14.7°C Not observed 
Why does one of my honeysuckles get powdery mildew every year and the other one doesn't?
Honeysuckles are highly susceptible to powdery mildew, so the fact that you're seeing this problem on one of your plants isn't at all surprising. That one of your honeysuckles is getting through the growing seasons unscathed says a lot for the general health of that individual plant.
There are a couple of reasons why only one of your plants seems to be prone to powdery mildew.
First, some honeysuckle species have greater resistance than others, so if you have two different species of honeysuckle, that could give you your answer right there. If, however, your honeysuckles are the same species there remains the possibility that one of them may just have better genetics which gives it greater resistance than that which is normally seen in that family of plants.
Growing conditions can also play a significant role.
Sometimes even a minor difference in how two plants are grown can have a major impact on overall health. For instance, honeysuckles prefer to grow in full sun and well-drained soil. If one is grown in slightly more shade or if the soil surrounding one is less porous than what plant prefers that could play a role. In addition, watering well once a week is better than water lightly several times per week for most plants, honeysuckles included.
Honeysuckles also like to have a lot of elbow room and yet for some reason they are often grown in locations where they get crowded by other plants. Opening up the space around them can be helpful as can pruning them every year to open up the core of the plant so that air can circulate freely around and between the branches.
If none of those suggestions help to bring your mildew-prone honeysuckle into line, then it may be time to consider nutrient deficiencies, which can often be corrected with a high-quality organic fertilizer. Any plant that is deficient in nutrients will be more susceptible to disease than a plant that is able to pull everything it needs from the soil.
The interesting thing about your problem is that the honeysuckle that's succumbing to powdery mildew each year is the one that is behaving pretty much as expected. The healthy plant is the one that is bucking the trend, so you may just have to shrug your shoulders and chock it up to one of nature’s quirks.
To submit a question to Riverview master gardener Vanessa Farnsworth, please send her an e-mail at vanessa@gardenmuse.ca or visit her website at www.gardenmuse.ca.
