Don Kinzler, Published August 02 2013
Bugs, blights and blemishes: Beware problems that rob garden of vitality
It’s been a pretty good growing season, but the ever-present diseases, yellow leaves and insect holes can be a headache for gardeners.
I’ve developed a checklist of ideas to help lessen the trauma of dealing with the disorders that appear on our vegetables, flowers, trees and shrubs.
E Diseases and insects tend to run in cycles with nature. Some are bad in wet years, others in dry seasons.
E Nearly every type of plant has an enemy, and every plant that has ever lived will die from something eventually.
E It’s wise to plant a variety of material in our yards and gardens. If it’s a bad year for one crop, chances are something else will flourish. Last year our tomatoes were superb, but I couldn’t get carrots to germinate. This year our carrots are beautiful, and the tomatoes are lackluster with blight.
E Once leaves develop spots, lesions and discoloration, the symptoms will not disappear from those leaves no matter what you do. But it is often possible to limit the spread to healthy leaves.
E Most products for disease control are best applied as a preventative before symptoms are noticeable or at first sign.
E You can anticipate some of the common diseases such as black spot and powdery mildew on roses, tomato leaf blights, and blight on potatoes, and treat preemptively.
E Diseases are sneakier than insects. Other than a plague of locusts, most insects nibble slowly enough to allow time to act. For example we can apply insecticide on cabbage and broccoli at the first sign of green cabbage worms before they destroy the crop.
But diseases are tricky. From one day to the next diseases can arise and decimate vegetables seemingly overnight. Last year my nice patch of watermelon vines went down within a day, never to recover.
E Many disease organisms require moisture on leaves to multiply and establish. Diseases often begin in damp, humid weather. Sometimes we contribute to the problem with our watering method. It’s best to water in the morning rather than evening so foliage dries before nightfall.
E Many disease organisms are spread by splashing water. Soaker hoses laid on the soil cause less disease transmission than overhead sprinkling.
E It’s important to identify causes of problems. It might be tempting to spray hosta plants with insecticide to remedy holes that are appearing. But holes in hosta leaves are commonly caused by slugs, which are not an insect and would require different treatment.
E Pests often overwinter on plant refuse in and around the soil, waiting to attack again next season. Practice good sanitation in the fall by disposing of tomato vines, potato plants and the vines of cucumbers, melons and squash. Remove diseased perennial tops on varieties frequently plagued, such as peonies.
E Although it’s not always pretty, plants can survive with problems. Minnesota research has indicated that tomato plants having one-third of the lower foliage diseased had no reduction in fruit quantity harvested.
E There might seem to be a mind-boggling array of pest and diseases with which to cope, but in practicality gardeners need only a small handful of treatments in our “medicine chest.”
Most insects can be controlled with malathion, sevin, insecticidal soap or rotenone. Disease control products vary with each chemical company, but the name is usually descriptive, such as vegetable disease control, rose and flower disease control, or fruit tree spray. The active ingredient on the label’s fine print often is chlorothalonil.
On the lookout for Japanese Beetles
Japanese Beetles are a huge potential threat headed our way. Although they are found in most states east of the Mississippi River, much of our region has been free of the problem until now.
Japanese Beetles attack over 300 species of plants ranging from rose bushes to field corn. They can quickly devastate plant material by turning the leaves into skeletons.
The North Dakota Department of Agriculture indicates that Japanese Beetles have now been found in monitoring traps. Recently 60 were found in West Fargo, 12 in Grand Forks and several in Fargo and Bismarck. The introduction of the beetle can be traced to nursery stock brought into the state by a major supplier from Minnesota.
I wanted to see the beetles firsthand. Charles Elhard, plant protection specialist with the Department of Agriculture, showed me several of the live beetles secured from a trap. They are a half-inch long with a metallic green broadly oval body with coppery bronze wing covers.
We can all help nip this in the bud if we keep a lookout. If we suspect seeing a Japanese Beetle, the department asks us to call (800) 242-7535.
Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler’s Greenhouse in Fargo. Readers can reach him at email@example.com