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

May 14, 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 Extension

Maryland’s Industrial Hemp Pilot ProgramBy: Andrew Ristvey

Last year, the Maryland Legislature passed House Bill (HB) 698 to allow farmers, contracting with the Maryland Department of Agriculture (MDA) or Institutions of Higher Education (IHE) in Maryland to grow industrial hemp for research purposes. Any farmer or grower wishing to produce hemp needs to obtain a Maryland Department of Agriculture license to do so, but they must be partnered with an IHE before their application is considered. While the 2018 U.S. Farm Bill legalized Industrial Hemp (removed it from Schedule 1 Status based on the 1970 Controlled Substances Act) and will no longer require growers to partner with an IHE or state department of agriculture, this ruling will not go into effect until 2020. In every state that has adopted an industrial hemp pilot program, the partnership requirement has not changed for 2019.

The most important issue surrounding the production of industrial hemp is the legal enforcement of the tetrahydrocannabinol (THC) content, the psychoactive phytochemical. In fact, the definition of industrial hemp is related to this THC concentration which needs to be less than 0.3% THC in any part of the plant. If the THC content is above that threshold, the plants need to be destroyed.

Cannabis sativa has had a long history in the U.S. long before it was regulated and then made completely illegal under the Controlled Substances Act. Originally grown for fiber and textiles, the species was commonly grown in the U.S. In an effort to bring back a hemp industry to the U.S., the Federal Government has, step by step, lifted the restrictions on the plant. While many other countries like China and Canada have cornered the hemp fiber, seed and textile markets, U.S. farmers will mainly grow hemp to produce cannabidiol (CBD), another Cannabis phytochemical. Cannabidiol is a similar phytochemical to THC but it is not psychoactive. It is purported to have anti-inflammatory properties and some medical evidence shows success with childhood epilepsy syndromes. Within the medical field, there is much interest in studying this compound. Regardless of the need for testing the effectiveness and safety of CBD for human use, tinctures, salves and a great deal of other products are making their way to the market.

With that said, the main interest for hemp production in Maryland is for CBD. Knowing that industrial hemp will become a specialty crop, at least for the short term in the Free State, the University of Maryland will need to develop nitrogen fertility recommendations for nutrient management planning. Therefore, for this year, the University of Maryland Extension has partnered with 13 growers under the Maryland Industrial Hemp Pilot Program. Most will be growing the hemp for CBD. The research, necessary for farmer participation, will be looking at how different nitrogen rates effect growth, yield, and phytochemical content including CBD and THC. We are also interested in understanding phosphorus requirements during the vegetative and flowering growth cycles. Additionally, we have interest in soil nutrient removal, especially phosphorus and how we may possibly incorporate this plant into a crop rotation. We have chosen partners throughout Maryland to better

understand production effects from different soil types or climate. Finally, we are very curious about the plant’s susceptibility to disease and pests. If you want to know if a plant gets a disease, grow it in Maryland. While many growers have been told the plant is bullet-proof, much of the present production has been occurring in drier-climate states. However, North Carolina research has seen disease pressure on the plants. Our climate is very conducive for a variety of plant threats. Even though this crop was grown successfully throughout the mid-Atlantic region for a couple hundred years, Cannabis has been bred into many varieties which may not retain the same resistance as the original plants. Another issue that cannot be ignored is that at this time, the plant is not labeled for pesticide use, making this growing season a little precarious for growers. Hopefully industrial hemp will be labeled in 2020 for pesticide use.

As for University of Maryland Extension, we hope that this crop will be a money maker for growers. As with all new crops, we expect some success and some failure. Good luck to all the pilot program growers this year!*The University of Maryland’s application process for partnering in the Industrial Hemp Pilot Program is over, however there may be other IHE’s in Maryland that are still willing to accept applicants.

Caterpillars Active in Cut FlowersBy: Stanton Gill

A commercial cut flower grower sent in a picture of a caterpillar feeding on cut flowers this week. It was Geometrid caterpillar, commonly called a looper. If you just find one or two caterpillars active in your cut flowers, I would not get really concerned. If the population is much higher than you like, then try using either Bacillus thuringiensis (Bt) or Spinosad (Conserve – one of the trade names). Both are bacteria that control caterpillars, but have minimal impact on beneficial organisms in your cut flower plots.

Botry-StopBy: Stanton Gill

BotryStop was introduced into the market by Bioworks of New York. Several greenhouse growers started experimenting with this bio-fungicide in 2017 – 2019. Mike Leubecker, Tidal Creek Growers, is one of the early, adopters and in a recent conversation, he felt it was working very well, rotating with standard fungicides This biofungicide is an organic biological fungicide developed specifically for the control of pathogens such as Botrytis cinerea, Sclerotinia sclerotiorum, and Monilinia spp.. Bioworks claims that BotryStop provides protection to blossoms, fruit, and plant tissues. The active ingredient is Ulocladium oudemansii strain U3.

If you are using this material, we would love to hear what you think on how efficacious it has been in your operation.

Be Prepared for FiresBy: Stanton Gill

On May 6, we had a large greenhouse operation in central Maryland that had a fire go through a storage building on the grounds. It caught them pretty much off guard. No one plans on a fire, but they do happen periodically. If you store pesticides such as insecticides, fungicides, growth regulators, and herbicides at your operation, be sure to notify the local fire department and give them a list of pesticide classes. If a fire occurs at your facility ,then they can react appropriately. They do not want to wash the area down with huge quantities of water and have the chemicals potentially runoff into streams and other non-target areas.

Looper caterpillar feeding on daisy flower

Botrytis blight on lily foliagePhoto: S. Gill, UME

Botrytis Blight in LiliesBy: Karen Rane.

Recent weather has been cool and wet, setting the stage for Botrytis blight in cut flower production. Lilies can be especially vulnerable to leaf spot and leaf blight caused by two Botrytis species, B. elliptica and B. cinerea. These fungi are excellent saprophytes, meaning they survive on colonized dead plant debris, and produce masses of gray spores which can easily move through air currents. Cultural practices that make the environment unsuitable for infection are critical for managing Botrytis diseases. Keeping leaf surfaces as dry as possible is key to disease management. Increasing plant spacing, and keeping weeds under control both serve to increase air circulation around the plant canopy and encourage quick drying of wet foliage. If plants are irrigated, using drip irrigation reduces leaf wetness. If overhead irrigation must be used, watering early in the day allows for rapid drying of foliage after an irrigation event. Removing old fallen leaves, dead stems and other plant debris around the lily planting will help reduce the stockpile of fungal spores near the planting.

For more detailed information on managing Botrytis blight in cut flower production, refer to this fact sheet from the University of Massachusetts: https://ag.umass.edu/greenhouse-floriculture/fact-sheets/botrytis-blight-of-cut-flowers

Plant debris and blighted lily (circled) due to BotrytisPhoto: S. Gill, UME

Deer Ticks – Very ActiveBy: Stanton Gill

I was visiting cut flower growers this week and noticed the day after the visits that I had a small spot on the joint of my arm and the area was swelling. I took out a 12 X magnifier and sure enough a deer tick had wedged into my skin. May is a prime time for activity of deer ticks. If you are working out in the nursery, cut flower fields or in the landscape, check yourself a couple of times during the day for deer ticks. They are small so it will take a little time, but it is worth it to detect them early. You do not want to experience Lyme disease. Do a search on the web for pictures of what the nymph and adult deer tick looks like. The ticks do not fly or jump. They do hang on tall plants and grass in fields. They are also active at the edge of woods where they extend their front legs and quest for CO2 given off by mammals. When I work in my orchard, I usually wear clothing treated with permethrin to prevent problems with ticks. This time during the visit to the cut flower growers, I was not wearing protective clothing.

The Affair Between Iron and ManganeseBy: Andrew Ristvey, UME

Both iron (Fe) and manganese (Mn) are essential plant micronutrients. Iron is primarily involved with the process of photosynthesis and manganese is utilized in several enzymatic processes in the plant. Both exist as cations, or positively charged nutrients and their availability to plant roots relies upon their concentration and the pH of the soil or substrate (as with all nutrients). Iron and manganese are most readily available in lower pH ranges. Because of their special characteristics as metals, they exist in different electrochemical forms, oftentimes binding with soil particles or organic particles. Their availability is also affected by other nutrients. For instance, phosphorus can inhibit the uptake of iron but can improve the uptake of manganese. When phosphorus levels are too high, iron becomes less available. On the other hand phosphorus aids in manganese uptake. According to Mills and Jones’ Plant Analysis Handbook, a ratio of 29 parts phosphorus and one part iron is best for plants. When formulating fertilizer mixtures, remember that phosphorus is not the second number on a bag of fertilizer; that’s phosphate, which is P2O5, and 44% phosphorus.

Among other nutrient interactions, iron and manganese have an interesting relationship and are actually rather antagonistic with each other. The more of one, the less available the other becomes, because they compete for absorption by the plant. Ideally, fertilizers should provide a ratio of one part iron and one part manganese. The picture shows manganese toxicity in azalea and the iron deficiency associated with the antagonism of high manganese.

There are some plant species that are very efficient in getting iron because they can acidify the soil or substrate around the roots. These plants, probably adapting to low iron environments, have developed the ability to secrete acids from their roots to lower the substrate pH, whereby making any iron available for uptake. These plants are called iron-efficient and they include white and blue salvia, geraniums, some marigolds, phox, impatians, gerbera, larkspur, alyssum, basil, and tomato, among others. These crops can exhibit true iron toxicity, even at normal iron levels because they are so efficient in iron assimilation. It is for this reason that when growing these crops in organic substrates, you monitor pH and keep it above 6.3. This will limit iron availability.

True iron toxicity shows up as a bronzing in the leaves and this coloration is due to the plant’s creation of enzymes that control free-radicals like peroxides that develop when nutrients like iron and manganese become too available. Stippling is another common occurrence for both iron (see picture of iron toxicity) and manganese toxicity (purple stippling).

Another common cause of iron toxicity with these plants is the use of some iron chelates like DTPA and EDTA. Even at low concentrations of chelate, African marigolds showed iron toxicity symptoms because the plants had begun root zone acidification. Even after iron chelate was applied, the plant continued to acidify the root zone and too much iron ended up in the plant.

However, most of the crops that you grow in organic substrates are very tolerant of high iron availability and iron toxicity is extremely rare and unlikely. Iron concentrations in leaves can be between 300 to 400 ppm before toxicity occurs (normally between 40 and 120 ppm in most plants). In many cases, high iron

Manganese toxicity in azalea and the associated iron deficiencyPhoto: Andrew Ristvey, UME

concentrations may first create manganese deficiency because of the antagonistic interaction between the two micronutrients. Manganese deficiency looks similar to iron deficiency, initially taking the form of interveinal chlorosis. However, manganese deficiency has been recorded on both new leaves and older leaves, even though manganese is relatively immobile in the plant. Symptoms are likely species dependent. Latent manganese deficiency may show as necrotic stippling on the leaf surface.

Four-lined Plant Bug By: Stanton Gill

We have received reports of four-lined plant bug nymphs feeding this week on native pussytoes (Antennaria sp.), lyreleaf sage. new foliage of panicle hydrangea (Hydrangea paniculata), Japanese anemone (Anemone x hybrida), and catmint. As they feed, the insects inject a toxin into the plant tissue that causes the tissue to collapse and go necrotic. You end up with a series of small roundish dead spots on the foliage. Once the damage is present, there is not a lot to do about it. There is one generation per year early in the season. Some other host plants include: Herbaceous perennials - chrysanthemum, Chinese lantern, liatris, and shasta daisy; Herbs - mint and basil; Woody ornamentals - azalea, dogwood, forsythia, viburnum; and Flowering annuals - zinnia and marigold

This four-lined plant bug nymph is causing damage to catmintPhoto: Marie Rojas, IPM Scout

Four-lined plant feeding causes necrotic spots on leaves of pussytoesPhoto: Christa Carignan, UME-HGIC

Large Insects in Cut Flowers in MayBy: Stanton Gill

Carrie Jennings at Honeybee Flower Farm sent in a large beetle hanging out in her cut flowers. This beetle is one of the large click beetles we have here in Maryland. Adult click beetles feed on nectar, so it not uncommon to find them in a cut flower operation. The one Carrie found is called the “eyed click beetle”. The name is because of the large eye-like spots on the thoracic shield. Click beetles get their name from the clicking sound they make when turned on their back and attempting to flip over. A click beetle does this movement to launch the beetle into the air so it can take flight. This snapping action makes the clicking noise you hear and launches the beetle into the air several inches. Most click beetle species are nocturnal and will hide during the day. The larval stage is called a wireworm and can be found

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.

Hold the Date: July 25th We will hold an herbaceous perennial program during the day with hands-on

diagnostic skill-building sessions. It will be at The Perennial Farm in Glen Arm, MD. MNLGA will take handle the registrations.

drilling into roots and tubers. The larvae are off white and very hard cylindrical insects. If levels remain low, then the damage to plants is not significant.

Adult click beetles feed on nectarPhoto: Carrie Jennings, Honeybee Flower Farm