Bermudagrass producers have been fortunate with the absence of an insect pest that preys solely on this common forage species. Unfortunately, that is about to change. Unlike grasshoppers or armyworms that feed on many species of plants, the bermudagrass stem maggot specifically targets bermudagrass fields.
It could also be aptly named the bermudagrass stem borer for the way the larvae bore through the stem killing the upper part of the plant. Now, it seems the stem maggot is making its way into Oklahoma and looking for an easy meal.
The stem maggot is a species of fly native to Japan, Indonesia, India and Hawaii. Its first appearance in North America occurred in 2010 in Georgia. By 2012, the fly had migrated over most of the Southeast U.S. It was thought that Oklahoma would be safe for five to 10 years. However, the summer of 2014 has shown cases across Arkansas and a pending confirmation from an entomologist, a potential case in Pittsburg County near McAlester, Okla.
This fly, which resembles a housefly, lays an egg on the stem of a bermudagrass plant near a node. A maggot emerges from the egg and moves toward a node on the plant where a leaf emerges. The maggot then bores into the shoot and begins to feed on the inner-stem. This feeding causes the shoot to cease elongation and the leaves above where the maggot enters begin to die. This is usually the top two leaves of the plant and contributes to the yield loss caused by this pest. These dead tops give the bermudagrass field a frosted appearance and is the first indication this pest is present. The plant may attempt to grow a new shoot from a node below the damage which can either restore some lost yield or be a potential host site for the next generation of maggots.
The amount of damage seems to depend on the stage of growth of the plant. Damage early in the season followed by poor regrowth conditions can drastically reduce yields, however good conditions can allow the plant to recover most of the lost yield.
Additionally, sites with poor soils or inadequate fertility can be the hardest hit because of low vigor within the plant. Current research is also finding that coarser stemmed varieties show fewer total stems are damaged when compared to fine-stemmed varieties.
Since little is known about this pest control strategies are still being refined. Using harvest as a tool is likely a producer’s best strategy to thwart this pest. Georgia and Alabama Extension have reported if damage occurs within one week of planned harvest, proceed as soon as possible. If damage is occurring one to three weeks after the previous harvest and yield is moderate, proceed with another harvest since little yield will be added after infestation. Harvest seems to break the lifecycle of the growing maggot if implemented before they pupate into an adult fly.
Insecticides are also a possibility, but since the life cycle spends a large proportion of time within the plant, contact insecticides can be ineffective.
Pyrethroid insecticides, which are labeled for pasture use, have proven somewhat effective if used immediately following a cutting in high damage areas. The best strategy has been two applications, the first following baling at initial regrowth and the second five to seven days later. The lowest labeled rate of these insecticides have proven sufficient for acceptable control.
If you think you have an infestation of stem maggot contact your local county extension educator so we can begin to map this pest within Oklahoma.
Additionally, before considering chemical control consult your educator for insecticide recommendations labeled for pasture use.