Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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Supplemental NEWSS Abstracts
(presented in alphabetical order, by author)
THE EFFECTS OF CULTURAL PRACTICES ON WEED ESTABLISHMENT IN
CONTAINERS. J. Altland, Oregon State University, Corvallis.
ABSTRACT
Cultural management practices in nurseries influence weed establishment and
growth in containers. The three cultural practices that have the most impact on container
weed management are substrate particle size selection, fertilizer management, and
irrigation management. Seeds of most container weeds are small. Small seeds must
germinate on or near the substrate surface because they do not have sufficient stored
energy to survive deep germination. Water within in a container is not constant from the
surface to the bottom. Due to matric potential of substrates, there is a gradient of
available water from high to low in the container bottom up to the surface. Coarse
substrates do not have sufficient water holding capacity to support seed germination,
particularly on the substrate surface where weed seeds germinate. For example, within
the range of bark grades used by nurseries, coarser grades reduce pearlwort (Sagina
procumbens) growth compared to finer grades. Water holding capacity is an important
physical property of container substrates, and also dictates the amount of water available
to the ornamental crop. Moderation in selecting coarse substrates is important.
Fertilizers can be used to impact weed growth. Bark substrates, including those
amended with peat, pumice, sand, or choir, have little or no available nitrogen (N). N is
required by weeds for successful germination and growth. Placement of controlled
release fertilizers (CRFs) below the substrate surface, commonly called dibbling, results
in no available N on the substrate surface and thus poor weed establishment.
Topdressing CRFs or injecting fertilizer through the irrigation system supplies abundant N
to the substrate surface and improves weed establishment. Incorporating composts with
high levels of available N into the substrate will also favor weed growth.
If nursery conditions dictate that fertilizers must be injected through the irrigation
system, N form can also influence weed growth. N in water soluble fertilizers is supplied
in the form of nitrate, ammonium, urea, or in combination. Fertilizers that supply N solely
in the form of nitrate, as opposed to either urea or ammonium plus nitrate, reduce weed
growth and flowering. Differences in weed growth due to N form are subtle; however,
reduced flower and seed numbers can result in significantly reduced weed pressure.
Irrigation is the most difficult cultural practice to manage. Over-watering reduces
herbicide effectiveness and improves weed establishment and growth. Irrigation
monitoring can be used to better manage irrigation rates, especially with micro-irrigated
crops. However, overhead irrigation systems lack uniformity. Non-uniform irrigation with
overhead sprinklers is the greatest limitation to strict management of irrigation rates.
Strict management of cultural practices alone will not eliminate weeds; however, it will
reduce weed vigor and improve overall weed control. The most effective weed
management program for nursery containers integrates sanitation, management of
cultural practices, and proper use of preemergence herbicides.
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