Q: Last year, my cucumber plants kept wilting, no matter how moist the soil was. How can I help them fare better this year?
A: You probably ran into bacterial wilt, a common disease that affects cucumbers and their muskmelon and summer squash relatives. It is transmitted by an insect (cucumber beetles) and is incurable once the disease symptoms appear. Both striped and spotted cucumber beetles chew on their namesake plants, though the former is more likely to spread the pathogen.
As the name implies, the first symptoms are the wilting of individual leaves, followed by longer sections of stem, then entire plants. To verify the beginnings of wilt are not due to underwatering, feel the soil a few inches below the surface for moisture content. A plant that remains wilted when the roots are damp is either suffering from root rot due to overwatering or poor drainage, or should be suspected of contracting a wilt disease.
Bacterial growth clogs the water transport vessels, which is why watering more won’t resolve this wilt. Affected plants may initially recover at night, but will collapse again the next day as their water needs increase with sun and rising temperatures. Infected plants die within one or two weeks after the onset of symptoms. Remove and compost the debris (composting won’t risk spreading this particular pathogen).
Plants are most vulnerable between the seedling stage and flowering. Planting late (about mid-June) can also reduce the risk of exposure since the beetles tend to congregate less by that point.
The most reliable way to prevent infection is to deny cucumber beetles access to the plant. Even though only a fraction of them carry the pathogen in their bodies, all it takes is one successful transmission to doom a plant. Cover new transplants or seedlings promptly with floating row cover or insect mesh netting. (You’ll need to remove it for bee access when flowers open.)
Remove crop debris at the end of the season so it doesn’t harbor overwintering adults. Although tilling the soil in fall or spring can kill overwintering beetles, it damages soil structure and can increase weed germination.
You could remove beetles manually, knocking them into a container of soapy water, but that might allow some to start feeding and transmitting the bacteria before they’re found. They’re also skittish, quickly hiding or dropping off the plant when disturbed, so it can be hard to catch them all.
If all else fails, you could resort to an organic insecticide; active ingredient options include spinosad, pyrethrum, or neem oil. Make sure the product is labeled for use on vegetables. A kaolin clay spray is another option that acts as a feeding deterrent to coat the foliage and stems, and might suffice to make beetles bypass the plant.
Q: Which trees and shrubs best support pollinators? I see plant lists focusing on small plants like perennials, but not many mentions of larger plants.
A: Tomorrow begins National Pollinator Week, a great time to think about how our home landscapes support pollinators and other wildlife. The primary pollinators in our ecosystem are insects, and among them, several major groups are important for pollination: bees and wasps, beetles, butterflies and moths, and flies. Hummingbirds also pollinate certain flowers whose nectar few insects can reach.
There are too many good candidates to list here. With such a diverse range of flower traits that attract these different organisms, you can plant just about anything native that has showy flowers and it should support pollinators.
Pollinator garden lists often focus on attracting bees and butterflies, which is somewhat limiting. To accommodate more pollinators, grow several tree and shrub species, whose blooms can vary in color, shape, size, orientation (hanging, upright, etc.), scent, and what time of day they are open or fertile.
When selecting plants, always consider their compatibility with the existing site conditions: summer sun exposure, soil moisture and drainage, and any deer problems. Although trees and some shrubs eventually outgrow a deer’s browsing reach, you still may need to protect young trunks from antler rubbing. Make sure a plant’s expected mature size will fit where you want it, since growth-restricting pruning should be avoided.
Pollinated flowers produce seeds, which can spread the plant long distances, especially if you leave them for birds or wind to disperse. For this and many other reasons, try to use locally native species.
University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.