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

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GERMINATION PATTERNS OF SWAMP DODDER SEEDS PLANTED NEAR A
COMMERCIAL CRANBERRY FARM. H.A. Sandler and K. Ghantous, Univ. of
Massachusetts-Amherst Cranberry Station, East Wareham.
ABSTRACT
Dodder (Cuscuta gronovii) is a serious weed pest in commercial cranberry that is
typically controlled with preemergence herbicides, such as Casoron (dichlobenil) or
Kerb (pronamide). Successful management is tied to proper timing of herbicide to
recently germinated seedlings. This study was initiated to gather information on the
germination patterns of dodder to facilitate timely applications.
Utilizing a simple system of simulated bogs constructed in plastic containers, the
germination pattern of MA dodder seed has been monitored for 9 years. In 1997, 8 cm
of peat was placed in the bottom of a 5-gallon container, covered by 10 cm of sand,
which was then covered with 13 cm of 50:50 sand:peat mix. In the fall of 1997 and
1998, one set of 10 containers was prepared in this fashion. On 8 Dec. 1997, 150 cc of
unscarified dodder seed was placed on the top layer and incorporated into the top 1 cm
of mixture. The containers were randomly arranged outside near a greenhouse,
approximately 15 m from the cranberry production area. Based on the large number of
germinated seedlings generated from this initial set, the seed amount was reduced to
15 cc for inoculation of the second set. The second set of containers was inoculated on
7 Dec. 1998. Pots were monitored twice weekly starting in early April until the first
seedling germinated. Seedlings were counted and removed daily and less frequently
during high and low germination periods, respectively. The containers were watered
and weeded as needed.
In 1998, over 50,000 seedlings germinated from the first set of containers, with a
peak 2-week period in early May (Julian date 121-134) that generated an average of
approximately 1,700 seedlings per container each wk. A second peak occurred in mid-
June (Julian date 163-169) that tallied an average of 372 seedlings per container. Even
in early July (Julian date 184-190), an average of 30 seedlings were germinating per
container. Germination was still robust for the next 3 yr, (44-66% of Year 1). By 2006,
germination was ~10% of Year 1, (3,700 seedlings). Numbers were lower in the second
set, but followed a similar trend.
Dodder seeds apparently have a definitive peak of germination in the initial year
after planting. Peaks can still be seen in subsequent years, but they are less definitive
and much lower in absolute numbers. Over the course of this 9-year study, the peak
germination period occurred later each year. The delay of peak germination may
contribute to the difficulties growers have in managing dodder. As new seed is
introduced into the system each year, its peak germination period may be different from
dodder germinating from the seedbank. Since most herbicides targeting dodder can
only be efficacious for a specific window of time, a portion of the population may always
escape preemergence control and provide enough viable seedlings to cause substantial
infestations in the vine canopy.
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