I’m not a physician; however I am strongly convinced that too many greenhouse growers suffer from this seldom-recognized affliction. What is lutheolentumpapyrophobia?

First, let’s consider the meaning and origin of this long word. It’s a combination of Latin and Greek words: Lutheo (from Latin) means yellow; Lentum (from Latin) means sticky; Papyro (from Latin) means paper; and Phobia (from Greek) means Fear. In other words, this lengthy word describes the fear that many greenhouse growers have of yellow sticky cards. I don’t know how this disease is transmitted but it must be very contagious because too many growers use yellow sticky cards incorrectly, or not at all.

Do you suffer of this often-undetected disease? If so, you need to take a deep breath, use all the will power you can muster, get yellow sticky cards, and start posting them among your crops. If you need help on how to proceed correctly, please get in touch with an Extension Educator or State Specialist for help.

As I write this, the poinsettia crop is underway. Be pro-active! Monitor the presence of flying insects and take control of them before they take control of your crop. You will have fewer headaches and save money at the same time.

Dr. Claudio Carlos Pasian
Department of Horticulture and Crop Science
The Ohio State University

By Dr. Claudio Pasian

Department of Horticulture and Crop Science

Columbus, OH 43210

During the month of May, every grower is (hopefully) very busy selling plants.  The goal is to have most of the greenhouses empty.  Empty greenhouses highlight the weeds that have been growing on floors and/or under benches along with the crops. When the “sell fever” subsides, growers start cleaning the greenhouses.  By then it may be too late.  The problem may have perpetuated itself through a “seed bank”.

Weeds are a no-no in greenhouses since they can harbor pests such insects, arthropods, or pathogens like virus.  The most common weed control is plastic weed barriers.  Some growers use mechanical control (physical removal) and occasionally herbicides. 

        Unfortunately, many growers lack a clear understanding of what is called “seed bank.”   A single weed plant can produce many seeds (hundreds or thousands depending on species).  After seed dispersal, most seeds reach the soil.  Only a small percentage of them will germinate the next season; most of them remain in the soil for years and a portion of them will germinate in successive seasons.  This represents a survival mechanism for many species: even if the environmental conditions are not adequate during several years, some of the seeds will germinate later enough for those conditions to have improved. 

 This means that leaving weeds to produce seeds in your greenhouse can result in having weeds for years to come. When the plastic weed barrier is old, it not only breaks down but also cracks between the barrier and walls, cement walkways, etc.  Seeds landing in these cracks will find soil where they will germinate and grow.

I advise growers to avoid the use of herbicides in greenhouses or use herbicides as a choice of last resort.  Many growers do not know that despite the fact that there are many herbicides, only a few are registered for greenhouse use.  The reason is that the active ingredient of many of them can volatilize and harm the plants in a closed environment such a greenhouse.  Also important to know is that there is no pre-emergent herbicide registered to be used in greenhouses.

             Herbicides that can be used in greenhouses:

 Non-residual, non-selective, systemic herbicides:

–          Glyphosate: Roundup Pro and other trade names

Non-residual, non- selective, contact herbicides:

–          Diquat dibromide: Reward

–          Pelargonic acid: Scythe

–          Ammonium nonanoate: Axxe

Selective, non-residual, systemic herbicides (control grassy weeds):

–          Clethodim: Envoy

–          Fluazipof-P-butyl: Fusilade II

             Also remember that seeds are moved into greenhouses by wind, transported by people, animals, etc.  Be sure, to keep the areas surrounding the greenhouses weed free by covering them with plastic weed barrier or gravel.

By Tom Dudek, Michigan State University Extension

Nursery and greenhouse growers have been challenged by recent cloudy and rainy weather to produce perennials and keep away Botrytis. Remembering cultural practices and correct fungicides will help until we get more sunshine.

The recent cool, dark, wet weather conditions along with perennials being in full flower in area poly houses and greenhouses can lead to Botrytis blight outbreaks. Crops like coreopsis, dianthus (Photo 1), heuchera, lavandul and rudbeckia can be especially vulnerable to this disease since they have a full flower canopy at this time.

Photo 1. Botrytis flower blight on dianthus. Photo credit: Cheryl Smith, Univ. of New Hampshire

Remember that botrytis is a fungus that can cause leaf spots, petiole blighting (Photo 2) and stem cankers on many different annuals and perennials. It will produce large masses of spores that are most often called “grey mold” (Photo 3). These spores or conidia will be spread on wind currents and can travel from infected to uninfected plants in that manner. The spores can live for upwards of 21 to 24 days before they germinate on a plant.

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Photo 2. Botrytis on petiole of delphinium. Photo credit: Maria Tobiasz, Cornell Univ.

Photo 3. Botrytis sporulation close-up. Photo credit: Tom Creswell, Purdue Univ.

Michigan State University Extension suggests these cultural control practices that will reduce the conditions that favor Botrytis infections, including: reducing the relative humidity in the greenhouse or poly house below 85 percent; making sure plants do not remain wet for six or more hours in a 24-hour period; and if possible, heat and vent mornings and evenings for at least a half-hour or more to reduce humidity and keep plant surfaces dry.

If plants are infected and need to be removed from the growing area, do not just remove the plants and throw them on the compost pile out back as the spores can blow back into the facilities on wind currents. Bag up plants where they were growing, seal the bags and remove them from the facilities.

As for preventative fungicides, MSU plant pathologists recommend fungicides that contain the following active ingredients: chlorothalonil, fenhexamid, iprodione, pyraclostrobin + boscalid, cyprodinil +fludioxonil or polyoxin D zinc salt.

Apply any of the above mentioned products and be sure to have complete coverage and do not go longer than seven days between applications for your best results. Some of the above mentioned products may “spot” open flowers or leave a residue.

Please contact Tom Dudek
at 616-994-4542 for more information on this disease.

This article was originally published by Michigan State University Extension. For more information, visit http://www.msue.msu.edu. To contact an expert in your area in Michigan, visit http://expert.msue.msu.edu, or call 888-MSUE4MI (888-678-3464).