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In Japan, the spread of morning glory (Ipomoea spp.) in soybean fields has become a serious issue. To establish a control approach for Ipomoea species, this study considered the optimal system combining cultural and chemical control methods. Field experiments were conducted for 3 years to investigate the effects of no‐tillage compared with tillage seeding in narrow‐row soybean and of application timing of selective post‐emergence herbicides bentazone and fluthiacet‐methyl. The cumulative emergence of entireleaf morning glory (Ipomoea hederacea [L.] Jacq. var. integriuscula A. Gray) in no‐tillage was 25–79% of that in tillage, and the initial growth was suppressed. In no‐tillage, the dry matter weight of I. hederacea var. integriuscula was suppressed compared to tillage methods. However, in no‐tillage, initial soybean growth was inferior, and reduction of the relative photosynthetic photon flux density (RPPFD) in the soybean canopy was delayed. A combination of selective post‐emergence herbicide applications at the second and fourth trifoliate leaf stages (TLS) of soybean was most effective in I. hederacea var. integriuscula suppression. The initial growth of soybean greatly fluctuated yearly, and the period when the RPPFD became less than 50% varied at the fourth through seventh TLS. Therefore, if the initial soybean growth is good, the end of the required period for weed control can be defined as the fourth TLS. No‐tillage cultivation combined with management to promote soybean growth, such as adequate soil moisture control by subirrigation systems, may be effective in controlling I. hederacea var. Integriuscula.
In Japan, the spread of morning glory (Ipomoea spp.) in soybean fields has become a serious issue. To establish a control approach for Ipomoea species, this study considered the optimal system combining cultural and chemical control methods. Field experiments were conducted for 3 years to investigate the effects of no‐tillage compared with tillage seeding in narrow‐row soybean and of application timing of selective post‐emergence herbicides bentazone and fluthiacet‐methyl. The cumulative emergence of entireleaf morning glory (Ipomoea hederacea [L.] Jacq. var. integriuscula A. Gray) in no‐tillage was 25–79% of that in tillage, and the initial growth was suppressed. In no‐tillage, the dry matter weight of I. hederacea var. integriuscula was suppressed compared to tillage methods. However, in no‐tillage, initial soybean growth was inferior, and reduction of the relative photosynthetic photon flux density (RPPFD) in the soybean canopy was delayed. A combination of selective post‐emergence herbicide applications at the second and fourth trifoliate leaf stages (TLS) of soybean was most effective in I. hederacea var. integriuscula suppression. The initial growth of soybean greatly fluctuated yearly, and the period when the RPPFD became less than 50% varied at the fourth through seventh TLS. Therefore, if the initial soybean growth is good, the end of the required period for weed control can be defined as the fourth TLS. No‐tillage cultivation combined with management to promote soybean growth, such as adequate soil moisture control by subirrigation systems, may be effective in controlling I. hederacea var. Integriuscula.
Morning glory (Ipomoea spp.), a problematic weed in soybean fields, is difficult to control due to its long emergence period. The intermittent germination of morning glory prolongs the emergence period, and the factors remain unclear. Therefore, we aimed to clarify the effects of different storage periods under natural conditions on germination conditions and emergence percentages of physically dormant entire‐leaf morning glory (Ipomoea hederacea var. integriuscula) seeds in the field. In 2017–2020, I. hederacea var. integriuscula was cultivated in outdoor planters. Each plant was tagged on the blooming flower peduncle to record the flowering date. The seeds of I. hederacea var. integriuscula germinated 23 days after flowering (DAF). The water content of the seeds decreased rapidly until 30 DAF, and no water absorption occurred thereafter. The germination percentage of seeds in bags outdoors was low from 45 to 210 DAF, and it increased after 270 DAF irrespective of the temperature (20–35°C). On the field surface, the shorter the period of storage in bags outdoors, the lower the cumulative emergence percentage of I. hederacea var. integriuscula. The cumulative emergence was 0% in the soil for seeds of more than 90 DAF. The survival percentage of seeds in the soil increased with the number of DAFs. Therefore, the longer the DAF of the seeds, the higher the emergence of the field and survival percentage in the soil. The long period of storage on mother plants may be one of the factors associated with the long emergence period.
Entireleaf morning glory (Ipomoea hederacea Jacq. var. integriuscula A. Gray) is a difficult-to-control weed that causes severe yield loss in soybean (Glycine max L.). It invades fields from the field margins and contributes to maintenance of the populations in the fields. This study aimed to determine the optimal period to control the populations in field margins effectively. We identified the naturally emerging plants in field margins and adjacent fields. We recorded the number of invading vines and the timing of flowering and fruiting of several cohorts (each cohort comprised a group of individuals that emerged within a certain time frame). The main seed-producing cohort on the field margins was a cohort that emerged from early August to mid-September and flowered and fruited after mid-September. The weed formed seed banks in the field margins, maintained by repeated depletion and accumulation during the emergence and seed production stages. The weed control rate by weed management practices was higher in field margins (100%) than in the fields (76%). In conclusion, the entireleaf morning glory populations were maintained by specific cohorts in field margins and weed management practices from early August to mid-September can effectively reduce its population size in the field margins.
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