Growing Degree Day Models for Predicting Narrowleaf goldenrod (Euthamia graminifolia) Phenology in Lowbush Blueberry Fields in Nova Scotia

Abstract

Narrowleaf goldenrod [Euthamia graminifolia (L.) Nutt.] is the most common goldenrod species in lowbush blueberry (Vaccinium angustifolium Aiton) fields in Nova Scotia, Canada. Knowledge of ramet emergence and phenological development of this weed is limited, and it is unknown if seedling emergence contributes to the maintenance of established populations. The objectives of this research were to 1) develop predictive growing degree day (GDD) models for E. graminifolia ramet emergence and phenological development, 2) determine if E. graminifolia forms seed banks in lowbush blueberry fields, and 3) determine if E. graminifolia seedlings emerge in lowbush blueberry fields. Cumulative E. graminifolia ramet emergence was explained as a function of GDD using a 4-parameter Weibull equation that predicted emergence to begin at 72 GDD and 90% emergence to occur at 458 GDD. Cumulative ramets at the flower bud and flowering stages was explained as a function of GDD using a 3-parameter Gompertz equation that predicted initiation of the flower bud and flowering stages at 644 and 1369 GDD, respectively, and 90% of ramets at the flower bud and flowering stages at 1522 and 2113 GDD, respectively. Cumulative E. graminifolia seedling emergence ranged from 2.4 ± 0.8 to 4 ± 1 seedlings m^-2, suggesting limited seedling emergence in lowbush blueberry fields. Seedling density from soil core samples, however, ranged from 38 ± 25 to 10,940 ± 1,456 seedlings m^-2. These results suggest that E. graminifolia forms seed banks in lowbush blueberry fields, despite the low levels of seedling emergence observed. Euthamia graminifolia seedling management should therefore be considered in current weed control programs and growers can use the developed GDD models to aid the management of established plants.