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Extension > Yard and Garden News > May 2018

Friday, May 25, 2018

Seven steps to prevent late blight of tomatoes in 2018

M. Grabowski, UMN Extension Educator

In 2017 a disease of tomatoes and potatoes, called late blight, appeared in Minnesota farms and gardens near the end of summer. This devastating disease rots leaves, stems, fruit and tubers of potatoes and tomatoes. Many gardeners lost most of their home grown tomatoes just as they were ripening last year and want to know what can be done to prevent late blight from striking again.

Tomatoes infected with late blight. M. Grabowski, UMN Extension

Late blight killed my tomato plants last year. Can I grow tomatoes in my garden this year?

Yes. The good news is that the late blight pathogen does not survive Minnesota’s winters very well. It can only survive on potato culls or tomato fruit that are sheltered in soil or a warm compost pile. Other common leaf spot diseases of tomato, like early blight and Septoria leaf spot, do survive in plant debris in the soil, however so it is a good idea to move tomatoes a minimum of 8 to 10 feet away from where they were grown last year.

Will late blight be a problem this year? 

It’s possible that late blight could be a problem in Minnesota in 2018 but not guaranteed. Since the late blight pathogen does not survive Minnesota winters very well it needs to be brought into the state for disease to occur. It can come in on infected tomato transplants, infected potato seed, or through wind-blown spores from warmer states. Once it arrives, disease will only be a problem if the weather is wet and rainy. Late blight is caused by a water mold and needs high levels of moisture to thrive.

What can I do to prevent late blight this year?


  1. Pull any tomato plants or potato plants that came up where you did not intentionally plant them. These volunteer plants arise from potato tubers or tomato fruit that were left in the garden or in the compost pile last year. Although the late blight pathogen does not survive Minnesota’s winters on its own, it can be protected by a warm compost pile or in tubers or fruit buried in the soil. If these left over tomatoes and potatoes sprout in your garden, they may be carrying the late blight pathogen. Pull them as soon as you see them and bury them in a compost pile that heats up to 148 F. 
  2. Inspect tomato transplants prior to purchase. Leaves and stems should be green and firm. Avoid any plants with dark rotten areas. 
  3. Look for late blight resistant tomato varieties. Check seed catalogs and plant labels to find disease resistant varieties. 
  4. Plant only seed potatoes from a reliable seed supplier. Do not use potatoes from the grocery store for seed. Seed potatoes from a seed supplier are grown using practices to prevent plant disease and tubers are inspected at harvest. Some potato seed is certified disease free. Do not use tubers saved from potato plants that were infected by late blight last year as seed.
  5. Provide ample space between tomatoes and stake the plants to promote good air circulation around the plant. This will help them dry off after rain or irrigation. Late blight and other fungal diseases need moisture on the plant surface to start new infections. 
  6. Check plants regularly for disease and identify any problems you find with the help of UMN Extension’s online diagnostic tool
  7. If late blight does show up, infected plants should be buried to prevent movement of airborne spores. Some gardeners prefer to place the infected plant in a closed plastic bag and allow it to 'cook' in the sun for several days before burying the plant in the compost or garden soil to make sure the pathogen is dead.


Wednesday, May 23, 2018

Black flies and midges are out now

Jeffrey Hahn, Extension Entomologist

There are two types of flies that are being commonly seen this spring: black flies, also called gnats, and chironomid (ki-ron-OM-id) midges. Black flies can inflict painful bites to people, while midges are just nuisances.

Black flies are small but many people think they inflict a more painful bite
than mosquitoes.  Photo credit: Jeff Hahn, Univ of MN Ext.
Black flies are stout, humpbacked, dark-colored flies. The larvae live in rivers and streams. The adults are good fliers and can be found miles from where they emerged. They commonly bite people on exposed skin during early morning and early evening as well as on cloudy days. Fortunately, black flies are not known to transmit diseases to people in Minnesota. Even if they don’t bite, they can still be annoying by flying around a person’s face.

It is challenging to avoid black fly bites. When possible, avoid the times when black flies are most common. When you are out, wear protective clothes to cover bare skin including long-sleeved shirts, long pants, socks and shoes, and hats. Wear something on your head as black flies love to bite around the hairline of heads. Although black flies can be active throughout the season, they are most common during spring.

Unfortunately, repellents, like DEET, are not consistently effective against black flies; but their use is still probably better than nothing. For more information, see Black flies.


Chironomid midges don't bite but often occur in large numbers
which can be annoying.  Photo credit: Jeff Hahn, U of M Ext.

Chironomid midges have also been common around Minnesota. They are mosquito-like in appearance; males have feathery antennae. Despite that, they do not bite. The larvae live in water but the adults are not strong fliers so it is common to see them on foliage near where they emerge.

These midges commonly fly in large clouds in order to mate. Anyone around such a cloud can get midges in their faces and their food and drink. Annoying but not the end of the world. Even though these midges do not have chewing mouthparts, they have been suspected of damaging turf and garden plants; fortunately they are incapable of injuring plants.

Midges are short-lived, usually not lasting more than a week or so. While there are different species that can occur at different times of the year, most hatchings are not noticed by people. There is no control for midges, ignore them (as best you can), and they will go away on their own. See also BugGuide for information on chironomid midges.

Tuesday, May 15, 2018

What to do with ornamental grasses in spring

Mary Hockenberry Meyer, Extension Horticulturist
Gail Hudson, Extension Communication Specialist


Volunteers and Minnesota Landscape Arboretum Gardener Erik Lemke used a gas powered trimmer, rakes, and tarp to move switchgrass tops to the compost pile on May 9, 2018. The other grasses were burned May 2nd before new growth started.
Photo: Mary Hockenberry Meyer
Perennial ornamental grasses, once established, can be one of the easiest plants to grow in your garden. And spring time may be the only time when you'll need to give them a bit of attention.  
Take a good look at your plant. Is the center of it dead? Large mature grasses with a dead center can particularly benefit if they're divided in the spring. 

Friday, May 11, 2018

Do not treat Japanese beetle grubs in spring

Jeffrey Hahn, Extension Entomologist

It is too late to treat white grubs now.  Photo: Jeff Hahn, U of M Ext.
People who experienced Japanese beetles last summer are looking to take action against them this year before they become a problem. However, if you are thinking of treating for grubs this spring it is too late (or too early depending on your point of view).

The bottom line is that grubs are too large to treat now. The best time to treat Japanese beetle white grubs is July through mid-September when they are small or moderate-sized. As they get larger, it is more difficult to kill them and by fall it is no longer practical to manage them. When spring arrives, these grubs are still too large to try to control.

3 Tips to reduce the need to weed

Annie Klodd, Extension Educator-Fruit and Vegetable Production

For most gardeners, weeding is one of the most arduous tasks in the vegetable garden. Save time, save your back, and save your energy: these 3 tips will reduce the need to weed.

1: Mulch in May once the soil has warmed

Thick straw mulch creates a physical barrier to suppress weeds.
Photo: Annie Klodd
Mulch creates a powerful physical barrier to weeds. Common mulch choices for vegetable gardens include straw, grass clippings, and chipped leaves. Apply these mulches liberally to create a 2 to 4-inch mat, which suppresses weeds from germinating and growing. Plant-based mulches have the added benefit of adding valuable organic matter back into the soil.

Landscape fabric also works well to suppress weeds. It is most appropriate for transplanted vegetables, since holes can be cut into it to plant seedlings.

Thursday, May 10, 2018

Giant water bugs just a curiosity

Jeffrey Hahn, Extension Entomologist

This giant water bug was found on the side of a building near a street light.
Photo:  Jeff Hahn, University of Minnesota Extension
Some people are finding a large, up to 2 1/3 inches long, insect outdoors around their homes or their work. Sometimes people think this insect is a beetle, a cockroach, or even an invasive species. In fact, it is the giant water bug, Lethocerus americanus.

This giant water bug is a common native species. It is olive brown with large front legs for grasping and holding prey and large, flattened back legs for swimming.

Tuesday, May 8, 2018

Future engineering gurus plant flowers for pollinators

4H club wanted an experiment and Master Gardener leader came through

Julie Weisenhorn, Extension Horticulturist


4H Engineering Club of Lyon and Lincoln counties
plant annual seeds for the Flowers for Pollinators study

The Lynd Community Center was a bee hive of activity on Saturday, May 5th as 11 members of the 4H Engineering Club of Lincoln and Lyon Counties joined the effort to help pollinators by starting seeds for their own Flowers for Pollinators studies. Five other 4H groups from Redwood county and another in Lincoln county will also participate.

Flowers for Pollinators (F4P), now in its 4th year at various MN sites, asks the question "Are annuals attractive to pollinators?" The 4H club of elementary and middle school youth is led by Extension Master Gardener Stephanie DeJaeghere. The club wanted to conduct some kind of experiment and DeJaeghere had heard about the F4P as an Extension volunteer. 

The club members - and their dedicated parents - started six of the 30 F4P varieties for planting and evaluation in their own gardens:
  1. Dwarf sunflower 'Suntastic bicolor pink' - blooms early, pollen-less yet attracts bees, large pink
    Seed packets and plant labels for the 6 varieties
    to dusky yellow flowers with black centers
  2. Melampodium 'Showstar' - prolific bloomer all season, small gold daisy-like flowers
  3. Zinnia 'Zahara Starlight Rose' - small bushy zinnia, white flowers with rosy center
  4. Zinnia 'Old Mexico' - prolific bloomer; red and gold medium sized flowers
  5. Cosmos 'Double Take' - Blooms more in mid to late summer; pinks and whites
  6. Marigold 'Bambino' - deep gold, medium flowers, low and bushy

They'll be evaluating the plants for insect activity and recording insects visits on the flowers. A F4P blog and an Instagram account (flowers4pollinators) are available for the club members to report their experiences and observations.

UMN Extension 4H Program Coordinator for Lyon county, Sam Jens, was so interested in the study that he and DeJaeghere decided to plant two study sites at the Lyon County fairgrounds.

Follow the progress of the Lyon county 4H Engineering club on the F4P blog!

Saturday, May 5, 2018

Start the season right with healthy plants

Learn what to look for while you shop!

M.Grabowski, UMN Extension 

Coleus for sale at a local garden center
Photo: M. Grabowski, UMN Extension
The first step to prevent disease problems in the garden is to start out with healthy disease free plants.

Many plant pathogens are able to hitch a ride from one garden to the next by infecting plants before they are sold or shared. This can result in disease problems for years to come as the new pathogen becomes established along with the new plant.

Tuesday, May 1, 2018

Reduce the risk of tar spot and apple scab now

M. Grabowski, UMN Extension
Apple scab at mid summer
M. Grabowski, UMN Extension 

Two common leaf spot diseases that blight Minnesota landscapes every year are tar spot of maple and scab of apple and crabapple. Both diseases are caused by fungi that survive winter on last year’s infected leaves.

As snow melts and tree buds begin to swell, gardeners have one last chance to remove these infected leaves before the fungal pathogens become active.

Build a home for bees

Make your garden a haven for bees

Aaron Irber, Research Scientist UMN Dept of Entomology and Elaine Evans, UMN Extension Educator

Photo: Heather Holm
We can help bees by planting flowers, but nesting habitat is important too. Roughly 60-70 percent of bees nest in the ground. You can help them by leaving patches of ground undisturbed and leaving some bare spots. The other 30 percent are cavity-nesting, using hollow plant stems or holes in wood.

You can make nesting habitat to provide homes for these cavity-nesting bees. There are many pre-made options for bee houses, but often these are more cute than effective.  

Watch the video at the end of this article to see a bee making its home in a cut-off plant stem!

Lawn care: 'Tis the season...Finally!

Learn how to use a growing degree day tracker to time herbicide applications

Remember this?!
Photo: Gail Hudson, UMN Extension
As you read this, it has likely been only a week or two that you’ve been able to see your lawn this spring.  What an interesting spring it’s been!

The University of Minnesota Climatology Team provided a summary of our weather conditions throughout the month of April, which, in many cases was a record setting month.  Needless to say, lawn care practices have been pushed back much later this year.  As we get into the swing of things with the growing season, here are several considerations for lawn care practices this spring.

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