In this issue
§ Greenhouse insect management
§ Malfunctioning greenhouse unit heaters and other air pollutants equal greenhouse crop problems!
Do not carry-over insects from one crop to
another. Keep thrips numbers down to less than 10 per
card per week in the fall and winter on poinsettias and Dracaena. Avoid keeping houseplants or allowing weeds to grow in
the greenhouse. When each batch of media arrives for a new crop, check it for
fungus gnats by filling a 1 gallon ziplock bag half full
with moist soil. If fungus gnat adults emerge within 2 weeks, consider applying
a fungus gnat treatment at planting time. Check incoming plant material
carefully for insects.
Monitor thrips and
whiteflies with yellow sticky cards. Change cards once per week. Use at least
one card per house or one per 2,000 sq ft. Check the first plants that flower
for thrips. For spider mites and aphids, check
susceptible plants like marigolds (mites) and peppers (aphids), weekly. Potato
wedges can be stuck in soil and checked 24 hours later for fungus gnat larvae.
Use
If yellow sticky cards or scouting indicates
an increase in aphids, mites, thrips, fungus gnats or
whiteflies, apply the following materials once per week until populations
decrease to acceptable levels.
|
Thrips |
Avid, Conserve, Mesurol,
Orthene 97, Safari, Sanmite,
Tristar. |
|
Aphids |
Aria, BotaniGard, Decathlon, Discus, Endeavor, Flagship, |
|
Whiteflies |
Azatin, BotaniGard, Decathlon,
Distance, Endeavor, Enstar, Flagship, Marathon, Ornazin, Orthene 97, Precision,
Safari, Sanmite, Talus, Judo, Tame, Tristar (Note: Q biotype may be resistant to Marathon,
Flagship, Tristar, Safari, Distance and Talus). |
|
Mites |
Akari, Avid, Floramite, Hexygon,
Judo, Ovation, Pylon, Sanmite, Shuttle, Tetrasan, Ultiflora. |
|
Broad
mites |
Avid, Akari, Judo,
Pylon, SanMite. |
|
Fungus
gnat (drenches) |
Azatin XL, Adept (not on poinsettias), Distance, |
|
Mealybugs/ Soft scales |
Aria, Flagship, Orthene,
Safari, Talus and Tristar. |
Now is the time of the year when growers need to be especially aware of the working condition of their gas-fired unit heaters and the impact of other activities that go on in the greenhouse that may contribute to some form of air pollution. The following article and web sites will be of interest as you begin to open up houses and re-fire unit heaters to warm up houses.
Crops grown in greenhouses that utilize gas-fired unit heaters can be susceptible to ethylene injury. Ethylene (C2H4) is an odorless, colorless gas that acts as a plant hormone. Plants are very susceptible to ethylene injury at levels from 0.01 to 1 ppm or more. No other air pollutant causes a greater range of symptoms than ethylene gas. Symptoms range from misshapen leaves and flowers, thickened stems, stunted growth, flower or leaf abortion to epinasty. See these examples for photos:
http://armstrong.extension.psu.edu/Horticulture/newsletters/EthylenePhotos.htm
The effects on greenhouse crops will vary with the plant
species and growth stage, temperature, length of exposure, and the
concentration of the ethylene. I have noted plant injury symptoms more often in
plastic greenhouses compared to glass greenhouses, due to the airtight nature
of poly-greenhouses. A good bulletin on the subject was written by faculty at
An indicator plant to use for ethylene is a tomato plant. They are highly sensitive and will twist or wilt when exposed to ethylene. Tomatoes will exhibit injury within 24 hours if ethylene is present.
To avoid ethylene injury, unit heaters need proper ventilation and intake of fresh air from the outside. One square inch of vent cross section (of outside air) for every 2,500 Btu’s of heater output is recommended. Consider using a laundry dryer vent hose as a fresh air intake. Thus, if you have a 125,000 Btu heater, you would need an 8-inch diameter fresh air inlet pipe that would give you the 50 square inches you need.
Also, unit heaters need to be maintained so that the heater itself is running properly, and the distribution tube, vent stack, ventilation louvers, and fuel line are all functioning correctly. Try this checklist for proper maintenance.
|
Annual heating unit checklist |
|
|
Item |
You should… |
|
Heat
exchanger |
Check for
cracks. While the furnace is running, inspect for light penetration. |
|
Furnace |
Check for
leaks. Place a smoke bomb or furnace candle within the firebox. |
|
Gas lines |
Check for
leaks. Paint soapy water on the joints and seams. |
|
Exhaust
chimney |
Check for
leaks and obstructions. |
|
Pilot
light |
Clean
pilot and orifice. |
|
Flame |
Make sure
the burner flame is clear blue. Yellow or orange flames represent impurities
or a wrong setting. |
If you suspect ethylene injury is occurring, contact your local MSU Extension floriculture agent. We can look at the crop and obtain air samples to verify if ethylene is the problem. Also, call your furnace maintenance firm to inspect the unit.
Most plants will recover from ethylene injury. However, those plants that bloom once (like lilies, tulips and hyacinths) that were exposed to ethylene when they were in the flower bud stage will likely not bloom.
Other activities can also lead to greenhouse plant damage
caused by air pollution besides faulty unit heaters. These include ozone (smog),unburned
fuel in your gas lines, herbicides that were used in and around a greenhouse, dibutyl phthalate (plasticisers
used in manufacturing semirigid plastics), use of wood preservatives and even
emissions from propane fired hi-lo's. A great article on this subject was
written by Dr. Theo J. Blom from the Vineland
Research Station,