In this issue of the Yard and Garden News:
- Leaf Spots are Sprouting in the Vegetable Garden
- Rose Classes and Their Performance in Minnesota
- Tasty Tomato Container Gardens
In this issue of the Yard and Garden News:
Jeffrey Hahn, UMN Extension Entomologist
Springtails are wingless and do not fly but they can jump. Unlike grasshoppers, crickets, and other insects that use large back legs for jumping, a springtail uses a forked appendage called a furcula (located underneath the abdomen) to propel itself. When not in use, a furcula is tucked up under the body, set like a mouse trap. When it is released, it extends down rapidly sending the springtail forward. A springtail can jump many times its body length.
Despite their small size, springtails can occur in tremendously large numbers and are one of the most abundant insects. One source estimates you would find millions of springtails in one hectare (about 2.5 acres) of land. They are associated with damp conditions and are found in soil, leaf litter, lichen, under bark, decaying plant matter, and other areas of high moisture. They feed on fungi, pollen, algae, or decaying organic matter.
They are occur indoors for several reasons. They can be found in the soil of overwatered houseplants and sometimes adjacent areas. They also occur in damp areas with high moisture, e.g. around plumbing leaks and damp basements. They can also move in large numbers indoors from the outside when moist conditions exit around the home. Springtails can vary in abundance indoors from just a handful to very large numbers. Fortunately, however many you find, they are harmless to people and property and are just nuisances.
If you are finding just a small number of springtails occasionally, just ignore them or physically remove them by hand or with vacuum. However, if you are seeing persistent number of springtails they are associated with a moisture problem. The best management is to dry out these areas with a fan or dehumidifier as springtails do not tolerate dry conditions. Also make any structural changes to correct the moisture problem.
If springtails are migrating in from the outside, check around the house for moisture problems. This could include rainspouts that do not carry the water far enough away from the foundation, landscapes that slope towards buildings, or excessive irrigation. It could even be a moisture problem with the roof. Correcting existing moisture conditions will help decrease springtails. As we receive less rainfall, the number of springtails will also naturally lessen.
Although it may be tempting to spray a springtail problem with an insecticide, the products available are not very effective against them. Moisture control is the most effective strategy.
Michelle Grabowski, UMN Extension Educator
Leaf spot fungi and bacteria come into the garden on infected seed or transplants or are blown in on the wind. Many of these pathogens can survive from one season to the next on infected plant debris. Splashing rain carries fungal spores and bacteria from the soil and plant debris onto this year's leaves. Moisture in the plant canopy then allows these pathogens to start new infections. Established leaf spots create a whole new generation of bacteria and fungal spores, starting the cycle all over again.
Luckily several basic cultural control practices can help to keep leaf spot pathogens in check.
1. Reduce moisture on leaves and fruit by watering the base of the plant with drip irrigation, a soaker hose, or simply by directly the hose at the soil and not the leaves.
2. Stake plants like tomatoes, runner beans, and cucumbers.
3. Mulch the soil with straw, wood chips or a plastic mulch to prevent the pathogen from being splashed up onto the lower leaves.
4. Inspect plants regularly. If a few leaf spots show up, pinch off the infected leaves and remove them from the garden. Never remove more than a third of the plants foliage!
5. At the end of the growing season, remove infected plants or till under the plant debris to speed up breakdown of infected plant parts.
6. Rotate crops. Wait 3-4 years to plant the same plant in the same location. It is best to rotate between plant families. Follow tomatoes with broccoli, corn or beans since they are not closely related. Peppers and eggplant should not follow tomatoes since they share many of the same diseases.
The leaf spot diseases below have been recently found in Minnesota.
Black Spot and Gray Spot - These two fungal diseases of brassicas are caused by Alternaria brassicae and Alternaria brassicicola. Disease can occur on cabbage, cauliflower, Chinese cabbage, broccoli, Brussels sprouts, kohlrabi, kale, turnip, and rutabaga. Leaf spots start out as small dark pinpoint spots, but quickly grow into a large gray to brown circle. Dark rings within the spot make them look like a target. Leaf tissue around the spots turns yellow, and dark brown spots may be seen on the heads of cauliflower andbroccoli.
The black spot and gray spot fungi can be blown into the garden on wind or brought in on infected seed. The disease thrives when high humidity occurs. To reduce problems with these fungal leaf spot diseases, remove diseased leaves from the garden and till in infected plants at the end of the season. Be sure to remove weeds from the brassica family because they can harbor these fungi even when vegetable plants are not around.
Early Blight - This common fungal disease of tomatoes is caused by Alternaria solani. The fungus can also infect potatoes and occasionally eggplant and peppers, but the most severe damage in gardens often occurs on the tomato plants. Fruit, stems and leaves can all be infected by the early blight fungus. Infection on all three plant parts results in large brown spots, with concentric dark rings, that look like a bulls eye.
Bacterial Brown Spot - This bacterial disease of beans is caused by Pseudomonas syringae pv syringae and can affect both the leaves and pods of the bean plant. Leaves have round brown papery spots. Leaf spots occasionally fall out, resulting in a shot hole appearance of the leaves. Infected bean pods also have brown spots and may be bent or twisted around the infected area. To reduce problems with bacterial spots on beans, space plants to allow good air movement between plants. Stake runner beans. Avoid working in plants when leaves are wet. Instead, wait until a cool dry day to pinch off infected leavesand pods. Remove this diseased material from the garden.
Septoria Leaf Spot - This fungal leaf spot disease of lettuce is caused by Septoria lactucae. Spores from this fungus often come into the garden on seed, but can also survive in plant residue and on some weeds. Gardeners that have problems with Septoria leaf spot of lettuce might consider looking for lettuce seed that is produced in a desert area, like the south western states, as these seeds are less likely to be contaminated by this moisture loving fungus. When growing successive crops of lettuce, be sure to seed the next crop in a location away from any currently diseased plants. Do not plant lettuce in the same area of the garden for one year to allow infected plant debris to break down.
Kathy Zuzek, UMN Extension Educator
The number of rose cultivars in the world defies logic. If you open a copy of Modern Roses 12, the most recent edition of the American Rose Society's rose cultivar list, you will find thousands of rose cultivars or varieties listed along with each rose's class, year of release, the breeder who developed the cultivar, parentage, and descriptions of each cultivar's floral and foliage traits, plant habit and thorns.
There are 18-20 roses native to the United States. Four of these (R. acicularis, R. arkansana, R. blanda, and R.woodsii) are native to Minnesota. All 4 of these species are single-flowered, pink, and bloom in spring (Photos 1 & 2).
Given the thousands of rose cultivars in the world, you might think that many of the rose species were used in developing all of these cultivars. With few exceptions, only 8 species are ancestors to our rose cultivars and all 8 are from Asia.
As rose cultivars are developed, they are placed into classes. There are 36 classes of roses. Classes that Minnesota gardeners might be familiar with are the Hybrid Teas, the Shrub Roses, or the Hybrid Rugosas. Every rose cultivar is placed in a class with other roses who share common ancestors and/or similar floral, foliage, or plant habit traits.
Which classes and which cultivars can be grown in Minnesota? That depends on a gardener's taste in rose appearance, the choice of how much time he or she wants to devote to maintaining their roses to insure good performance and long term survivability, and a willingness or reluctance to spray pesticides. Some of the biggest factors that impact these decisions are choosing between repeat-blooming and spring-blooming cultivars, cold hardiness and pest tolerance of individual rose cultivars, and the pH of your soil.
What is important in Minnesota is a plant's ability to re-grow vigorously during the following growing season after experiencing some winter injury. Because repeat-blooming roses produce flowers on the current year's wood, a repeat-blooming plant that grows vigorously in spring and summer after some winter injury can perform beautifully in spite of our harsh winters. There are also entire classes of roses that are not hardy in Minnesota. Unless a gardener is 1) willing to consider a rose as an annual plant or 2) tip and bury roses or provide some other measure of winter protection, these roses should not be grown in Minnesota.
Blackspot is a fungus that results in defoliation of rose plants across all classes (Photo 5). Roses without leaves cannot photosynthesize to produce and store the energy reserves that a plant lives on. Many roses that defoliate from blackspot in early or mid-summer also try to produce a new second set of leaves in late summer. This depletes the energy resources of the plant even more. Plants that are susceptible to blackspot are severely weakened by repeated rounds of defoliation and have little ability to survive our harsh winters. Plant size and vigor is diminished with each year of blackspot incidence until finally the rose is too weak to survive over winter. Along with blackspot's impact on winter survivability, few gardeners are willing to tolerate a defoliated rose in their garden. This leaves two options: planting blackspot-tolerant roses or repeated fungicidal sprays during the growing season. Some classes of roses have a higher percentage of blackspot-tolerant cultivars than other classes.
Roses prefer a soil pH of 6.0 to 7.0. As pH increases above these levels, iron chlorosis becomes a problem and can lead to plant stress, low vigor or mortality. Cultivars within the Hybrid Rugosa class are particularly susceptible to iron chlorosis on high pH soils (Photo 8).
Karl Foord, UMN Extension Educator
There is little doubt that one of the best taste treats in a Minnesota Summer is a vine ripe tomato. In this case I am referring to a vine that you grew and a tomato that you picked when you decided it was ripe. In addition the distance it had to travel to your kitchen is measured in feet not thousands of miles. As an aside where did tomatoes come from in the first place?
There are advantages and disadvantages to growing tomatoes in containers. The advantages may include avoidance of; damage by critters, problems associated with soil born diseases, and most leaf diseases because the leaf surfaces dry quickly when containers can be placed in an airy location such as an elevated deck. The ambiance created by container tomatoes on a deck or patio is very appealing.
A demonstration of variety type matched to pot size is on display at the Minnesota Landscape Arboretum as part of the Powerhouse Plants exhibit.
This demonstration shows 5 different cultivars of various growth types and maturity dates in several different pot sizes (Table 1 and photo of varieties).
Correction from July 1 edition of Y&G News. Past editor and Rose expert David Zlesak noted an error in last editions rose pictures. The Frau D.H. rose that is labeled at the Arboretum in the main garden is incorrect. There was one there, but a sucker from a neighboring rose snuck in and people pruned the true Frau out accidentally. See attached picture for correct flower.
Time to renovate strawberries!
We are still in the picking season for summer raspberries.
Wondering what those spots are on your rose? Black spot is common this time of year but so are several other leaf spot diseases. Check out "What's Wrong with my Plant?"
Yard and Garden News Editor: Karl Foord
Technical Editor: Bridget Barton
Jeffrey Hahn, UMN Extension EntomologistActually they are already here as their presence was reported on June 21 (in the Twin Cities area). Japanese beetles are typically first active in the Twin Cities the first week of July but the early spring allowed them to emerge sooner than normal. These beetles are broadly oval and about 3/8th inch long with a bright emerald green head and prothorax (the area directly behind the head) and shiny bronze colored wing covers. An important distinguishing feature are the five small white tufts of hair along each side of the abdomen and two larger white tufts on the tip of the abdomen.
If you are interested in using a low impact insecticide, try a product containing neem. This insecticide deters Japanese beetle from feeding but it's much less effective on large numbers of Japanese beetles. Spinosad, usually effective against other foliage feeding insects, does not have much effect against Japanese beetles. There are a variety of residual garden insecticides that you can spray on the leaves of plants, including carabaryl and pyrethroids such as bifenthrin, cyfluthrin, lambda-cyhalothrin, or permethrin. Repeat applications may be necessary, especially if large numbers are present.
There are a couple of systemic insecticides available to home gardeners, imidacloprid and Safari (dinotefuran). If you are treating trees and shrubs, there will be some lag time (days or weeks) while the product moves up the plant. However, these insecticides are generally long lasting and should only require one treatment during the summer. There has been concern recently about imidacloprid adversely affecting pollinating bees so it would be best to avoid treating plants that are attractive to bees.
Some people want to manage adult Japanese beetles by treating their lawn for Japanese beetle grubs. This would work if the Japanese beetles in your yard and garden only came from your property. However, Japanese beetles are quite mobile, and there will still be a lot of them that will come from outside your yard to find your garden. Only treat your lawn if you are finding damage due to Japanese grubs but don't rely on treating your grass to reduce Japanese beetle adults.
Karl Foord and Kathy Zuzek, UMN Extension Educators
I photographed the rose collection at the Arboretum last week and tried to make sense of the many rose classifications and the varieties within each classification. Twenty three classes are evaluated in the publication Roses for the North(1). The British Association of Rose Breeders (BARB) has identified 30 rose classes, and the American Rose Society has identified 56. Regardless of which system you choose, the situation is complicated. Being faced with this situation, I consulted our rose expert Kathy Zuzek, who is the lead author of the Roses for the North publication. We decided to address the issue with two articles. The first would suggest the best rose cultivars for Minnesota based on Kathy's twenty plus years of experience. The second would be an historical article describing why there are so many categories, what each looks like, and how that category performs in Minnesota. The second article will appear in the July 15 edition of the Yard & Garden News.
The choice of best rose cultivars for Minnesota is based on three criteria, cold hardiness, tolerance to black spot disease, and repeat blooming. Simply put, the rose has to tolerate Minnesota winters through a minimum of cane die back and good regrowth vigor in the spring. The plant must tolerate black spot and not defoliate in July from pressure due to this fungal disease. The plant should produce a good flower show throughout the season.
Fourteen varieties met the criteria mentioned above. Twelve of the varieties are pictured below; varieties Cuthbert Grant and Topaz Jewel were selected but are not pictured below. Consult Roses of the North for more complete descriptions of the selected varieties.
Photo credits: Karl Foord
1. K. Zuzek, M. Richards, S. McNamara, and H. Pellett. Roses for the North - Performance of Shrub and Old Garden Roses at the Minnesota Landscape Arboretum. Minnesota Agricultural Experiment Station University of Minnesota, Minnesota Report 237-1995. 1995.
Michelle Grabowski, UMN Extension Educator
Often these two simple steps combined with warm dry summer weather, reduce bacterial blight of lilac to the point where only a few small leaf spots remain.
Michelle Grabowski, UMN Extension Educator
Sapwood fungi infect a wide variety of common shade trees. Maple (Acer), linden (Tilia), willow (Salix), elm (Ulmus), oak (Quercus), ash (Fraxinus), poplar (populus), and many more may all suffer from this disease.
How to Recognize Sapwood Rotting Fungi
Gardeners often first notice dead branches throughout the canopy of infected trees. Cracked and peeling bark may be seen on the main trunk or branches. Upon close examination, clusters of small white shelf fungi can be found growing on the infected wood. These are reproductive structures of the sapwood rotting fungi and can be easily seen this time of year in Minnesota. A gardener can determine which of the two fungi is causing the problem by closely examining these fungal spore producing structures.
Schizophyllum commune also produces small shelf fungi on infected wood. These shelf fungi are smaller (1/4th to 2 inches across), cupped downward, and pure white. When examined up close, the upper surface appears fuzzy. Gills can be seen on the lower surface of these shelf fungi.
Keep Trees Healthy and Strong to Avoid Sapwood Rotting Fungi
Prevention is the best management strategy to control sapwood rotting fungi. Avoid wounding trees with weed whips, lawn mowers or other lawn equipment. If trees are damaged in a storm or by ice, remove broken and cracked branches with a clean pruning cut. This cut will be easier for the tree to heal than a long jagged rip caused by a storm. Water trees during times of drought. Mulching the base of the tree out to the canopy drip line with an organic mulch like wood chips can help maintain soil moisture and reduce competition with turf grass.
If infection appears on a branch, prune the infected branch on a cool dry day and remove it from the area. If the infection appears in the main trunk, the only thing that can be done is to reduce stress on the tree and hope for the best.
Bob Mugaas, UMN Extension Educator
With the recent rains and storms across the state, most lawns have had sufficient moisture to remain actively growing and green through the month of June. In fact, in some instances there has been too much rain causing lawns to remain in excessively wet conditions for several days or more at a time.
Moist conditions in the lawn have also given rise to the random appearance of many different kinds of mushrooms. These are the result of fungi feeding on the dead and decaying organic matter in the soil and thatch layers of the lawn. As these fungi continue to grow and carry out their decomposer role in the soil and thatch, they will periodically, especially under moist conditions, send up fruiting structures that we know and see as mushrooms. See Pictures 2 & 3.
With the excessive amount of rainfall and the continued vigorous growth of our grasses all during June, it is very possible that our lawns will benefit from a light application of nitrogen fertilizer. Nitrogen can be lost in a number of ways from the lawn including leaching (i.e., carried with water draining through the soil), gaseous loss back to the atmosphere and taken up and used by grass plants for growth. Hence, under the moist conditions and rapid grass growth that we have been experiencing lately, many of our lawns will benefit from ¼ to ½ pound of actual nitrogen, per thousand square feet. It's important to not fertilize excessively going into and during the potentially hot summer months of July and August. That can unnecessarily stress the grass plants and perhaps result in injury during those hot, dry summer periods we expect to encounter in Minnesota during July and August.
The loss of large amounts of leaf tissue all at one time forces the use of stored plant reserves just to survive. As a general rule, when our grass growth gets a little too far ahead of us, initially mow as high as your mower will safely allow. Then, begin lowering the height of cut by mowing more frequently and gradually reduce the mowing height back to the desired level. This is much healthier and less stressful for our lawn grasses.
Jeffrey Hahn, UMN Extension Entomologist
Despite their name, the larvae actually feed on the roots of a variety of plants including strawberry, arborvitae and other evergreens, raspberries, and grapes. The adults notch feed along the edges of leaves. However, despite this feeding, strawberry root weevils are not considered a plant pest in Minnesota.
It is common for strawberry root weevils to enter homes looking for moisture. They are commonly found around sinks, basins, and tubs. Fortunately, strawberry root weevils are harmless to people and property. Once, they are indoors, the only necessary control is physical removal.
Jeffrey Hahn, Extension Entomologist
People have been commonly reporting European earwigs recently. An earwig is about 5/8 - 3/4 inch long, with a flat, reddish brown body and very short wings. They are beetle-like and are sometimes confused with cockroaches. However, it's easy to identify an earwig as they have forcep-like pincers on the tip of its abdomen: males have stout, curved pinchers while females possess more slender, straight pincers. Despite these pinchers, earwigs are harmless to people and our property.
People are most concerned about earwigs when they come into their homes. To keep them out, caulk and repair any obvious spaces, cracks, or gaps around the outside of your home, especially at ground level. Also clean up debris around the house that earwigs can hide under, such as leaves and plant debris. It may also be useful to thin out or remove mulch to reduce earwig numbers. You can supplement this with a residual insecticide treatment, e.g. permethrin or cyfluthrin, around the perimeter of the building. However, if earwigs are determined, some will still get inside your home. For those interlopers, just remove them with a vacuum or a broom and dust pan.
- Time to set out apple maggot traps in apple trees.
- Strawberry picking is just beginning in the north, and starting to wind down in the south.
- Raspberry picking is underway.
Spotted at the Arboretum: Canada Geese and Wild Turkey
Yard and Garden News Editor: Karl Foord, UMN Extension Educator
Technical Editor: Bridget Barton