In this issue
§ My aphids are not dying after I treat them!
§ Downy mildew on coleus: A new problem
§ Tobacco mosaic virus
§
The 2006
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 reistance 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.
Last year, a downy mildew on coleus was detected for the
first time in the
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.
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.
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.
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%).
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.
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.
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
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.
C. Raker and Sons, Inc.
Duwayne’s Greenhouse Inc.
Four Star Greenhouse Inc. Carleton,
Glass Corner
Greenhouses Inc.
Pell Greenhouses,
Inc.
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
§ 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.