Rainy, warm weather and diseases: West Nile and leaf fungus

By John Fulton

[June 02, 2008]  West Nile virus has quickly, and unfortunately, become a household phrase. With Illinois leading the nation in deaths from the virus, it behooves us all to take proper precautions. The excess moisture in much of the Midwest has led to one of the worst springs for mosquitoes in recent history. This is a more full-blown accounting of WNV.

WNV was first isolated in Uganda, Africa. It can harm humans, birds and other animals. It is transmitted by infected mosquitoes, primarily the northern house mosquito. The mosquito becomes infected after biting wild birds that are the primary host of the virus. The mosquito is actually able to transmit the virus after 10-14 days after biting the infected bird.

The mosquito life cycle has four life stages: egg, larva, pupa and adult. The female mosquito lays eggs on water or moist soil. Most of the larvae hatch after 48 hours, and the larvae and pupae live in the water. The females need a blood meal before they can lay eggs, so only the females bite. They bite every few days during their adult lives, which may last several weeks.

The first symptoms of WNV are often the deaths of susceptible bird species, such as crows and blue jays. We have had bird deaths in the county many of the past summers, and I'm sure that this year will be no exception. The Illinois Department of Public Health is the agency in charge of testing birds for WNV.

Symptoms of WNV are rare in humans. A small percentage of people do develop fever, headaches, body aches, swollen lymph glands and a body rash. Encephalitis develops in less than 1 percent of infected people, and this group can have headache, high fever, neck stiffness, tremors and other symptoms.

Preventing mosquitoes is a first step. Homeowners can best accomplish this by eliminating standing water. Tires and old containers are obvious places to start. Drill holes in the bottom of recycling containers; clean clogged gutters; don't allow stagnant water in anything such as birdbaths; change landscape slopes to eliminate standing water; and use larvicides in standing water that can't be eliminated. Bt israelensis is the strain that is effective against mosquito larvae -- not the Bt variety commonly used on trees and gardens!

Also, protect yourself from bites. Mosquitoes can travel up to three miles from their breeding sites! Make sure that screens and doors are tight; use proper outside lighting, such as fluorescent lights; stay indoors at dawn and dusk, when mosquitoes are most active; wear long-sleeved shirt and long pants when you must go outside; and use insect repellents properly applied. Exposed skin should be sparingly treated with a repellent containing up to 30 percent DEET (up to 10 percent for children), and make sure to treat thin clothing as well, since mosquitoes can bite through the thin clothing.

Elimination of mosquito breeding sites, treatment of larvae and proper protection for people will go a long way in reducing the incidence of WNV in our area this summer. Further information on WNV can be found at http://www.urbanext.uiuc.edu/westnile/.

Leaf spot fungal diseases

It seems the leaf spot fungal diseases are present with a vengeance. Anthracnose and apple scab are very noticeable now. If you think your trees have escaped infection, hold a leaf up to the light to make sure. If you see light areas along the edges or between veins, you'll probably have the full-blown symptoms within a week.

As there is no cure, keep the plants watered with an inch a week during dry spells. A little fertilizer also will help. Severe leaf drop early in the season will usually lead to another set of leaves being out in four to six weeks.

[By JOHN FULTON, University of Illinois Extension, Logan County]