Jen Llewellyn Reflects on 2004

May-June 2005

LAST YEAR I HAD THE WONDERFUL OPPORTUNITY to take maternity leave. I was looking forward to not having to work during the heat of the summer, but as luck had it, 2004 was the year for cool temperatures and rain. Although the weather was a welcome respite to many woody ornamentals and lawns, there were some drawbacks including a lot of complaints regarding nutrient deficiency symptoms on trees (especially Acer, Betula and Quercus).

Could it have been due to abundant soil moisture? In container production, over-watering often results in nutrient deficiency-like symptoms. This is because excess water actually replaces the needed air pore space (oxygen) with water-filled pores. The result is dead roots, especially fine feeder roots. Since a reduction in functional roots means a reduction in water and nutrient uptake, what you get is a plant that is wilting and showing signs of nutrient deficiency. Could this explain some of the nutrient deficiency-like symptoms we saw in 2004?

Of course, foliar diseases were also quite extensive in 2004. The extended cool, wet spring conditions actually prolonged the leaf emergence period. It is during this period that foliage is most susceptible to pathogens, especially before their protective waxy cuticle forms. Protect susceptible varieties from foliar diseases starting at bud swell. This will ensure that newly emerging foliage has the best chance of withstanding pathogenic infections.

It is important to note that the infection period for most diseases is during the leaf emergence period in spring and again during the second flush (if there is one). Where warm, dry conditions are present during leaf emergence, the period between fungicide applications can be much longer than during cool, wet weather. This is because most pathogens require leaf wetness periods to grow and infect leaf tissue. One thing we know for sure is that the overwintering diseased tissue from last year will present a lot of pressure during leafing out this spring. Protect emerging foliage where cool, wet conditions persist during leaf emergence and where a history of disease was evident last year.

Insect pressure was staggered in 2004. Late emergence and staggered infestations were quite common. As gypsy moth populations have been climbing, diseases such as Entomophaga maimaiga had a large impact on the viability of late instar larvae, causing population crashes around the province last year. Again, the cool, wet conditions were perfect for the development of this fungus. Trees and shrubs had an easier time regenerating tissues after feeding damage.

Spruce spider mite populations were steady throughout the growing season while two-spotted spider mite populations skyrocketed with the heat at the end of summer. Aphid populations also increased at the end of the season, giving grief to arborists and landscape service providers. Winter 04-05 had meteorologists recording several days below 20oC, which will hopefully have a negative impact on overwintering populations.

2005 Nursery-Landscape Agriphone
For weekly updates of pest management and issues related to the production and maintenance of outdoor ornamentals (mainly woody), send me an email and I’ll put you on our distribution list.

Pest and Disease Watch for May
For more information on pest management, phenology indicators and growing degree day summaries, check out publication 383, OMAF Nursery-Landscape Plant Production and IPM. 2003. Refer to the tables starting on page 42. To order a copy, call 1-877-424-1300. Click here to view table excerpts (pdf) from this publication.

— Jen Llewellyn, Ontario Ministry of Agriculture and Food (OMAF) Nursery Crops Specialist

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