Protect your plants from Powdery Mildew

Figure 1: PM on Tomato

 Powdery mildew is a fungal disease that affects a wide variety of plants. The affected plants have a dusted-with-flour appearance with white to gray powdery spots on the surface of leaves and fruits (Fig 1). It causes cosmetic damage, and defoliation and decreases the quantity and quality of fruit (Fig. 2).

Disease and Development 
There are many different species of (Powdery Mildew) fungi. Most species only attack specific plants in the same or closely related plant families.

Figure 3: PM on roses

For example, powdery mildew on roses does not spread to grapes.

Powdery Mildew fungi overwinter in buds, twigs, bark, and plant debris. Their spores are carried by wind to new hosts. Low relative humidity during the day favors spore dispersal.

Fig 2: PM on grapes

The optimum conditions for spores to germinate are temperatures between 68 to 77°F and high relative humidity (> 70%). Powdery Mildew spores can germinate in the absence of water and can infect in arid conditions (40% humidity). Water on plant surfaces can kill or inhibit germination. Spores and fungal growth are sensitive to extreme heat (above 90°F) and direct sunlight. Shady conditions are favorable for PM development.

Management
The disease triangle is a useful tool to understand and manage diseases like Powdery Mildew (Fig. 3). The severity of Powdery Mildew infections is a function of the presence of the pathogen, the host susceptibility, and the environment. Powdery Mildew can be managed by good cultural practices.   

Fig 3: The Disease Triangle

The best control is to plant only resistant species or cultivars. Avoid excess fertilizer since plants with abundant succulent tissues are more susceptible to infection. The fungi can be eliminated by removing and burning all infected plant tissues and debris. Tools must be disinfected after use.

Another good control method is making environmental conditions less favorable for the disease. Avoid dense canopies by proper plant spacing and pruning to provide good air circulation, reduce humidity and increase sunlight penetration. Plants should not be planted in poorly drained soils or shady damp areas.

Overhead watering of the leaves during the day and when humidity is low can reduce infection. Water washes spores off the plant and inhibits its germination. This control method is not recommended for vegetables since it may contribute to other pest problems.

Powdery Mildew seldom needs chemical control in residential plantings, but it may be warranted in commercial plantings of susceptible crops like grapes and cucurbits. Chemicals are most effective when combined with cultural control. They should be applied before the disease symptoms appear. Further spread may be stopped or slowed with chemical treatment. Materials like horticultural oil or neem oils have a low environmental impact. Apply every 7 to 14 days throughout the season. Do not apply to drought-stress plants when the air temperature is above 85° nor within 2 weeks of a sulfur spray. Wettable sulfur is very effective in preventing infection. Like oil application, it should not be applied when the air temperature is over 90° nor within 2 weeks of an oil application.

Love My Roses, But Not Rose Diseases!

Do you love your roses, but hate seeing the diseases that can hurt them? I love making flower arrangements for myself and my friends throughout the summer and fall. I love all the different colors and varieties. But I hate diseases that threaten my lovely rose bushes! I hope the following information about Idaho’s 3 most common fungal rose diseases will help you to better understand how to keep your roses healthy. 

Rust

The symptoms of this fungal disease are small orange blisters on the underside of leaves. A small amount will not cause a lot of damage to the rose, but the spores can blow to other roses and infect those roses. This disease can survive the winter, so it's best to control it so it doesn't carry from one year to the next.

Black Spot
This fungal disease fungus looks like spots on the surface of the leaves and causes the leaves to drop off early. It can survive the winter and in the spring the rain will splash on to the rest of the plant and spread it. It is recommended to prune off the disease for winter, allowing plenty of air flow between the major branches. Additionally, water the bottom of the plant to avoid getting water on the leaves.

Powdery Mildew
This fungus looks like grey and white powder. It will show up anywhere on the plant. This does not need water to spread and can survive the summer. Remove any infected leaves that you see on the plant and prune for winter. Water to avoid leaves, as with Black Spot. Once into the summer weather you can give your rose a wash with the hose to remove mildew and aphids. 

The following fungicides and natural pesticides can be helpful in keeping your rose bushes healthy:

Potassium bicarbonate is a chemical relative of baking soda. We also see it as antacid in over-the-counter medications.  It will control Black Spot and Powdery Mildew.  A few of the names you can find it under in the garden center are: Bi-Carb Old Fashioned Fungicide, Kaligreen, and Bonide Remedy. 

Bacillus subtilis is a microbial pesticide. It is a bacteria found in air, water and soil.  According to the product label, it is effective in controlling all three important rose diseases. It is sold as “Serenade Garden Disease Control”.

Neem Oil is a naturally-occurring pesticide found in seeds from the neem tree. It kills a variety of insects, including aphids.

Along with the tips above, it is important to keep the ground area under roses clean, of leaves, rose buds, and debris. I hope this helps you to keep your roses looking beautiful and healthy all season!

Pictured above:
My 5 year old rose bush

Powdery Mildew

Figure 1: PM on Tomato

Powdery mildew is a fungal disease that affects a wide variety of plants. The affected plants have a dusted-with-flour appearance with white to gray powdery spots on the surface of leaves and fruits (Fig 1). It causes cosmetic damage, and defoliation and decreases the quantity and quality of fruit (Fig. 2).

Disease and Development
There are many different species of (Powdery Mildew) fungi. Most species only attack specific plants in the same or closely related plant families. For example, powdery mildew on roses does not spread to grapes.

Powdery Mildew fungi overwinter in buds, twigs, bark, and plant debris. Their spores are carried by wind to new hosts. Low relative humidity during the day favors spore dispersal.

Fig 2: PM on grapes

The optimum conditions for spores to germinate are temperatures between 68 to 77°F and high relative humidity (> 70%). Powdery Mildew spores can germinate in the absence of water and can infect in arid conditions (40% humidity). Water on plant surfaces can kill or inhibit germination. Spores and fungal growth are sensitive to extreme heat (above 90°F) and direct sunlight. Shady conditions are favorable for PM development.

Management
The disease triangle is a useful tool to understand and manage diseases like Powdery Mildew (Fig. 3). The severity of Powdery Mildew infections is a function of the presence of the pathogen, the host susceptibility, and the environment. Powdery Mildew can be managed by good cultural practices.   

Fig 3: The Disease Triangle

The best control is to plant only resistant species or cultivars. Avoid excess fertilizer since plants with abundant succulent tissues are more susceptible to infection. The fungi can be eliminated by removing and burning all infected plant tissues and debris. Tools must be disinfected after use.

Another good control method is making environmental conditions less favorable for the disease. Avoid dense canopies by proper plant spacing and pruning to provide good air circulation, reduce humidity and increase sunlight penetration. Plants should not be planted in poorly drained soils or shady damp areas.

Overhead watering of the leaves during the day and when humidity is low can reduce infection. Water washes spores off the plant and inhibits its germination. This control method is not recommended for vegetables since it may contribute to other pest problems.

Powdery Mildew seldom needs chemical control in residential plantings, but it may be warranted in commercial plantings of susceptible crops like grapes and cucurbits. Chemicals are most effective when combined with cultural control. They should be applied before the disease symptoms appear. Further spread may be stopped or slowed with chemical treatment. Materials like horticultural oil or neem oils have a low environmental impact. Apply every 7 to 14 days throughout the season. Do not apply to drought-stress plants when the air temperature is above 85° nor within 2 weeks of a sulfur spray. Wettable sulfur is very effective in preventing infection. Like oil application, it should not be applied when the air temperature is over 90° nor within 2 weeks of an oil application.

Or I'll huff, and I'll puff, and I'll dry your ground out!

Or I’ll huff, and I’ll puff, and I’ll dry your ground out

One of the trademarks of living in Idaho seems to be wind. Learning how to adapt can be challenging to any newcomer. Unless you are from, say, Chicago? In any case, being aware of how wind affects your landscape can help in protecting them during our often dry, windy fall and winter seasons.

Drying winds strip plants, turf, and the soil of much needed moisture. As the wind blows it wicks the moisture out of the plant, and the soil. As the low humidity and wind blow, plants can’t replenish the water they lose through their leaves, or needles. This is one reason you may have a brown cast on the edge of your evergreen needles.

On perennial shrubs, such as roses or lilacs, damage to terminal growing points can occur.

There are several things to keep in mind about your landscape if you live in these windy areas.

1. Fall and winter watering is not an option. Failure to water your plants is the most common cause of plant stress I see in landscapes. And just because your landscape is mature, does not mean you can stop watering it. You don’t stop drinking water just because you've matured, do you?

2. Mulch can help retain moisture in the soil. Yes, I know, it’s windy and the wind blows your mulch all the way to Kansas. Well, I am sure the people of Kansas appreciate your contribution to their fine state. Really though, mulching can make a big difference in how much water your soils will hold.

3. Add organic matter to your soil. Incorporating 2-3 inches of plant based organic matter at a depth of 4-6 inches will help hold in water if you have sandy soil, or help water drain if you have clayey soil. Either way, adding organic matter such as composted plant material will benefit your plants. Just be careful if you use animal manure as compost as these contain salts and heavy metals that build up in the soil over time, and can increase the risk of food borne pathogens if used improperly in vegetable gardens.

For more information on fall or winter watering, visit your county Extension office.

For Me, Pruning Roses is Personal

According to family records, the year  would have been 1958,  just

prior to my 6^th birthday. The Rosarians, who were in charge of

the annual Rose Parade in Portland, Oregon, decided to sponsor a contest to

draw attention to the event, which was always a family favorite.

The grand prize for the first rose in Portland to come into full bloom

was a brand new black and white T.V.,  and 2^nd prize was $50,

 both of which would have been a boon to our large family.

My father loved his garden, which was full of camelias, rhodies,

grapes, and especially roses (the Queen of the Garden, as they are  some-

times referred to). My dad was excited. He had a rose in full bloom

and invited the Rosarians to come see it. And that they did. According

to them, after much scrutiny I'm sure, they decided the rose was too

small and not showy enough to draw attention in the newspaper

to the parade.  Needless to say, Dad was deflated!

He may not have won the contest that year, but despite a bruised ego he still had a beautiful garden, and unbeknownst to him, he was showing me how to take care of it. My father was responsible for my love affair with gardening, and most especially of growing roses. I guess you could say it is in the genes!

For this short article on pruning roses, I will be referring primarily to Hybrid Tea roses, as they are my rose of choice because of their long stems and slightly larger flower than the Florabunda, although pruning techniques are similar. Because of the cold weather here in Idaho, I wait to prune my roses until early spring after the last frost but while the rose is still dormant. Before actually starting to prune, I like to stand  back and just look the plant over and imagine how I want it to present. They are all so individual. This is easier with a mature plant as opposed to a new one.

I obviously start by removing all the dead and diseased wood, removing canes from the middle, and canes which cross over or rub against other canes. Then I take another quick look. With a bush that is at least 2 to 3 years old, I look down at it from the top and imagine a round vase in the center with several  (8 to 10 canes) surrounding it.

In this manner, it gives the rose plenty of airflow, room for pollinators, and keeps it healthy and vigorous as well as keeping disease to a minimum. An established rose can be pruned to within 8 to 10 inches from the ground.  I prefer to look at pruning roses more as shaping the plant. You can prevent overcrowding and can restrict the size. An open-centered rose, with well-spaced shoots that do not rub against each other is much more pleasing to the eye and less prone to disease. One of the beauties of roses is that by proper pruning, you can keep them blossoming for the entire season.             

All varieties of roses have alternating buds. So when making the cuts to shape your rose, after a flower has faded  look down the cane from the top to the second leaflet of 5 leaves and cut approximately  ¼ inch above the leaf axil at a downward angle away from the leaflet, so that water drips away from the bud. Generally, I look for a 5-leaf leaflet pointing outward, but to maintain the open-centered and rounded shape, you may need to fill in a space, so you could prune at an inward facing leaflet. You design your rose bush.

So, have a little fun and shape by pruning as part of your gardening routine. Roses are somewhat forgiving, they are beautiful, and you could get flowers all season long, a benefit you don't get from many other flowers.

Sources:

            Pruning and training by Christopher Brickell and David Joyce

            Portland Rose Society Rose pruning Guide

            https://catalog.extension.oregonstate.edu/ec1624