| dc.description.abstract | Aminopyralid often is used for invasive weed control in Conservation Reserve Program
(CRP) land. As CRP land is returned to crop production, aminopyralid persistence in soil
could limit future planting options. Field experiments were established near Casselton and
Fargo, ND to evaluate the effect of aminopyralid soil residue on alfalfa, com, soybean, and
sunflower planted one or two growing seasons after treatment. Aminopyralid caused no
injury or yield reduction to alfalfa, com, and sunflower when seeded 20 or 23 mo after
treatment (MAT) in Fargo. However, soybean yield was reduced when aminopyralid at
120 or 240 g ae/ha was fall- or spring-applied 20 or 23 months prior to seeding. In
Casselton, aminopyralid applied in September caused much greater crop injury than when
applied in June the year prior to planting. For example, aminopyralid at 120 g/ha applied
in September caused 95, 94, and 100% injury to alfalfa, sunflower, and soybean,
respectively, compared to 10, 8, and 44% injury when applied in June. Com yield was not
affected by any aminopyralid treatment when planted 8 or 11 MAT. Com appeared to be
the best cropping option for land that was recently treated with aminopyralid. The effect of
temperature and moisture content on aminopyralid dissipation in four North Dakota soils
was evaluated in growth chamber and greenhouse studies. Aminopyralid dissipated 2 to 8
times faster at 24 C than at 8 C and aminopyralid 50% dissipation rates (DT 50) ranged from
9 d in a Svea-Barnes loam at 24 C to 256 d in a Lamoure loamy sand at 8 C. Aminopyralid
dissipation rates were similar in soils with moisture contents of 22.5 to 90% field capacity
(FC) when incubated at 16 C and the average aminopyralid DT 50 ranged from 66 to 200 d. Soil conditions favorable to microbiological growth such as warm temperatures, moderate
moisture contents, and high organic matter contents appeared to favor aminopyralid
dissipation. In greenhouse trials, prairie forb susceptibility to aminopyralid varied by
species. Azure aster, blanket flower, closed bottle gentian, purple coneflower, and showy
goldenrod exhibited good tolerance to aminopyralid while great blue lobelia, harebell,
prairie coneflower, and white prairie clover were sensitive. | en_US |
