Powdery and downy mildews are two common pathogens that impact plant and crop health. Powdery mildew is a fungus that results in distinct white spots on plant leaves and stems. It’s common among many plants and crops including legumes, cucurbits, apples, pears, onions, maple trees, and grapes. It requires low humidity with warm temperatures, making greenhouses a great environment to infect. On the other hand, downy mildew is a fungus-like parasite that is actually more closely related to algae. It also results in spots which are distinct in that they are more angular, and often yellow or gray in color. In grapes, downy mildew spots are yellow and oily-looking. In mint and basil, downy mildew spots are darker brown or black. Downy mildew is most common in spring and fall with cool nights and high humidity, warm days.

With both mildews, they survive by stealing nutrients from plants which can stress, weaken and even kill the plant. They can also make plants vulnerable to other pathogens and insect damage. Similarly, they can spread via insects like aphids, wind, rain, runoff, irrigation, and contact with infected plants.

Downy mildew is a zoospore, making it capable of “swimming” through water to infect one plant to the next. Spots on leaves can grow larger and denser until they even impact photosynthesis. This can lead to defoliation, sunburn, soft rots, plant death, and can affect the level of sugars that develop in fruit and vegetables and therefore their flavor. Both also have unique varieties that affect particular crops, for example the variety of powdery mildew that has infected squash cannot infect grapes. It is important to be aware of plant families though, as mildew that has attacked basil can be transferred to mint.

Despite their differences, their management techniques are similar. Because they need high humidity to proliferate, it’s best to avoid over-watering techniques, avoid fertilization during outbreaks, properly space plants particularly in greenhouses, and prune overcrowded areas particularly for trees and crops like grapes. Since downy mildew can overwinter, it is critical to dispose all infected plants. For cucurbits, there are some mildew-resistant crop strains. For grapes, berries will naturally protect themselves after 2-3 weeks of their development. However, certain fungicides like sterol inhibitors and strobilurins don’t completely kill mildew and others like difenoconazole are phytotoxic to grapes.

For grapes in particular, and any other affected plant or crop, there are environmentally friendly fungicides and algaecides that can contain both powdery and downy mildew. BioSafe PerCarb is a biofungicide based in sodium carbonate peroxyhydrate that should be applied every 7-10 days to field crops or within greenhouses. To maximize treatment efficiency, it is recommended to supplement with a foliar treatment such as Oxidate 2.0. These fungicides work together to provide increased stability, and again can be applied from seed to harvest via spray, soil drench, or pre-plant drip with a 0-hour re-entry interval and 0-day pre-harvest interval. They are also both EPA certified, OMRI approved, and biodegradable.

Phytophthora – which translates from Greek as “plant destroyer” – is one of the most common and destructive blights. It is difficult to manage with hundreds of Phytophthora species existing, each capable of destroying a host of different plants. Phytophthora blight can affect ferns, grasses, crops such as strawberries, curcurbits, tomatoes, potatoes, cocoa, onions, and soybeans, trees such as cedar, birch, dogwood, and citrus trees, and shrubs such as rhododendron and azaleas. In fact, it was Phytophthora infestans that caused the Irish potato famine in the 19th century.

Phytophthora is a water-mold made up of cellulose, therefore is behaves similar to a fungus but is actually more closely related to algae. Because of its preference for environments with excess water, it is most common in spring and fall, and in temperatures ranging from 59-82°F. In potatoes, phytophthora blight that happens later in the season can sometimes be accompanied by a virus making the damage as much as 125-times more detrimental (PotatoPro, 2019). It can be spread through wind-borne rain, runoff, irrigation, and through contaminated soil or equipment. Phytophthora can also overwinter and spread through plant debris. Phytophthora needs only a few hours (4-8) of standing water to take hold. It is also common for newly imported plants to infect others, particularly in greenhouses. Dependent on the plant variety, some symptoms of phytophthora blight include plant weakness, wilting, foliage discoloration, signs of drought-stress or other distress. Many plants also exhibit no symptoms. In trees and shrubs, younger trees are more vulnerable where it may take years for the infestation to kill older trees.

Because phytophthora blight is so proliferate, most management techniques include preparation such as ensuring proper drainage or mitigating damage through digging up infected soil and drying out roots. In trials with tomato seedlings, TerraClean 5.0, an environmentally-friendly fungicide/algaecide, has been found to reduce Phytophthora by 23-55%. It also reduced root-knot, where similar alternatives such as methyl bromide and Ridomil Gold reduced either Phytophthora or root-knot, but not both. Tomato seedlings were inoculated with Phytophthora in August, then the fungicide was applied via drip irrigation once every two weeks until November. Apart from receding the blight outbreak, tomato plant vigor and yield both increased. In a separate trial with strawberry plants, yield increased by 19%.

TerraClean 5.0 can be used to attack phytophthora blight during any plant stage. Composed of hydrogen peroxide and peroxyacetic acid, it kills pathogens, enhances nutrient uptake, and develops a healthier root zone. It can be applied via drip irrigation, drench, flood, and drip application. It is also EPA and OMRI approved as it has no mutational resistance and a 0-hour re-entry interval. While management techniques may work to battle phytophthora blight, it is also reassuring to know there are proactive solutions for the “plant destroyer” as well.

Have you recently noticed those pesky cankers typical of fire blight in your orchard? Fire blight is one of the most common diseases afflicting apples and pear orchards, with around 200 species being susceptible to its damage. Young trees are most vulnerable with complete loss possible in just one season. Even in more established trees, fire blight can kill blossoms, fruit, shoots, twigs and branches. Symptoms can be present in bark, leaves, flowers, and roots from pre-blossom through to blossom and onto fruition.

Fire blight is most adept to happen when trees are in flower, the weather is warm (70-95?), and in humid environments. At temperatures below 70? and higher than 95?, bacterial growth is still present, but grows at slower rates. As a general rule, fire blight is most likely to take root in three weeks following petal fall. This generally happens during May and June in North America. The fire blight bacteria is perpetuated by insects like bees and flies, and can also be transferred during wind-blown rain. Further, diseased cells can survive in plant tissue from one season to the next.

Now, taking this into consideration you may be wondering what your options are to attack this plight, particularly what organic-safe options are out there. Pruning is an option, but presents risks during warmer months where fire blight can actually proliferate from pruning. Fortunately, Enviroselects offers Oxidate 2.0 which can prevent, cure, and even rescue apple and pear orchards from fire blight. Its active ingredient is hydrogen peroxide, and this oxidizing fungicide kills bacteria, fungal pathogens and spores present in apple and pear trees. It can also be used for crops including beans, berries, nuts, potatoes, and herbs among others.

After six applications, more than 70% of fire blight bacteria or fungus was under control (BioSafe Systems, 2012). It begins to work on contact with apple and pear plants or trees. It can be applied every 5-10 days for preventative purposes, every 3-5 days for curative purposes, and depending on the crop variety even more frequently for rescue purposes. It can be applied on field crops or in greenhouses to seeds, growing plants, and mature fruiting trees.

Apart from its successes, Oxidate 2.0 also boasts approval from both the Organic Materials Review Institute (OMRI) and the EPA. It’s safe for both growers and consumers with a 0-day pre-harvest interval, as well as a 0-hour restricted entry interval. With a 2-year shelf life, and no refrigeration necessary, it can also be safely used next season should any fire blight bacteria survive the winter. This product is available right on our website, with further information on the specific pathogens exterminated and related resources.

An increasing number of gardeners are looking for solutions to soil-borne diseases such as Verticillium (maple) wilt. In trees Verticillium can be hard to diagnose as symptoms are often confused with other causes such as drought stress or compacted soil. If the tree is exhibiting die-back of branches or leaf scorch there may be a possibility that these symptoms could be caused by Verticillium. To make a sure determination of the cause of the symptoms make a slanted cut in the affected branch below where the tree is wilted or scorched. Discoloration of vascular tissue (olive-green streaks) in the wood will indicate the presence of Verticillium wilt. To prevent further spread of the disease in the tree, some experts recommend removing the infected limbs.

Treatment & Prevention

In order to prevent the spread of Verticillium to other trees and plants we recommend the following treatment. As Verticillium spreads through the soil and root-to-root contact, ZeroTol 2.0 can be applied as a preventative application. Make a strong solution with a 1:50 solution and soak the root zone. Repeat with 1-2 additional applications in a 7-14 day interval.

Keep the tree well-watered during dry periods to help the tree recover from the disease.

Plant diseases can be grouped into 3 main microscopic categories: bacterial, viral and fungal. Here is some information to keep in mind about these common plant diseases and the preventative steps that can be taken to defend against them.


The most common plant diseases one encounters in the garden are those brought on by fungi and fungus-like organisms. The fungi reproduce via the production of spores that may be spread long distances by air or water, or they may be soil borne. Proper watering techniques and drainage are an important preventative defence since many of the fungi that cause plant diseases thrive in moist conditions. Fungal diseases can be controlled through the use of fungicides in agriculture, however new races of fungi often evolve that are resistant to many conventional fungicides. Alternatively, fungicides like OxiDate use a chemical reaction that oxidizes enzymes and proteins that make up simple cell organisms, on contact. As the oxidation happens very quickly and leaves no residual chemical, the disease has no opportunity to mutate and form resistance. Some of the most common plant diseases brought on by fungi and fungus-like organisms include, Downy and Powdery MildewGray Mold (Botrytis)Fusarium wilt and Blight.


Bacterial diseases can occur within houseplants and greenhouse-grown varieties, but are more common in outdoor plants. This is partly due to the fact that many types of bacteria that infect plants are often transmitted by insects that create a wound in the plant, allowing the bacteria to get inside. Several types of parasites like whiteflies, scale and aphids can act as carriers of the bacteria, which is transmitted to the plant when the insects feed on it. Bacteria can also be transmitted by pruning equipment shared between infected and non-infected plants.

A two-pronged approach to bacterial prevention would include include controlling the parasites with a natural insecticide like AzaGuard. Plant wounds can be treated for bacteria using a foliar spray like OxiDate (for food crops) or ZeroTol (for ornamentals). These organic chemistries can be tank-mixed for ease of application.


Viruses, like bacterial infections, require an opening in the plant through which the virus can get past the cell’s rigid cell wall. Humans can transmit plant viruses via grafting and parasites can also act as carriers of the virus. Unlike bacteria, viruses actually infiltrate the plant’s cells, and then replicate themselves to create more infected cells. Since the virus lives inside the plant’s cells, there is no way of removing a virus without destroying the plant cells in the process, making chemical treatments futile.

Normally plant viruses only cause a loss of crop yield. Therefore it is not economically viable to try to control them, the exception being when they infect perennial species such as fruit trees.