Powdery mildew -- please explain the concept to me

[clowntown]

 

[rawheineman]

im not very good at explaining it but i got a word describes it perfectly ,,,BASTARD,,,
ive just about tried everything and still cant shift it ,i nearly did ,latest concoction i'm trying is the dutchmaster zone as explained in link below

http://www.icmag.com/ic/showthread.php?t=43220&highlight=powdery+mildew

even when u think you got rid of it it pops back ,,i was clean for over 12 months ,then 3-4 weeks of high outside humidity an it formed outside on a few normal plants ,next thing its in the grow ,,,for some reason it usually shows 3 weeks b4 harvest which makes it harder to see and harder to shift ,too early to chop em but if u leave the pm to grow it makes em useless ,catch 22 innit

we could use this thread as a powdery mildew rant thread

 

[southwind]

Powdery Mildew

Powdery Mildew

Hello Clowntown;

I have grown jus every kind of plant other than commercial wheat and grains for most of my life. About 30 years or more..

Primarily ornamentals but plenty of berries, citrus, stone fruit [nectarines, peaches, etc]

PM is a fact of life on alot of ornamentals, and cut flowers, i.e. delphinium,sweet peas [lathyrus], some dahlia,columbines even have a specific species that attacks it.

PM spores are part of natures batallion of FUNGI breakdown dead or dying plant material[ and often NOT dead or dying stuff] ..PM can help breakdown dead tissue, but PM likes to live on living plants mostly..

it feeds on living cells by infiltration into the cell wall and pulls nutrients out.

PM exists in spore form everywhere on the earth.

It does not grow actively in dry conditions.

It likes heat and humidity, or cool and humid.

It can handle and like both.

Humidity is the key. Once an area stays humid for a certain amount of time you will see PM, but by the time you SEE PM it has been with you for a few weeks already.

PM [ the dusty grey stuff we see]is the final stage of the disease when it flowers and makes spores.

As you know all fungi grow from threadlike mycellium / mycellia that are almost invisible and when the flower or fruit they often make a MUSHROOM like fruiting body or an actual MUSHROOM.

But of course not all fungi make mushrooms, but they all make FRUTING BODIES.

and its the fruiting bodies of PM we SEE.

by then we are well on the way to our plants being badly infected.

when you shake a powdery looking leaf and dust seems to shake off that is the spores, hundreds of thousands of them.

in the nursey biz we use, soap, sulphur, potassium bicarbonate and a hsot of others to try to control it.

the problem is once the conditions [as you observed] are right you WILL get it, unless you aggressivley attack the first stages by spraying PHOPHYLACTICALLY.

[heading en off at the pass, so to speak.]

sw

 

[420247]

http://www.hgca.com/hgca/wde/diseases/Mildew/Milcyc.html

Life cycle

Mildew overwinters primarily as mycelium on volunteers and autumn-sown crops. The cleistothecia produced during late summer are resistant to cold and drying out, and they allow the fungus to survive for a time in the absence of a host. In the UK green plant material is nearly always available and cleistothecia are thought to be of secondary importance. In humid weather, cleistothecia release the sexually produced ascospores which can initiate autumn infections. As temperatures rise in the spring, dormant mycelium starts to grow and spores are quickly produced. These germinate over a wide range of temperatures, from 5 to 30°C, although 15°C is optimal with relative humidity above 95%. Free water inhibits spore germination. Under dry conditions, fresh spores can be formed in about 7 days. At the end of the season, volunteers and early autumn-sown crops may become infected, providing inoculum for the next years crop.

Importance

Late-sown winter wheat crops are often particularly prone to attack, especially when growing rapidly in the spring. Excessive nitrogen fertilisers also encourages the disease and mildew can be particularly severe in dense crops. The visual appearance of the disease usually outweighs its damage potential especially during the autumn and winter. In susceptible varieties yield losses can be high (up to 20%) and early control can be very important. However, the disease generally causes much smaller yield losses and late attacks (after flowering) on the flag-leaf and ear rarely cause significant losses in most varieties.

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7493.html

Powdery Mildew on Ornamentals
Published 11/01

In this Guideline:

Identification and damage
Life cycle
Management
About Pest Notes
Publication
Glossary



--------------------------------------------------------------------------------

Powdery mildew is a common disease on many types of plants and is very prevalent under the dry summer conditions found in many areas of California. Different powdery mildew fungi cause disease on different plants (Table 1). Powdery mildew fungi tend to be either family-specific, infecting plants in the same family, or host-specific, infecting only one species of plant.

Table 1. Host Plants and Control Measures for Powdery Mildew Species. Hosts Fungus species Controls
begonia, Composit family (chrysanthemum, dahlia, phlox, sunflower, zinnia)
Erysiphe cichoracearum
water sprays; fungicides if necessary

crape myrtle
Erysiphe lagerstroemiae
use resistant cultivars

rose
Sphaerotheca pannosa
use resistant cultivars; fungicides if necessary


IDENTIFICATION AND DAMAGE
Powdery mildew can be recognized easily on most plants by the white, powdery mycelial and spore growth that forms on both surfaces of leaves, sometimes on flowers and fruits, and on shoots . Powdery mildews may infect new or old foliage. This disease can be serious on woody species such as rose, crape myrtle, and sycamore where it attacks new growth including buds, shoots, and flowers as well as leaves. New growth may be dwarfed, distorted, and covered with a white, powdery growth. Infected leaves generally die and drop from the plant earlier than healthy leaves.

LIFE CYCLE
All powdery mildew fungi require living plant tissue to grow. On perennial hosts such as roses, powdery mildew survives from one season to the next as vegetative strands in buds or as fruiting bodies, called cleistothecia, on the bark of branches and stems.

Most powdery mildew fungi grow as thin layers of mycelium on the surface of the affected plant parts. Spores, which can be seen with a hand lens, are part of the white, powdery appearance of powdery mildew fungi and are produced in chains on upper or lower leaf surfaces or on flowers, fruits, or herbaceous stems. In contrast, downy mildew, another fungal disease that produces visible powdery growth, has spores that grow on branched stalks and look like tiny trees. Also, downy mildew spores occur mostly on the lower leaf surface. Environmental conditions that favor the growth of downy mildew are different than those that favor powdery mildew and include low temperatures (50° to 70°F), high relative humidity (90% or higher), and free moisture.

Powdery mildew spores are carried by wind to new hosts. Although relative humidity requirements for germination vary, all powdery mildew species can germinate and infect in the absence of free water. In fact, spores of most powdery mildew fungi are killed and germination is inhibited by water on plant surfaces for extended periods. Moderate temperatures (60° to 80°F) and shady conditions generally are the most favorable for powdery mildew development. Powdery mildew spores and mycelium are sensitive to extreme heat and sunlight, and at leaf temperatures above 90°F, some may be killed.

MANAGEMENT
The best method of control is prevention. Avoiding the most susceptible cultivars, providing plants full sun, and following good cultural practices will adequately control powdery mildew in many situations. However, some ornamentals require protection with fungicide sprays where conditions are most favorable for mildew. Fungicide applications are most often needed on susceptible varieties of rose and crape myrtle.

Resistant Varieties
Cultivars that are resistant to powdery mildew are available for some susceptible plants (Table 2). Purchase resistant cultivars of rose, crape myrtle, euonymus, and sycamore. Be aware that control actions will probably be needed when more susceptible varieties are planted.

Table 2. Some Common Ornamental Plants that are Highly Susceptible to Powdery Mildew and Resistant Varieties. Susceptible plant Resistant cultivars (if available)
aster

azalea (decidous)

begonia (tuberous)

calendula

California poppy

China aster (Callistephus)

chrysanthemum

Clarkia

columbine

coral bells (Heuchera)

corn flower

cosmos

crape myrtle
those with Native American names, e.g.,'Catawba,' 'Cherokee,' 'Hopi'

dahlia

delphinium

euonymus
variegated varieties more resistant than nonvariegated types

forget-me-not

gaillardia

hydrangea

lilac

London plane tree
'Yarwood,' 'Columbia,' 'Liberty'

lupine

mint

monarda
'Marshall's Delight,' 'Blaustrumph,' 'Colrain Red'

oak

pansy

phlox
Phlox maculata 'Natasha'; P. glaberrima 'MorrisBerd'; P. paniculata 'Robert Poore' and 'David'

ranunculus

rose
'Simplicity' and 'Meidiland' roses; Rosa rugosa varieties

rhododendron
R. yakushimanum, R. macrophyllum, R. 'Nova Zembla,' R. 'Palestrina'

rudbeckia

snapdragons

sweet pea

verbena

vinca

zinnia
Pulcino and African zinnias


Cultural Practices
Shade and moderate temperatures favor most powdery mildews. Locate plants in sunny areas as much as possible, provide good air circulation, and avoid excess fertilizer. A good alternative is to use slow-release fertilizer. Overhead sprinkling may actually reduce the spread of powdery mildew because it washes spores off the plant; also, if spores land in water, they die. The best time to irrigate is in mid-morning so that the plants dry rapidly, reducing the likelihood of infections by other fungi, such as the ones that cause rust or black spot infections on roses. As new shoots begin to develop on perennial plants, watch closely for the appearance of powdery mildew.

Fungicide Applications
In some situations, especially when growing roses, fungicides may be needed. Fungicides function as protectants, eradicants, or both. A protectant fungicide prevents new infections from occurring, whereas an eradicant can kill an existing infection. Apply protectant fungicides to highly susceptible plants before the disease appears. Use eradicants at the earliest signs of the disease. Once mildew growth is extensive, control with any fungicide becomes more difficult.

Fungicides. Several least-toxic fungicides are available, including horticultural oils, neem oil, jojoba oil, sulfur, potassium bicarbonate, bicarbonate of soda (baking soda), and the biological fungicides AQ10 and Serenade. With the exception of the oils, these materials are primarily preventive, although potassium bicarbonate has some eradicant activity. Oils work best as eradicants but also have some protectant activity.

Oils. To eradicate mild to moderate powdery mildew infections, use a horticultural oil such as JMS Stylet Oil, Saf-T-Side Spray Oil, Sunspray Ultra-Fine Spray Oil, or one of the plant-based oils such as neem oil (e.g., Powdery Mildew Killer) or jojoba oil (e.g., E-rase). Be careful, however, to never apply an oil spray within 2 weeks of a sulfur spray or plants may be injured. Also, oils should never be applied when temperatures are above 90°F or to drought-stressed plants. Some plants may be more sensitive than others, however, and the interval required between sulfur and oil sprays may be even longer; always consult the fungicide label for any special precautions. Of the horticultural oils, JMS Stylet Oil is the most highly refined and therefore the least likely to damage plants, but it may be more difficult to obtain than the others.

Sulfur. Sulfur products have been used to manage powdery mildew for centuries but are only effective when applied before disease symptoms appear. The best sulfur products to use for powdery mildew control in gardens are wettable sulfurs that are specially formulated with surfactants similar to those in dishwashing detergent (e.g., Safer Garden Fungicide). However, sulfur can be damaging to some ornamental cultivars. To avoid injuring any plant, do not apply sulfur when temperature is near or over 90°F and do not apply it within 2 weeks of an oil spray. Other sulfur products, such as liquid lime sulfur or sulfur dust, are much more difficult to use, irritating to skin and eyes, and limited in terms of the plants they can safely be used on.

Bicarbonates. Also available is a fungicide containing potassium bicarbonate (e.g., Kaligreen) and a fungicide that can be made at home by combining 2-1/2 tablespoons of horticultural oil (Sunspray Ultra-Fine, Saf-T-Side, etc.) in a gallon of water and adding 4 teaspoons baking soda. This solution is sprayed on plants to prevent powdery mildew infections. Sprays of both potassium bicarbonate and baking soda can injure the plant, so use these materials with caution. Also, baking soda sprays can have deleterious effects on soil structure and should be used sparingly.

Biological Fungicides. Biological fungicides (AQ10 and Serenade) are commercially available beneficial microorganisms formulated into a product that, when sprayed on the plant, destroys fungal pathogens. AQ10 is a parasitic fungus, Ampelomyces quisqualis, that actively attacks and destroys the powdery mildew fungus. The active ingredient in Serenade is a bacterium, Bacillus subtilis, that helps prevent the powdery mildew from infecting the plant. These products have some effect in killing the powdery mildew organism but are not as effective as the oils or sulfur in controlling it.

Synthetic Fungicides. Myclobutanil (Immunox) is also available to the home gardener and functions as an eradicant and protectant against both powdery mildew and rust.

How to Use. Apply protectant fungicides to susceptible plants before or in the earliest stages of disease development. Once mildew growth is mild to moderate, it is generally too late for effective control with protectant fungicides. The protectant fungicides are only effective on contact, so applications must thoroughly cover all susceptible plant parts. As plants grow and produce new tissue, additional applications may be necessary at 7- to 10-day intervals as long as conditions are conducive to disease growth.

If mild to moderate powdery mildew symptoms are present, the horticultural oils and plant-based oils such as neem oil and jojoba oil can be used.

 

[clowntown]

Thanks much for the information, both of you.

southwind, seems like you've become an extremely valuable, highly contributing member since we last really ran into each other, and I must say I feel like a complete d-bag for having said what I said to you more than a year ago. Please accept my apologies.

 

[southwind]

Powdery Mildew

Powdery Mildew

Powdery Mildew on the ornamental Columbine and on Sweet Peas

You can see from these photographs that PM eventually begins to kill the leaves and eventually will make the plant more susceptible to other pests. Aphids, Spider Mites, and Whitelflies.

It also works the other way, especially with Aphids. Once Aphids get a good foothold on your plants they weaken the plant both by sucking the internal fluids of the cells out and weakening the plants strength and also by their droppings which provide a perfect purchase on your plants for PM and other diseases, such as black scab, black rust, rust, other fungi and virus, and bacterial blight.


In this post I show photos of plants BEFORE treatment with Potassium Bicarbonate and AFTER treatment.

Also photos of equipment I use and the Product, GREENCURE.



This is PM on Sweet Peas and Culumbine, Before application of GREENCURE-POTASSIUM BICARBONATE.










And this is a few days later AFTER APPLICATION OF GREENCURE.









PRODUCT AND EQUIPMENT.




COULUMBINE LEFT TREATED WITH GREENCURE / RIGHT TREATED WITH FUNGICIDAL SULPHUR




I have had good success with GREENCURE.

 

[Brother_Monk]

You must spread some Reputation around before giving it to southwind again.

Good info guys! If I ever need this stuff, I'm glad I heard it here first.

Clowntown, Southwind IS an invaluable asset to the community. I'm honored to call him friend.

 

[Iluvtomatoes]

I've had a couple strains susceptible to it. (I got rid of them). Ultimately it's more of a problem in flowering, I guess the dark cycle obviously helps most mildews. I've tried the sprays baking soda etc. but nobody likes spraying the last 4 weeks of flower. Since I've had PM before,

-I run fans one speed higher in summer, especially if I'm foliar feeding regularly.
-I run a dehumdifier elsewhere in the house to lower ambient humidity aiming for 45-55%, problems occur for me at 65% humidity and above.
-I might turn the a/c down a a degree to also help condense more water out of the air and keep temps in the 72-78F range.
-I've used damprid hangars as well, but not since I got the dehumidifier.
-and oh yeah, I don't smoke around the plants, and I'll clean the floors of the house, change the hvac air filter, buncha work, but i have less problems/pests with a clean house.

my .02

 

[PharmaCan]

CT - read that thread that rawheineman posted a link to. There seems to be some consensus that when PM gets into a strain it can be systemic and needs to be treated as such.

Also, don't think low humidity will protect you from PM. I got PM last summer when the RH was 20%.

I made new Moms using 2nd generation PM free clones that were dipped frequently in various concoctions, fed Zone and Hydroguard, I used about every technique they had in that thread. I still use Zone & Hydroguard weekly on alternating weeks, but nothing else, and I haven't seen any PM in a couple of crop cycles.

PC

 

[clowntown]

PharmaCan, I'm already on the Zone + Penetrator foliar treatment. Dunking is out of the question at this stage, but I've given them a foliar on the lower leaves so far, and will do so for the rest of the plants at lights out (regardless of what the label says, I'm not comfortable spraying during lights on). This is really just a preventative step, and/or killing what little amounts that might be infected now... since the only two plants that showed symptoms so far were the Burkle's.

 

[southwind]

PM and environment

PM and environment

Hello

Where I live our summers are foggy, cool and moist.

Cool compared to alot of other places..60 low 70's..

Our winters are very cool but not COLD and wet wet wet..my house is in shade most of the winter also..so my ornamentals suffer greatly from fungi in general.

Rust, black spot, downy mildew, powdery mildew, both common and Aquilegiform..mold of all types,pythium, botrytis..and on and on.

Where I do any outdoor growing of Cannabis it is hot hot hot and the rain comes exactly at the highest bud density about 2 -3 weeks before harvest..so I have to try to be aware of conditions BEFORE they happen not when its happening ..because then it is too late for me.

and yes...PM is systemic alot of fungi are, wilt is systemic in clematis, columbine , and cannabis..it lives IN THE CELLS, we only see it when it is FRUITING.

by then we have had it for along time [relatively]

sw

 

[Whatever]

All this talk of 'killing' type treatments. What about Serenade or even AQ-10? Good luck finding AQ-10 cause it's not being manufactured anymore but did find some stock and put away for a rainy day and good for many years in the sealed foil packs. AQ-10 is a parasitic fungus that lives on PM. If the enviro supports PM growth it will just keep coming back and only so far into flower you can use certain stuff. You can use Serenade late into flower like 1 week+ before harvest. I have and never noticed any negative effect on flavor. If you see PM your enviro is now heavily contaminated with spores for one...just think about those oscillating fans blowing that PM around...lol. Gotta get your enviro better dialed in and even possible in an open system. I've had pouring down rain and fog outside yet my open system room never went over 55%. Big thing for sure is some strains are more susceptible than others.

When you use things like neem, baking soda, etc. you strip all the microlife off the leaves...including the 'good' stuff. I've seen peeps use bacterial teas as foliars to deal with PM successfully. The leaf microlife is part of the plants natural immune system.

I know peeps in the area who have strains going indoors and no PM ever yet know PM is in the air due to what I've seen in others outdoor grows. The biggest problem I've seen with PM is from passing infected clones around.

 

[clowntown]

I've been reading some mixed-bag reviews from Serenade's performance to begin with; not to mention the horrid smell and how it might not be recommended for use this late... I've heard the exact opposite in terms of smell/flavor from folks who claim to have used it weeks prior. Again, a mixed bag.

Again, understood about the environment and that's why I'm asking the question here to get an understanding of how big a role the environment plays. Please re-read the question / post.

 

[Whatever]

I've been reading some mixed-bag reviews from Serenade's performance to begin with; not to mention the horrid smell and how it might not be recommended for use this late... I've heard the exact opposite in terms of smell/flavor from folks who claim to have used it weeks prior. Again, a mixed bag.

Again, understood about the environment and that's why I'm asking the question here to get an understanding of how big a role the environment plays. Please re-read the question / post.

OK...re-read the question/post and not changing my tune much. I've used Serenade extensively and no problem for me applying late into flower affecting flavor (like 10 days before harvest)...none. Problem I've seen with Serenade is it seems to lose effectiveness if you start in veg/early flower and continue through the cycle cause by late flower the PM will come back faster than early on. The horrid smell is just the base/carrier it needs to survive in the bottle on the shelf...almost vinegar smell and actually really low pH...like vinegar (just test the pH of Serenade and it at it's recommended dilution)...which dissipates very quickly after application...maybe like a few days max.

The environment is only part of the puzzle..so you correct your enviro mid stream and still have susceptible strains in the grow space and all those spores and then what? What about a congested canopy? After awhile I ended up cleaning out the bottom 1/3 of the plants and running a fan between the medium and bottom of the canopy 24/7. What is your max humidity lights off? That's when %RH really climbs as temps drop. Easy to control RH lights off with a properly sized dehumidifier and cutting air flow.

I've had my fair share of dealing with PM...first thing is to eliminate susceptible strains.

I've already done this work in another thread...

 

[clowntown]

RH peaks out in the high 50's with lights out, usually high 40's to low 50's during lights on. I'm expecting these numbers to go up, though, and not much I can do about it until I have a sealed room.

So far the rest of my plants have not exhibited any signs of PM, but then again I realize this is no guarantee of those plants not being infected with PM.

OK...re-read the question/post and not changing my tune much.

Well, my reason in posting this thread is to get an understanding of how PM spreads... so if only 1 particular strain (which I've found now is notorious for having low PM resistance) was affected while the rest of the room seemingly unaffected, what's the likelihood the rest of the room is really OK even w/o showing any symptoms?

The bottom 1/2 of the plants have been trimmed up real good, and I have a floor fan (well, a pedestal fan with one of the risers removed)... just a bit better coverage now, especially of that one low table in question.

 

[Whatever]

RH peaks out in the high 50's with lights out, usually high 40's to low 50's during lights on. I'm expecting these numbers to go up, though, and not much I can do about it until I have a sealed room.

So far the rest of my plants have not exhibited any signs of PM, but then again I realize this is no guarantee of those plants not being infected with PM.

Well, my reason in posting this thread is to get an understanding of how PM spreads... so if only 1 particular strain (which I've found now is notorious for having low PM resistance) was affected while the rest of the room seemingly unaffected, what's the likelihood the rest of the room is really OK even w/o showing any symptoms?

The bottom 1/2 of the plants have been trimmed up real good, and I have a floor fan (well, a pedestal fan with one of the risers removed)... just a bit better coverage now, especially of that one low table in question.

PM spreads by spores...if you have visible PM you have an incredible amount of spores released and your grow space is totally infected. Next cycle get rid of that/those strains that are susceptible. From what I understand if your RH maxes out about 45% there are strains that will show problems. From everything I've learned PM can become systemic thus the need for dipping clones and space sterilization...prolonged heat will help.

An old friend said something that still seems to apply...with PM you end up chasing it around the room...so true.

As for how it spreads...if you're healthy and are daily put in a closed room with people with the flu how long do you think you can hold out?

 

[Whatever]

Part of it also comes down to general plant health.

 

[clowntown]

I've also come to realize that as well... I know I've posted it either here or on TCC (or both), but the Burkle's out of the whole batch (being fed from the same reservoir) looked the least happy in terms of color / look of the fan leaves. No doubt it had a role in lowering her resistance lower than it already was.

Thanks for your input, as always, Whatever.

 

[Whatever]

but the Burkle's out of the whole batch (being fed from the same reservoir) looked the least happy in terms of color / look of the fan leaves. No doubt it had a role in lowering her resistance lower than it already was.

...sounds true...but I''m sure if the common res was tuned to the Burkles it would have helped and the heartier strains might (?) have held up OK. When it comes to hydro one strain per res...eh?

 

[clowntown]

It's actually coco (so technically hydro I suppose), but yeah these two Burkle's wasn't what I was focusing on... there are more than 50 other plants for "production" that I care about more, and I'm not going to tune the single rez (I'm too broke for more rez's and pumps at this moment) just to accommodate them. Instead, I've given them the chop and hope that's that, until I have a better environment for them in the future runs.

Those two Burkle's were in 1 of 4 tables, and that table was a "mix variety" table meant for "testers" and head-stash. I considered hand-watering this 1 table, but after a short amount of deliberating I decided "naaah". Serves me right...