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Extension > Yard and Garden News > Archives > March 2013 Archives

March 2013 Archives

March 1, 2013 Issue


University of Minnesota Extension is still seeking feedback from members of the public through the month of March to help direct future lawn care and turfgrass education programs.

Take a brief (10-15 minute) survey and be entered into a drawing for two chances to win an iPad Mini. Congratulations to Karen Wennberg ('82 Horticulture) - the iPad Mini winner from the first drawing!

The remaining two drawings will be held on February 28th, and March 31st 2013. Find the survey here.

Lawn Care Survey

For questions regarding this contest or the survey, please contact:
Sam Bauer, Extension Educator - Turfgrass Science
University of Minnesota Extension
Phone: 763-767-3518

Editor's note:

We always appreciate the time you take to inform us of your needs and wishes. Your input guides our programming. Thanks for taking the time communicate with us!

M. Grabowski, University of Minnesota Extension

H. Schwartz, CSU, Bugwood.org

Photo 1: Coffee Rust

Although coffee does not grow here in Minnesota, it is a regular part of daily life for many Minnesotans. Some might even suggest that they could not survive without their morning coffee. In the major coffee producing regions of Central and South America an epidemic of the fungal disease coffee rust (or la Roya in Spanish) is taking a devastating toll on the coffee crop this year.


Coffee rust is caused by the fungus Hemileia vastatrix which causes powdery yellow to orange spots on leaves. These leaf spots eventually turn brown and infected leaves drop from the coffee plant prematurely. Severe defoliation by coffee rust weakens the coffee plant, reduces yield and can eventually kill the coffee plant.

The powdery yellow spores that form on infected leaves spread easily on wind and splashing water. It is estimated that a single rust pustule on a coffee leaf contains 150,000 spores and a single leaf contains hundreds of pustules. Spores need moisture on the leaf surface to start a new infection and in warm rainy weather disease can spread at an incredible rate.

In 1875, the coffee rust fungus was found in Ceylon (now Sri Lanka) which contained nearly 400,000 acres planted in coffee. At the time little was known about coffee rust and the disease essentially wiped out coffee production in Ceylon, Indonesia and the Philippines. Coffee production was moved to the Americas and quarantines successfully kept the pathogen at bay for 100 years. In 1970 however the coffee rust fungus was found in Brazil and was identified in 1975 in Nicaragua. Since then La Roya (coffee rust) has spread throughout Central and South America.

Coffee rust was not as severe in the Americas as many had first predicted. In part coffee was grown at cooler higher altitudes that did not favor growth of the rust fungus. In addition American coffee growers had many more management options available to them than the plantation owners of Ceylon 100 years earlier.

J.VIola, Northeastern University

Photo 2: Coffee plant with green coffee berries

Arabica coffee (Coffea arabica) is in general highly susceptible to coffee rust where as robusta coffee (C. canephora) has some resistance to the disease. When the coffee rust fungus first arrived in the Americas, almost all coffee farms were planted with one of two varieties of arabica coffee. Both were susceptible to disease. Over time researchers have developed disease resistant cultivars.


Unfortunately, there are many different races of the coffee rust fungus. Races are strains of the pathogen that are unaffected by the resistance genes within a specific cultivar, so a cultivar resistant to one race of the rust fungus may not be resistant to another race. Breeders struggle to combine genes for disease resistance in a plant that produces high quality coffee in a way that new races of the rust fungus will not be able to overcome the plants resistance.

Fungicides are also used to manage coffee rust on coffee farms. Fungicides protect leaves from infection. Unfortunately fungicides can be quite expensive and need to be repeatedly applied when weather conditions are favorable for disease. Cultural control practices like pruning and spacing plants in wide rows can help leaves dry quickly after rain, there by reducing disease. Unfortunately these management strategies have little affect in a very rainy year.

This years epidemic of coffee rust in Central and South America has made headlines. The coffee crop from Colombia through Mexico is severely affected by the disease and coffee rust is being reported at higher altitudes than normal. In February Guatemala declared a state of emergency, reporting over 70% of the coffee crop infected with the disease. The coffee harvest is expected to be reduced both this year and the next.

Boxelder Bugs in Homes

Jeffrey Hahn, Asst. Extension Entomologist

People have recently been experiencing problems with boxelder bugs in their homes, sometimes in large numbers.  Despite the circumstantial evidence, these insects are not reproducing indoors; all of the boxelder bugs you see now entered homes last fall.  When they get into wall voids, attics, and similar places, they often cluster in large groups.  As the outdoor temperatures warm up (or sometimes as people turn their heat up), the outer layer of these insects will receive the most warmth and become active.  They will then move to the inside of buildings where it is warm.  Eventually another layer of insects becomes active and so on.  This is why boxelder bugs and other dormant insects do not all emerge at the same time.

Jeff Hahn

Photo 1: Boxelder bugs will stay dormant until warm temperatures 'wake' them up.


Unfortunately, there are not many good options for dealing with boxelder bugs and other overwintering insects at this time of year.  There is nothing practical for treating them while they are dormant in hidden areas and preventing their emergence.  And once they are in your home, they only real option is to physically remove them, e.g. with a vacuum cleaner. 

The best time to deal with boxelder bugs and other insects that seek harborage for the winter is in late summer or fall before they start to move to buildings seeking overwintering sites.  The best methods for reducing these insects are by sealing up cracks and spaces that may allow them entrance into your home combined with a timely treatment of an appropriate residual insecticide.  Some insects will still get inside but you should be able to reduce the number that would otherwise get inside.  Keep in mind that boxelder bug populations vary from year to year and in 2012 many people experience an above average number of them.  If you traditionally do not see many, you may see populations return to normal in 2013.

Click here for more information on boxelder bugs.


Karl Foord - Extension Educator, Horticulture


At a recent conference on high tunnel horticulture we received an update on biological control from Carol Glenister, the president of IPM Laboratories. IPM Laboratories supplies and supports the successful use of healthy beneficial organisms for the biological control of pests.




nhm ac uk


Photo 1: Parasitoid Wasp Encarsia formosa


ipm UC Davis

Photo 2: Parasitoid Wasp Encarsia formosa

Encarsia Biological Services AU

Photo 3: Life cycle of parasitoid wasp Encarsia formosa

Forestry Images

Photo 4: View of a leaf surface with evidence of parasitoid wasp Encarsia formosa activity

www.bugsforbugs.com.au

Photo 5: Parasitoid wasp Eretmocerus spp.

bugguide.net

Photo 6: Small lady bird beetle Delphastus spp.

Carol has coined the term "guardian plants" that function in the following ways: 1) are more attractive to the pest species than the crop being grown i.e. 'indicator' or 'trap' plants, 2) provide forage for natural enemies of the pests i.e. 'habitat' plants, and 3) provide forage for non-pest prey species that serve as an additional food source for natural enemies or serves as a reproductive site for natural enemies i.e. 'banker' plants.




Biocontrol Cornell


Table 1: Parasitoids




The indicator plants let you know the pest is present and the habitat and banker plants provide resources that encourage the natural enemies to remain and thrive on site.

Biocontrol Cornell

Table 2: Predators

Biocontrol Cornell

Table 3: Pathogens

In natural populations the predator numbers shadow the prey numbers, but the prey species always reproduce more rapidly so there is often a delay in control. If the control comes after the prey has damaged our plants then the predator hasn't benefited our production system. If the two-spotted spider mites are finally controlled by the predatory mites but your tomatoes performed poorly during the battle, there is little cause for celebration. The key is to have predator numbers in sufficient quantity early in development to keep prey damage below an acceptable threshold.

This means knowing what pest you expect to encounter, placing the proper indicator plants, monitoring for pest activity, getting predator species in a timely fashion, providing habitat plants and tracking pest and prey activity and numbers.

Natural enemies such as the following are presently being used to control whiteflies in greenhouses; two parasitoid wasps (Encarsia formosa Photos 1 - 4, and Eretmocerus eremicus Photo 5), and a small lady bird beetle (Delphastus catalinae) Photo 6. Note the incredibly small size of these insects - less than 1 mm in length.

In one experiment Lantana was used as a guardian plant among herbs such as oregano and lemon verbena, and the Encarsia formosa wasp was used as the prey species. The ratio of whitefly pests found on Lantana to those on the herbs was 79 to 1. The whitefly pest was drawn to the trap plant where it met its demise at the "hands" of the Encarsia wasp. This experiment can be viewed in greater detail at http://www.ipmlabs.com/whitefly-predators/plant-pests/whiteflies/biological-controls/

There is a great deal of research being conducted in this area, especially on the functioning of these bio-control organisms in outdoor environs. Consider the number of organisms functioning as parasitoids, predators, and pathogens as noted in Tables 1 - 3.

This is a fascinating research arena and one worth tracking advancements.

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