Botrytis on plants and in trash cans?

My aphids are not dying after I treat them!

Downy mildew on coleus: A new problem

This is the last issue of the 2006 season.
See you in December!

Botrytis on plants and in trash cans?
Dean Krauskopf
MSU Extension Educator

Cool, dark, wet weather when plants are in full flower can lead to a massive Botrytis attack. However, there are things you can do to reduce the severity of the problem. The most effective way to prevent Botrytis is to keep the foliage and flowers dry. Make sure you have plenty of air movement, water only when absolutely necessary and then only early in the day. Heat and vent morning and evening for at least one-half hour or more.

Botrytis is not a strong pathogen; it attacks petals and senescing or damaged plant tissue so sanitation is critical. However, too often growers do a good job of cleaning plants and then put the debris in a trash can and leave it in the house. Botrytis continues to develop and produce spores even in trash cans so have your employees put plant debris in plastic bags, seal them right at the bench and then take them out of the house. Don’t put this material on top of your compost pile – the spores can be moved by the wind or your fans right back into the range.

Dr. Mary Hausbeck, MSU greenhouse plant pathologist, suggests using chlorothalonil (Daconil), fenhexamid (Decree) or iprodione (Chipco 26019) for heavy attacks. For less disease pressure: trifloxystrobin (Compass), azoxystrobin (Heritage) or mancozeb (Dithane).

My aphids are not dying after I treat them!
Thomas A. Dudek
MSU Extension Horticulture and Marketing Educator

Over the past couple of weeks we have been hearing reports from greenhouse growers that have had aphid outbreaks  and that certain insecticides are not working as well as they have in the past. The word RESISTANCE then is mentioned as the reason for the lack of control . Before implicating resistance to a certain insecticide think about the following items.

1.Did you apply the correct insecticide? Is it labelled for aphids?

2.Did you apply the correct rate? Check your math twice to be sure you put enough product in the tank to treat the area you intend to.

3.Are you using a high pressure sprayer? They work considerably better than a fogger for aphids. Aphids tend to be on the undersides of the foliage. Get good coverage.

4.Rotate your Mode of Action of the insecticides you choose to reduce the risk for resistance.

5. Aphids reproduce much faster in temperatures over 75 degrees F. than in a cooler greenhouse. We have seen 85 degrees F. in many greenhouses now. If your interval between aphid sprays is 5-7 days your going to have newly hatched aphids coming out between your spray intervals. Tighten up your intervals.

6.If you still suspect resistance spray half a bench or range where the aphids are with the product you suspect resistance with and spray the other half wit another aphid insecticide. Then observe the mortality differences.

7. Best aphid materials  as sprays at this time of the crop cycle are: Aria, Endeavor, Marathon 2,  and Orthene.

Downy mildew on coleus: A new problem
Mary Hausbeck
Plant Pathology

Last year, a downy mildew on coleus was detected for the first time in the United States. This spring, downy mildew has occurred again in the United States and was recently verified in Michigan. (view images)

Coleus, snapdragons, roses, and impatiens each have a unique downy mildew pathogen. While the disease may look similar on the different crops, the downy mildew organisms are quite different. The downy mildew on snapdragons cannot blight roses, nor can the downy mildew on impatiens spread to any plant outside of the Impatiens group. The downy mildew that infects coleus can also infect basil. It is currently not known how many different plants can be infected by the downy mildew affecting coleus. Plants that are closely related to coleus may be at risk.

Downy mildew distorts plants and blights the foliage. Severely infected plants drop their leaves. A very characteristic symptom of the disease is purplish, gray, or white fuzz that develops on the underside of the leaves. Perhaps other than an especially severe case of Botrytis, no other disease on produces gray or purplish fuzz on the underside of the leaf.

Scout for the disease
Downy mildew can be explosive, so early detection is especially important. This disease can reproduce heavily and make plenty of seeds (spores) to be dispersed to nearby healthy plants. These spores can serve as “hitchhikers” on coleus plant material coming into the greenhouse. Be especially vigilant when scouting vegetatively-propagated coleus.

Keep the production area clean
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.

Monitor and control the environment
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 6 hours) and keeping relative humidity to a minimum (less than 85%).

Apply effective fungicides preventively
Fungicides should be applied preventively before disease develops. Protectant fungicides act as a barrier to the downy mildew pathogen. Protectant fungicides include mancozeb (example: Protect T/O) or copper-based products (examples: Kocide, Champion, Nu-Cop). Mancozeb is the preferred protectant fungicide. These products are not absorbed by the plant, so the spray program must begin before downy mildew becomes established. While copper hydroxide could also be helpful, it has not been tested as widely and repeated use with short intervals could increase the risk of phytotoxicity. Systemic fungicides can be especially helpful in managing downy mildew because these products are absorbed by the plant and can help fight newly-established infections. Systemic fungicides include mefenoxam (example: Subdue Maxx, applied to the soil) and dimethomorph (example: Stature DM 50WP). Aliette 80WDG is applied as a foliar spray and is a unique fungicide because it helps prompt the plant to defend itself. In research trials on snapdragon, mefenoxam (example: Subdue Maxx) applied to the soil performed well against downy mildew. Stature WP, a relatively new product, was also effective.

Keeping the fungicides working: A sample program
Downy mildew has the bad habit of changing and becoming resistant to the systemic fungicides. Subdue MAXX is especially at risk and should only be used once in a production program and must only be applied as a drench.

An example of an intensive fungicide program
Subdue MAXX drench. Weekly foliar sprays could include the following:
Spray 1: Heritage 50WG + Mancozeb
Spray 2: Stature DM 50WP+ Mancozeb
Spray 3: Aliette + Mancozeb
Spray 4: Repeat the program beginning with Spray 1

An example of a protective fungicide program
Subdue MAXX drench. Weekly foliar sprays could include the following:
Spray 1: Mancozeb
Spray 2: Heritage 50WG + Mancozeb
Spray 3: Mancozeb
Spray 4: Stature DM 50WP + Mancozeb
Spray 5: Mancozeb
Spray 6: Aliette + Mancozeb
Spray 7: Repeat the program beginning with Spray 1

Two cases of tobacco mosaic virus have recently been diagnosed by the Diagnostic Services lab.

Tobacco mosaic virus affects many ornamentals and is easily spread in the greenhouse. This virus has a wide host range including impatiens, chrysanthemums, geraniums, African violets, and several vegetables including tomato and potatoes. The impact of the virus varies greatly, depending on the host and the age of the plant at infection. Symptoms can also vary depending on the host. (petunia pictures)

Unlike some of the other common viruses of ornamentals, TMV is not vectored by insects. The virus can be spread by sap, through vegetative plant production, and through mechanical means. Handling of plants during normal irrigation, pruning and maintance practices can spread the virus. The virus can also be introduced into production areas by workers after handling infested tobacco products. Workers should be encouraged to wash their hands thoroughly after handling tobacco and/or cigarettes.

Once plants are infected with a virus, the virus cannot be eradicated from those plants. Symptomatic plants should be removed and destroyed. Equipment used to prune or take cuttings from these plants should be cleaned well with a bleach solution to remove sap residue left from infected plants. The virus can also persist in some weeds, all weeds should be removed from within and around the greenhouse walls.

Michigan State University is proud to announce the third annual Michigan Garden Plant Tour, July 31 to August 11. Greenhouse growers, landscapers, and retail garden center employees are invited to visit the five participating companies to see new garden varieties and evaluate plant performance. MSU is also holding their annual Garden Plant Showcase on Wednesday, August 2, which features educational sessions on a variety of topics.

The participating companies of this year’s tour are:
C. Raker and Sons, Inc. Litchfield, Michigan
Duwayne’s Greenhouse Inc. Hudsonville, Michigan
Four Star Greenhouse Inc. Carleton, Michigan
Glass Corner Greenhouses Inc. Grand Rapids, Michigan
Pell Greenhouses, Inc. Hudsonville, Michigan
MSU Horticulture Gardens East Lansing, Michigan

Last year, over 1,500 people participated in the Michigan Garden Plant Tour. Each location has different specialties and product lines, making the entire tour a “must see” for wholesale and retail greenhouses, garden centers, and landscapers. It’s a great way to stay on top of the garden plant market and observe plant performance and trends under a variety of outdoor conditions. Survey how plants perform in the ground and in containers, alone or in combinations with other plants.

Companies are open Monday through Friday during normal business hours. The MSU Horticulture Gardens are open 7 days a week, dusk to dawn. We suggest that you call the sites in advance so they know that you are coming. Travel directions and more information can found at www.hrt.msu.edu/planttour, or by calling Sandy Allen at 517-355-5191 ext. 1339. There is no fee to attend the Tour, and the program at MSU on August 2 is only $35 per person.

The classes being offered at the MSU Garden Plant Showcase on August 2 include
Great Container Combinations, by Tom Smith, Four Star Greenhouse
More Light, Less Energy, by Ryan Warner, MSU
Plants and Kids: Growing Your Future, by Norm Lownds, MSU
Tough Plants for the Landscape, by Art Cameron, MSU
The All-America Selections, by Dan Bulkowski, MSU
The Bordine’s Way to Display & Market Plants, by Heather DeRuiter, Bordine Nursery
Landscape Plantings for Autumn, by Mary Wilson, MSU Extension

In addition, walk the MSU gardens to view the All-American Selections, enjoy lunch, and tour of some of the other gardens on campus. To register, visit http://www.hrt.msu.edu/planttour/MSU_showcase.htm.