Floriculture Greenhouse Update

It's that time of year when Oriental bittersweet berries are in abundant supply and show up as wreaths, swags and in other decorative crafts for sale at roadside stands and other retail outlets. This is just a reminder that bittersweet (Celastrus orbiculatus) is considered an invasive plant along with purple loosestrife (Lythrum salicaria), yellow iris (Iris pseudacorus) and many others. Connecticut has 96 plants on the official state list that are invasive or potentially invasive and 81 of those are banned. Massachusetts has 140 plants identified as either noxious and/or invasive that are banned. In MA a few woody ornamentals have an extension until January 1, 2009. When choosing plants to grow and sell and when using plant material for crafts, obtain a list of prohibited plants from your state Department of Agriculture. Noxious and/or invasive plants are prohibited from being sold, traded, purchased and distributed. Invasive plants, as defined by the Massachusetts Invasive Plant Group, are "plants that have spread into native or minimally managed plant systems in Massachusetts. These plants cause economic or environmental harm by developing self-sustaining populations and becoming dominant and/or disruptive to those systems." For a list of prohibited plants in Massachusetts and Connecticut and for more information, see the websites below.

USDA National Invasive Species Information Center:  Massachusetts   Connecticut  (Other States)

Massachusetts Department of Agricultural Resources - Massachusetts Prohibited Plants

Massachusetts Nursery Landscape Association (Includes alternative plants)

Connecticut Invasive Plant Working Group

Purple Loosestrife Biological Control Projects Massachusetts: Massachusetts Wetlands Restoration Program's Purple Loosestrife Biocontrol Project  

Connecticut: Beetle Farmers Project http://www.hort.uconn.edu:80/ipm/general/biocntrl/beetlefarm/beetlfarmmain.htm

Tina Smith, University of Massachusetts Extension Donna Ellis, University of Connecticut Extension

Many growers (who are growing their garden mums in outdoor fields) may have a few greenhouses empty between crops. If so, it's a good time to do a thorough clean up, including removing existing weeds (either hand pulling isolated weeds) or using a post emergence herbicide such as glyphosate that can be used in an empty greenhouse between crops as well as outside greenhouses.  However, both of these measures do not prevent reseeding of weeds. So, repair any tears in the weed block fabric or replace if needed. 

For more information see: Managing Weeds In and Around Greenhouses

Leanne Pundt University of Connecticut

Liverworts (Marchantia polymorpha) are branching, ribbon-like plants lacking distinct roots, stems and leaves. They reproduce by spores and vegetatively. Stalked, umbrella-like structures release spores. Small, bud-like branches produced in cup-like structures on the surface of the plant also help spread liverworts from pot to pot by water droplets during irrigation. Liverworts thrive in conditions of high fertility, moisture and humidity.

Inspect incoming plants for signs of liverworts and isolate infected plants. If the growing media stays moist, small infestations of liverwort can quickly spread through an entire greenhouse. Clean and disinfect empty greenhouses to remove spores. Store growing media properly to prevent contamination from the spores.

Avoid overwatering crops and water according to plant need. Use of coarse textured mulch helps reduce surface moisture levels. Topdressing slow release fertilizers contributes to increased fertility levels on the media surface and to the growth of liverworts. Proper plant spacing helps to reduce humidity levels. Liverworts lack true roots, so allowing the media to dry between watering, helps reduce their vigor.

Sodium carbonate peroxyhydrate (TerraCyte®) is labeled for the prevention and control of algae, moss, and liverworts. Terracyte® is water activated. Several precautions are noted on the TerraCyte®label. First test a small section of ornamental plants at labeled rates for potential phytotoxicity before large-scale use. Phytotoxicity may occur on sensitive crops. Thoroughly rinse granules of foliage to prevent contact burn. Repeat applications can also raise soil pH to levels that can adversely affect plant growth. TerraCyte® is also incompatible with metal-based fungicides and fertilizers.

Photo of Liverworts

Leanne Pundt Extension Educator University of Connecticut

Over watering and compacted growing media, especially in newly planted bedding plants and hanging baskets, often leads to the buildup of algae on the surface of the growing media. Train employees on proper watering practices so that the upper surface of your media dries out between watering.

Avoid excessive fertilization, runoff and puddling water on floors, benches, and greenhouse surfaces to discourage algae growth. Proper drainage is needed so that water, especially water containing fertilizer, does not stand on the floor.

A number of different algaecides are commercially available. Read the labels carefully before use. Many algaecides including Green-Shield, GreenClean and Triathlon are only labeled for use on greenhouse surfaces.

ZeroTol, Physan 20, and TerraCyte have broader uses listed on their labels so may be used on both greenhouse surfaces and plants - but read the labels carefully for plant safety use restrictions. For example, Physan 20 is only labeled for use on orchids, roses and African violets. According to the Terracyte label, it states to test a small section of plants at labeled rates for potential phytoxicity before large-scale use. Repeated applications of TerraCyte can also raise the soil pH.

Many growers have reported good results using Selectrocide. Phytotoxicity may occur at concentrations above 20 ppm  so the shock treatment to clean irrigation lines needs to be done between crop cycles   when the greenhouse is empty of plants. Once the lines have been cleaned, the continuous dose is below the 20 ppm level.

For more information see: www.griffins.com/tech_service/pdfs/selectrocide_faqs.pdf

Leanne Pundt

Before placing a crop in a greenhouse this growing season, be sure the greenhouse is free of weeds. One way to prevent weeds is to use weed block fabric on greenhouse floors. To prevent water from puddling and creating a safety hazard, start with a well-drained gravel floor. Place the weed fabric over the gravel and leave the weed fabric bare so it can be easily swept. Covering the fabric with crushed stone will make it difficult to remove spilled growing media and make an ideal environment for weeds to grow.

Also, growers are reminded that the herbicide Surflan is no longer registered for use in enclosed greenhouse structures. Currently there are no preemergence herbicides (applied before weeds emerge) labeled for greenhouse use. However, there are several postemergence herbicides available (applied after the weeds have emerged).

For more information see the fact sheets: Managing Weeds in Your Greenhouse Disinfecting the Greenhouse

Tina Smith