Time for a greenhouse cleanup

July 22, 2014 by Francesca Peduto Hand, Nancy J. Taylor, Beth Scheckelhoff and Luis Cañas.

Over the course of a growing season, plant pathogens and algae flourish on greenhouse surfaces – often harboring pests such as fungus gnats and shore flies. Plant diseases and other insects cause havoc during the production season. Proper disinfection and cleaning should be done routinely though timing does not always allow for it.  Now that your greenhouses are emptying, it is the perfect time to thoroughly clean them!

Pests and diseases are much easier to prevent than to cure, so we strongly suggest cleaning debris from the previous growing season now.  The goal is to eliminate pathogen inoculum and pest populations prior to the next growing cycle. Do not wait until shortly before re-opening to clean.

Here are a few steps for proper greenhouse cleaning:

  1. Physically remove pet plants, plant debris, soil, and weeds from benches, underneath benches and all floors.  Begin at the top and work your way down.
  2. Next, use a cleaning product specifically labeled for greenhouse use to remove algae, dirt and other deposits from greenhouse surfaces. Don’t forget to thoroughly clean walls, internal structures, and textured surfaces as pathogens can hide in many places including the folds in plastic, porous materials, rafters, on top of overhead piping etc. Thoroughly clean benches and worktables, which, as a reminder, should be made of non-porous materials that are easily disinfected.
  3. Wash all containers that will be reused to remove soil particles and plant debris.  Next, treat them with a labeled disinfectant regardless if there was a disease present in the crop. ***Spores of some common root pathogens such as Pythium and Thielaviopsis can survive in root debris or soil particles on pots, flats or other containers. If you have a history of these diseases affecting your crops, it is recommended not to reuse them.***


The picture above shows debris and plants that need to be removed during the summer cleanup process.

Examples of cleaning agents (the list is not all inclusive):

Quaternary ammonium compounds

1- Green-Shield® – Quaternary Amine

2- KleenGrow™ –    Didecyl dimethyl ammonium chloride

3- Physan 20® –      n-alkyl dimethyl benzyl ammonium chloride +

n-alkyl dimethyl ethylbenzyl ammonium chloride

Hydrogen dioxide

4- ZeroTol® 2.0 – Hydrogen Dioxide

5- Oxidate® 2.0 – Hydrogen Dioxide, OMRI listed

Hydrogen peroxide & peroxyacetic acid

6- Sanidate® – Hydrogen Peroxide + Peroxyacetic Aci


7- Chlorine bleach

8- Alcohol, useful to disinfect propagation tools.

Other resources

University of Massachusetts


Oregon State University



Note: Remember to read all labels. It is always the applicator’s responsibility, by law, to read and follow all current label directions for the specific product being used. The authors and Ohio State University assume no liability resulting from the use of these recommendations.


Francesca Peduto Hand

Assistant Professor and Extension Specialist

Department of Plant Pathology



Nancy J. Taylor

Program Director

C. Wayne Ellett Plant & Pest Diagnostic Clinic



Beth Scheckelhoff

Extension Educator – Greenhouse Systems



Luis Cañas

Associate Professor and Extension Specialist

Department of Entomology


Marengo® now labeled for use on greenhouse floors


My colleague Hannah Mathers just shared with me that the label of the herbicide Marengo® now includes greenhouses floors.  This is good news because of the limited number of herbicides available for greenhouse growers.

Marengo® is a pre-emergent selective liquid herbicide that offers long-term residual control of both grassy and broadleaf weeds on ornamentals.  It controls tough grassy weeds such as crabgrass, annual bluegrass, and annual sedge. Marengo also demonstrates early post-emergence activity against some weeds, including annual bluegrass, crabgrass, and oxalis.  The active ingredient (Mode of Action Group 29) prevents weed seed germination by inhibiting cellulose biosynthesis. Marengo does not move once applied to the soil and does not volatilize.

Users should avoid applications when spray particles may be carried by air currents to areas where sensitive crops and plants are growing. Avoid spraying with winds in excess of 10 mph.

For more information, go to: http://www.ohp.com/Products/marengo.php.


Claudio Pasian

Associate Professor



OSU Annuals Trial Open Houses

OSU’s Annual Trial Garden is where YOU can get info on annuals to include in your sales plans.  We at the OSU Annuals Trials will have a couple of open houses for you to evaluate the performance of numerous plants in ground beds, containers in the sun and shade, and hanging baskets.

Growers, independent garden center buyers, landscape designers, and installers are encouraged to visit and take note of the new varieties being grown. You can also observe and study the different growth habits, tolerances, and visual characteristics of the many different varieties that have been put on display. In addition, 2014’s trial celebrates the “Year of the Phlox.” Attendees will have access to the Ornamental Plant Germplasm Center’s Phlox collection, displays, and research.  On top of that, visitors will have an opportunity to enjoy the newly inaugurated Howlett Hall “green roof”.

July 12 and 14

Are you coming to the AmericanHort Cultivate’ 14?  If so, you will be able to take a bus (courtesy of AmericanHort) at the Columbus Convention center which will bring you to campus.  Please check the Cultivate’ 14 program for details.  If you come on Monday July 14, we will have a reception sponsored by Blooms of Bressingham and the organization of the Chadwick Arboretum.

 July 29, 2014

OCNT, Landscape Industry Certified, and ODA pesticide credits will be available.  A wide variety of annual plant material will be presented so industry professionals can evaluate and note those that have commercial application in Ohio.

 Speakers that day include:

 • Mr. Dean Bemis (Syngenta), “Annuals you Should Know & Use”

 • Dr. Luis Cañas (OSU Department of Entomology), “Alternatives to Manage Insects on Ornamental Plants for Home Owners”

 • Dr. Claudio Pasian (OSU Department of Horticulture and Crop Science), “Sanitation, Key to Headaches Prevention”

For more information, please contact:

 Dr. Claudio Pasian


The OSU Department of Horticulture and Crop Science



Don’t Stop Scouting!

It’s tempting to stop scouting for insect and disease pests this time of year – there is already so much to do and not enough hours in the day to get it all done.  Remain vigilant and continue to look for signs of insects and diseases lurking in your crops!  Recent greenhouse visits have uncovered two usual suspects – thrips and aphids.  If you aren’t sure what to look for here are a few examples. remember to put out sticky cards and have someone check them weekly – as well as walk through the greenhouse making note of anything out of the ordinary.  The goal is to be proactive in dealing with greenhouse pests, not reactive!


Aphids feed on plant sap and can often be detected by the presence of a sticky honeydew.  They are notorious for multiplying quickly on greenhouse crops so thorough scouting and control measures are important to keep populations in check.  Growers might find both winged and non-winged aphids on their crops.  Some control recommendations can be found in a previous post by Dr. Ray Cloyd here:

aphids-for-web Aphids on sweet potato vine.










Thrips are tiny, cigar-shaped insects that can often be found in the flower heads of on gerber daisies, osteospermum, dianthus, marigold, petunia, vinca, and countless other bedding and flowering plants.  Thrips feed on leaves and flowers by piercing the plant parts and sucking out its contents.  They not only damage leaves and flowers but can also transmit plant viruses like tomato spotted wilt virus (TSWV).  One good way to detect thrips is to tap or shake a few flowers heads over a white piece of paper.  If thrips are present, a few will generally fall onto the paper and can be easily seen. Dr. ray Cloyd’s recommendations for thrips control can be found here.

close-up-thrip A thrip on Gerbera petal









Thrips damage to osteospermum petals include markings with loss of coloration.thrips with damage on osteos









thrips damage on foliage Thrips damage on foliage due to piercing and sucking of the tissues.






How Local is “Locally Grown”?

I enjoy visiting the independently-owned-and-operated greenhouses and garden centers in my region of Ohio – and when doing so also make it a point to visit the surrounding box stores.  I like to compare the product selection and quality, pricing, and see what type of consumer shops in each store.  This can be an eye-opening experience!

The growers in NW Ohio have worked together for several years on a educational/media campaign to promote “buying local”.  You can check out some of these branding and marketing efforts at www.maumeevalleygrowers.com. Today I ran across this “locally grown” signage at a box store in NW Ohio:

locally grown wave sign cropped

In looking at the individual container labels, these wave petunias and other plants similarly advertised were grown 158 miles and 2 hours and 21 minutes away (according to MapQuest).  While I couldn’t find a description or definition of local in the store itself, the box store website explains that they work with “local growers in the five states” they service to source their flowers and plants.  So how far can a “locally grown” product be grown and still be considered “local”?  I’m not sure this question can be answered in a way that would satisfy all of us.  Do you consider this to be truth in advertising or misleading to the general public?  One thing is certain, it is interesting to see how businesses are defining and sourcing “local” products.

We would love to hear how you are promoting “buy local” in your greenhouse or garden center! Please leave a comment below: