs are far more resistant to bacterial spot. But it can still be an issue for peach and nectarine growers in Massachusetts and Connecticut depending on what varieties they grow, the season's (wet) weather, and the diligence of their control effort, including copper and bactericide (FlameOut) sprays. A form of biological control (other than cultivar selection) would be highly desirable.

Note that we also found some nice (if you are a plant pathologist) brown rot in fruit. Brown rot is going to be be problematic with all the wet weather we are having. Consult this table of brown rot fungicide options from Cornell to stay on top of it.

While in the peach orchard, Lorraine noticed twist-ties used for peach tree borer mating disruption. (They were from 2008.) Lorraine and Bo have a SARE research-extension grant to promote peach IPM. Lorraine said adult peach tree borers are likely at peak emergence, and indeed we found the spent pupal case at the base of an infected peach tree. (We also found similar for lesser peach tree borer in a scaffold limb.) Ties for mating disruption and/or broad-spectrum insecticide sprays (pyrethroids) will prevent the adults from laying eggs and infecting trees. Based on my experience, peach tree borers are a major pest of peaches in Massachusetts, and need to be aggressively managed with mating disruption, Lorsban trunk sprays, and/or cultural practices that discourage egg laying such as white trunk paint, no mouse guards, and keeping weed-free strips at the base of trees. Note that peach trees damaged by borer infestation will particularly attract more adult egg-laying. For infested trees, it's the beginning of the end of the peach orchard.

Finally, while looking for more bacterial spot in a Southampton, MA orchard, we apparently found choke cherry (Prunus virginiana) on the woods edge of a peach orchard that had some trees showing signs of X-disease. The suspect plant, however, was later identified as pin cherry, Prunus pennsylvanica, which is not an host of X-disease. Nevertheless, choke cherry, when found, should be destroyed (systemic herbicide best) within 500 feet of peach orchards to prevent the disease from infecting your peach trees! Alan Eaton, UNH entomologist, has a good write-up on X-disease in his July 15, 2008 IPM Newsletter.

Here are the picture albums (all pictures) from our field day by Botond Balagh, Dan Cooley, and Jon Clements.