In this issue
§ Downy and powdery mildews showing up now
§
§ Out-the-door treatments for insects on bedding plants
§ New plant growth regulator research website
§
Last scheduled offering of the
Downy and powdery mildews showing up now
May 1, 2008 --Greenhouse growers need to pay attention to a couple of mildews that are occurring in area greenhouses. Downy mildew has shown up on Jamesbrittania cultivars. Look for the greyish/purplish fuzz on the undersides of the leaves. Plants in question may show a slight yellowing on the upper leaf surface.
Downy mildew can be explosive when the weather is wet and
humid. The downy mildew pathogen requires free moisture from condensation or
watering on the plant surface to germinate. Limit disease by venting, reducing
the time that leaves are wet (fewer than six hours) and keeping relative
humidity to a minimum (less than 85 percent). Downy mildew has a unique
thick-walled survival structure that allows it to persist in soil, growing
media or diseased plants for years. If downy mildew is found, dispose of all
diseased plants immediately. Place the entire plant, including the growing
media and pot, in a bag and promptly seal it. Do not carry diseased plants
through the greenhouse for disposal because spores on the infected plants will
be released and may infect nearby healthy plants of the same plant type.
Disposing of diseased plants removes a source of spores that would otherwise
allow the downy mildew to spread.
Powdery mildew is being observed on Torenia and
Non-Stop Begonias at this time. Look for the whitish flour like dust on the
leaves. Powdery mildew, unlike many foliar diseases, does not need free
moisture on the leaf to thrive. Favorable environmental conditions include high
relative humidity (greater than 95 percent), moderate temperatures of between
68oF to 86o F and relatively low light levels. Infections
may be more common in the spring and fall when changes between the day and
night temperatures encourage high relative humidity levels, especially at
night.
Spores (conidia) are produced in chains. Air currents and water splash in the
greenhouse easily move these spores. The spores germinate and thread-like strands
(hyphae) grow along the leaf tissue. Powdery mildews
obtain plant nutrients by sending feeding organs (haustoria)
into the epidermis. Once a spore lands on a plant, it may take as little as
three days but more often five to seven days for infection to develop.
In both cases intensive fungicide programs are essential. The following
recommendations are from Dr. Mary Hausbeck, MSU Plant
Pathology.
Downy mildew
Control by using a Subdue MAXX drench once followed by sprays of :
1. Heritage 50WDG plus mancozeb
2. Stature DM 50WP plus mancozeb
3. FenStop plus Mancozeb
Repeat foliar sprays beginning with 1.
Powdery mildew
Heavy disease pressure-treat with a rotation of: Eagle followed by Terraguard 50W.
Light disease pressure-treat with a rotation of: Heritage, Insignia, Strike and
then Compass.
Michigan
May 13, 2008 -- Congratulations Mark Elzinga of Elzinga and Hoeksema Millennium Greenhouse.
Michigan Agricultural Environmental Assessment Program (MAEAP) is an innovative, proactive program that helps farms of all sizes and commodities voluntarily prevent or minimize pollution risks. It teaches producers how to identify and prevent environmental risks and how to apply effective land stewardship practices that comply with the state and federal environmental regulations.
Mark has successfully satisfied the three-phase program by first participating in an educational program explaining the Greenhouse*A*Syst and MAEAP program, secondly by having an on-farm risk assessment and making changes to issues of concern. The final step, which occurred today, was having the facility verified by a third-party verifier. Michigan Department of Agriculture employee Josh Appleby verified the greenhouse operation and honored Mark with the MAEAP sign to showcase the greenhouse operation.
Out-the-door treatments for insects on bedding plants
Warmer temperatures and longer periods of daylight always give insects a big boost in April and May. Consequently, it is not unusual to discover yellow sticky cards covered with thrips or whiteflies, or outbreaks of spider mites and aphids in greenhouses full of flats scheduled to be shipped in the next week. If you discover an insect problem now, I suggest using a safe, effective contact spray that will knock down the infestation enough to provide good protection for two weeks. This will get your bedding plants through the shipping and retail phase. Once they have been planted outdoors, the aphids, mites, whiteflies and thrips will disappear naturally. Some good choices for out-the-door treatments are:
§ Thrips, aphids, whiteflies: Avid, Marathon II, Orthene 97, Safari, Sanmite, Tristar, Flagship, and Talstar.
§ Mites: Avid, Floramite, Hexygon, Sanmite.
With everything in bloom, you want to use the
safest products available. None of the products listed above are known to cause
a phytotoxicity problem when used at the rate on the
label. Usually wettable powder and flowable formulations are the least likely to be phytotoxic. With wettable powders,
make sure the pesticide is completely dissolved in the spray tank and the tank
is agitated. This will prevent sludge from forming at the bottom of the spray
tank, which could be phytotoxic if sprayed on plants.
The re-entry time-period following application of the products listed above is
12 hours with the exceptions of Floramite (4 hours), Orthene (24 hours) and Tristar
(24 hours).
Check out MSU’s Landscape
Alert newsletter
This is the end of season for the Greenhouse Alert
newsletter. Throughout the next few months, we may send out additional articles
as they become available. In the mean time, many readers will find items of
interest in our Landscape Alert newsletter. To access past issues,
visit: http://www.ipm.msu.edu/land-cat.htm
The Landscape Alert addresses pest management and plant care for a wide ranging audience that includes nurserymen, commercial landscapers, turf managers, master gardeners and Christmas tree growers. Here is a list of contents in the May 2, 2008.
Landscape and nursery
Right
tree, right place
Scouting
for weeds: corn speedwell
Tar
spot on maple fungicide timing is now
Turfgrass
Lawn
tips to save cash
Christmas trees and forestry
Herbicide-resistant
weeds in Michigan Christmas tree plantations
Charcoal
of Fraser and Canaan fir
Christmas
trees and forestry insect update for May 2
Gypsy
moth spray window update May 2
Around the home
Ground
nesting bees are scary but harmless
Warm
weather brought the ticks out
Polyxenus millipedes
Red
squirrel injury to arborvitae
Where
did all those winter cutworms go?
Other news
Weather
news
You can sign up to get an email announcement for the Landscape Alert similar to the one you receive for the Greenhouse Alert at: http://www.ipm.msu.edu/email-landscape.htm
New plant growth regulator research website
Controlling stem extension of greenhouse crops can be a
challenge on naturally tall crops. To manage plant height, growers often apply
various plant growth retarding chemicals as well as utilize nonchemical
strategies such as infrequent irrigation or a temperature drop in the early
morning. Over the past 15-plus years, researchers in the floriculture group at
A new MSU floriculture web page, http://www.hrt.msu.edu/florAoE/PGRinfo, has been developed to provide a summary of research results from many of these PGR trials. The information presented is limited to research performed at MSU and includes PGR responses for both herbaceous perennials and annual bedding plants. Visitors to the web page can select a species from a drop-down menu and then one or more photographs are displayed that demonstrate the PGR responses.
The web page does not provide recommended products or application rates; rather, it is intended to serve as a guideline to help growers determine whether a PGR is effective on a particular species. A summary table is also provided that lists the commercially available PGRs commonly used on greenhouse crops and their active ingredients. In most cases, we would expect similar responses among products containing the same active ingredient.
We hope that this web page will be a valuable resource for greenhouse growers when making PGR application decisions. As with all growth regulators, we recommend that growers perform their own trials on a small scale to determine appropriate rates given the species and cultivar, desired response, and environmental conditions. As additional research is performed at MSU on PGRs, this web page will be updated to provide growers with the most recent research-based information. We welcome your feedback on this new grower tool. For more information, please visit the MSU PGR research web site at: http://www.hrt.msu.edu/florAoE/PGRinfo.
Floriculture diagnostic updates
Jan Byrne, MSU Diagnostic Services
Over the past few weeks, the diagnostic lab has received quite a few greenhouse ornamental samples. Below is a review of some of the diseases we have seen.
Impatiens necrotic spot virus has been detected on various hosts from multiple
locations. The range of symptoms caused by this virus continues to impress me.
Typical ringspot symptoms were present on
Calibrachoa samples are frequently submitted to the
lab. Several samples in the last week were submitted with phytophthora
stem or root rot. Infected plants wilt and quickly collapse, the stem tissue is
often discolored. Other common diagnoses for these plants include iron
deficiency (caused by high pH), tobacco mosaic virus and phytophthora
root rot.
I have heard reports of problems with geranium bacterial wilt (Xanthomonas campestris pv. pelargonii).
To date, one case has been confirmed in the lab. Growers having problems with
geraniums should review the symptoms of bacterial wilt and consider sending a
sample to a diagnostic lab for testing.
Downy mildew has been a problem for at least one grower of strawflowers (Bracteantha bracteata). The pathogen was sporulating
heavily creating a thick white fuzzy layer on the underside of the foliage.
They symptoms can easily be confused with powdery mildew. Downy mildew problems
have also recently been seen or reported on Jamesbrittenia
and coleus.
Bacterial leaf spot of zinnia (Xanthomonas campestris pv. zinniae) has
been confirmed on two different zinnia samples. Symptoms include small water
soaked lesions that may be fairly evenly distributed across the foliage. Plants
of varying ages are affected.
Last scheduled offering of the Floriculture
College of Knowledge in Ohio
Erik Runkle, Horticulture
The Floriculture College of Knowledge certificate program
will be offered in
Each class is approximately four hours long and provides intensive, research-based information on each topic. You’ll learn from university faculty and staff how to improve your knowledge and skills in growing greenhouse crops. Participants that complete all 12 production courses and pass their exams receive a professional certificate that recognizes than as a certified greenhouse grower.
Registration includes the cost to participate in the
classes, presentation notes, textbooks and handouts, as well as refreshments
during breaks. For more information on the classes offered or on the program,
please visit the
Courses in Track III will be offered in