Conifer Pest and Disease Update 5/15/2023

Needle cast diseases (adapted from Modified from Dr. Anne Gould’s post – “Needles may fall”

Rhizosphaera Needle cast – Spruce (Steven K. Rettke – RCE)

Swiss Needlecast – Douglas Fir (Steven K. Rettke – RCE)

Rhabdocline Needlecast – Douglas Fir (Steven K. Rettke – RCE)

• About: The infection period for needle cast fungal diseases occurs in the spring. These diseases affect new needles and will cause them to turn brown and fall off later in the season or in subsequent years. “There are at least 40 needle cast diseases in the United States; most affect pine, spruce, fir, larch, cedar, hemlock, and Douglas-fir.  These diseases are caused by fungi that have only one infection period per year; in most cases (but not all), the new growth is infected by the offending fungus and, once the infection cycle is complete, is eventually cast from the tree (hence the name)”. “A week or two before bud-break, orange fruiting bodies develop within these spots on the lower needle surface.  When the fruiting structures are mature, they rupture and release abundant spores (called ascospores) during wet weather.  These spores infect newly expanding needles.  “Once the needles fully elongate and the weather is warm and dry, ascospores are no longer released, and the needles infected the previous year are cast from the tree.  Symptoms on the newly infected needles do not appear until the following fall or winter, and spores are not produced again until the following spring.” (Dr. Anne Gould).
• Douglas fir is susceptible to Rhabdocline and Swiss needle cast. Spruce trees, especially Colorado blue spruce, are extremely susceptible to Rhizosphaera needle cast problems.
• Cultural management:
  • Use healthy stock and provide an optimal growing environment.
  • Inspect trees during late winter/early spring and look for symptoms and signs.  The pattern of infection will likely follow portions of the canopy or field where moisture in the canopy is most abundant.
  • Remove sources of inoculum.  For best results, remove old and severely infected (30% or more) trees prior to budbreak. Prune severely affected branches during dry weather, and disinfest tools between cuts with rubbing alcohol.
  • Manage the moisture.  Choose sites with good air drainage and promote rapid drying of needles through spacing and row orientation.  In existing plantations, remove weeds and consider mulching. Avoid overhead irrigation if at all possible.
• Material considerations:
  • For many needlecast diseases, begin chlorothalonil sprays when the first 10% of the trees in the planting first break bud (or the candles are about ½-inch long). Repeat the sprays twice more at 7- to 14-day intervals until needles are fully elongated or until conditions are no longer favorable for disease development.  Add an additional spray to control Swiss needlecast when the weather remains wet.  For all fungicides, thorough coverage is essential.  Unless your product includes a spreader sticker, add one to enhance coverage.
  • Other compounds labeled for control of one or more of these needlecasts include azoxystrobin, coppers, (ammonium complex, basic sulfate, cuprous oxide, hydroxide, salts), mancozeb, thiophanate-methyl, and combination products. Read and understand each label prior to use to guard against known phytotoxicity issues.

Phytophthora, Pythium, Phytopythium root diseases 

• Compounds used to control Oomycetes (Phytophthora, Pythium, Phytopythium) are called Oomycides and are fundamentally different than those used for fungal and bacterial diseases. Therefor, proper identification is required, as a plant with a fungal root rot (ex: Annosum root rot) would require completely different materials. Contact the Rutgers Plant Diagnostic Lab for diagnostic services.  Within available materials there are three main groups, which describe where they will work on the plant given the application technique. Cultural practices are always more important than materials, especially in this case. 
  • Please review this handout for material and cultural practice considerations – Oomycete considerations in the nursery (Phytophthora, Pythium, Phytopythium, Downy mildews)
• Management focuses around treating the roots, or providing materials that reach the roots.
  • Protectants – are non-mobile, meaning they stay exactly where applied, must be root / drench / watered-in, applied.
  • Xylem mobile systemics – move upwards, and the roots must be treated.
  • Translaminar systemics – move very short distances into tissues, again meaning the roots must be targeted.
  • Amphimobile/Fully systemics (P07 / phosphonate group)– can move upwards to needles (xylem) and down to the roots (phloem) meaning foliage or roots can be targeted.

Refer to each label for treatment intervalsas they vary greatly, however it is valuable to get ahead of this pathogen as very few materials can “cure” plants. Additionally, more than one material should be in your tool kit as Mefenoxam-resistance has been identified in the Mid-Atlantic region. Contact twaller@njaes.rutgers.edu for more information.

Do not apply group P07 and copper-based fungicides within 14d of one another, as phytotoxicity is likely to occur!

NJ PLANT SPOTLIGHT

B. Errickson (Monmouth County RCE)

Our native NJ azalea species are currently in bloom, including dwarf azalea (R. atlanticum), pinxterbloom azalea, (R. periclymenoides), and swamp azalea (R. viscosum). These deciduous azaleas offer showy flowers that support pollinators and colorful fall foliage. As forest edge/understory plants, these species thrive in partial shade in well drained, acidic to slightly acidic soils.

Please SHARE what you SEE!! If you see a pest, disease, otherwise interesting or troublesome issue please report it to the Working Group by following the QR Code on the front of the Pest Scouting Guides or by filling out this reporting form.