Greenhouse TPM/IPM Report
Central Maryland Research and Education Center
Ellicott City, Maryland
May 4, 2016
From: Stanton Gill, Extension Specialist – IPM for Greenhouse and Nurseries, Central Maryland Research and
Education Center, University of Maryland Extension
Karen Rane, Extension Specialist, Director of the Plant Diagnostic Clinic, University of Maryland Extension
Andrew Ristvey, Extension Specialist, Wye Research and Education Center, University of Maryland Extension
Suzanne Klick, Technician, CMREC, University of Maryland Extension
Shore Fly Biocontrol
By: Stanton Gill
Shore flies tend to build up in greenhouses at this
time of year when plants are filling the growing
space and there is plenty of moisture in the
greenhouse. The moisture allows algae to grow
on susbtrates, under benches, and below flats.
Where algae grows the shore flies lay their eggs,
and you quickly have epic levels of adult shore
flies showing up within 10 -1 4 days after the egg
laying occurs.
One of the best predators to release in a
greenhouse for shore fly control is rove beetles.
When they are released some growers have made
Atheta Boxes. The boxes might be something to
consider, though I have no data on efficacy. Shore flies have robust bodies and spots on their
wings
There’s a photo and a description of them in this
article: http://www.ballpublishing.com/GrowerTalks/ViewArticle.aspx?articleid=22186
John Sanderson, Cornell University, had the following comments about shoreflies in greenhouses: “ A very
large greenhouse business in NY has been using regular nematode applications for shore flies, fungus gnats,
and Western flower thrips pupae, and I’ve never seen such amazing shore fly control. NO shore flies in his large
propagation areas, even though he said they were once a constant battle for him. And plenty of algae around.”
As for the source of shore flies, if the greenhouse is anything like a normal greenhouse, there is no need to look
for a source of algae. It grows anywhere that there is a substrate, light, water, and a source of nutrients. Algae
is common in irrigation water. And if there is algae in any greenhouse, then shore flies will soon follow. All it
takes for a healthy shore fly population is the very thin amount of algae that typically covers the soil surface of
any plant container in a greenhouse, as long as it’s watered. I’ve even seen shore fly larvae developing on the
tiny patch of algae that was growing on a slowly-leaking jet on a watering boom in a greenhouse. No need to
look for an isolated source of shore flies or algae.
Botrytis Blight
By: Karen Rane
Cloudy, wet weather outside, greenhouse full of
flowering plants inside – it’s a scenario that sets
the stage for Botrytis blight problems. Petals are
particularly susceptible to infection by this everpresent fungal pathogen. The fungus produces a
huge amount of gray-brown spores on infected
tissue. These spores can germinate and cause
infection in as little as 4-8 hours in films of water,
so avoiding condensation on plant tissues and
minimizing leaf wetness from irrigation is critical
for disease management. Increased plant spacing,
watering early in the day and heating and venting
the greenhouse at sunset are all strategies to reduce
humidity and minimize leaf wetness.
High moisture levels, tight spacing, and a lot of
flowers provide ideal conditions for Botrytis blight
problems in greenhouses
Once flowers become infected, petals can fall and
initiate leaf and stem infections. Even fallen leaves
on greenhouse benches and floors can be the source of Botrytis infection, so sanitation plays an important
role in Botrytis management. There are a number of fungicides effective in managing this disease, but these
must be used in conjunction with cultural practices to reduce leaf wetness. Keep in mind that flower tissue is
more susceptible to spray injury than leaf tissue, and some products leave unsightly residues. Many growers
find fenhexamid (Decree) with a surfactant like Capsil is a safe and effective late season Botrytis product, but
resistance to the active ingredient has been reported. Other late-season products for Botrytis control include
polyoxin D zinc (Affirm WDG) and the biological control product Cease (Bacillus subtilis QST 713 strain). It’s
always a good idea to test products on a few plants at first to check for phytotoxicity and residues, and follow all
label instructions.
For excellent pictures of Botrytis symptoms and additional management information, check out the pdf on
Botrytis Blight posted on the e-GRO website: http://www.e-gro.org/pdf/505.pdf.
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and no endorsement by University of Maryland Extension is implied.
Read labels carefully before applying any pesticides.
Photographs are by Suzanne Klick and Stanton Gill unless stated otherwise.
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