Greenhouse TPM/IPM ReportCentral Maryland Research and Education CenterEllicott City, Maryland

July 2, 2019From: Stanton Gill, Extension Specialist – IPM for Greenhouse and Nurseries, Central Maryland Research and Education Center, University of Maryland ExtensionKaren Rane, Extension Specialist, Director of the Plant Diagnostic Clinic, University of Maryland ExtensionAndrew Ristvey, Extension Specialist, Wye Research and Education Center, University of Maryland ExtensionSuzanne Klick, Technician, CMREC, University of Maryland ExtensionLeafhopper and True Bugs Active in JulyBy: Stanton Gill

A couple of dahlia growers sent in pictures of a leaping bug that was causing stippling of the foliage on dahlias this week. One sample was brought into the CMREC lab. We forwarded pictures to a University of Delaware taxonomist/systematist for identification. Dr. Charles Bartlet identified it as a fleahopper, Halticus sp.

If you shake the foliage of the infested plant, the insect leaps off the foliage rapidly. They have very large thoracic hind legs that enable them to leap high and quickly to evade predators. The stylet mouthpart of this insect causes stippling damage to the foliage. We did not have any reports of the insect on the flowers, but foliage can be heavily damaged.

If damage is heavy enough, a systemic material such as Acephate, Altus, or Endeavour should provide good control.

Stippling and yellowing on these dahlias is caused by fleahoppers, Halticus sp.

Fleahoppers, Halticus sp., are causing a lot of damage to dahliasPhoto: Heather Zindash, IPM Scout

The stipping on this Crocosmia is caused by spider mites

Hot Weather – Watch for Mite OutbreaksBy: Stanton Gill

It is July, and we finally moved into the really hot weather period of the summer. Twospotted spider mites can explode in this weather pattern. Examine plants such as Crocosmia (lily family) and other species susceptible to mite feeding.

Mites can be controlled with a fine mist of 0.5 – 1.0 horticultural oil, but you need a mist blower that lifts the foliage so the oil can make contact with the mites on the undersides of the foliage. Insecticidal soap will also help suppress mite populations. Use the same application methods as with the horticultural oils.

It’s hot! Substrate Monitoring is a Must!By: Andrew Ristvey

I guess you have heard this information from me before and I don’t want to sound like a nag, but just in case, it’s definitely time to start your container sub-strate monitoring if you have not done so yet. Daytime temperatures have been consistently above 90 °F, and we have had many days where plants are really transpiring a lot of water out of the containers. So allow me to remind you that testing for substrate electrical conductivity (EC) is an important management practice during these hot periods. For both soluble and slow release fertilizer users, plants are pulling out more water from the substrates than fertilizer. This means that fertilizer salts are becoming concentrated in the pot as the day progresses. There are two procedures that you can use; the Pour-Thru or the Saturated Media Extract (SME). Be consistent, and use one.

The Pour-Thru procedure is easy. After an irrigation, you simply wait between one-half to a full hour after containers are at water holding capacity. Simply find five or so containers randomly, from a block or irrigation zone and tilt them at an angle sufficient enough to have water come out the bottom of the container (see picture). Sample each container individually. Collect the released water from the container in a small cup. You need only enough water to cover the EC and pH probes for an accurate reading. If you cannot retrieve a sample, simply pour a small amount of water evenly over the top of the container. You are trying to displace the water at the bottom of the pot, so you need just enough to get an ounce of water out the bottom. Don’t forget to re-wet the con-tainers after taking your sample.

Should you use distilled water instead of your irrigation water? No, not really, but you need to know your well-water EC to gauge the amount of fertilizer in the pot. Look for levels between 0.5 dS/m and 2.5 dS/m. Anything below 0.50 dS/m after subtracting your well-water EC value, and you may want to consider additional fertilizer.

Tipping pot after an irrigation event to gather a water sample for a Pour-ThruPhoto: Andrew Rsitvey

Anything above 3 dS/m would indicate that leaching may be needed, especially if a hot day is expected. Electrical conductivity of 4 dS/m will kill roots.

Another monitoring method is the SME, which is simply making a slurry with some substrate from the bottom of a container. The slurry can be made with close to equal parts water and substrate. The slurry should sit for at least 15 minutes or more so that salts in the substrate can dissolve into the water you have applied. Either method works. Electrical conductivity levels could be lower in SME’s since you are diluting the sample, however, practically speaking, the same EC limits as in the Pour-Thru could be used. The key is consistency. Do the same thing all the time and keep records.

As a reminder, the following EC units all mean the same thing: mmhos/cm (milli-mhos per centimeter) = mS/cm (milli-siemens per centimeter) = dS/m (deci-siemens per meter) = 1000 μS/cm (micro-siemens per centimeter).

Don’t forget to keep an eye on your pH. The pH range for soilless potting media is between 5.5 and 6.3 for optimum nutrient availability (a little higher for iron efficient plants like geranium). Some say that since you apply fertilizers in soluble form, pH is not very important for nutrient availability in organic potting media, but I disagree.

Electrical Conductivity and pH meters can be purchased through nursery supply businesses, catalogs and via internet orders where you can shop for the best prices. You can even purchase combination meters that read both EC and pH. You want an EC meter with a range of 0 to greater than 4 dS/M or 4000 μS/cm. It is extremely important to purchase pH and EC standard solutions to calibrate your meter and an electrode holding solution to protect the pH electrode.

Monitoring your container root zone EC and pH goes a long way for preventing nutrient related problems in-cluding deficiencies, toxicities and root damage. Certainly, pathogen infections may be kept in check simply by keeping your roots healthy. If time is a premium, know where your trouble spots are and focus your efforts.

You can call me for additional information or with any questions you have at 410-827-8056 x113. Good luck with the rest of this growing season!

A saturated media extract test using a pH/EC probePhoto: Andrew Rsitvey

Strange Activity With VerbenaBy: Stanton Gill

Mike Leubecker at Tidal Creek Growers gave us 4 plants to try out as potential cut flowers with few pest problems. Verbena Finesse® has beautiful small blue to purple flowers on long 3 ft stems. We planted it last Friday. In the morning, an animal had dug up all four plants, not chewing on the foliage but feeding slightly on the roots. We moved the four plants to new locations with 4 locations at least 100 yds apart. Same thing happened on Saturday night. We replanted and same thing happened again. We are puzzled as to what is digging up the plants each time and what is the attraction to the root system for some animal. If you have any brilliant ideas, send them to at Sgill@umd.edu.

Verbena Finesse®Photo: Mike Leubecker, Tidal Creek Growers

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by University of Maryland Extension is implied.

Read labels carefully before applying any pesticides.Photographs are by Suzanne Klick and Stanton Gill unless stated otherwise.

The University of Maryland Extension programs are open to any person and will not discriminate against anyone because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry, national origin, marital status, genetic information, political affiliation, and gender identity or expression.

All Day Session on Herbaceous PerennialsJuly 25, 2019

Location: The Perennial Farm in Glen Arm, MDRegistration info will be posted at the MNLGA calendar site when available

Publications to Help Greenhouse and Cut Flower Growers

This winter, we published a new 470 page manual for people growing herbaceous perennials. This manual has information on water and fertility management, disease control, insect and mite control and many biologi-cal control options. We have authors from Extensions of University of Maryland, Virginia Tech, and Cornell University working together to pull together a complete information manual for growers. The manual is called “Total Plant Management of Herbaceous Perennials”, Bulletin 359. We have copies available for $30 plus $5 S&H. An order form for this manual (and the one for greenhouse production) is available on-line.