It may be this from recent UMASS Ag posting What can I do to protect two- and three-needle pines from Diplodia blight? A: Diplodia blight of two- and three-needle pines, caused by Diplodia sapinea, has been abundant this growing season. The disease primarily occurs on Scots (Pinus sylvestris), red (P. resinosa), mugo (P. mugo) and Austrian (P. nigra) pines. However, the pathogen has a very broad host range among the Pineaceae and can also attack five-needle pines (e.g. P. strobus, P. flexisand P. koraiensis), false-cypress (Chamaecyparis), spruce (Picea), true cedar (Cedrus), among other landscape conifers. Diplodia sapinea has even been found on oaks (Quercus), illustrating its dynamic nature. Symptoms of Diplodia blight appear as shoot tip blight in early summer, and browning needles/scattered dieback throughout the canopy during the summer. Infected needles often turn from brown to grey over the growing season. Drought stress from 2020 likely predisposed many landscape pines to infection, despite their natural drought resistance. Many two- and three-needle pines are adapted to dry and nutrient poor sites. By maintaining a naturally sparse canopy, these trees avoid the conditions that allow needle and stem blight pathogens to proliferate. Specifically, many conifer pathogens thrive within lower and interior portions of the canopy where dense branching and heavy shade allow moisture to linger. However, many dwarf and intermediate cultivars of two- and three-needle pines have very dense, mounded canopies that create ideal conditions for the disease (i.e. P. resinosa ‘Morel’). These forms can create major problems should Diplodia blight establish. If Diplodia blight is a concern or has been present in the past, consider pruning to improve sunlight penetration, increase air flow and accelerate drying through the canopy. This is especially true of lower canopy branches, especially if they receive little to no direct sunlight. Maintain a thick mulch layer around the base of the plants, remove underlying or surrounding plantings that cast shade, and provide supplemental irrigation during extended dry periods to manage drought stress. Care should be taken when fertilizing two- and three-needle pines with nitrogen. An abundance of succulent tissues in the spring can allow Diplodia blight to rapidly intensity when the pathogen is present. Early detection is important when managing Diplodia blight. Carefully scout as new candles and needles are elongating. When Diplodia blight is present, the needles at the shoot tips will typically die when they are 1/3 to 1/2 elongated. Immediate pruning and removal of this diseased tissue when it appears can keep the infection from spreading throughout the canopy. Locally-systemic fungicides, such as azoxystrobin and thiophanate-methyl, when applied to the new growth can be helpful in keeping these new sensitive tissues protected. Systemic fungicides with a single mode of action should be rotated to avoid resistance development. Broad-spectrum protectants, such as copper hydroxide, metconaozle and mancozeb are effective chemicals as well.
Ruth Ann (She, her, hers) > On Oct 15, 2021, at 11:26 AM, Rich Rosenbaum <s...@bcdef.com> wrote: > > > At this time of year, I normally see browning of needles (as described at > here ) but it has been more intense this year (see photo). > > FYI, this month's Hort Notes from UMass Amherst has an article on a different > problem. > > https://ag.umass.edu/landscape/newsletters/hort-notes/hort-notes-2021-vol-328# > (click on Q&A) > > Rich > > <brown_needles3a.jpg> > -- > The LincolnTalk mailing list. > To post, send mail to Lincoln@lincolntalk.org. > Search the archives at http://lincoln.2330058.n4.nabble.com/. > Browse the archives at https://pairlist9.pair.net/mailman/private/lincoln/. > Change your subscription settings at > https://pairlist9.pair.net/mailman/listinfo/lincoln. >
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