January 15, 2009
By Jen Llewellyn
OMAFRA Nursery Crops Specialist

Every year, without fail, I receive several inquiries about needlecast issues on spruce. It’s usually Colorado spruce (Picea pungens) and its cultivars. Most complaints are about blue cultivars of Colorado spruce involving the needles “turning purplish-red and dropping.”

When we read about needlecast issues with spruce, we find a similar description for the symptoms of Rhizosphaera (Rye-zo-sfara) needlecast disease. When Rhizosphaera infects needles, it produces black sporulating structures in place of the tiny, white stomata (tiny white pores that can be found in rows along conifer needles). However, when I put the needles under my magnifying lens or stereoscope, I don’t always see the tell-tale black stomates so characteristic of Rhizosphaera infection. So if it’s not a disease, what’s going on?

We’re finding out as time goes on that Colorado spruce may not be adjusting very well to our climate and may be a little more sensitive to transplanting than other species. Unless you are very careful about site preparation, transplanting and after-care, these specimen trees can really struggle to become established. By planting them into an extremely heavy clay or a very light sand, they can really suffer with the extremes in our precipitation (consider the hot, dry year of 2007 followed by the waterlogged growing season of 2008). I had several calls about newly planted Colorado spruce this summer, all of which were in compacted, heavy clay soils that created a virtual bathtub for the root system. Soil aeration and mulching with organic material will help these trees to establish their root systems in our tight urban soils.

One other thing I’ve noticed time and again is canopy spacing. I’ve been monitoring a Colorado spruce windbreak and it is the last six trees at the edge that exhibit the most extreme symptoms. When I stood back and looked at the windbreak from the neighbouring farm, it became clear that these symptomatic trees were planted a little closer together than all of the others. Reduced light and air circulation in the canopy creates more humidity and longer leaf wetness periods, which results in greater needlecast issues (pest and abiotic).

So what about those trees where you are seeing little black dots in the place of the white stomates? Rhizosphaera is certainly one of the most common fungal diseases that causes these symptoms….or is it?

Each year, I consult with the nursery-landscape industry about their pest management problems and “needlecast diseases of conifers” always come up as a major priority for growers (landscape and Christmas trees) across Canada. We take these priorities to the annual Minor Use Workshops in Ottawa where we ask the Pest Management Centre (PMC) to conduct trials to find pesticide solutions and generate data for the registration of new products. Last year, the PMC agreed to fund a screening trial for needlecast diseases, and we quickly assembled a cross-Canada team (Ont. and N.S.) to do the trials. This involved several people. In Ontario, Dr. Tom Hsiang with the University of Guelph has been a pivotal resource. Dr. Hsiang and his research team discovered the presence of a fairly new fungus on spruce, Stigmina.

Recently, Stigmina has been detected in the north-eastern U.S. Much like Rhizosphaera, Stigmina also produces black fruiting structures in the stomata. But where Rhizosphaera fruiting structures are smooth and spherical, Stigmina fruiting structures are black with tiny little appendages growing out of them (you’ll need at least 20x magnification to see this). Quite often the needles infected with Stigmina are still green and attached to the twig, which poses the question: Is Stigmina a pathogen? It is on some other crops, but for spruce we don’t know yet.

When you examine the literature on Rhizosphaera, you’ll question whether the sporulation period has been well documented; “from spring to fall” is what you’ll find. One of the components of the screening trial was monitoring for sporulation of needlecast fungi. We took several samples of symptomatic foliage throughout the growing season and Dr. Hsiang’s lab meticulously dissected the samples and examined them for disease identification. They found that Rhizosphaera kalkhoffii started producing spores in July, and spores were still present in November. Stigmina spores were present at first sampling in early May and spores were still present in November. These long spore dispersal periods make such pathogens more difficult to manage, because multiple chemical applications may be required to control the diseases.

One would think that newly-emerging growth in the spring would be most sensitive to fungal attack. This is why it is recommended to use protectant fungicides to reduce foliar diseases during leaf emergence. However, if pathogens are sporulating long after new growth hardens off, chances are they are doing it for a reason. In Sinclair and Lyon’s Diseases of Trees and Shrubs, they state that released spores can survive for weeks on spruce foliage and wait out periods that are not favourable for infection. It is possible that Rhizosphaera is able to infect various years’ needles, but that it takes at least 12 months before symptoms become noticeable. Typically, we see symptoms on growth from two and three years ago, but not on last year’s or the current season’s foliage. What does this mean for the management of Rhizosphaera and other needlecast diseases? They could be more difficult to manage than previously thought.

Tar Spot Research at U. of G.

The research team of Dr. Tom Hsiang, Lynn Tian and Angie Darbyson from the University of Guelph continued their research on tar spot of maple in 2008 with renewed funding from Landscape Ontario. They made an exciting discovery that tar spot on Manitoba maple is caused by the European species of the fungus, as well as reconfirming the finding from last year that tar spot on sugar maple is also caused by the European species. This is potentially very serious news, since it seems that the European tar spot commonly found on Norway, field and sycamore maples has adapted to native maple species. If this adaptation continues to progress, and the European tar spot becomes as virulent on these native maples as it is on the European species, then industries that are dependent on native maples may face some problems.

Dr. Hsiang’s research group also initiated some research with diplodia blight of pine with funding from the International Society of Arboriculture, Ontario Chapter. It found that the fungus produces spores throughout most of the year. This will pose a problem for disease control, since inoculum may be available to start infections almost year round.

A destination for plastic waste?

Plastic waste is a real issue for nurseries, garden centres and landscapers in Ontario. Soil and debris residues and sheer amounts of plastic waste from greenhouse and nurseries have impeded its appropriateness for recycling in the past. Quite often, the recycling companies have not been able to accept the vast majority of plastic waste because of the bulk supply. Over the last year, more plastic recycling companies have been popping up and luring the nursery industry and has been actively pursuing partners that can take their waste plastics and turn them into another marketable product. The nursery industry is working closely with recycling companies to help facilitate shipping of waste plastics and ensure good communication and standards for waste plastics that would be acceptable for recycling.

I had a chat with one company, Re-Source Ontario (www.resourceontario.com) at LO’s Garden Expo trade show this fall. The company is based in Toronto and is working with Landscape Ontario to implement recycling programs for the horticultural industry. They recycle several different types of plastics: pots, cell packs, flats, plug trays, films, pallet wrap, poly bags, plastic pallets, seed sacks, drip tubes, planter trays and more. They grind the plastic and then wash it before it can be sold to a plastic manufacturer for processing into a product, like plastic lumber. You can get together with a neighbouring operation and ship the plastic to them, or they can also arrange shipping for you. Also, at Garden Expo, Jack Van Klaveren Ltd. was talking about its pilot project for a consumer recycling program. The program is designed for garden centres who purchase the majority of their horticultural containers from JVK. They accept plastic products with a #5, #2 or #6 symbol on them.

Jen Llewellyn may be reached at (519) 824-4120, ext. 52671, or by e-mail at jennifer.llewellyn@ontario.ca. See her Nursery-Landscape Report: http://apps.omafra.gov.on.ca/scripts/english/crops/agriphone/index.asp