At Ease Disease, There's a Fungus Among Us

Powdery Mildew

We’ve had a wet spring and that
means two things—mosquitoes and diseases.  It doesn’t matter if it is cold and wet or warm and wet, some disease thrives in it.  Some plants are naturally more prone to fungal infections.  My monarda get powdery mildew every year and garden phlox are also susceptible.  Powdery mildew usually doesn’t do lasting harm, tho it can look a little unsightly.  Roses are also prone to many types of disease, including powdery mildew and black spot.  Other types of diseases can be devastating to some crops, including tomatoes, squash, and potatoes.

Mosaic disease

Plant diseases are spread in a variety of ways.  Sucking insects, like aphids, can transfer the disease and some diseases are spread by spores in the soil.  Rose Mosaic Virus is spread through vegetative propagation (cuttings).  Some are preventable, most are not treatable.

Late blight on tomatoes

The best way to fight disease is to follow good horticultural practices.  Water early in the morning and don’t water from overhead; that is water the soil not the plant.  In the vegetable garden, rotate your crops from year to year.  Mulch between the rows so soil borne spores aren’t splashed up onto the undersides of the lower leaves when it rains or when watering.  If you know you have plants that are susceptible to certain diseases, such as the monarda, or if your vegetables become diseased year after year, start applying fungicides before you see the problem and follow the good horticultural practices outlined above.  If you don’t catch it in time, the only thing to do is to remove the affected leaves or stems and begin a spaying program.  Dispose of the diseased material by putting it in a bag and then in the trash.  Do not throw the diseased prunings in the compost pile.  There are organic fungicides that you can use on vegetables and other edible crops, but always, always read and follow the label. 

You can also use seed or buy plants that are certified disease resistant.  When buying tomato plants, for example, you may see the letters VFNT, or only some of those letters.  The V stands for verticillium, the F for fusarium, the N for nematodes and the T for tobacco virus.  The Champion tomato variety is certified VFNT, which means it is genetically bred to be resistant to those for pathogens. 

Black Knot Disease



Branches afflicted with Black Knot



My friend Janice called last week to ask about a problem she was having with her ornamental plum in front of her house. It had black growths on some of the branches. I was pretty sure it was some type of fungus, but I didn’t know what or how to treat it. I told her to take a branch into Countryside and ask for KC or Kelly. They are both certified nursery professionals and have training in disease identification.



Kelly O'Leary
Nursery Staff



Well, the diagnosis was Black Knot. Kelly advised her to prune out the affected branches, cutting at least 4" back from the infected sites and to carefully bag the branches and dispose of them. You don’t want diseased plant material going into a compost pile or back in the woods where the fungal spores can continue to spread. After cutting out the infected branches Kelly recommended treating the tree with Bonide Fruit Tree Spray or any spray containing captan.



Black Knot affects plum and cherry trees. The fungus disrupts the twig growth and causes a tumor like growth. At first the swelling is light brown in color but by the second year the swellings have become hard and black. It takes a year or two before the disease even becomes noticeable and by the time you do see indications of the disease, it is usually too far gone for any remedy to work. As with all fungal diseases, it is easier to prevent than to cure.



Close up of Black Knot fungus



The best time to prune out the diseased wood is in the late fall or early winter when the tree and the fungus are dormant. This way you won’t be inadvertently spreading more spores. When you do prune make sure you dip your pruners in rubbing alcohol between cuts to again insure that you don’t spread the disease to healthy tissue.

We got about half way through the job of trimming when we realized that we wouldn’t be left with much of a tree when we were through. Janice decided to just replace the tree with a more disease resistant one. This time she is thinking of a crab apple. Though crab apples are also susceptible to fungal infections such as apple scab and fire blight, new varieties have been introduced that are very disease resistant.

Planting Roses

The Gardening Trivia Quiz Last week I asked for the technical term for the "thorns" found on roses. The answer and explanation is below. Keeping with the rose theme, here is this week’s question: Roses are part of a much bigger family. What other fruiting shrubs are related to roses?



Planting Roses
One way to ensure at least one growing season, is to plant the rose properly. This means selecting the proper site, with full sun and good drainage. Full sun means 7-8 hours of sun, although it doesn’t have to be all at one time and in this case, more is better. To check for drainage, dig a hole 18" deep and fill it with water. If the hole drains within 5-6 hours, you have adequate drainage. If not, consider raising the soil level by using top soil or building a raised bed. Roses also prefer a neutral to slightly acidic soil. Having slightly acidic soil allows the plant to take up nutrients more efficiently. We ask a lot of our roses (all those magnificent blooms) and to perform roses need a soil that is light, porous, moisture holding and full of nutrients. To achieve this, most soils, especially ours here in No. Illinois, need to be amended. A 50-50 blend of native soil and some type of organic compost is best. There are many products available commercially. Composted cow manure, mushroom compost, or Cotton Burr compost are recommended.



If you are planting a large bed, you can dig the compost in the whole bed. Otherwise, when you back fill the planting hole, use a 50-50 mix of native soil and compost. When digging the hole, dig it at least 2 feet in diameter and slightly deeper that the container you purchased the rose in. It does not hurt to plant the rose graft an inch or two below the soil surface. This helps protect the bud union during our winters. It is extremely important that you dig the hole at least 2 feet in diameter so that the feeder roots, the ones responsible for taking up water and nutrients, can get established. Adding bone meal or super phosphate at the root level when planting will also help these feeder roots develop. We also recommend using a root stimulator, such as Plant Start or Quick Start, when planting. These are low in nitrogen and high in phosphorus, to encourage root growth over top growth. Once the plant is established (6 weeks or so), you can switch to a regular fertilizer.


Summer Care for Roses
Assuming you have established plants, the most important thing you can do for your roses is water and fertilize. Use a good rose or all purpose perennial fertilizer. I usually recommend using a granular, slow release fertilizer, so that nutrients are being leached into the soil continuously. If you use a water soluble fertilizer, such as Miracle-Gro, you will have to fertilize every time you water, or at least once a week. I’m not that motivated. Spread the fertilizer in a 2-3 foot diameter circle around the plant and work into the top several inches of soil, then water thoroughly. Fertilize once a month until August 1. Fertilizing after that time will cause weak canes to develop that will not survive the winter. Also this is a good time to quit deadheading. Deadheading also encourages new growth which leads to weakened canes.

Most plants need an inch of water a week. They prefer to be watered deeply to encourage the roots to grow deep rather than frequent, shallow waterings. It is best to water in the morning, and to water the soil rather than spray the foliage.

Deadheading In order to keep roses blooming it is important to remove the spent blooms, called deadheading. For the first deadheading of the season, you can cut back to 1/4 inch above the first set of 3 leaves. After that you can deadhead back to the first 5 leaf set.

Rose Diseases and Pests

Roses are susceptible to fungal infestations and several insects. Powdery mildew and blackspot are two of the most common fungi. Fungi are usually present in the soil and are best dealt with before you see them on your plants. Use a good systemic such as the Bonide Rose 3 in 1 that is a fungicide, miticide and insecticide. It is sprayed on the leaves on a regular basis. If you find powdery mildew or black spot on your rose leaves, remove the leaves and throw in the trash and begin a spray program. Make sure you water properly as this will help reduce the incidence of fungal infestations.

Roses are also susceptible to aphids and Japanese beetles. The aphids will be killed if you use the Rose 3 in 1. If you want an organice treatment, you can release ladybugs into the rose garden and they will eat the aphids. We had a customer in last week with another insect problem, the rose slug. The rose slug is actually the larvae stage of the sawfly and it can skeletonize a rose leaf very quickly.

Garden Trivia Quiz: Thorns develop from the branch tissue of a plant. The "thorns" of the rose are actually the superficial outgrowth of the stem and are correctly termed "prickles." Now, doesn't that make you feel better?