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Extension > Yard and Garden News > September 2017

Friday, September 29, 2017

Maple tar spot strikes again

M. Grabowski, UMN Extension Educator
Tar spot may look different on different
species of maple. M. Grabowski, UMN

For the second summer in a row, tar spot, a fungal leaf spot disease is showing up in large numbers. Tar spot causes large black raised spots on leaves. Black spots are often shinny and look like wet tar. Although the symptoms of tar spot are most dramatic in the fall, the fungus actually infects the leaves early in spring when wet weather coincides with spore release. The fungus can only infect leaves, and will survive Minnesota’s winter in fallen leaves within leaf spots.


M. Grabowski, UMN Extension
Tar spot is not a serious threat to the health of the tree. The leaf spots may cause leaves to drop a bit early but not early enough to do significant harm. Gardeners interested in reducing problems with tar spot in the following year should rake up leaves and place them in a back yard or municipal compost pile.

Thursday, September 28, 2017

Prepare for boxelder bugs

Jeffrey Hahn, Extension Entomologist

Boxelder bugs are starting to congregate around the outside of buildings. Take action now if you wish to minimize problems with them later, especially if you have had a problem with them in the past. Although boxelder bugs are just a nuisance, they can potentially enter homes in large numbers. People can see them in their homes not only in the fall, but also during the winter and early spring.
Watch out for boxelder bugs trying to get into your home. 
Photo: Jeff Hahn, University of Minnesota Extension

It is not effective to spray the boxelder bugs found in the landscape. Adults have wings and can easily fly onto your property from adjacent areas. It is much more effective to take steps to help prevent boxelder bugs from entering a home to begin with.

There are two basic ways for dealing with boxelder bugs (and other insects, like lady beetles) that try come into your home seeking sheltered areas for the winter: sealing cracks and spaces and timely insecticide sprays. These are steps you can take yourself or hire a professional to do for you.

For more information on boxelder bugs, including control, see Boxelder bugs.

Tuesday, September 26, 2017

Plant hardy bulbs now for early spring pollinators

Honey bee on crocus
By Julie Weisenhorn, Extension Educator - Horticulture

Pollinators need pollen and nectar as early as April in some parts of Minnesota. Hardy spring-blooming bulbs such as scilla, allium, daffodil, fritillaria, and crocus provide this much needed early season nutrition. These bulbs require a cold period in order to flower successfully and therefore must be plant them in fall (September - October) - in other words: right now!

Bee inside a daffodil flower
Bulbs are relatively inexpensive and easy to plant. Bulbs may be purchased locally or ordered from suppliers either through a catalog or online. Most bulbs require warm, sunny locations. Tip: Sun-loving bulbs can be planted underneath deciduous shade trees because they will bloom before the tree leafs out.

Follow planting instructions on the bulb package for depth and site specifications. Make you mark your planting location with a plant label so you remember what you planted next spring. After planting, soak the soil with water. If conditions are dry (little rainfall), soak the soil with water when dry until the soil freezes.  
Bee on Scilla siberica

Read more from Extension about spring flowering hardy bulbs.


Japanese beetles: Aftermath

Jeffrey Hahn, Extension Entomologist

Now that we are safely past the bump in the road called Japanese beetles (JB), it is time to take stock in what happened this year, whether we should be doing anything now, and even what to expect for 2018. Clearly, 2017 was a year of above average numbers of JB. However, this is not the first time we had high numbers of JB in Minnesota and it is unlikely to be the last. So why did we have so many Japanese beetles this year?
Japanese beetles were bad this year.  However, most plants
will survive this damage just fine.  Photo: Jeff Hahn,
University of Minnesota Extension

Although it might appear that JB occur in cycles (like forest tent caterpillars), in fact their numbers are driven by weather. The most important factor influencing their abundance is a lack of soil moisture. JB eggs and newly emerged grubs are very susceptible to dry soils so during years when we experience drought we typically see relatively fewer JB.

This was true about three to five years ago when we had some very dry summers. However starting in about 2014/2015 we started receiving more normal rainfall and JB numbers responded by becoming more numerous.

There has been a lot of concern by residents as to whether JB feeding would kill plants, especially trees.  While JB feeding definitely affects the appearance of plants, as long as (deciduous) trees and shrubs are healthy and mature, they can tolerate severe, even complete, defoliation.  However, if trees and shrubs are severely damaged for several consecutive years, they can sustain more lasting injury.  Maintain normal care for trees and shrubs to keep up their health.  Herbaceous plants are more vulnerable to JB feeding but also are able to tolerate some damage.  Look for most plants to rebound and be fine next spring.

Many residents also wanted to know about treating grubs to reduce the number of JB numbers on a person’s property. While it makes some sense to try to kill the grubs in your lawn so the adults don’t emerge and find your plants, the reality is that treating the grubs has no impact on how many adults you will find on your property next summer. The reason is that adult JB are good fliers and can fly from as far away as several miles.

If you have plants that are attractive to JBs, the adults will find them regardless of whether you treat for grubs or not. Only treat your turf if grubs are found damaging the grass. This is best done in July and August and into early September. By fall, the grubs are getting too large to effectively treat. They are definitely too large to treat the following spring.

So what about next year? We received pretty regular rains in 2017 throughout areas where JB is common. That strongly suggests that if you saw a lot of JB this year, you most likely will see at least similar numbers next summer. Stay tuned!

2017 Flowers for Pollinators: Which annuals attract pollinators?

By Julie Weisenhorn, Extension Educator - Horticulture


Honey bees on Music Box Mix sunflower, one of the annual flowers in this study

Planting for pollinator health is on just about every gardener’s mind these days.

Bumble bee on Envy zinnia
While there is a lot of research on how native plants help pollinators, there’s not much on the interaction of pollinators and annual flowers. Many people want to do their part, but may only have space for annual plantings. There are conflicting references to the value of annual flowers as pollinator-friendly plants. Which annual flowers attract pollinators? We want to find out, so we designed this study to address how home gardeners might help reverse pollinator decline. Pollinators are attracted to such plant features as flower form, color, size, and pattern. We've been counting pollinators that visit selected varieties of annual flowers like Salvia, Zinnia, annual Rudbeckia, sunflowers, marigolds, cosmos, snapdragons, hyssop, etc. Read more: Flowers for Pollinators

Wonder how your own yard and garden measure up when it comes to pollinator-friendly habitat? Take the eight-question survey that asks "How pollinator-friendly is my landscape?" Are you a "Wanna Bee Pollinator Gardener", a "Bee Benefactor" or a "Pollinator Protector"? Find out!

From our Turf Blog: Q&A on Fall Lawn Care


Fall is the best time to perform many of our lawn care tasks. Our cool season lawn grasses are
actively growing again after warm summer months, and people want to do want they can now to ensure we have a healthy start to our lawns next spring. Here's a helpful post from turfgrass extension educator Sam Bauer that addresses some current questions about fall lawn care: U of M Turf Blog

Thursday, September 21, 2017

Ground beetles are only nuisances

Jeffrey Hahn, Extension Entomologist

Some residents have been finding ground beetles in their homes lately. Ground beetles are a common group of beetles that are usually medium sized and dark-colored. As their name suggests, they are typically found on the ground where they hunt other insects. Because of their predaceous activities, they are considered to be very beneficial.
Ground beetles captured in a stick trap.  Ground beetles are
just nuisance and should be tolerated when possible.  Photo:
Jeff Hahn, University of Minnesota Extension

Occasionally in August and September, ground beetles can be found entering homes. Fortunately they are harmless to people and do no damage to property. Some people mistake them for cockroaches which is an insect that can infest homes so it is important to correctly identify any insects that are found. Ground beetles are short-lived and do not reproduce indoors.

Tolerate ground beetles when found in homes as much as possible. The only necessary control is physical removal, especially when only a few are seen. An option for controlling ground beetles is the use of sticky traps. Set out the traps in areas where ground beetles are being found; it is then an easy matter to remove the traps when they have captured ground beetles.

Regardless of what is done, ground beetles are a temporary problem that will go away on their own by the time the weather starts to cool off.

For more information, see Ground beetles in homes.

Monday, September 11, 2017

Late summer butterfly explosion

Photo: Britt Forsberg
Elaine Evans, Extension Educator

If you have been spending time in your flower gardens recently, you may have noticed many brown and orange butterflies visiting plants to drink nectar. Adults of the Painted Lady butterfly, Vanessa cardui, are gathering at flowers in unusually large numbers to prepare themselves for migration down to the southwestern U.S. and northern Mexico. The Painted Lady butterfly is one of the most widely distributed of all butterfly species, but is not frequently seen in Minnesota most years. According to Chip Taylor, director of Monarch Watch at the University of Kansas, this is probably the largest migration he has seen in over 30 years (LJWorld.com September 8, 2017). These larger migrations often follow rainy periods in their wintering grounds. 

You can help these butterflies on their journey south by making sure that you have flowers to provide them with the nectar they need to fuel their long journey and keeping these flowers free of pesticides. According to butterfliesandmoths.org these butterflies prefer nectar from composites 3-6 feet high, especially thistles; also aster, cosmos, blazing star, ironweed, joe-pye weed, red clover, and milkweeds. Many of these plants can also serve as food for the caterpillars if the adults make it this far north again next year. Unlike monarch caterpillars, which require milkweed, the painted lady caterpillars have been found on over 100 different host plants, but favorites include thistles and legumes.
Photo: Britt Forsberg

If you have not already seen them, a visit to a pollinator garden planted with a variety of blooming flowers is likely to reward you with a stunning showcase of insect beauty.

Here are a few links with more information about Painted Ladies.

Friday, September 8, 2017

Late blight takes out tomatoes

M. Grabowski, UMN Extension Educator
Late blight symptoms on tomato leaves.
M. Grabowski, UMN Extension 


After carefully cultivating tomato plants throughout the summer, many Minnesota gardeners have been shocked to see their plants devastated by blight and fruit rot in a matter of days. The culprit is late blight, a disease of potato and tomato plants. Late blight does not cause significant damage every year in Minnesota but prolonged cool wet weather this year has created ideal conditions for disease.

Late blight is cause by the pathogen Phytophthora infestans, a fungus like organism that thrives in wet conditions. The scientific name of the pathogen translates to ‘plant destroyer’ and the pathogen lives up to its name.  Late blight is the plant disease that ruined the potato crop in the infamous Irish potato famine of the 1840’s and the disease has been responsible for numerous epidemics since then.

How to identify late blight

  • Leaves have large, dark brown blotches with a green gray edge.
  • Stem infections are firm and dark brown.
  • Disease progresses very rapidly in cool wet weather and the entire plant may turn brown and collapse in just a few days.
  • Fruit have firm dark brown blotches. If the tomato is cut open, dry brown rot can be seen extending into the fruit. Fruit only become soft and mushy when bacteria invade after the initial infection.
  • In high humidity, thin powdery white fungal growth appears on infected leaves, fruit, and stems.

Late blight on tomato fruit. Mold appears in high humidity.
M. Grabowski, UMN Extension 

Management options for home gardeners

Once late blight has been found in a garden, there is little that can be done to help the plant. The disease simply moves too quickly. Harvest any tomatoes that are not showing symptoms and keep them in a well ventilated area to ripen. It is likely that a few are infected but not showing symptoms at the time of harvest, so check on tomatoes regularly and discard any infected fruit. Potatoes from infected plants should be dug up as soon as possible. Uninfected tubers can be eaten but should be checked regularly for rot during storage. Discard infected tomato fruit and potato tubers along with infected plants.

Infected plants should be removed or destroyed as soon as possible to prevent the thousands of airborne spores forming on the leaves from spreading to neighboring plants.
  • Infected plants can be placed in a plastic bag or under a plastic tarp and left to cook in the sun for several days. Once all of the plant material is killed, the plant can be composted or buried.
  • Plants can also be shallowly buried in soil, as the freezing winter temperatures will kill both the plant and pathogen.
  • Infected plants can be placed in a compost pile that completely heats up and breaks down all plant material. Do not use a compost piles that does not thoroughly heat up or completely break down plant material. These mildly warm piles can sheltered infected plant material from the freezing cold and allow the late blight pathogen to survive from one season to the next. If you are unsure how hot your compost pile gets, heat infected plant material in a plastic bag before placing it on a compost pile.   

Can fungicides help?

Fungicides are not effective once a plant has become infected with late blight. For many gardeners, it is too late to apply fungicides. Fungicides only work to protect healthy plants and prevent new infections. Gardeners that have not yet seen late blight may choose to protect their tomato or potato crops with a fungicide that has copper as the active ingredient. The product MUST list tomato and/or potato on the label and the gardener MUST follow all label instructions to use the pesticide safely. There are a number of copper fungicides registered for use in home gardens. Some are certified for organic use.

Will late blight come back next year?

The late blight pathogen can only survive Minnesota’s winter if sheltered from extreme cold in infected plant material. This typically only occurs in large piles of unmarketable potatoes that are sometimes left on field edges or in infected potatoes that are buried deep enough to survive the winter. Most years the late blight pathogen must be brought into the state on infected potato seed, infected tomato transplants, or as windblown spores from other areas. Once the pathogen arrives, the right weather conditions (cool and wet) must be present for the disease to become established and spread.

There are a few tomato and potato varieties with resistance to late blight. Look for resistant varieties in your seed catalog for next year. 
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