Across Iowa, crabapple trees have been dropping leaves this summer.
The cooler fall temperatures bring welcome relief from the summer heat. As we trade bare feet for shoes, the grass underfoot in our lawns is relieved to see some cooler, wetter weather. But the autumn weather also makes many fungi happy, and several fungal diseases of lawns may show up this time of year.
Houseplants are susceptible to attack by various pests and diseases. While rarely lethal, pest and disease outbreaks can compromise the aesthetic quality of indoor vegetation. Even tightly sealed houses and conscientious tending cannot always prevent attacks on our houseplants.
Verticillium wilt is a fungal disease that affects over 300 species of plants, including many common trees and shrubs. In Iowa, it is most commonly seen on maple, ash, and catalpa trees, although it is also frequently found on smoke tree, viburnum, lilac, cherry, plum and several other trees and shrubs.
Scales are a unique appearing insect. Most of us learned insect basics in grade school and are looking for three body parts (head, thorax and abdomen) and six legs. Then someone tells us a scale is an insect and we look at it and it appears to be one smooth surface and there are certainly no legs in sight. It is at this point where most of us basically just take the entomologist's word for it that these things are indeed insects. It is primarily the females that we see on plants, and female scales are wingless and usually legless as adults. Scale insects start as eggs. The nymphs hatch and do have legs, and this is the stage referred to as crawlers that moves around and infests different parts of the plant. After that first stage that is mobile, all the rest of the stages do not move.
Sooty blotch and flyspeck may be as old as apples themselves. Drawings of apple varieties from the 1820s clearly show sooty blotch on every fruit. It wasn’t until sprayed-on pesticides, such as lime sulfur and lead arsenate, became popular around 1900 that consumers began to expect to buy apples without a heavy coating of sooty blotch and flyspeck. The cosmetically perfect apples found in today’s supermarkets weren’t common until the middle of the 20th century, when more effective organic fungicides appeared.
Willows and poplars are common trees for use in windbreaks or privacy screens because they grow very fast, providing effective screening within a few years. One of the most popular willows is the Austree, a hybrid willow (a cross of white willow and corkscrew willow) developed in New Zealand. However, many people are dismayed when these beautiful screens start declining and dying after a dozen or years, or even sooner. These fast-growing trees exemplify the saying, “live fast, die young” because, despite their fast growth, they are highly susceptible to several lethal diseases.
Spruces are a favorite evergreen for yards and windbreaks in Iowa. However, they are susceptible to a few problems that can leave them unsightly. Knowing about these common spruce ailments is the first step toward minimizing problems with these beautiful trees.
The first “side” of the triangle is so obvious it may be overlooked. In order to have a plant disease, you must have a plant. More specifically, you need a susceptible plant, one that is able to get a particular disease. Each plant species is prone to a unique set of maladies. Crabapples and oaks get different diseases. Within a species, plant varieties differ in their susceptibility to various diseases. For example, some crabapple cultivars are decimated by apple scab while others are unaffected. The overall health and vigor of an individual plant also affects its susceptibility to disease.
Late summer/early fall is the time of the year when leaves of bur oaks in Iowa are showing V-shaped brown discoloration and browning of the leaf veins. The affected leaves eventually die and fall to the ground or hang dead on the twigs through the winter and into the following year. The disease may affect the entire tree and if only a portion of the tree is affected, the disease is generally most severe in the bottom of the tree.