Powdery Mildew Chemical Controls

Chemical Controls for Powdery Mildew

Some of our past posts have looked at cultural and biological controls for powdery mildew. These, along with Greencure, are all typically approved for use in certified organic agriculture.

Now, it’s time to talk dirty. So, get out your PPE (personal protective equipment), take a deep breath, and prepare to kill some bacteria and fungi…

Synthetic chemical fungi killers come last in this series because, ideally, they are a last resort. While undeniably useful components in an integrated disease management plan, they should not be relied upon as a substitute for good gardening practices.Powdery Mildew of on a leaf of the tree

You may be familiar with foggers or “bug bombs” for pests like spider mites. They also exist for fungal diseases. Fungaflor TR‘s active ingredient is Imazalil. TR stands for total release. Once you trigger the fogger, the entire contents of the canister are emptied. One small two ounce fogger treats up to 1,500 square feet (1,000 square feet for powdery mildew). As with other bombs, thoroughly read and follow all directions on the label. The fog is flammable so make sure there aren’t any open combustion sources, like a pilot light. Once the treatment is over, ensure ventilation has completely removed the product from the space prior to reentry. We recommend airing out your grow space for a minimum of 24 hours to protect you and your pets from the harmful fumes.

Fungi bombs work very well as a preventative measure when preparing a new garden or to treat a space that previously contained pathogenic spores. Foggers provide excellent coverage over a large area and won’t leave residue behind, as burning sulfur tends to do.

Use with Caution

While Fungiflor can be used in a garden while plants are in it,  be careful. Do not trigger a bomb too close to your plants or they may be cause damage. In the Keys to Success listed by the maker of the product, it says to “clear out a three-foot area around the canister to prep for application”. Remember, one small can is intended to treat 1,000-1,500 square feet which is larger than many indoor gardens. If used in too small of a space, the increased concentration could also cause damage to your plants.

Eagle 20EW  is effective and, therefore, popular with many gardeners. The active ingredient is Myclobutanil. Eagle 20EW acts as a systemic with a residual presence in the plant. For this reason, treating a plant once or twice in its vegetative stage is often sufficient enough to successfully suppress powdery mildew. This is also the reason to avoid treating plants with it during the latter stages of growth.

Eagle 20EW can be used as a preventative treatment when introducing new plants to your garden from outside gardens. It can also be an effective knockdown treatment when other options have failed to break the pathogenic cycle. That being said, it should not be overused. Science has proved that overuse of fungicides, like Eagle 20EW, can result in some fungi becoming resistant to them. For this reason, the product label recommends alternating it with other products after two consecutive uses.

Do Your Homework & Use Caution

Carefully read the label/instructions prior to using the product. Since you shouldn’t require too many applications for the life-cycle of a plant, make them count by combining Eagle 20EW with a surfactant (like Coco Wet or Humboldt Sticky) to maximize plant coverage and keep it in place. If plant size permits, consider mixing enough solution to dunk the entire plant in order to guarantee complete coverage.

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Mildew is also known as ‘downy mildew’ and as the disease spreads, the leaves curl up, necrotize and eventually fall off. The parts of the mycelium that contain the spores of the fungus emerge through the stomata of the plant. In good light it can readily be identified by the gray or purple felt like covering on the back of the leaves.

About mildew

  • What is mildew?
  • The term mildew refers to a group of phytopathogenic fungi that causes diseases in plants.
  • What can you see?
  • In general, mildew is found on the upper side of the leaf, but there are exceptions. One type of mildew only grows on the underside of the leaf. The leaf looks as if it has been dusted with powder.
  • What can you do?
  • Keep humidity low and keep your growing area clean.

About powdery mildew

Powdery mildew is also known as Oidium. Before any symptoms become visible the leaf starts to develop blister-like patches, which is followed by the characteristic white powder where the blister was. The leaf looks as if it has been dusted with powder. In general, mildew is found on the upper side of the leaf, but there are exceptions. One type of mildew only grows on the underside of the leaf, so it’s no surprise that this often gets overlooked. However, as the disease advances, the leaves can end up being completely covered in this white layer and it can even colonize the fruits, with subsequent losses in crop size and quality.

How to prevent the disease?

The best treatment against these types of fungi is prevention; once they have set in and developed, they are very difficult to eradicate, sometimes even with chemical fungicides. Try to prevent spores coming in from elsewhere and contaminating your plants by keeping your growing area clean. You can do this by using only clean equipment and washing your hands thoroughly before entering.



How To Identify Powdery Mildew Damage

  • Plants infected with powdery mildew look as if they have been dusted with flour.
  • Powdery mildew usually starts off as circular, powdery white spots, which can appear on leaves, stems, and sometimes fruit.
  • Powdery mildew usually covers the upper part of the leaves and affects the older leaves first; the leaves turn yellow and dry out.
  • The fungus might cause some leaves to twist, break, or become distorted.
  • The white spots of powdery mildew will spread to cover most of the leaves or affected areas.
  • The leaves, buds, and growing tips will become distorted as well. These symptoms usually appear late in the growing season. 

Control and Prevention

How To Control Powdery Mildew 

  • Rubbing the infected leaves together can help partially remove the disease from your plants.
  • Remove all the infected plant parts and destroy them. Remember, do not compost any infected plant, as the disease can still be spread by the wind.
  • Spray infected plants with fungicides. Effective fungicides for powdery mildew treatments or cures include sulfur, lime-sulfur, neem oil, and potassium bicarbonate.

How To Prevent Powdery Mildew

  • Choose plants that are resistant or tolerant to powdery mildew.
  • Powdery mildew thrives in hot and humid weather, so avoid overhead watering to reduce humidity. Also selectively prune overcrowded areas to increase air circulation; this also helps reduce humidity for your plants.
  • Spray your plants with fungicides according to their directions. If you don’t want to use fungicides, try spraying your plants with a solution of 1 teaspoon baking soda in 1 quart of water. Remember to spray your plants thoroughly.

Plumeria that grow in crowded, humid or shaded conditions are susceptible to powdery mildew, a form of mold. Powdery mildew is a common fungal disease that affects many types of plants, from squash to plumerias. The signature symptom of powdery mildew is white or gray powdery spots on the upper sides of plumeria leaves. The spots sometimes appears on flowers, buds, the undersides of leaves and new shoots. As the infection progresses, the leaves turn yellow, become distorted and drop off prematurely, and flower buds fail to open. The fungus overwinters in brown or black fruiting bodies.