Bermudagrass stem maggot
Bermudagrass stem maggot
A new exotic invasive fly, Atherigona reversura, also known as the bermudagrass stem maggot (BSM), was discovered in Georgia in 2010 damaging bermudagrass pasture and hay fields. This was the first record of this species in North America. Preliminary greenhouse and field studies demonstrated the potential for economic damage to Georgia turf and forage producers. Field studies at the UGA Tifton Campus provided data to support these fears, with yield losses in excess of 50% for susceptible varieties in late summer harvests. Those studies also established protocols to be used in refining management recommendations for insecticide applications to minimize yield loss from the maggots.
Bermudagrass is the most widely grown grass for forage, pasture and hay production in the coastal plain region of the southeastern U.S. Bermudagrass also is widely used as a turf grass in the southern U.S. and around the world and represents the bulk of sod grown in Georgia, a crop worth an estimated $116 million in 2009. In summer and fall of 2010, extensive damage to bermudagrass pastures by BSM was reported by county agents in southern Georgia. The damage consisted of the death of top leaves and growing point of infested stems in a manner that had not been observed before. Many fields were heavily infested and gave the appearance of frost or cold damage. Damage in late summer and fall of 2011 was even more widespread and severe, and combined with severe drought to reduce hay production in many areas. The worst hit fields lost an estimated 20% of the late season hay crop. Damage was also observed in turf-type common Bermuda on the UGA Tifton campus. By summer, 2012 the fly had spread across the southeast and yield losses appeared to be rising. While range expansion has slowed since, the fly continues to be a significant pest across the southern U.S. and has persisted at unacceptable population levels through 2018. Calls for information and control recommendations regularly come from as far away as Texas and Arkansas.
Preliminary investigation suggests the fly will not be a significant problem in turf.
Cultivar preference trials demonstrated distinct preferences for some forage types over others, but also showed that the fly can and will attack all widely used bermudagrass varieties. Valuable information about the biology and life cycle of the fly was also gathered. These results allowed us to produce recommendations for control of the fly in late season that showed promise for reducing damage if applied in a timely manner. Field trials in 2012 allowed us to refine the control recommendations and demonstrate their effectiveness, reducing crop loss to negligible levels.
Preference trials with turf had similar results with a range of turfgrass varieties. All tested cultivars were attacked, although damage was less severe than in forage type bermudagrasses. Additional work on sampling techniques provides researchers and growers with a way to accurately estimate fly populations in the field.
Small plot studies have now shown yield reductions for susceptible varieties in late season harvests to be over 80% in some cases. Based on our results, we estimate the BSM has the potential to cost hay producers in GA as much as $40 million in lost yield annually if not controlled. The techniques developed in 2015 were used from 2016 through 2018 to refine our understanding of timing of treatments to minimize both yield loss and insecticide applications, protecting both the bottom line and the environment.
We began a series of laboratory and field research studies to examine further the biology of A. reversura and its potential economic impact. Development of effective methods for controlling this new pest provides immediate options for growers while we evaluate the potential for long term management strategies. Sampling methods are key to any ecological studies but have not proven useful for management decisions. However, we have developed broad recommendations for management decisions based on accumulated damage which have been used successfully by growers across the region. Small plot studies have produced data indicating potential yield loss of more than 80% in some varieties in late summer, providing growers with an economic value to use when making cost-benefit decisions. The protocols developed in 2015 were used in small plot trials to determine the optimal timing for insecticide application and to screen some candidate materials for efficacy. Larger scale trials with more field-realistic plot sizes were initiated in 2017, along with on-farm studies with grower cooperators. Our current treatment recommendations can reduce yield losses to less than 5%, but only insecticides in the pyrethroid class of chemistry have shown consistent efficacy. The search for additional control products continues, as reliance on a single insecticide class not sustainable in most agricultural situations.