§      Restrictions on ornamental herbicides for use in enclosed structures
§      Check for fungus gnat larvae using potato disks
§     Downy mildew on impatiens in the UK, a problem for U.S.?
§     Core manual now offered in Spanish
§      North Central Regional Publication 481: Biocontrol in Greenhouses

Restrictions on ornamental herbicides for use in enclosed structures
Rob Richardson
Horticulture

In Michigan, no preemergence (residual) herbicides may be applied in an enclosed structure, including greenhouses.  However, a few products are available for postemergence weed control.  Diquat (Reward), pelargonic acid (Scythe), glyphosate (Roundup and others), clethodim (Envoy), fluazifop (Fusilade II) and glufosinate (Finale) may be applied under labeled conditions.  Reward may be used to control weeds beneath greenhouse benches.  Scythe may be used before planting, before crop emergence, directed around desirable plants, or applied to floors and walkways.  Roundup and most other glyphosate formulations may be applied in greenhouses, but no desirable plants may be present.  Finale may be applied as a directed spray in greenhouses void of edible crops.  Do not allow Reward, Scythe, Roundup, or Finale to contact desirable foliage or severe crop injury may occur.  Envoy and Fusilade II may be applied in greenhouses for control of grasses.  These two herbicides may be applied over many broadleaf crops that appear on the label.

Some products are also available for control of "lower plants" in greenhouses, such as moss, algae, liverwort, etc.  These products include Cinnamite, Terracyte, Zerotol, and Valero.

The following summarizes label restrictions of selected preemergence herbicides for enclosed houses:

§      Barricade 65 WG - Uncovered polyhouses must remain open for seven days and ornamentals must receive two irrigations (at least a half inch of water) before enclosure.
§      Devrinol 50DF - No relevant verbiage on label.
§      Gallery 75DF - Do not use in greenhouses or enclosed structures.  Do not apply within three weeks of enclosure.
§      Goal 2XL - Do not use in greenhouses or enclosed structures.
§      OH2 - Do not use in greenhouses or enclosed structures.
§      Pendulum 3.3 EC - Do not use in greenhouses or enclosed structures.
§      Pennant Magnum - Do not use in greenhouses or enclosed structures.
§      Pre Pair - Do not use in greenhouses or enclosed structures.
§      Ronstar 50WSP - Do not use in greenhouses.
§      Rout - Do not apply in enclosed greenhouses.  Apply two weeks before placing plants in an enclosed structure.
§      Snapshot 2.5 TG - Do not apply in enclosed greenhouses.  Do not apply within three weeks of enclosure.
§      SureGuard - Do not use in greenhouses or enclosed structures.
§      Surflan AS Specialty - Do not apply in enclosed greenhouses.  Do not apply within three weeks of enclosure.
§      Treflan 5G - Do not use in greenhouses or enclosed structures.

As with all pesticides, refer to the label prior to application to determine the appropriate manner in which the product may be applied.

Check for fungus gnat larvae using potato disks
Dean Krauskopf
Integrated Crop Management Agent, Southeast Michigan

Most growers use yellow sticky cards to monitor for fungus gnat adults, but significant numbers of larvae can be attacking plant roots before you see many adults on the cards.  To get on top of an infestation early, use potato disks or cubes to trap the larvae so they can be easily seen.  The disk or cube should be about an inch across and an inch tall and should be pressed into the media so just the top surface is showing. 

Dr. Ray Cloyd and his fellow researchers at the University of Illinois (Effect of Monitoring Technique in Determining the Presence of Fungus Gnat, Bradysia spp. [Diptera: Sciaridae], Larvae in Growing Medium. Cabrera, Cloyd and Zaborski, J. Agric. Urban Entomol, Vol. 20, No. 1, 2003) have shown 48 hours is the optimum time to leave the disks in the pots before looking for larvae.  If you wait longer than 48 hours the potato disk or cube starts to break down and it's harder to see the larvae.  Larvae are easy to spot because they have a black head that stands out against the white potato.  Place the potato disks or cubes in pots scattered throughout the bench or house since the infestation may be quite localized.

Downy mildew is a pathogen of Impatiens spp. throughout the world and has been reported in the U.S., Canada, Asia, Europe, and India. In the U.S., downy mildew on Impatiens spp. was first reported in 1942. Since that time, downy mildew on Impatiens spp. has occurred sporadically throughout the U.S.

The downy mildew that affects Impatiens spp. is caused by a fungal-like microscopic organism called Plasmopara obducens. The downy mildew on snapdragons cannot blight roses, nor can the downy mildew on impatiens spread to any plant outside of the Impatiens group. Plants in the Impatiens group include bedding plant impatiens, New Guinea impatiens, vegetatively-propagated impatiens, and garden balsam.

Downy mildew checklist
§      Yellowish or pale green foliage
§      Downward curling of the leaves
§      Distortion of the leaves
§      White to light gray fuzz on the undersides of the leaves
§      Emerging leaves that are small and/or discolored (yellow or pale green)
§      Flower buds may fail to form
§      Plants may be stunted

The most obvious sign of downy mildew is the white, grayish fuzz that develops on the underside of the leaves. This can go unnoticed because growers are not accustomed to turning over the leaves to look for plant problems. Perhaps other than an especially severe case of Botrytis, no other disease causes such obvious gray fuzz, especially on the underside of the leaf. This disease should not be confused with powdery mildew, which affects some floriculture crops and has white fuzzy growth.

Scout impatiens when received
When receiving impatiens, scout them immediately by examining fully expanded leaves, paying special attention to the undersides of leaves. Scout a minimum of 1 out of every 30 plants. Since plants may be infected with downy mildew but not show white or grayish fuzz immediately, they should be scouted weekly. If diseased plants are discovered they should be discarded immediately. Diseased plants should not be placed in a cull or compost pile. Healthy-appearing plants adjacent to the diseased plants should also be discarded. All remaining impatiens anywhere on the premises should be treated with fungicides.

Fungicides should be applied preventively before disease develops. Downy mildew has the bad habit of changing and becoming resistant to the systemic fungicides (example: Subdue MAXX). Since Subdue MAXX is especially at risk it should only be used once in a production program and must only be applied as a drench.

An example of a fungicide program for downy mildew
Subdue MAXX drench at planting only.
Weekly foliar sprays could include the following:
Spray 1 - Mancozeb
Spray 2 - Stature DM 50WP+ Mancozeb
Spray 3 - Mancozeb
Spray 4 - Aliette + Mancozeb
Spray 5 - Mancozeb
Spray 6 - Strobilurin (examples: Compass 50WDG or Heritage 50WG) + Mancozeb
Spray 7 - Repeat the program beginning with Spray 1

Greenhouse, landscape and many other agricultural businesses depend on Spanish speaking employees. According to Araceli Diaz from the Michigan Department of Labor & Economic Growth, 45,000 migrant workers are employed in Michigan's agricultural businesses.  MSU's Floriculture Area of Expertise team identified this ever-increasing trend and began offering the College of Knowledge in Spanish to help educate your permanent employees about the basic skills and knowledge needed to become an effective grower. 

I was asked, "If we have put these individuals through the College of Knowledge and they are ready to take more responsibility as a grower, what do we do about getting them certified as a pesticide applicator?"  Our bedding plant producers and the fruit producers pushed Michigan Department of Agriculture to offer the exam in Spanish and once that was established, Michigan State University moved forward to develop/translate the Spanish core certification manual. For many it's been a long time coming however I can announce that it is officially available.

This Spanish version is now available through the MSU bulletin office for $15.00 as E-2195SP, Manual Basico de Entrenamiento para Aplicadores de Pesticidas.  This manual was edited by individuals speaking several different Spanish dialects, so there is more consensus in the translation. The manual is also available FREE when printed from on the MSU Pesticide Education web site, http://www.pested.msu.edu/BullSlideNews/bulletins/E2195sp.html

Note from the editor: If you are interested in Spanish-speaking materials, http://www.espanol.gov/ may be of interest to you. It allows non-English speakers to get information in Spanish on government-provided services.

North Central Regional Publication 481:
Biological Control of Insects and Other Pests of Greenhouse Crops

Tom Dudek
Regional Extension Agent

An excellent reference book has been published by a team of entomologists from the University of Wisconsin, University of Illinois and Purdue University.  This 100-page text provides practical approaches to the biological control of insects pests of greenhouse crops.  If you are considering trying biological controls in your greenhouse for aphids, fungus gnats, shore fillies, mites, thrips, whiteflies, etc., this publication will be very helpful.  For each greenhouse insect pest it discusses the damage caused by the pest, how to monitor for the pest and a very complete list of the natural enemies, and possibilities for effective biological control.  Also, alternative control methods are shared. 

Copies of the publication may be ordered from your local MSU Extension Office or on-line at the MSU Educational Materials web-site: http://web2.msue.msu.edu/bulletins/intro.cfm