Powdery mildew is a major factor in my decision NOT to plant cucumbers in 2019.
Luckily I still have pickles in the cupboard, but for those who must have pickles …. try these preventative measures to get ahead of any mildew problems.
3 PREVENTION methods that won’t harm the bugs…
- Better site the cucumbers – A Sunny spot with good air circulation.
- Use Milk as fungicide (1 whole milk: 10 water) doing preventative every 10 days as foliage appears – and keeping trimmed to allow airflow.
- Use Bicarbonate and liquid soap as fungicide (1tsp baking powder / cup) . once every Review Does this lower the ph of soil as well? (1)
Things to know about powdery mildew
a. Only grows on living plant tissue. Avoid late-summer nitrogen fertilizing to reduce succulent tissue.
b. Overwinters on plant debris… clean up your beds of all debris at end of harvest – throw it away.
c. Mulch affected beds in spring to reduce soil born spores release (wind, rain splash)
d. Powdery mildew Spores (conidia) spread by wind; die in water
e. Live in hot place where leaves are dry and air is humid and wet leaves aren’t required for spore germination
Fungus are particular to their host plants (you won’t see a cucurbit lover on a rose, a rose lover on a zinnia )
There are many kinds of powdery mildew fungi. Some do infect families though like the composite family (aster, daisy, composite, or sunflower family).
Powdery mildew fungi are obligate parasites; that is, they can grow only on living plant tissue. When the mildew-infected plant part dies, so does the mildew unless cleistothecia (resting stages of the fungus) are formed. The fungi overwinter on plant debris as cliestothecia.
conidia – Spore of Powdery mildew ; water = death for these guys, because they need to spread to plant leaves to feed.
cleistothecia or mycelium – a type of Ascocarp (round fruiting body) of a fungus. These overwinter on plant debris and is resistant to drying and other adverse environmental conditions. In the spring, the cleistothecia produce spores that are moved to susceptible host tissue by splashing raindrops, wind or insects (1).
haustoria – food-absorbing projections the pierce epidermal cells of plants to feed.
PM survives as mycelium in dormant buds of roses or actively on plant tissues. Powdery mildews are particularly severe in semiarid states like our Colorado front range. (2). They are also less of an issue in rainy places (how much?)
Powdery mildews are favored by warm days and cool nights and moderate temperatures (68° to 86°F). At leaf temperatures above 90°F, some mildew spores and colonies (infections) are killed. Shade or low light intensities also favor powdery mildew fungi. Greenhouse conditions are often ideal for development of the disease.
- bright sun
- low humidity
Creating an alkaline environment inhibits spore growth. Bicarbonate fungicides mixed with soap can raise the leaf surface pH. (3)
For more info See: