What's the White Powder On My Plant?

Powdery mildew is a common fungal disease that frequently infects rose, phlox, lilac, crabapple, begonia, zinnia, alpine currant, and other shrubs.  It is unlikely it will cause serious damage to the plant, but it can impact photosynthesis when too many leaves are infected and can slow down the plant's normal growth.  Infected leaves may drop prematurely, discolor, or pucker.
 
Fungal growth and spores give the leaf a white to light gray color. The leaf may also appear powdery or dusty, since some of the spores can be rubbed off the plant tissue onto your fingers
 
Temperature and high humidity are important factors in disease development. Powdery mildew is most prevalent under conditions of cooler temperatures and high humidity. These conditions occur with poor air circulation or when cool night temperatures follow warm day temperatures. Consequently, in Minnesota we see increased levels of powdery mildew in the spring and fall of the year.
 
Avoid or control powdery mildew by increasing air circulation and light penetration around the plant.  Shrubs may need to be thinned or pruned and don't overcrowd the garden.  Avoid overhead watering to help reduce the relative humidity or water in the early morning to let the tissue dry as soon as possible.  Purchase mildew resistant plants. 

 

Pruning infected tissue and throwing it away may temporarily help with its appearance, but pruning stimulates new plant growth and many powdery mildews infect new tissue.  One nontoxic control to try on roses is combining 1 tablespoon of baking soda with 2.5 tablespoons oil in 1 gallon of water. 

 

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Looking for a unique flower that probably isn't used in any of your neighbors' landscapes?  Ratibida columnifera or R. columnaris , commonly called Mexican Hat, is a perennial with an interesting look to it because of its red/yellow sombrero-like flower.  Native to North American plains from Canada to Mexico, Ratibida will thrive in a hot, sunny location and handles dry, poor soil conditions well. 
 
Mexican hat will grow to 2-3 feet tall and form an expansive clump.  Plant it with its close relatives which include sunflowers, black-eyed Susans, shasta daisies, and purple coneflower in perennial or wildflower gardens.  Expect this flower to have a long bloom period.  Ratibida makes a great cut flower and a good choice when creating a butterfly garden.

 

This perennial might be tough to find at local garden centers.  One place to look is Ambergate Gardens located near the MN Landscape Arboretum.  Or check out Outback Nursery, a nursery specializing in native species in Hastings, MN, for Ratibida pinnata, yellow-headed coneflower, for a similar look.
 

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I welcome your feedback on the newsletter.  If there are topics you want to learn more about, please email me at nancy.dahl@integra.net.

 

Perhaps you were cleaning out the garage and came upon a pile of plastic plant containers from your spring plantings or you just installed new plants around your front walkway and don't want to toss all that plastic into the garbage can.  Don't. 
 
Thanks to partnerships between the Minnesota Nursery & Landscape Association (MNLA), Choice Plastics, and local garden centers and greenhouses, consumers can toss these plastic pots out at drop sites throughout the metro area.  Many companies will take the plastic from April 15 - October 1 while some sites will take pots only on June 19-20 and September 18-19.

 

To see a list of drop off sites and when they accept pots, visit GardenMinnesota.com.

 
Pots must be clean and free of debris.  Do not bring household plastic or clay pots.   Remove metal hangers from hanging baskets.   Remember your garden center will only take plastic for a limited time.  Each garden center is ONLY able to take PLASTIC pots, trays & baskets.
 
MNLA began this environmental initiative in the spring of 2006. Plastic pots take up substantial space in landfills; they do not readily decompose and remain intact for many years. Do your part to rescue plastic from the landfills, and recycle your plastic pots, trays and baskets at a neighborhood garden center.