Its a busy time in the greenhouse, but our next topic is timely! Rot rots like Fusarium, Pythium and black root rot are often the bane of spring bedding crops. Dr. Mary Hausbeck, a Distinguished Professor from Michigan State University, is going to share her vast knowledge on this topic, including which fungicides work best. Check out the details below, and don’t forget to register!Continue reading “Upcoming Webinar: Root Rots – What You Can’t See CAN Hurt you.”
By Sarah Jandricic and Chevonne Carlow
It’s that time of year again, when baskets of Million Bells (Calibrachoa) are going up in the greenhouse. Here’s how to deal with and prevent some of their most common issues.
From a nutritional standpoint, the best thing you can is keep the pH of your calibrachoa in its ideal range; between 5.5 and 6.0. A pH higher than this can inhibit nutrient uptake, especially micronutrients such as iron.
Iron deficiency can be difficult to distinguish from other issues (like Black Root Rot – see below), but typically leads to yellowing of new growth. Leaves may only show chlorosis between the veins, or it may be spread throughout the leaf. This is different from nitrogen deficiency where yellowing occurs in the oldest leaves. If iron deficiency occurs, adding a chelated form of iron is best for uptake.
Million bells are also highly susceptible to Black Root Rot (Thielaviopsis) – I’ve seen this take out a good chunk of a crop. Symptoms include:
- Stunting of foliage and roots
- Plants in a tray will have uneven heights
- black areas on roots
- yellowing of leaves
Prevention is worth a pound of cure with this disease, as it is difficult to eradicate once established. Important steps to take include:
- Proper Sanitation. To avoid an issue with Black Root Rot year after year, immediately dispose of diseased plants, limit water splashing, and sanitize benches, floors and used pots/plug trays. Always physically wash surfaces with a cleaner to remove organic matter, then follow up with a disinfectant such as KleenGrow (ammonium chloride compound).
- Consider prophylactic applications of fungicides on plug trays. Products include Senator (thiophanate-methyl) or Medallion (fludioxonil). Preventative applications are an especially good idea if you’ve issues in the past. Adding bio-fungicides containing Trichoderma harzianum (e.g. Rootshield, Trianum) may also help.
- Lowering your pH. This disease is significantly inhibited by a lower pH – between 5.0 and 5.5.
- Manage fungus gnats and shoreflies, since these insects can spread Black Root Rot between plants. Treatments include nematodes, Hypoaspsis mites , or applications of Dimiln (diflubenzuron) or Citation (cyromazine).
If already established, rotated applications of Senator and Medallion may limit Black Root Rot, but are unlikely to cure it.
Lastly, Million Bells are highly attractive to aphids. With baskets hung up in the greenhouse, they can be “out of sight, out of mind”, but regular monitoring is needed to prevent large aphid outbreaks. Place sticky cards directly in baskets, and routinely check plant material for aphid cast skins and honeydew.
Once aphids are detected (and they will be!), applications of Beleaf (flonicamid), Enstar (kinoprene) or Endeavor (pymetrozine) will usually take care of them. However, be aware that all of these insecticides take around 4-5 days to start causing aphid death.
That’s right! As of today, flower growers have 2 new weapons against fungal diseases at their disposal. Heritage MAXX (azoxystrobin) and Medallion (fludioxonil) are now registered for use in outdoor and greenhouse ornamentals.
Heritage (a Group 11 fungicide) is a systemic fungicide, and is appropriate for control of Pythium, Grey mould (aka Botrytis blight) and Rhizoctonia. It can also be used for foliar diseases such as Powdery Mildew, Downy mildew, Rust, Anthracnose and Alternaria Leaf Spots. You can find the new label here: HeritageLABEL2016.
Medallion (a Group 12 fungicide) is a contact fungicide, and is appropriate for control of root rots such as Fusarium, Rhizoctonia, and Black Root Rot (Thielaviopsis) when applied as a drench. It can be applied foliarly for Grey Mould, Anthracnose Leaf Spot and Rhizoctonia Stem Rot. MedallionLABEL2016.
Both are broad-spectrum fungicides that can be used curatively or prophylactically.
As with any chemical control product, make sure to read and follow the label carefully prior to use.
(Also, 1000 points each to the team that helped push these label expansions forward:Cary Gates, Flowers Canada; Jim Chaput, OMAFRA; Jennifer Llewellyn, OMAFRA and Graeme Murphy, formerly of OMAFRA).
Diagnosing a plant with vague symptoms like wilting, yellow and stunting is much like being a “plant detective”. First, you need to profile the “victim” — here, Callibrachoa plugs. Then, collect DNA evidence. Finally, use knowledge and instinct to narrow down your “suspects”. Only then can you come up with a plan to stop the assailant.
In this case, our DNA evidence (c/o UofG Lab Services) gave me 3 possible suspects: Pythium disotocum, Fusarium oxysporum and Thielaviopsis basicola. But which of these was the real culprit?
P. disotocum is rarely documented as an aggressive pathogen in flowers, so we can eliminate that. Similarly, Fusarium is often “around” at low levels without causing a problem. But, T. basicola, better known as Black Root Rot, is a common problem in Callibrachoa, specifically. Rotting roots are not always directly evident (even under a microscope), but severe discoloration of the foliage is a good clue, since this pathogen produces toxins that result in yellowing. Left unchecked, Black Root Rot causes severe stunting and plant death.
Luckily, there are treatments for Black Root Rot, and preventative measures that can be taken.
- Drenches of Senator 70 WP (thiophanate-methyl) are the best option for dealing with an existing outbreak of Black Root Rot
- Black Root Rot is often transmitted by fungus gnats and shoreflies. Management of these insects is key to prevention. They can be controlled with soil applications of nematodes, predatory mites (e.g. Hypoaspis), or insect growth regulars like Dimilin (diflubenzuron). These products are compatible with biocontrol programs for other pests, like thrips and aphids.
- A high soil pH encourages the growth of Black Root Rot. pH should be kept below 5.6.
- Bio-fungicides containing the beneficial organism Trichoderma harzianum (e.g Rootshield) can help protect plants from this Black Root Rot if applied at planting.
For additional information on Black Root Rot, check out http://plantclinic.cornell.edu/factsheets/blackrootrot.pdf