Modeling the relationship between estimated foliar fungicide use and soybean yield losses due to foliar fungal diseases in the United States

Abstract

24Fungicide use in the United States to manage soybean diseases has increased in recent years. The 25 ability of fungicides to reduce disease-associated yield losses varies greatly depending on multiple 26 factors. Nonetheless, historical data are useful to understand the broad sense and long-term trends 27 related to fungicide use practices. In the current study, the relationship between estimated soybean 28 yield losses due to selected foliar diseases and foliar fungicide use was investigated using annual 29 data from 28 soybean growing states over the period of 2005 to 2015. At a national scale, a 30 significant quadratic relationship was observed between total estimated yield losses and total 31 fungicide use (R 2 = 0.123, P < 0.0001) where yield losses initially increased, reached a plateau, 32 and subsequently decreased with increasing fungicide use. The positive phase of the quadratic 33 curve could be associated with insufficient amount of fungicides being used to manage targeted 34 diseases, application of more-than-recommended prophylactic fungicides under no/low disease 35 pressure, application of curative fungicides after economic injury level, and reduced fungicide 36 efficacy due to a variety of factors such as unfavorable environmental conditions and resistance of 37 targeted pathogen populations to the specific active ingredient applied. Interestingly, a significant 38 quadratic relationship was also observed between total soybean production and total foliar 39 fungicide use (R 2 = 0.36, P < 0.0001). The positive phase of the quadratic curve may suggest that 40 factors like plant physiological changes, including increased chlorophyll content, photosynthetic 41 rates, water use efficiency, and delayed senescence that have been widely reported to occur after 42 application of certain foliar fungicides could have potentially contributed to enhanced yield. 43Therefore, the current study provides evidence of the potential usefulness of foliar fungicide 44 applications to mitigate soybean yield losses associated with foliar diseases and their potential to 45 3 positively impact soybean production/yield at national and regional scales although discrepancies 46 to the general trends observed at national and regional scales do prevail at the local (state) level. 47 48 49 50 51 Soybean [Glycine max (L.) Merrill] is a key agricultural commodity in the United States and has 52 been cultivated on 34.7 million hectares on average annually between 2015 and 2019 (USDA-53 NASS). Similar to the production of other economically important crops, numerous abiotic and 54 biotic stressors like adverse weather, variation in soil characteristics, diseases, insects, and weeds 55 present enormous challenges to soybean production [1, 2]. Soybean diseases are detrimental to 56 production due to their deleterious effects on yield. In the U.S., the average annual disease-57 associated soybean yield losses are approximately 11% [3]. However, the relative importance of 58 diseases and concomitant yield losses vary both tempora...

Dissecting the economic impact of soybean diseases in the United States over two decades

“…The ability to scout and monitor fields is potentially more challenging with farms where there are large soybean hectares (e.g., harvest zones 3 and 4). Furthermore, one of our different study showed that the mean per hectare foliar fungicide use was significantly low in high harvest zones while the use was greater in low harvest zones [59]. This could potentially result in poor foliar fungal disease control in high harvest zones, leading to greater economic losses.…”