Grower Notes and Pest News
I have gathered some more information after my first blog and here is an update on the maggot issue we are seeing in Santa Maria and parts of Oxnard.
Santa Barbara Co entomologist, Brian Cabrera and UC Davis entomologist, Frank Zalom both recovered larvae of the dark-winged fungus gnat (Family: Sciaridae) from the strawberry plants they received. These larvae primarily feed on fungus and decaying plant material, but they can also feed on plant roots. They are also known to mechanically vectoring plant pathogenic fungi.
Dark-winged fungus gnat larva from strawberry plants (Courtesy: Brian Cabrera)
A PCA had reported finding seedcorn maggot-like larvae in the strawberry fields near Oxnard. A few growers had also mentioned similar findings in Santa Maria. I too found similar maggots in fields I checked later on. So, we have two species infesting the strawberry plants at this time.
Seedcorn maggot flies are attracted to decaying plant material, but their maggots feed on living plant material. Dark-winged fungus gnats do not appear to be new in the strawberry fields. Brian Cabrera found them early this year in dead strawberry plant specimens. The probable reason for seeing more of them now is that there is more dead plant material from the other maggot damage. Is it possible that we have a primary invader, seedcorn maggot-like one and a secondary invader, the dark-winged fungus gnat larva? This is just a thought. High soil moisture from recent rains can also worsen their problem. Damage from both maggots can also increase vulnerability of plants to pathogens.
Organophosphates will control these maggots, but Frank Zalom mentioned that growth regulators like azadirachtin can also be effective. Neonicotinoids like imidacloprid are not known to have any effectiveness.
We need to continue close monitoring of this problem and share the information.
Whitish maggots with a tapering body (above) and about 1/4 inch long (below)
Several growers in the Santa Maria area reported maggot infestation in their young strawberry fields. I have visited some fields and collected some specimens. These maggots are whitish with a tapering body and approximately ¼ inch long. They are legless and seemed to have a thick and opaque skin. These look like seedcorn maggots [Delia platura (Family: Anthomyiidae)], but accurate identification is pending. UC researchers, CDFA and Ag Commissioner's office has the specimens and we are working on identifying the pest.
Maggots were found feeding in the root area at the base of the crown. Seedcorn maggot adults are usually attracted to decaying crop residue and moist soil. It is a good idea to set up yellow sticky traps in the fields for catching adults to help with the identification. It appeared that some growers have treated the fields with imidacloprid, diazinon and chlorpyrifos.
Someone at the field mentioned that these are thought to be fungus gnats. But these are not. Fungus gnat larvae have a whitish to translucent and elongated body. They have wormlike appearance and have a conspicuous shiny black head capsule.