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INSECTS AND DISEASES ZEROING IN ON OUR GARDENS
With recent rains, rising temps and lush plant growth, insect pests and plant diseases can't be far behind. Here are some of the more common pests and diseases you may encounter.
On the insect front, you may already have spotted some eastern tent caterpillar activity. I've noticed several tents in the plum trees around my house. Eastern tent caterpillars make silken webs in the forks of apple, cherry, flowering crabapple, plum and chokecherry. You may also find them defoliating birch, ash, maple, oak and willow.
Eastern tent caterpillars feed during the day and retire to the tents at night and in rainy, cold weather. As they grow, the caterpillars enlarge their nests. Caterpillars feed for about four weeks and generally don't seriously damage healthy, mature trees, even if they completely defoliate the tree. Trees will leaf out again in a couple of weeks.
Full-grown eastern tent caterpillars grow to 2 in. in length and sport a hairy, bluish appearance with a conspicuous white line running the length of the back.
Easiest method to control eastern tent caterpillars is to remove webs with a stick and crush, burn or bury the webs along with the caterpillars. This task should be done in the evening or early morning when the critters are in their nest, rather than during the day when they're busy consuming your tree. Registered insecticides include Bacillus thuringiensis, acephate, permethrin or carbaryl. Spraying caterpillars over an inch long doesn't help the tree, explains Jeff Hahn, University of Minnesota extension entomologist, because caterpillars will likely have finished feeding at this stage.
Cutworms can raise havoc with stems of tomatoes, peppers, beans and other vegetables and flowers. You'll know they're active when you find stems chewed off an inch above the ground. Damage is most common on tender, young seedlings.
Cutworms do their damage at night and hide under the soil during the day. Non-chemical control methods include drowning in soapy water or fabricating protective collars on plant stems. Approved insecticides include diazinon and carbaryl (Sevin).
White grubs, which turn into June beetles, are common in many lawns. Just because you had white grubs last fall, however, doesn't mean they're present this spring.
If you have lots of June beetles hitting your windows in the evenings, it may mean that you can expect white grubs in your lawn next year because June beetles lay their eggs in lawns. If you discover white grubs in your turf this spring, they can be treated with one of the following insecticides: diazinon, halofenzamide (MACH-2), imidacloprid (Merit or Grub-ex), or isofenphos (Oftanol). Be sure treated areas are watered thoroughly after application to help move the insecticide into the root zone where the white grubs are located.
One of the most-common plant diseases gardeners may notice this spring, according to Chad Behrendt, University of Minnesota plant pathologist, is necrotic ring spot in lawns. Rings vary in size but generally are about one foot in diameter in the shape of a donut. The center of the ring is filled with green grass and the surrounding ring is brown. Often the ring is sunken or lower than the surrounding grass.
Two common diseases may cause these symptoms: yellow patch and necrotic ring spot. Behrendt says a laboratory analysis of a lawn sample is necessary to diagnosis which disease is causing the browning. (To submit a sample, call the Yard and Garden Line, 612-624-4771 for instructions; cost is $5.)
Necrotic ring spot is most common on newly sodded lawns (2-5 years old). When sod is laid on top of a couple of inches of soil, which is laid over clay, these layers create drainage problems and poor root growth. And, since most newly sodded lawns are heavily watered and fertilized, the vigorous grass growth produces a thick layer of thatch, which stimulates fungal growth.
The best way to prevent necrotic ring spot is sound cultural practices. Water, fertilize and mow your lawn according to University of Minnesota recommendations. De-thatch and aerate your lawn to help reduce the thatch layer. If disease is severe, fungicides can be applied in the spring.
Probably the most common diseases reported by gardeners are fungal leaf spots such as oak and ash anthracnose, iris leaf spot and apple scab. Each disease is caused by a different fungal organism, according to Behrendt, but all of them require moisture for germination and infection.
During wet springs, anthracnose turns the edges of leaves brown and leaves drop from the tree. No treatment of ash and oak anthracnose is recommended, since trees generally recover on their own.
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